260AI "Palma" brass v 260 Lapua brass

[SDDasher]

I've tested the performance on the two different mentioned brass with a significant difference in velocities of the "308" small primer brass vs fire formed 260 Lapua brass.
Components were the same using 140 Berger Hybrids, H4350,& CCI 450's-BR2's.

At each powder weight separation the reformed "Palma" brass 260AI loads were 50-70 FPS slower than the same loads in the FF 260 Lapua brass. Interested in hearing if anyone else has experienced similar or different results.

Interestingly, accuracy did not seem to be significantly impacted by the difference in velocities when cross checked to equivalent speeds.

 

[mikecr]

What was the MV difference with both kinds of brass at fully fire formed?

 

[SDDasher]

What was the MV difference with both kinds of brass at fully fire formed?

Mike, if I understand your question, the Maximum Velocity difference between fully fireformed brass of both kinds was 70 FPS for the same load in both cases. The Palma 308 being 70 FPS slower.

 

[Sheldon N]

My understanding is that the velocity difference can be somewhat explained by the extra energy imparted by larger primer size of standard brass, assuming that the internal capacity of both fireformed brass was the same.

 

[Sniper338]

Interesting. I use regular lapua 260 brass. Ive thought about trying palma brass, but dont sound like its worth fixing something that aint broke..

 

[JohnKielly]

Possibly H4350 is a mite slow to be well lit by SR primers with that case capacity. I've never used anything slower than Varget with similar case capacity calibres, but of course, translating from one to the other ain't exact science.

 

[SDDasher]

My understanding is that the velocity difference can be somewhat explained by the extra energy imparted by larger primer size of standard brass, assuming that the internal capacity of both fireformed brass was the same.

I don't have my data book in front of me, but I'm pretty sure the Palma brass has about one full grain more H2O capacity than the 260 Lapua brass. I've wondered if this extra internal volume might be the cause for the slower speeds.

 

[Terry Altom]

Very interesting. I'm working on my first 260AI now. Just formed some from Winchester 243. Have five Lapua 260 from a friend for comparison along the way. I ordered 200 Lapua 308 Palma as those are supposed to handle a little higher pressure, which seems like a good idea as I'm using H4831(sc). I will definitely be using small rifle magnum (CCI450).

 

[Quickoz]

I run a 7mm08AI and run RL19, H4350 fine with CCI450 primers. Several people in Australia have run 260AI with palma brass with varied powders to great success aswell.

In my 7mm08AI, the case life is awesome running 180gr and H4350.

 

[SDDasher]

Looks like it is taking about 5-6tenths of a grain more of H4350 in the Palma brass to reach same velocities of the FF 260 Lapua loads.

At 44.4 grns of H4350, CCI BR2,140 Berger Hybrid velocity averaged 2908fps.

At 45.0 grns of H4350, CCI 450,140 Berger Hybrid velocity averaged 2905fps

The "only" difference I can detect is that the BR2's seemed slightly flattened.
All brass was checked with a go/no go primer pocket tool with none showing signs of loosening up.

 

[Sheldon N]

Have you measured case capacity to compare the two?

 

[Laurie]

I can't comment on 260 / 260AI, but in 308, the Palma case usually needs around an extra half-grain of powder compared to the standard version to produce the same MVs. My lots of the pair have near identical fireformed capacity, so it's not a capacity issue in this instance. It's generally ascribed to the less powerful primer and the small dia. flash-hole which changes the charge burn rate / behaviours. A 1gn water capacity variance will affect pressures and MVs too.

In 308 with 'heavies' SR Magnums / BRs happily and reliably ignite charges as high as 47 and 48gn of relatively slow burners such as Viht N150/550. I'll shortly try N160 , N560, and N165 in 7mm-08 with heavy bullets in a long-throated 7mm-08 in reformed Palma brass, so will see how the small primers work out with them compared to the standard Lapua case.

In several years experience with these cases in 308 Win for FTR, I've had trouble (hangfires) with one ball powder (H. CFE223), but good results with another (H414). The only other ignition issue I've seen has been performance (reduced MVs / increased ES values) with some extruded single-base powders in temperatures below 5-deg C (~40 F), but again it was powder grade specific even with a single make.

 

[SDDasher]

I went back and checked the H2O volume in both formed cases and found the fire formed 308 brass has almost 5 more grains of H2O volume than the 260 Lapua fire formed brass. This could possibly explain the difference in velocity with the same components sans brass.

 

[Terry Altom]

If the 308 Palma has more capacity that's a good thing so I can fit more 4831 in there

 

[SDDasher]

If the 308 Palma has more capacity that's a good thing so I can fit more 4831 in there

This is true; however I read on another thread the small primer brass does not show the pressure the way the large primer brass does, so carefully work up your loads.

 

[Sheldon N]

I went back and checked the H2O volume in both formed cases and found the fire formed 308 brass has almost 5 more grains of H2O volume than the 260 Lapua fire formed brass. This could possibly explain the difference in velocity with the same components sans brass.

That would definitely explain the velocity difference. Small rifle primer, more resistance to pressure, plus more case capacity? Win-win if you ask me.

 

[SDDasher]

Oooooops math correction; difference is 3.34 grain of H2O volume instead of almost 5. Sorry, I'm mathematically challenged sometimes w/o a calculator.

 

[Sheldon N]

That makes sense. Quickload predicts almost exactly a 70fps swing with a 3.3g change in case capacity.

 

[Geno C]

Looks like Palma brass form my new 260ai! Cheaper than 260 brass and more room for powder?! I was always told if it sounds too good to be true it probably is. We shall see

 

[mikecr]

Why is more powder a good thing here?
Do you not have enough capacity from improved Lapua 260 brass?