Case capacity effect on pressure?

[Trey Veston]

Loaded up some .308 rounds last week using PPU virgin cases and 44 grains of Varget. Max load is 46 grains. According to my Hornady manual, 46 grains is a compressed load with the 165 grain bullet I was using.

But I noticed that even with the mid load of 44 grains, it was compressed.

Someone suggested that PPU brass is military spec and thicker and might have less case capacity.

Tonight, I checked both my PPU and Winchester virgin brass and sure enough, the PPU cases have nearly 2 grains less capacity.

I'm thinking it should be fine, since I was down 2 grains from max. Correct?

 

[Trey Veston]

Hodgdon seems to think so...

http://www.hodgdonreloading.com/reloading-education/reloading-beginners/compressed-loads

Normally a pistol or rifle shellcase is considered full, or 100% loading density, when the powder charge sits at the base of the bullet when the bullet is fully seated. It is possible with some powders and cartridges to increase the powder charge slightly above this point, such that when the bullet is seated it actually compresses the powder charge slightly. This condition is known as a compressed load.

Hodgdon notes in its reloading data if the subject charge is a compressed load. A full case, or lightly compressed charge is an ideal condition for creating loads with the most uniform velocities and pressures, and oftentimes, producing top accuracy

 

[TBL65]

I had a similar situation loading 223 in LC brass using H4895 and hornady 69gr bthp.

Hodgdon says 26grs is a compressed load but I could start to feel it being compressed before then and I was seating a little longer than the listed OAL. That’s where I stopped, haven’t had a chance to test it though so I can’t comment on it’d affects but the above post makes a good point!

 

[ArchAngelCD]

Loaded up some .308 rounds last week using PPU virgin cases and 44 grains of Varget. Max load is 46 grains. According to my Hornady manual, 46 grains is a compressed load with the 165 grain bullet I was using.

But I noticed that even with the mid load of 44 grains, it was compressed.

Someone suggested that PPU brass is military spec and thicker and might have less case capacity.

Tonight, I checked both my PPU and Winchester virgin brass and sure enough, the PPU cases have nearly 2 grains less capacity.

I'm thinking it should be fine, since I was down 2 grains from max. Correct?

If there are no signs of pressure and the load shoots well I would say it's fine.

 

[Grumulkin]

Whether or not case capacity matters depends on how big the case is. For cases the size of the 308 Winchester and larger and a load that isn't hot rodded, I have never found varying case capacities to make a difference safety wise.

Safety is one thing; load performance is another. For instance if you take the same load with say Federal cases and Remington cases, it is likely that the performance won't be the same accuracy wise or velocity wise. Even if you take virgin Federal cases and compare the same load with once fired full length sized Federal cases, performance will likely be different between the two sets of cases.

 

[lordpaxman]

I'm thinking it should be fine, since I was down 2 grains from max. Correct?

This would be a perfect case for Quickload, assuming that software can predict your assemblage of components. I don’t have it but maybe someone on the forum does.
There’s nothing wrong with published compressed loads, as you point out they may provide an optimum load. If it were me, I’d load a handful of the starting load and test those first, watching for pressure signs and work my way up to your mid-loads. In all likelihood you’re mid loads are ok but I wouldn’t want to be the one saying “go for it” and then have something bad happen. My Varget loads seem to be well behaved (mid to max loads) but they’re not in .308.
Edit: Forgot to ask, you’re implying since you were -2gr of H2O in case capacity and that’s related to being -2gr of Varget from max, and is ok? There’s a correlation but not 1 for 1.

 

[sparkyv]

Should be, but if you're concerned, load up a few lighter loads and work up to 44gr., checking for signs of overpressure as you shoot them in progressive load order.

I'm thinking it should be fine, since I was down 2 grains from max. Correct?

 

[243winxb]

Varget is said (internet) to be different from lot to lot. Some fast, some slow. Add in the brass & 44 grs could be maximum?
I would load 1 shell at starting load of edit 42.0 grs .Check for pressure.

Make sure the chamber is free of oil or solvent.

Example of H4831 https://apps.dtic.mil/docs/citations/ADA572333

 

[MEHavey]

CAUTION: EXAMPLE CURVE SHAPE ONLY -- THIS IS NOT LOAD DATA
The following includes data generated by calculation in QuickLOAD software based on a particular powder lot, the assumption the primer is as mild as possible, and assumptions about component, chamber and gun geometry that may not correspond well to what you have. Such data should be approached by working up from published starting loads. DO NOT USE THIS DATA FOR ANY ACTUAL LOAD. Neither the writer, The High Road, nor the staff of THR, nor QuickLOAD's author nor its distributor assume any liability for any damage or injury resulting from use of this information or information derived from it.

Appears pressure goes (is calculated) as a 2nd-order polynomial relative to case capacity:

 

[FROGO207]

I will usually weigh a few random cases before any trimming of a headstamp and average the weight. Then compare weight with a sampling of the standard case used and adjust my charge accordingly. Weighing and getting H2O seemed like more work than needed for hunting/blasting ammo.

 

[243winxb]

I would load 1 shell at starting load of edit 42.0 grs .Check for pressure.

I looked at Hodgdons starting load.

Compressing powder may change its burn rate, when the units are crushed, making them smaller.

