Is there a relationship- formula between the lead BH factor and FPS when it comes to possible leading ? And, is there a relationship- formula between BH and gas checks as to when the checks are needed based on hardness ? Sorry if it has been talked about before.
Lead hardness vs speed
- Thread starter HIGHRPM
- Start date
I don't know if there is a formula as there is far to many variables to give you an exact answer. You might get leading with a hardness of 14 at a speed of 2500fps with one type of lube but not another. It's all about experimenting.
The 1st 185gr .303 bullets I made a few weeks ago all keyholed at 25yd without gas checks. They were accurate with gas checks. The BHN was about 14 with water quenching. Now I quench and heat treat them making at least BHN 25-30 on the Lee tester. Also use Lee Liquid Alox to prevent possible leading. Leading is not hard to clean out if you don't let it build up. Copper is not though. 2500 fps is too fast for cast bullets in most cases. Light loads producing 1700 to 2000 would be my objective. I use 28gr of H4895 but haven't had a chance yet to chrono them.
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Yomomma got it right. 80% of the time leading is due to bullet diameter. Lead hardness is part of the equation but so is rotational stress and powder selection. Generally speaking, slower powders will give you more velocity before they start leading, as compared to faster powders. The pistol powders like Unique and Blue Dot, etc, will start leading hundreds of fps earlier than a medium rifle powder like H/IMR4895 or IMR4064. If you are going for rifle velocity then you need to have a properly sized bullet, a good alloy, and the right powder.
I regularly load 280 gr 9.3 mm bullets well over 2000 fps with no leading. This is a gas checked cast bullet with a BHN of 18-20.
- Location
- Ottawa origanally Muskoka
The thing is HOW you make the bullets hard and HOW. You get them to go fast.
The more tin you add to a bullet alloy the worse off you are. The good thing with tin is its abillity to lower the surface tension of the alloy to make the alloy fill out the mold well and allow antimony to wix in with the alloy in larger percentages. The bad thing about tin is that it melts at a lower temperature.
Lead= 621.4*F
Tin= 449.4*F
Antimony= 1167.1*F
So the more heat the bullet absorbs on the way down the bore the worse things get. A gas check, wad, powder selection, and good friction reducing lube are just as important as bullet hardness. The design and fit are two other factors often overlooked. For instance a bore with narrow lands up. To 50/50 bore/groove shoot bore riding bullets poorly. Long barels and shallow/tumble lube grooves do not fair well as the bullet runs out of lube before it reaches the muzzle. Look for a greasy lube star at the muzzle to determine if you are running out of lube, either from being toosoft or not enough.
Too small of a bullet will also lead to leading of the bore and poor acuracy as hot gasses push past the bullet they melt and gas cut the bulletcausing irregular, uneaven release from the muzzle, melted, powder dented, poorly formed bases leave the muzzle the same as a good bullt from a damaged crown. A soft bullet that fully obtureates in the bore carries a good amount of the proper lube with a vegatable wad protecting the base shot at a moderate 1800fps can be every bit or more accurate than a gas checked hard bullet of bore dia. lubed with alox shot at a high velocity of 2100fps. It is all dependant on so. Many things including cartridge design, bore condition, rifling style and more
The more tin you add to a bullet alloy the worse off you are. The good thing with tin is its abillity to lower the surface tension of the alloy to make the alloy fill out the mold well and allow antimony to wix in with the alloy in larger percentages. The bad thing about tin is that it melts at a lower temperature.
Lead= 621.4*F
Tin= 449.4*F
Antimony= 1167.1*F
So the more heat the bullet absorbs on the way down the bore the worse things get. A gas check, wad, powder selection, and good friction reducing lube are just as important as bullet hardness. The design and fit are two other factors often overlooked. For instance a bore with narrow lands up. To 50/50 bore/groove shoot bore riding bullets poorly. Long barels and shallow/tumble lube grooves do not fair well as the bullet runs out of lube before it reaches the muzzle. Look for a greasy lube star at the muzzle to determine if you are running out of lube, either from being toosoft or not enough.
