Flash hole size

[scott/r]

When I first starting using lapua's palma brass just recently, I was under the impression that my speeds wojld have gone up, but they have dropped by about 40fps for the same powder loads compared to the large primer lapua brass.
Initially I thought it may have been a combination of new batch of powder and changing to cci 450 primers, so I tried some left over powder and br 4 primers in a few rounds to confirm this idea. No such luck, it was about 10 fps slower again.
So then I tried a few of the old large primer brass, which weighs within .2grn as the palma brass, with the br 2 and load I was was using, and presto, the speeds were back to normal.
So, now I'm thinking that it's got to be the small primer causing the slower speeds, but then I sort of remember reading or hearing somewhere about flash hole sizes making a difference as well.
Am I dreaming or is this an actual thing? I was going to drill out the hole to the same size as the large primer brass, in a couple pieces of brass to try, but I thought I better ask people that would have an idea of whether I'm just wasting brass and time, or if I'm just going to hand grenade my rifle?
And info or ideas would be great fully received.
Scott.

[sungazer]

I have seen the same thing and went through the experimenting process. The size of the hole makes the majority of the difference.

[UL1700]

An absolute mine of information regarding SRP 308 Brass...

http://www.targetshooter.co.uk/?p=2613

[scott/r]

An absolute mine of information regarding SRP 308 Brass...

http://www.targetshooter.co.uk/?p=2613

That's a good read. Thanks
Scott.

[Rich4]

I would suggest that you are just seeing the difference between energy of large to small primers, they do contribute significantly to the overall fire

[Pommy Chris]

I would suggest that you are just seeing the difference between energy of large to small primers, they do contribute significantly to the overall fire

My conclusion too, and as we cant control how much energy each primer has but we can control the powder by accurate loading IMO the small rifle primer should be more accurate as there is less variance as the overall energy from the primer is a smaller proportion. In other words if the primer is 5% of the load or 2 % of the load and the primers vary by 10% primer to primer then that is 10% of 5% or 10% of 2 % and the latter is better of course.
Chris

[Tim N]

I thought the Palma brass was preferred not due to the small primer- rather the extra brass at the rear allowing the loads to be increased somewhat for higher velocities?

[scott/r]

I would suggest that you are just seeing the difference between energy of large to small primers, they do contribute significantly to the overall fire

My conclusion too, and as we cant control how much energy each primer has but we can control the powder by accurate loading IMO the small rifle primer should be more accurate as there is less variance as the overall energy from the primer is a smaller proportion. In other words if the primer is 5% of the load or 2 % of the load and the primers vary by 10% primer to primer then that is 10% of 5% or 10% of 2 % and the latter is better of course.
Chris

Makes sense. I've got a maximum of 4.9 sd in powder loads from 45.0 to 45.4, but as I said it's 40 fps slower than lrp cases.
Scott

[Pommy Chris]

I thought the Palma brass was preferred not due to the small primer- rather the extra brass at the rear allowing the loads to be increased somewhat for higher velocities?

It is, but IMO the smaller primer has its advantages too.
Chris

[Rich4]

Much more so than relying on the thicker brass, to me that’s only extra insurance, not carte blanche to load er up, as Chris said it’s to minimise variables , easy to weigh powder, primers are a bit trickier

[sungazer]

Like I said I did some experimentation and found that the Large Primer pocket brass to weigh exactly the same as the small primer pocket brass. Given the variation in both cases they were the same. I dont think the more brass in the base of the SR Primer Palma brass is still true.

I also did the tests with the small primers with the the hole drilled out to the same as the LR primers the velocity increased by 30fps. The actual primer made very little difference. it was all about the size of the hole.

[scott/r]

Sungazer, did you have the same good consistency with the larger flash hole as the smaller one?
Scott.

[sungazer]

The smaller holes tightened up the ES. I think that is a common finding of people when they switch to Palma Brass. so from what I found the hole size was responsible for a lot of that.
What I couldn't do was try large primers with small holes. Perhaps you could get some brass from Bertram that he had not, put holes in them and experiment further.