Thoughts on switching primers

[laylowlong]

I am working on loads for my 7mm saum, and am currently running 57.5 gr of 4350 on rem brass with 180 berger VLD's. My testing has been superb using the BR-2 primer, but now I am out of them and must switch either to the CCI military primer, or a batch of CCI 200. Any thoughts on which might be more consistent or other considerations between the primers... hotter... colder.
I did some testing yesterday using the 200's and noticed the groups have opened up slightly, which is a bit discouraging. Any thoughts would be appreciated.

 

[Jon Lester]

Re: Thoughts on switching primers


just my 2 cents butt......... I have fooled with a lot of different primers in my TRG-22 and a super accurate PA 308 during the great primer shortage of 08-09.
My findings reveal that I cant really tell any difference in Group size or Vel in any syd primers that is definately within the noise of my shooting ability.
However to attain the same vel with mag primers I can cut the varget by about .2-.3 gr.

 

[Hummer]

Re: Thoughts on switching primers

Switching primers is a deep subject and subject to more variables than can be imagined.

For instance I was running some studies where I took the same cases and loaded Federal, Winchester and CCI BR2 primers with the same loads and same bullets. 10 rounds each.

I went out and chronographed them and the difference in velocity was as much as 50 fps. SD could not be relied on with only a ten round sample but there was a definite velocity shift between them.

You get another big variable with neck tension. The name of the game is uniform neck tension shot to shot. This will affect velocity between rounds. Also another big variable is propellant.

You can do the above test with a different propellant and get totally different results. You slowest average velocity per primer manufacturer in first test my well be the fastest velocity in the second test. The differences are not repeatable between propellants.

The biggest variable I found is propellants.

 

[laylowlong]

Re: Thoughts on switching primers

Thanks Hummer. Yesterday, I tried a number of different variables as far as powder charges, and seating depth, all still using 4350. The brass is once and twice fired,
and I was neck sizing. Interesting thing is, I tried FL sizing some cases, using my "sweet spot" seating depth, and bumped the powder charge up two grains to 57.7
and that seemed to give the best result. Still the grouping was not as consistent,
and of course consistency is what I want. Another variable is that I worked up the
best loadings a few weeks ago in extremely low humidity, high temp conditions
(105deg outside temps) and now its 80% humidity and 7o deg. I will be back at the range tomorrow for further work. After working up a load that bested my own expectations, it is hard to accept less, and I want to make it back to the promised land.