Too small of a bullet will also lead to leading of the bore and poor acuracy as hot gasses push past the bullet they melt and gas cut the bulletcausing irregular, uneaven release from the muzzle, melted, powder dented, poorly formed bases leave the muzzle the same as a good bullt from a damaged crown. A soft bullet that fully obtureates in the bore carries a good amount of the proper lube with a vegatable wad protecting the base shot at a moderate 1800fps can be every bit or more accurate than a gas checked hard bullet of bore dia. lubed with alox shot at a high velocity of 2100fps. It is all dependant on so. Many things including cartridge design, bore condition, rifling style and more
Most leading is caused by incorrectly sized bullets but it is possible to get leading from going too fast. I had terrible leading in a 45-70 while shooting .459" bullets in a .4575" bore if I exceeded around 1700fps. They were plain base bullets, pure WW, water dropped, tumble lubed with alox. If I stuck to 1300-1500fps I had no leading at all. This was all with rifle powders; I only use pistol powders for 900-1100fps loads.
Some factors that can effect the maximum speed your bullets can go before they start to lead:
-gas check or no gas check
-bore roughness/pitting
-groove depth
-maximum pressure reached
-pressure curve
-throat dimensions
-lead hardness
-lead composition
-lube type
-bearing surface area
and I'm sure there are several other factors I'm missing.
Some people make reference to a chart that shows maximum velocity for given hardnesses of bullet but there are far too many factors for any such chart to be even close to universal.
I've never seen any real evidence that bullets melt in the bore. Temperature doesn't seem to have much to do with it. Leading from an undersized bullet is from "gas cutting" where the high pressure gas cuts into the bullet and parts break off. It isn't caused by melting. The heat of combustion isn't maintained for nearly long enough for enough heat to transfer to the bullet. A gas check, wad, or other piece works to stop the gas, not the heat, from having as great an effect on the bullet. Rifle powders have a less steep pressure curve and don't kick the bullet as hard right from the start. This means peak pressure wont be reached until the bullet is at least a couple inches down the bore and, most importantly, past the throat. Slamming all the pressure into the bullet when it's nearly stationary (pistol powders) is more likely to cause issues than gently applying the pressure over a longer period of time (rifle powder).
For me personally, with pure WW's, water dropped, a properly fitted bullet, and rifle powders I use the following as rough limits:
Crisp bore - 1500fps without gas check, 2200fps with (a barrel that looks new)
Worn bore - 1200fps without gas check, 1900fps with (not-new looking but still fairly smooth)
Rough bore - 1000fps without gas check, 1500fps with (some pitting or rough spots) <-- also all Marlin Micro Groove barrels in my experience even if they're new
Velocities can be pushed higher in a crisp bore with other considerations but I've never found a need to.
Some factors that can effect the maximum speed your bullets can go before they start to lead:
-gas check or no gas check
-bore roughness/pitting
-groove depth
-maximum pressure reached
-pressure curve
-throat dimensions
-lead hardness
-lead composition
-lube type
-bearing surface area
and I'm sure there are several other factors I'm missing.
Some people make reference to a chart that shows maximum velocity for given hardnesses of bullet but there are far too many factors for any such chart to be even close to universal.
I've never seen any real evidence that bullets melt in the bore. Temperature doesn't seem to have much to do with it. Leading from an undersized bullet is from "gas cutting" where the high pressure gas cuts into the bullet and parts break off. It isn't caused by melting. The heat of combustion isn't maintained for nearly long enough for enough heat to transfer to the bullet. A gas check, wad, or other piece works to stop the gas, not the heat, from having as great an effect on the bullet. Rifle powders have a less steep pressure curve and don't kick the bullet as hard right from the start. This means peak pressure wont be reached until the bullet is at least a couple inches down the bore and, most importantly, past the throat. Slamming all the pressure into the bullet when it's nearly stationary (pistol powders) is more likely to cause issues than gently applying the pressure over a longer period of time (rifle powder).