 

[kcofohio]

I had the same thing happen to me with Perfecta brass. The load had been worked up on LC brass. Same charge of CFE223 and same bullet. I shot 3 rounds and stopped. The shots were harsher. And the primers were flush with the case head. The rest of the loads were put away to be pulled one day.

 

[jmr40]

Yea, it can matter. I have some military LC 308 brass. A max load of Varget won't even fit in the case. It will spill out on the loading bench with that much powder, yet works easily with most commercial brass.

 

[Trey Veston]

Didn't get to go to my dad's range, which has official 50, 100, and 300 yard targets, plus a shooting bench all sorts of sandbags and rests. I had to run down to the family cabin to check on wind damage, but I brought the rifle to at least get a function test done.

I made a impromptu rest on the deck using deck chair cushions and guestimated 100 yards and used factory Federal ammo in 150 grain to sight it in. It was windy and the scope is sketchy, still, was able to walk the rounds into where I wanted them and put the last two rounds touching. Looked promising...



Then I broke out the compressed load ammo to check for pressure signs. Noticeably more recoil and an awful group...



But the primers look fine. Compressed load on the left and factory federal on the right...



Was out of time since I had to get back to town and meet my girlfriend for dinner, so only fired one more group using 150 grain Hornady boat tail bullets and 44 grains of Varget.

They were weird. First two shots were centered and about an inch apart, then the last three shots were 3" low and to the right, but were all touching.



I can't begin to figure out what is going on yet. I was using a crappy rest, in wind, with a crappy scope, and my first time firing the rifle. I think some better glass, a solid rest, and some more trigger time will get me to the sub-moa I was hoping for.

Still, rifle functioned 100%, recoil wasn't bad, and I think the potential is there.

My impromptu shooting bench...

 

[AJC1]

Your hold, body position, wind and trigger discipline are large percentages of accuracy. Your loads and shots will get better as you practice. Moa at is a decent first goal. Run OCW tests and then use the same cases and your results will get better. If you mix cases your work will take much longer. Varget is not easily overloaded so you should be safe as long as your not using long drop tubes and crushing to the max.

 

[GotHim]

Yes long drop tubes like the one Forester makes helps with really full cases. Its hard to say whether it was the gun/scope or if you pulled or jerked when firing. Id try from a bench or table with a rest/sled on it taking the human equation (except trigger pull) out of it.

 

[lordpaxman]

Then I broke out the compressed load ammo to check for pressure signs. Noticeably more recoil and an awful group...

I’ll admit I experience a certain pucker factor when touching off new rounds so close to precious body parts. It hinders good trigger discipline and in general precision. It’s good to see everything hung together, congrats on the reloads!
If it’s a new rifle, barrel break in may take a bit and as far as groups go you might not be on an accuracy node wrt powder and COL. There’s a good many variables all working against you and the sled suggestion above can take away some of them.
Those Federal primers in your picture are typical of what I see in my reloads. They say Federal primers are “soft” and more sensitive meaning less firing pin activation required for setting off the round so they may flow a bit more even in normal pressure rounds. What primers were you using?

 

[Trey Veston]

CCI Magnum large Rifle.

 

[AJC1]

CCI Magnum large Rifle.

You may find that you get a lot better standard deviations and accuracy using a standard primer on a 308 case. They've gone as far as changing to a small rifle primer to improve accuracy

 

[Trey Veston]

You may find that you get a lot better standard deviations and accuracy using a standard primer on a 308 case. They've gone as far as changing to a small rifle primer to improve accuracy

I have 1000 or so Remington 9 1/2 primers and I think around 1000 of the CCI regular large rifle. The magnum version was all that was left locally, so I was trying to use those before dipping into my stash. I'll have to try the other ones on subsequent loads.

 

[AJC1]

I have 1000 or so Remington 9 1/2 primers and I think around 1000 of the CCI regular large rifle. The magnum version was all that was left locally, so I was trying to use those before dipping into my stash. I'll have to try the other ones on subsequent loads.

Just use standard for testing and once your load is dialed in you will know what kind of compromise your making.

 

[lordpaxman]

You may find that you get a lot better standard deviations and accuracy using a standard primer on a 308 case. They've gone as far as changing to a small rifle primer to improve accuracy

Yes but the published load data used a Fed 210M. It’s a best practice to start with published data or as close to it as possible. I’ve only done limited testing on different brands and M vs non-M, and haven’t found any significant differences - of course that doesn’t mean there aren’t any. There’s also the case prep step of flash hole uniformity that can add consistency to ignition. For SDs you’ll need to get a chrono but can make an assessment on precision without one. Welcome to the world of variables!
I’d expect that primer picture that was posted with CCI’s. They look like similar to mine in ‘06.

 

[AJC1]

Yes but the published load data used a Fed 210M. It’s a best practice to start with published data or as close to it as possible. I’ve only done limited testing on different brands and M vs non-M, and haven’t found any significant differences - of course that doesn’t mean there aren’t any. There’s also the case prep step of flash hole uniformity that can add consistency to ignition. For SDs you’ll need to get a chrono but can make an assessment on precision without one. Welcome to the world of variables!
I’d expect that primer picture that was posted with CCI’s. They look like similar to mine in ‘06.

Following a load manual is good.
Understanding the cartridge your loading and reading multiple manuals is better.