Bullet stability

I

IMR4320

CGN frequent flyer
Rating - 100%
133   0   0
Location
Vancouver
Hey reloaders.
I've got this ongoing problem with one of my rifles. Rem 700/308W, I built it from components, used Rem OEM heavy barrel with 1/12 twist I had shortened from 26" to 20" and re-chambered so my leade is some .020"
I developed a round with Hornady Match 168gr. bullet that does consistently .7-.8 MOA at 100m and as weird as it may be, factory Fed SMK 168 does consistently .5 MOA. So the results I would say so so given, I have used OEM barrel and had it modified. Where things go strange is, when I extend the range to 200m or God forbid 300 Yards. At 200, I have all of a sudden 1 MOA rifle at best and at 300 Yards it's more like 1.3-1.5 MOA. I'm not new to precision reloading and while, true, I only use average components, I've actually had reasonable results with my other rifles, meaning .5-.7 MOA that actually improves with longer range to not unusual .5 MOA The only thing that comes to mind is, the bullet is not correctly stabilized, which does not show up much at shorter range such as 100m but starts gradually showing up at longer ranges. Has anyone come across something like this ? I checked the muzzle crown for anything unusual but could not find anything, my optics is good for parallax, good case head space and those same components work well in other rifles. Powder load is not maxed up and velocities are pretty much where they should be and I don't think the barrel is warping because the results are the same irrelevant of if it's first 5 rounds cold or last 5 rounds of session when the barrel is warmed up but not very hot.
Thanks for any ideas
 
Last edited:
Bullet stability actually increases as the bullet goes down range, assuming it is stable when it leaves the barrel. This is because the bullets velocity decreases at a faster rate then the rate of decrease in RPM.
You shouldn't have any issue stabilizing a 168gr in a 1-12 twist. Something else is causing your groups to get bigger.
 
IMR4320 said:
Hey reloaders.
I've got this ongoing problem with one of my rifles. Rem 700/308W, I built it from components, used Rem OEM heavy barrel with 1/12 twist I had shortened from 26" to 20" and re-chambered so my leade is some .020"
I developed a round with Hornady Match 168gr. bullet that does consistently .7-.8 MOA at 100m and as weird as it may be, factory Fed SMK 168 does consistently .5 MOA. So the results I would say so so given, I have used OEM barrel and had it modified. Where things go strange is, when I extend the range to 200m or God forbid 300 Yards. At 200, I have all of a sudden 1 MOA rifle at best and at 300 Yards it's more like 1.3-1.5 MOA. I'm not new to precision reloading and while, true, I only use average components, I've actually had reasonable results with my other rifles, meaning .5-.7 MOA that actually improves with longer range to not unusual .5 MOA The only thing that comes to mind is, the bullet is not correctly stabilized, which does not show up much at shorter range such as 100m but starts gradually showing up at longer ranges. Has anyone come across something like this ? I checked the muzzle crown for anything unusual but could not find anything, my optics is good for parallax, good case head space and those same components work well in other rifles. Powder load is not maxed up and velocities are pretty much where they should be and I don't think the barrel is warping because the results are the same irrelevant of if it's first 5 rounds cold or last 5 rounds of session when the barrel is warmed up but not very hot.
Thanks for any ideas
Click to expand...

Problems often appear as the range increases, but if these are new problems which have not been evident until you modified the factory barrel, some investigation will be required.

If you want to check your bullet stability, fire at targets from 5-25 yards in 5 yard increments. Its normal for a bullet to precess (yaw) upon exiting the muzzle, but this is fixed by its rotational velocity. An elongated bullet hole at 5 or even 10 yards isn't necessarily indicative of a problem if it clears up by 25, but keyholes are unacceptable at any range. If the holes in the target are round at the range you are shooting at, they are stable at the moment they impact, if they are elongated, that is indicative of a problem. A stable bullet will tend to remain stable until it drops to the transonic velocity, about 1250-1300 fps. A 168 gr MK or Hornady Match bullet would normally shoot well in a 1:12 barrel at the ranges you indicate.

When you shorten a barrel, where increased barrel stiffness should improve accuracy, if the barrel is not cut off at a point where the bore is as tight, or tighter, than the bore diameter at original muzzle, deteriorated accuracy might be observed. This is of course refers to very little differences, measured in three decimal places.

With respect to handloads, given enough attention to detail, there is no reason why American bulk brass cannot shoot as well as the big dollar match brass, it just takes a bit of work to get there. One area often overlooked is bullet pull weight. There are three ways to uniform bullet pull weight. The first, is to anneal the case necks, thereby softening and uniforming the work hardened necks, the second is to apply some degree of crimp, which is usually unhelpful to the accuracy we expect form match ammo, and thirdly is to seat the bullet well into the lands, which uniforms, and dramatically raises, the pressure at which the bullet begins to move.