For me personally, with pure WW's, water dropped, a properly fitted bullet, and rifle powders I use the following as rough limits:
Crisp bore - 1500fps without gas check, 2200fps with (a barrel that looks new)
Worn bore - 1200fps without gas check, 1900fps with (not-new looking but still fairly smooth)
Rough bore - 1000fps without gas check, 1500fps with (some pitting or rough spots) <-- also all Marlin Micro Groove barrels in my experience even if they're new
Velocities can be pushed higher in a crisp bore with other considerations but I've never found a need to.
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just having some fun
CGN Ultra frequent flyer
How would you like 3000 fps at muzzle
30 cal cast lead bullet
less than 1.5 moa At 300 yds with 10 shot groups
go to post 182 and 212 (pictures of targets) as well as other posts if interested
h ttp://castboolits.gunloads.com/showthread.php?268811-SLOW-Twists-and-FAST-Casts-Using-CUSTOM-Barrels-Results-Please/page10
gun / guns being shot are a wildcat (several rifles are being shot by different owners and results vary with barrel twist
barrels being tested at high velocity are 1/12 -1/14 -1/15 - 1/16 twist
Max speed With accuracy is directly related to barrel twist RPM of the bullet
30 cal cast lead bullet
less than 1.5 moa At 300 yds with 10 shot groups
go to post 182 and 212 (pictures of targets) as well as other posts if interested
h ttp://castboolits.gunloads.com/showthread.php?268811-SLOW-Twists-and-FAST-Casts-Using-CUSTOM-Barrels-Results-Please/page10
gun / guns being shot are a wildcat (several rifles are being shot by different owners and results vary with barrel twist
barrels being tested at high velocity are 1/12 -1/14 -1/15 - 1/16 twist
Max speed With accuracy is directly related to barrel twist RPM of the bullet
RPM threshold twist/velocity chart
I’m posting this at request for an easy reference to see the velocity range where the RPM threshold will most likely be found based on the twist of the barrel.
The RPM threshold is that point where accuracy begins to deteriorate when the RPM is sufficient to act on imbalances in the bullet in flight to the extent the bullet begins a helical arc in flight or it’s flight path goes off on a tangent. It is best noted when working up a load as velocity increases flyers begin to happen. Then as velocity is further increased the total group size increases sometimes to the point some bullets fly so far off they miss the target. A further indication the cast bullets at or over the RPM threshold is (or some of them in a load that is on the edge of the RPM threshold) the non linear dispersion of the group size as range increases.
Let us keep in mind the RPM threshold most often falls in the 120,000 to 140,000 RPM range with regular lube groove cast bullets. Exactly where the RPM threshold will be in fps depends on numerous factors; alloy, bullet design, fit, sizing, lube, GC’d and seated square, powder burning rate and the length of the barrel, etc. The RPM threshold may be lower than 120,000 RPM by careless casting and loading techniques or when using very soft alloys with very fast burning powders. Conversely, the RPM threshold can be above 140,000 by careful casting and bullet selection and preparation along with careful accuracy enhancing loading techniques, especially those for cast bullets at high velocity such as using slow burning powders that ignite easily and burn efficiently at lower pressures. The trick is to get the cast bullet to exit the muzzle as balanced as possible with as little deformation to it during accelleration. The more balanced the bullet is and the closer the axis of rotation coincides with the center of mass on exit from the muzzle and during flight the more accurate the bullet will be and thus, the higher the RPM threshold will be.
The RPM threshold is not a set “limit” of RPM or velocity. Best accuracy will be just under the RPM threshold or lower. Useable accuracy can be had above the RPM threshold if the ranges are not long and the accuracy requirement is not small. Keeping .223 cast bullets on a silhouette target out to 200 yards for example or keeping hunting cast bullet accuracy at say 4 moa if the max range to be used is 50 – 100 yards.
