COL vs. Pressure vs. accuracy = ????

I

ILoveBigRacks

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Am still working up a load for my new .270 Wby and have had some mixed results so far.

Have been working up a load with the 140 gr. TSX and RL22. The Barnes book recommends coming .05" off the lands for the bullet but I was unable to do that due to mag length limitations. Not wanting to have feeding issues i erred on the side of caution and allowed myself some fudge-factor room in the magazine and seated the bullets quite a bit shorter than the recommended length - ended up with an OAL of 3.24". I'm pretty sure I shorted the rounds too much as accuracy wasn't what I hoped for - I had a couple of holes touching at various powder weights but always a couple of flyers too. Also, I had some pressure issues as I worked it up a bit hotter than planned - had a couple of spikes that jumped quite a bit on the chrony - and ended up sticking my ejector up into the bolt face :redface: . In all fairness, the first sign of pressure was a round with a shiny mark from the ejector and the next round spiked and jammed it.

So, I decided to quit shorting the rounds as much and just go with the bare minimum to clear the mag box. Now, i've loaded up some rounds at an OAL of ~3.32-3.33" and they just clear the box but i've cycled them all through and they cycle fine. Question is, what difference can I expect to see at the range as far as accuracy and pressure? In theory, the accuracy should improve somewhat as I'm that much closer to the lands. Also, if I'm understanding pressure correctly, the pressure should drop with the lengthier rounds, correct? The bullets should have less of a jump into the lands resulting in less pressure and also reduce the chance of a pressure/velocity spike, correct?

I'll be putting all of this to the test this afternoon but just wanted to confirm my thought process and get input.

Cheers,
ILBR :)
 
According to my own chronograph testing ,and that of many other loaders,the pressure will climb as you increase the COL and seat the bullets closer to the lands.As far as accuracy is concerned,that depends totally on the individual rifle.
 
ILoveBigRacks said:
. In all fairness, the first sign of pressure was a round with a shiny mark from the ejector and the next round spiked and jammed it.

Cheers,
ILBR :)
Click to expand...

When you get that shiny mark, you are not supposed to put ANOTHER cartridge of the same powder charge in your rifle...:runaway:

Other than that SJ pretty much nailed it.:dancingbanana:
 
In my Sako 270 Weatherby, I had excellent results loading 67grs of IMR 7828 at 3.245 with 140 TSXs. All about 1/2in to 3/4 groupings. I had the exact same results with 140 Accubonds, again about 1/2 to 3/4 groupings. I have found 7828 to work extremely well in both the 270 and 257 Weatherby...
 
Gatehouse said:
When you get that shiny mark, you are not supposed to put ANOTHER cartridge of the same powder charge in your rifle...:runaway:

Other than that SJ pretty much nailed it.:dancingbanana:
Click to expand...


I know, I know... :redface: :redface: Unfortunately my common sense was left in the truck that day. I figured, ah WTF, I've only got another round of this load and that's the first pressure sign I've seen, what can it hurt???? :redface: :redface: Guess I found out.

So, as far as pressure is concerned, I'm reading it backways???? I was under the impression when the bullet had a greater distance to jump to the lands you had a greater chance of a spike. However, overall pressure is greater with a longer COL, eh? Hmmm, definately good to know :runaway: .
 
Think of it this way,if a bullet has a longer running start to the rifling,the rifling will engrave the bullet easier,resulting in less of a pressure spike.
 
Mostly I agree with Stubblejumper, there may be a place where you can reduce the temporary internal case volume enough to increase the pressure.
Typically, tho' the low-case-volume- pressure spikes occur in straight-walled cases with relatively fast powders and heavy bullets.
.38spl, with 158 grn bullets, burning Bullseye or RedDot is somewhat sensitive to OAL.
.270 Wby, burning 7828 or N-165 or RL-22... not so much.
 
