Case capacity vs pressure

[Puppy1971]

How much does available case capacity for the various manufacturers of brass affect the pressure at the same powder charge wt? Does smaller capacity equal greater pressure or the opposite? Trying to work up a AH load and can't get to the charges some are using before reaching pressure with all else being the same except brass.
Thanks in advance for any insight?
Aaron

 

[FEENIX]

How much does available case capacity for the various manufacturers of brass affect the pressure at the same powder charge wt? Does smaller capacity equal greater pressure or the opposite? Trying to work up a AH load and can't get to the charges some are using before reaching pressure with all else being the same except brass.
Thanks in advance for any insight?
Aaron

Go directly to their site. They have forums dedicated specifically to their product. Owners can also provide you with advice/recommendations.

 

[Pdvdh]

Smaller case capacity = higher pressure, with equivalent powder charges and primers and bullet.

The larger the cartridge capacity, the lesser the difference in pressures due to different brands of brass. I've weighed more than 4000 .223 Rem cases one winter from various manufacturers and cataloged their average weights. The PPU cases that weighed more than 10 grains heavier than some of the lesser weight brands of casings gave significantly higher pressures and MVs. An additional 150 - 200 fps MV.

A 338 RUM case that weighed 10 grains heavier than another brand 338 RUM case would certainly not cause as large of an increase in pressure and MV. Because the decreased case volume in the 338 RUM case would constitute a smaller percentage volume decrease (and therefore smaller pressure increase) than in the much smaller .223 Rem cartridge case.

 

[DoneNOut]

Smaller case capacity = higher pressure, with equivalent powder charges and primers and bullet.

The larger the cartridge capacity, the lesser the difference in pressures due to different brands of brass. I've weighed more than 4000 .223 Rem cases one winter from various manufacturers and cataloged their average weights. The PPU cases that weighed more than 10 grains heavier than some of the lesser weight brands of casings, gave significantly higher pressures and MVs. An additional 150 - 200 fps MV.

A 338 RUM case that weighed 10 grains heavier than another brand 338 RUM case would certainly not cause as large of an increase in pressure and MV. Because the decreased case volume in the 338 RUM case would constitute a smaller percentage volume decrease (and therefore smaller pressure increase) than in the much smaller .223 Rem cartridge case.

Good stuff here. I also discovered with brands of brass that the cartridge matters. Brand "A" .223 might have less case capacity than other brands of similar cartridge, but hop up to say, a 300 WM and Brand "A "has the most case capacity.

 

[PddPdd]

I've recently seen 3 grains variance between Peterson & Winchester brass in 7-08. Definitely needed to modify the load to get back in tune on pressure/velocity.

 

[martinakl]

How much does available case capacity for the various manufacturers of brass affect the pressure at the same powder charge wt? Does smaller capacity equal greater pressure or the opposite? Trying to work up a AH load and can't get to the charges some are using before reaching pressure with all else being the same except brass.
Thanks in advance for any insight?
Aaron

Do you have a chronograph (or know someone with one) to check what speeds you're getting?

 

[Mark37082]

Interesting posts and it makes a great deal of sense to me. I believe ADG recommends reducing powder charge by 10% from other brass loads. 10% seems like a significant decrease when loading cartridges in the 60+ grain range. I start usually at the minimum recommended book load and work my way up watching for excess pressure signs both in velocity and bolt lift changes. It is my understanding that undercharging can actually create pressure issues as well. I have never started below the book minimum. Should I rethink this?

 

[Pdvdh]

I have never started below the book minimum. Should I rethink this?

IMO, no.

 

[Puppy1971]

Do you have a chronograph (or know someone with one) to check what speeds you're getting?

Yes, been running the loads over a Magneto but pressure out several grains under loads on AH load data page.

 

[Veteran]

When I measured my .338 LM
cases I found huge differences in different manufacturers volume for my brass.

I had some Hornady cases and the average volume by weight of water was only 107.

On the other hand my Lapua brass averaged 116.1

So, the same charge I would shoot in the Hornady cases would have a wild increase in muzzle velocity and pressure vs. my Lapua cases

Say I developed a hot load using my Lapua cases.......that load could blow me up if I shot it in a Hornady case.......

You have to measure your case volumes and develop loads using only 1 brand and type of brass if you want to be safe and get low ES and SD and consistent small groups.

 

[James DeTorre]

Shot 7-08 with Stabil and HH 131 using PPU brass and got pressure signs real bad with the " mid book" load.Using brass I got no pressure signs With exact same same primer and powder charge. Interesting to know it wasn't me.

 

[James DeTorre]

Had pressure issues with PPU compared to Nosler brass all else ( powder primer rifle ) same.
thought it was me.

 

[QuietTexan]

Interesting posts and it makes a great deal of sense to me. I believe ADG recommends reducing powder charge by 10% from other brass loads. 10% seems like a significant decrease when loading cartridges in the 60+ grain range. I start usually at the minimum recommended book load and work my way up watching for excess pressure signs both in velocity and bolt lift changes. It is my understanding that undercharging can actually create pressure issues as well. I have never started below the book minimum. Should I rethink this?

Per ADG's current website:

We recommend using a reputable load data source and working up from their recommended minimum starting loads.

Don't rethink it, you're doing the correct process for load development by using a starting load and working up. The 10% reduction recommendation is if you're changing brass on a known load, not a starting load. For example, I hit max pressure at 61.0gn in a 30-06 with thrice-fired Hornady brass, and changed to Peterson brass. I dropped from 61.0gn to 56.0gn and moved back up and found where speed and pressure were in the new brass at 60.0gn.


Undercharging can definitely cause pressure spikes, if there's too much air space in a case a larger amount of powder can ignite faster and cause pressure to spike. That's why when loading subsonics you work DOWN towards a speed target and powder charge instead of trying to start slow with a super small charge and work up to 1050fps. Also so you don't stick a bullet in the barrel, but that's a different issue.

 

[Steves1911]

Had pressure issues with PPU compared to Nosler brass all else ( powder primer rifle ) same.
thought it was me.

Ive used ppu in 30-30, 308 and 300 win and found they seem to run on the low end of case capacity and reach max pressure sooner.