Again; the RPM threshold will generally be found between 120,000 to 140,000 RPM with regular commercial cast bullet designs and loading techniques most cast bullet shooters use.
In the chart below I’ve computed the fps for various common barrel twists for 120,000 and 140,000 RPM. For other twists in between anyone shouldn’t find it too difficult to interpolate. These fps figures should give you an idea in what fps range your loads, as you work them up, will probably bump into the RPM threshold and when accuracy will probably begin to deteriorate. Some pundates will crticise this chart saying they, or someone else, gets accuracy above the figures in the chart. For those who understand how to push the RPM threshold up with higher velocity cast bullet loads that can indeed be the case. However, as mentioned, the chart is for the majority of cast bullet shooters who do not care to push the RPM threshold up but simply want to understand where and why accuracy will probably deteriorate with their regular cast bullet loads. This chart was done for them.
RPM……….120,000……….140,000
Twist……….FPS…………..FPS
7”…………1166…………..1361
8”………….1333…………..1555
9”………….1500…………..1750
10”………...1666…………..1944
11”………...1833…………..2139
12”…………2000………….2333
14”…………2333………….2722
16”…………2666………….3111
18”………….3000…………3500
Larry Gibson
I’m posting this at request for an easy reference to see the velocity range where the RPM threshold will most likely be found based on the twist of the barrel.
The RPM threshold is that point where accuracy begins to deteriorate when the RPM is sufficient to act on imbalances in the bullet in flight to the extent the bullet begins a helical arc in flight or it’s flight path goes off on a tangent. It is best noted when working up a load as velocity increases flyers begin to happen. Then as velocity is further increased the total group size increases sometimes to the point some bullets fly so far off they miss the target. A further indication the cast bullets at or over the RPM threshold is (or some of them in a load that is on the edge of the RPM threshold) the non linear dispersion of the group size as range increases.
Let us keep in mind the RPM threshold most often falls in the 120,000 to 140,000 RPM range with regular lube groove cast bullets. Exactly where the RPM threshold will be in fps depends on numerous factors; alloy, bullet design, fit, sizing, lube, GC’d and seated square, powder burning rate and the length of the barrel, etc. The RPM threshold may be lower than 120,000 RPM by careless casting and loading techniques or when using very soft alloys with very fast burning powders. Conversely, the RPM threshold can be above 140,000 by careful casting and bullet selection and preparation along with careful accuracy enhancing loading techniques, especially those for cast bullets at high velocity such as using slow burning powders that ignite easily and burn efficiently at lower pressures. The trick is to get the cast bullet to exit the muzzle as balanced as possible with as little deformation to it during accelleration. The more balanced the bullet is and the closer the axis of rotation coincides with the center of mass on exit from the muzzle and during flight the more accurate the bullet will be and thus, the higher the RPM threshold will be.
The RPM threshold is not a set “limit” of RPM or velocity. Best accuracy will be just under the RPM threshold or lower. Useable accuracy can be had above the RPM threshold if the ranges are not long and the accuracy requirement is not small. Keeping .223 cast bullets on a silhouette target out to 200 yards for example or keeping hunting cast bullet accuracy at say 4 moa if the max range to be used is 50 – 100 yards.
Again; the RPM threshold will generally be found between 120,000 to 140,000 RPM with regular commercial cast bullet designs and loading techniques most cast bullet shooters use.
In the chart below I’ve computed the fps for various common barrel twists for 120,000 and 140,000 RPM. For other twists in between anyone shouldn’t find it too difficult to interpolate. These fps figures should give you an idea in what fps range your loads, as you work them up, will probably bump into the RPM threshold and when accuracy will probably begin to deteriorate. Some pundates will crticise this chart saying they, or someone else, gets accuracy above the figures in the chart. For those who understand how to push the RPM threshold up with higher velocity cast bullet loads that can indeed be the case. However, as mentioned, the chart is for the majority of cast bullet shooters who do not care to push the RPM threshold up but simply want to understand where and why accuracy will probably deteriorate with their regular cast bullet loads. This chart was done for them.