You could check the run-out of your case necks. Check a fired round, which is essentially a mirror image of the chamber. Then check the run-out of the same case after resizing, is there a significant difference? Are you using an expander button when you resize, or a bushing die? An expander button can create runout. Finally check the run-out of a round with the bullet seated? How does this compare to the run-out of the fired unsized brass? Have you measured the uniformity of your neck thickness, if the neck thickness varies .004" or more, neck turning would be helpful.

One area you have not discussed is the stock of your rifle. Inspect the stock for failure, such as cracks or indication of movement in the bedding area? Is the stock rigid or does it bend or torque easily? Has anything changed, particularly in the bedding of the rifle since the barrel work was completed? Does the stock have a pressure point, or is the barrel free floating back to the chamber? Have you attempted to maintain the torgue on the action screws, and is the torque uniform between the two screws?
 
Would expect as good or better accuracy from a shortened barrel due to increased stiffness.

Crown would have been re-cut after shortening it. Is the crown square? If you didn't rechamber then that's the only obvious thing that has changed. If the chamber is re-cut then should check concentricity with the barrel by measuring fired case run-out as described by Boomer.
 
Do your load tuning at 300yds... it will come back to 1/2 MOA or the mechanical accuracy of you and your barrel. wind flags help alot here... as does proper mirage reading.

If you want to shoot far, tune at the longest distances you can... or at least 200yds out with 300yds preferable. It will be a subtle change in your load but the load will change.

Good luck.

Jerry
 
Mystic Precision said:
Do your load tuning at 300yds... it will come back to 1/2 MOA or the mechanical accuracy of you and your barrel. wind flags help alot here... as does proper mirage reading.

If you want to shoot far, tune at the longest distances you can... or at least 200yds out with 300yds preferable. It will be a subtle change in your load but the load will change.

Good luck.

Jerry
Click to expand...

Thanks Jerry, I develop all of my loads at 200m exactly so I could detect the best load. I'll keep looking, I see I have some responses here.
 
What powder and primer are you using?\

What were the ambient temps?

It is not a stability issue wrt to twist. Both of these bullets work just fine in 12 twist barrels. You can run up to 185's without issue.

So the spread in groups is happening due to something else.

Jerry
 
Mystic Precision said:
What powder and primer are you using?\

What were the ambient temps?

It is not a stability issue wrt to twist. Both of these bullets work just fine in 12 twist barrels. You can run up to 185's without issue.

So the spread in groups is happening due to something else.

Jerry
Click to expand...

Jerry,
I use Federal cases weight sorted out by 1 grain for consistency, head spaced to .002" for my specific 700 action and all uniformly trimmed to 2.010", Federal F-210 primer off large number of single batch, IMR 4064 @44.5 grain, this is a developed load that grouped best of other loads (IMR manual states maximum 45.9) and Hornady 168 HPBT sorted out by weight and seated .020" off lands measured by ogive and all rounds within .002" tolerance and light crimp with separate crimp die. Seating force monitored and those being outside of the majority set aside to avoid result distortion.
I have been doing this same procedure for my other rifles, all with good to excellent results. The rifle itself is set in MDT LSS stock with Timney 510 trigger set at 2lbs, again as my others. Action on this rifle was used with its original barrel, again with good results, which leads me to suspecting this newer barrel, which came off different rifle. The newer barrel is as mentioned re-chambered Rem varmint shortened to 20". I have very good experience with short barrels, they cannot flex as much and while losing some velocities, generally have better accuracy and take longer to heat up. This same barrel in question, I cannot positively verify round count as it came off rifle I bought used but it did not appear to have very many rounds and I myself have put some 1000 rounds thru it. It is a Rem OEM barrel, 1/12 twist, which leads me to suspecting there might be something with it, we all know what Remington can be capable of sometimes.
What I usually see is good accuracy at 200m and then when I stretch it, the MOA # gets lower. This one is the opposite, it shoots well factory at 100m and then it gets worse. My reloads, which in any other rifles beat the factory by 20-30% in accuracy are actually little worse than factory, which prompted me to test factory at longer ranges to eliminate the possbility of bad reloads. I can't help it, I suspect the rifle, most likely the barrel because as I mentioned, this same action shot well with other barrel. All shooting was done during temperatures of 0-20 degrees celsius.
 