:p The reason on 5 thou to the lands is very simple: the closer to the lands, the less chance of the bullet entering crooked (YES) into the lands. It usualy does increase pressure somewhat. A properly turned neck will provide equal pressure of retention which in turn will cause a concentric bullet lift off to the lands.

Try Ken Waters Pet Loads for some extensive experimenting with many a caliber!:dancingbanana: Amazingly, trying his pet loads will reduce much wasted time coming up with an accurate load.:runaway:

Best regards,
Henry;)
 
Arent Weatherby cartridges designed to have a bunch of freebore? As I understand the wby idea is just load to standard length and hope for the best, that's the reason they are more known for knocking trees over than winning longrange matches.
 
Rifles chambered for the weatherby cartridges do normally have a substancial freebore. because it does allow a bit more velocity to be reached with the same chamber pressure.
 
That's the theory behind freebore,but I think it eases pressure spikes allowing loads to be closer to the edge.Both Norma and Weatherby tip toe pretty close.The reason a second cartridge will spike is barrel heat. Avoid RL-25,every one in a string increased velocity,very quickly to scary.For my 264 the best powders were MagPro and Magnum.

I would like to hear your results,to pass on .
 
I use r-25 exclusively in two of my own rifles,and have tried it in other rifles,and I haven't seen any significant changes in velocity with successive shots as the barrel heats up.I do however limit my groups to three shots fired one after the other with no cooling time between, other than to reload and reaim.
 
Other 264 shooters have given the same warning and posted their velocities,they climbed even worse than mine. I only shoot three shot groups with the 264,but I do try to aim.;) I think it's a case of the skinny spikey bore. Case volume comes into play,less powder to heat up. But that's just a guess.
 
I don't shoot a 264 win mag myself and I have no experience with reloading the cartridge,so I certainly don't dispute your findings.My use of r-25 was with my 7mmstw's,my 300 ultramags ,and a couple of friends 7mmremmags.However the 7mmremmags are very similar in powder capacity and bore size to the posters 270wby.That being said,I found that r-22 offered better performance in the 7mmremmags than r-25.
 
As far as I know, Weatherby factory ammo and Weatherby loading data *assume* that you are using the Weatherby freebore.

In a custom rifle, without freebore, you may find higher pressures with lower loads than max.

From my (limited) expeience wiht Weatherby ammo, they not just run on the edge, they run on the ragged edge. Then again, I htik that some of the Olin WSM ammo does, too...

RL-25 I have used int eh 7RM and the 300WSM. In the 300WSM it seemed it got good velocities, with low pressure. Ony problem was that I had to basiclaly fill the case to the brim and compress it withthe bullet!:)
 
Well, unfortunately I got tied up today before work and never made it to the range. Will have to wait until Tuesday now to see what sort of difference the longer OAL gives me in accuracy, not to mention pressures. I've back off between 1, 1.5 & 2 full gr. on the loads from the pressure spike load so we'll start low and work it up again.
 
ILBR,
For what it's worth, with my 7 and 9.3 Mauser's I have been working on gettting loads ready, I have similar challenges as you do, even though your running completely different cartridges.

Both my rifles have very long throats so in developing the loads, bullets were seated as long as possible to determine if better accuracy could be achieved by getting closer to the lands and also to cheat to get a smidgen more powder capacity in the case. Keep in mind when doing this, your bullet may or may not be in the neck deep enough to allow the case to hold it straight, it was just for testing, not for normal hunting use.
Anyway, I could get more powder in the case for sure, but I actually reached peak pressures faster with the bullet seated out that far than if the bullet was seated .060" deeper and perhaps slightly compressing the powder charge.

The groups in my 7 Mauser got better with the shorter OAL too.
To be honest, I seem more often than not to have a heck of a time getting my rifles to group well with the bullets anywhere near the lands. I have tried from .015" to .050" and depending on each firearm the best result can be all over the map.

Best of luck in your search!
Noel
 
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