RPM……….120,000……….140,000
Twist……….FPS…………..FPS
7”…………1166…………..1361
8”………….1333…………..1555
9”………….1500…………..1750
10”………...1666…………..1944
11”………...1833…………..2139
12”…………2000………….2333
14”…………2333………….2722
16”…………2666………….3111
18”………….3000…………3500
Larry Gibson
I commented some time ago that probably RPM is a less likely answer than could be had from something akin to "rim speed" on the bullet. It seems to me that rpm is only applicable to one caliber at a time. I suggest this meaning no disrespect to Larry Gibson or anyone else who does good work on this or any other forum and would be glad to hear the rationale if I'm wrong.
Grouch
Grouch
just having some fun
CGN Ultra frequent flyer
Rpm can be valid point
Example take a 20 round box of 223 50 or 55g ammo ---- pick 10 at random
Now shoot it in a ar15 1/9 twist it at target 200 or 300 yds how large of a group are you going to get ?
Now take the remaining 10 rounds and shoot it in a ar15 1/7 twist at target 200 or 300 yds which group will be smaller / bigger
RPM is the biggest variable
Velocity at the muzzle will be close so it has to be RPM that makes the change
RPM makes more of a difference with lead rounds
Example take a 20 round box of 223 50 or 55g ammo ---- pick 10 at random
Now shoot it in a ar15 1/9 twist it at target 200 or 300 yds how large of a group are you going to get ?
Now take the remaining 10 rounds and shoot it in a ar15 1/7 twist at target 200 or 300 yds which group will be smaller / bigger
RPM is the biggest variable
Velocity at the muzzle will be close so it has to be RPM that makes the change
RPM makes more of a difference with lead rounds
Yes.
Did you know that the lifespan of a barrel is typically less than 10 seconds, and in some cases it's less than one second?
That's because upon firing, even a slow bullet in a long barrel is typically only in the bore for about 1 ms (1/1000 second).
That's not nearly enough time for any significant amount of heat to be transferred to the bullet base from the hot expanding gasses - there's likely more heat transferred from friction in the bore than from the gasses.
Just to keep it somewhat simple, the general rule of thumb, for using gaschecks, is approx 1700fps, some rifles won't get past 1600, some will go a little further, up towards 1800. And the lube you are using can make a difference past about 1600, it needs to be capable of a little higher temp tolerance than some that you can use below that area. And you have to watch the ambient temp you are shooting in with some lubes, some don't like cold weather, some don't like being in the sun on an 80deg day. I have used Emmerts in 0degF to 80deg on plain base 1/20 up to 1500, but it needs to be adjusted to being a little thicker for the summer heat. A combo of Lyman brown/Red Rooster worked well on a couple of 22-250's w/gaschecked, oven hardened Lyman #2 at 2300 in the summer. I have used LBT blue in the summer on #2 waterdropped, gaschecked, in the 450/400, at 2050 and had good results also. Everyone has a pet lube, there are lots out there, just keep an eye, on what it was used on, and what it was used in, and how fast it was driven, in what temps.
The guns I used all had good bores, however I was surprised by a 22-250 that had a rust pitted area from fire damage, in the middle of the barrel, that shot 3/4" groups. It shot a whole bunch better than I thought it would, just had to brush it every 50rds or so. The 32-40 with the Emmerts, would go 2-300 and just need a quick wipe to get residue out. I ran 7x57 and 6.5x55 with gaschecks at 1400 because I didn't trust the bores in the old military rifles I had at the time, with brown Lyman, never had an issue with any of them.
And there is a pretty good chance that PC will do it all, haven't tested that out for myself yet though.