Last edited:
I have a 13 twist 308 barrel on a savage action ... that i have yet to shoot

When I was doing research.... bullet .... Bullet length.. twist .... velocity ....Bullet rpm

chatting with some one I know that does a lot of long range shooting with different twist barrels

He said 13 twist 308 ... 165- 175g = varget would be my best choice

He said bullet length would play a key role he said don't waste your $$ on the long bullets for the 308 / 13 twist

he said 150-155g flat base I could all most use any powder in the 308 case speed range
 
IMR4320 said:
Jerry,
I use Federal cases weight sorted out by 1 grain for consistency, head spaced to .002" for my specific 700 action and all uniformly trimmed to 2.010", Federal F-210 primer off large number of single batch, IMR 4064 @44.5 grain, this is a developed load that grouped best of other loads (IMR manual states maximum 45.9) and Hornady 168 HPBT sorted out by weight and seated .020" off lands measured by ogive and all rounds within .002" tolerance and light crimp with separate crimp die. Seating force monitored and those being outside of the majority set aside to avoid result distortion.
I have been doing this same procedure for my other rifles, all with good to excellent results. The rifle itself is set in MDT LSS stock with Timney 510 trigger set at 2lbs, again as my others. Action on this rifle was used with its original barrel, again with good results, which leads me to suspecting this newer barrel, which came off different rifle. The newer barrel is as mentioned re-chambered Rem varmint shortened to 20". I have very good experience with short barrels, they cannot flex as much and while losing some velocities, generally have better accuracy and take longer to heat up. This same barrel in question, I cannot positively verify round count as it came off rifle I bought used but it did not appear to have very many rounds and I myself have put some 1000 rounds thru it. It is a Rem OEM barrel, 1/12 twist, which leads me to suspecting there might be something with it, we all know what Remington can be capable of sometimes.
What I usually see is good accuracy at 200m and then when I stretch it, the MOA # gets lower. This one is the opposite, it shoots well factory at 100m and then it gets worse. My reloads, which in any other rifles beat the factory by 20-30% in accuracy are actually little worse than factory, which prompted me to test factory at longer ranges to eliminate the possbility of bad reloads. I can't help it, I suspect the rifle, most likely the barrel because as I mentioned, this same action shot well with other barrel. All shooting was done during temperatures of 0-20 degrees celsius.
Click to expand...

I have stopped investing much time in factory barrels given their spotty performance so getting a new pipe is most definitely a good idea. However, the points you made intrigued me so just spit balling here:

Overly long throat. All too common in Rem 700 308 chambers. Just measure and see if the bullet will fully engrave in the lands BEFORE leaving the case neck.

If factory shoots better then my hand loads, I would definitely be tweaking my hand loads. Suspecting an overly long throat, you may need to go with a heavier bullet with a longer bearing surface. For factory to shoot well at 100m and fall apart further out, that would be expected as the chances any random load will be tuned for LR shooting is low. A big reason I don't shoot factory ammo if I can handload

Beyond that, I wouldn't invest any more time, energy and money in a factory pipe. Spin on a prefit match Remage and tune in a few rds... then spend the next several thousand rds hitting targets near and far.

Compared to the cost of ammo and the resources to test, it is far cheaper to get a quality barrel upfront

Jerry
 
Twist is not an issue. 1:12 will shoot Sierra 190s.

You have just proven ( for 9,376th time) that 100 yard groups don't mean anything, unless the objective is 100 yard group.

The problem is barrel harmonics, and where the muzzle is (flipping up or down) as the bullet exits.

Do your load development at 300 yards and try 0.2 gr increments (0.6 up and down). You need to find the sweets spot (velocity) for 300. And 600 would be a better distance to test unless you wanted to shoot long range.
 
todbartell said:
how did it shoot in the 2550 fps ballpark? I think your load is too fast
Click to expand...

This I don't know, this velocity would have been in the lower load, which I did but did not have the luxury of setting up chrono at that time. 2700 fps may seem fast but from what I've measured on other 20" barreled rifles, it is not that unusual. I typically get from 2620 to 2720 fps depending on the load the rifle likes I developed the load starting 42 grain and did series with .4 increments, finding what grouped better and refined it to the last .1, which normally gets me to a load that even if my scale fluctuates by .1 it is still a good load. My average good load is around 44 grains but a while back, I had a CZ 550 that only liked a hot load of 45.6, which was only .3 under the IMR4064 official maximum. It was a stock varminter rifle and it shot around .7 MOA and it improved with range and I was getting 2830 FPS out of that 26" barrel with no pressure signs or premature casings wear. My load developments worked every single time, till now.
 
Ganderite said:
Nothing wrong with your load development regime.

The problem is assuming that a 100yd load would group at 300. Not so.

100-yard groups hide the effect of harmonics. They show up at longer ranges.
Click to expand...

I actually develop all of my load at 200m(218 y) and they certainly show a lot more at that range than at 100.
 
You must log in or register to reply here.
Back
Top Bottom