The guns I used all had good bores, however I was surprised by a 22-250 that had a rust pitted area from fire damage, in the middle of the barrel, that shot 3/4" groups. It shot a whole bunch better than I thought it would, just had to brush it every 50rds or so. The 32-40 with the Emmerts, would go 2-300 and just need a quick wipe to get residue out. I ran 7x57 and 6.5x55 with gaschecks at 1400 because I didn't trust the bores in the old military rifles I had at the time, with brown Lyman, never had an issue with any of them.
And there is a pretty good chance that PC will do it all, haven't tested that out for myself yet though.
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A cast bullet loader can manipulate various aspects of his load combination. When a cast bullet load fails to perform, it is usually one or a combination of component failures.
Over pressure/acceleration can deform the bullet base to the point of gas leakage between the bullet surface and the bore surface. This can cause the gasses to "wash" (so to speak) lead from the bullet bearing surface. This can cause a few issues. Such as erratic pressures that cause inaccuracies. A bullet that is damaged during the firing sequence can have gyroscopic instalilities due to moved/damaged material. Causing an imbalance, Yawing or tumbling.
A damaged cast bullet base will leak expanding gasses unevenly around the bullet base circumference as it leaves the bore and create a gas induced/influenced tipping off bore axis. The bullet will then spend the rest of its flight trying to restabilise on its original axis/center of gravity.
The best cast bullet loads maintain a balance that allow a load to work. As you increase pressures, the weakest link will eventually surface.
If the expanding gasses leak past the bullet base, this can allow the lube to be sprayed ahead of the bullet as well. When the lube is not in the lube groove, it cannot offer the lubrication or bullet surface support.
I tend to doubt that combustion temperatures affect/cause much melting due to the extreamly short time frames of which these temps are imparted to the bullet base. You can pass your hand through a flame, and not get burnt if you keep it moving fast.(very low exposure time).
Pressure on the alloy, on the other hand, is a bit different story.
A full lube groove can offer allot of load enhancing benefits.
I shoot my 200 grain Lyman 311299 cast bullet at velocities as high as 2425fps. In my 308win cast rifle. At this speed and pressure, the components are just starting to yield. The accuracy is around 1-1/2 to 2" at 100 yards.
When I drop my pressures and velocity down to around 2350fps, my average group size improves noticably. I have had many groups well under an inch, and some around 1.25".
This load exhibits some great ballistic uniformity for cast! I have shot this load clear out to 900 yards. Only after 800 yards does the accuracy start to decay rapidly. I am not at home, so my records are not available at this time, but 1.5 to 2.5 MOA "ish" is the rule past 500 yards.
My alloy is 18 pounds wheel weight lead +8 feet of 50/50 lead/tin solder. Air cooled.
Bullet is sized to .310" and lubed with Lymans Super Moly.
Gas checks I have tested with my load combinations are brass,copper and aluminum.
As can be expected, my maximum velocities that can reached while maintaining decent accuracy, varies with the gas check material as well. Aluminum cant get me much past 1800fps before failing with this alloy.
Both Copper and Brass were able to reach the 2425fps level, but brass gas checked loads were more consistent on the chronygraph. But not by much.
Powder that is "PREFERRED" is IMR4831. This is not the typical powder associated with cast shooting, but more for jacketed bullets.
I dont feel most failures of a cast bullets base are caused by melting due to combustion temperature, but extrusion caused by the loads expanding gases surpassing the alloys physical elastic/compressible limit. (Surpassing the yield point of the alloy). The gasses will simply go to the point of least resistance, where ever on the bullet to bore surface that happens to be. Both the Pressure limits and the timing of the maximum pressures affect the bullets ability to accelerate without damaging the bullets alloy. A push rather than a kick, so to speak.
Add to this mix, that the bullet surface is exposed to a significant "Torquing" force from the rifling. The more gradual gas pressure application, the better for the cast bullet to bore interface seal preservation.
When I used the powders most commonly reccomended for cast bullets, as I approached near the maximum charges reccomended for that powder, the accuracy would start to fall off. To be expected. The pressures were surpassing the bullet/lube/ and gas checks ability to seal the gases during the acceleration of the firing sequence.
Using another slower powder allowed me to achieve a higher velocity before the accuracy started to fail.
With IMR4831, I believe that the slower burning characteristics allowed the expanding gasses to apply the pressure over a longer burn period. Thus delaying the highest pressure point at a higher velocity. Less of an impact/g force imparted on the bullet base and the alloys yield point pressure. A softer-longer start/push.
To initiate an adquate pressure to get the IMR4831 to burn fully, I seated the bullets into the rifling firmly. With this technique, the rifle shoots great, and the bore stays suprisingly clean and free of powder residue.
In a nutshell, maximising your velocity with any lead based bullet will depend on your alloys yield point strength, and how fast and high the pressures are applied.
Fast burning powders will produce slower velocities at maximum pressures. A sharp kick so to speak.
Having the bullet sized .001-.002" larger than bore diameter will help seal the combustion gasses, and offer the accelerating bullet support to reduce any kind of bullet shape "slump". The cast bullet obturates slightly during the combustion and accelleration of the firing sequence. This, in turn, causes the bullets diameter to swell (obturate) and compresses the bullet bearing surface more firmly to the bore surface. Pressure and acceleration, if well balanced can produce great load performance.
Some bullet designs will shoot better in some barrels than others. The only way to know which one your rifle likes is to try them.
Shooting cast can be as easy or as challenging as you desire. Just have fun with it.
I hope this info was useful to someone.
Over pressure/acceleration can deform the bullet base to the point of gas leakage between the bullet surface and the bore surface. This can cause the gasses to "wash" (so to speak) lead from the bullet bearing surface. This can cause a few issues. Such as erratic pressures that cause inaccuracies. A bullet that is damaged during the firing sequence can have gyroscopic instalilities due to moved/damaged material. Causing an imbalance, Yawing or tumbling.
A damaged cast bullet base will leak expanding gasses unevenly around the bullet base circumference as it leaves the bore and create a gas induced/influenced tipping off bore axis. The bullet will then spend the rest of its flight trying to restabilise on its original axis/center of gravity.
The best cast bullet loads maintain a balance that allow a load to work. As you increase pressures, the weakest link will eventually surface.
If the expanding gasses leak past the bullet base, this can allow the lube to be sprayed ahead of the bullet as well. When the lube is not in the lube groove, it cannot offer the lubrication or bullet surface support.
I tend to doubt that combustion temperatures affect/cause much melting due to the extreamly short time frames of which these temps are imparted to the bullet base. You can pass your hand through a flame, and not get burnt if you keep it moving fast.(very low exposure time).
Pressure on the alloy, on the other hand, is a bit different story.
A full lube groove can offer allot of load enhancing benefits.
I shoot my 200 grain Lyman 311299 cast bullet at velocities as high as 2425fps. In my 308win cast rifle. At this speed and pressure, the components are just starting to yield. The accuracy is around 1-1/2 to 2" at 100 yards.
When I drop my pressures and velocity down to around 2350fps, my average group size improves noticably. I have had many groups well under an inch, and some around 1.25".
This load exhibits some great ballistic uniformity for cast! I have shot this load clear out to 900 yards. Only after 800 yards does the accuracy start to decay rapidly. I am not at home, so my records are not available at this time, but 1.5 to 2.5 MOA "ish" is the rule past 500 yards.
My alloy is 18 pounds wheel weight lead +8 feet of 50/50 lead/tin solder. Air cooled.
Bullet is sized to .310" and lubed with Lymans Super Moly.
Gas checks I have tested with my load combinations are brass,copper and aluminum.
As can be expected, my maximum velocities that can reached while maintaining decent accuracy, varies with the gas check material as well. Aluminum cant get me much past 1800fps before failing with this alloy.
Both Copper and Brass were able to reach the 2425fps level, but brass gas checked loads were more consistent on the chronygraph. But not by much.
Powder that is "PREFERRED" is IMR4831. This is not the typical powder associated with cast shooting, but more for jacketed bullets.
I dont feel most failures of a cast bullets base are caused by melting due to combustion temperature, but extrusion caused by the loads expanding gases surpassing the alloys physical elastic/compressible limit. (Surpassing the yield point of the alloy). The gasses will simply go to the point of least resistance, where ever on the bullet to bore surface that happens to be. Both the Pressure limits and the timing of the maximum pressures affect the bullets ability to accelerate without damaging the bullets alloy. A push rather than a kick, so to speak.
Add to this mix, that the bullet surface is exposed to a significant "Torquing" force from the rifling. The more gradual gas pressure application, the better for the cast bullet to bore interface seal preservation.
When I used the powders most commonly reccomended for cast bullets, as I approached near the maximum charges reccomended for that powder, the accuracy would start to fall off. To be expected. The pressures were surpassing the bullet/lube/ and gas checks ability to seal the gases during the acceleration of the firing sequence.
Using another slower powder allowed me to achieve a higher velocity before the accuracy started to fail.
With IMR4831, I believe that the slower burning characteristics allowed the expanding gasses to apply the pressure over a longer burn period. Thus delaying the highest pressure point at a higher velocity. Less of an impact/g force imparted on the bullet base and the alloys yield point pressure. A softer-longer start/push.
To initiate an adquate pressure to get the IMR4831 to burn fully, I seated the bullets into the rifling firmly. With this technique, the rifle shoots great, and the bore stays suprisingly clean and free of powder residue.
In a nutshell, maximising your velocity with any lead based bullet will depend on your alloys yield point strength, and how fast and high the pressures are applied.
Fast burning powders will produce slower velocities at maximum pressures. A sharp kick so to speak.
Having the bullet sized .001-.002" larger than bore diameter will help seal the combustion gasses, and offer the accelerating bullet support to reduce any kind of bullet shape "slump". The cast bullet obturates slightly during the combustion and accelleration of the firing sequence. This, in turn, causes the bullets diameter to swell (obturate) and compresses the bullet bearing surface more firmly to the bore surface. Pressure and acceleration, if well balanced can produce great load performance.
Some bullet designs will shoot better in some barrels than others. The only way to know which one your rifle likes is to try them.
Shooting cast can be as easy or as challenging as you desire. Just have fun with it.
I hope this info was useful to someone.
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VERY useful!
Thank you for a very detailed post.
I notice you suggest slower powders to prevent a sharp pressure spike deforming the bullet upon ignition.
If I load for a Garand, the common wisdom is to use a medium fast powder, so that the pressure curve has dropped as the bullet passes the gas port, so as not to overgas the system.
So, do I go with H4895 and hold the velocity down to avoid deforming, or use IMR4831 and try to avoid overgassing it?
Would Gas Checks, WW lead, and Powder coating together be the way to go?
I personally think you should keep the velocities down so that you can use the H4895. The Garand is all about managing the gas for reliable functioning. If your powder is a little too slow, powder fouling in your gas port will soon follow.
My experience with loading for the garand is limited to my reloading for my BAR in 30-06.
Drop Larry Gibson a pm on the Cast boolets site. He is a wealth of knowledge in the powder suitability relm.
I am glad you enjoyed my post. I am learning every time I go out shooting. Thats why I love it!
Powder coating is something I havent dabbled in "yet". It may simplify a few issues like lube viscosity stability in significant temperature swings. Hmmmmmm! Will look into this!
My experience with loading for the garand is limited to my reloading for my BAR in 30-06.
Drop Larry Gibson a pm on the Cast boolets site. He is a wealth of knowledge in the powder suitability relm.
I am glad you enjoyed my post. I am learning every time I go out shooting. Thats why I love it!
Powder coating is something I havent dabbled in "yet". It may simplify a few issues like lube viscosity stability in significant temperature swings. Hmmmmmm! Will look into this!
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