Why are my primers flattening?

[noone]

Here are some of my reloading steps?
LAPUA CASES
1. Tumble cases to clean them
2. brush out inside of the case necks
3. Grease cases by rolling them on a pad
4. full length size to set the shoulder back .003-.004 inch
5. trim to length
6. brush out primer pocket
7. deburr inside and outside of case neck
8. use 30.3 grains of W748, CCI 450 primer, 123 grain Scenar seated to C.O.A.L. of
2.260 (max load is 30.5)
9. Chrono says that the velocity in winter is 2470 fps. It goes up to 2540 in the heat of summer.
10. Loads are consistent with velocity, yet most of my primers seem quite flattened.

The brass has been fired many times, and case necks were annealed, and will be annealed again after the next firing as they are already primed to be loaded.

If my velocities are remaining consistent, is the flattening of primers anything to be concerned about?

[Drifter]

Which brass?

[noone]

Sorry, I did leave out an important consideration. It is Lapua brass, I bought all the brass new, and although primers flatten, all the primer pockets are still very tight. I modified the original posting to put in the Lapua cases. Thanks for catching that.

[mongoosesnipe]

Flat primers are usually a sign of pressure but if cases have had a lot of loads through them your flash holes maybe a little eroded and letting a little more pressure back to the primer the cases may be nearing the end of their useful life how many times is many times

[LRRPF52]

Flat primers are also caused by extra headspace. If you aren't seeing erratic spikes on your chronograph, and the primer pockets are tight, sounds like you're good to go. I have some factory loads that flatten the primers, but ES is 8fps, brass looks fine, no noticeable bulges in the case web above the extractor groove on the wall, and I've fired a bunch of them. They also group .79 MOA.

Looks like you're using the AA load data for W748 and the 123gr Scenar. Do you have the 6.5 Grendel Reloading Handbook? It has a good chapter on detecting pressure signs, starting with chronograph reading and interpretation, brass & primer signs, along with an AR15 gas system explanation and how that relates to reloading for the AR15.

[noone]

The brass is mixed lots. Some has been reloaded 2-3 times, others closer to 10 times. I discard cases when necks crack, or the primer pockets are loose. When I initially received the Lapua cases had inconsistent primer flash holes. So I uniformed them with a drill bit so they were all the same size. My velocity spread is pretty consistent in both summer and winter, although the ball powder is tremendously effected by temperature. I get 50-70 fps more velocity in the summer than winter, so I make up the loads so that when the velocity is at it's peak, I'm still a wee bit under the max load.

The rifle operates very smoothly, and I don't think it is a headspace issue as I measure the brass to a datum line on the shoulder, then only set it back about .003 shorter than the longest Grendel chamber I have. Rounds have about .0015 between the datum and chamber of the short grendel chamber as there is about .0015 difference between the two chambers.

[rickOshay]

Have you measured your chamber with the scenar? You may be too long?

[sneaky one]

rick, exactly-
what is the jump to rifling contact-Noone ? Yikes, have you measured it? At all?
From federal-there maybe-maybe will be an off batch of primers. Very rare, very.
Bill A stated long --ago--that all bullets need a bit of jump, he posted -IIRC-.020. or .030 as the minimum- yes I know most of usl found the sweet spot on our own.

[noone]

HOLY CRAP! I can't believe I overlooked something as basic as the jump to the rifling. I haven't even checked this rifle for that. Something I always check on my precision rifles is jump distance, and I wrongly presumed that the chambers in these rifles would be OK.

Thanks for the idea. I'm going to check and see if that is the issue. I have a couple of different mechanisims to measure jump to rifling, but oddly the one that seems to give me the most consistent and reliable readings is putting candle soot on a dummy round and dropping them into the chamber until there is no displacement of the soot. Then I know I am no longer touching the lands. The "precision" ones from Hornady, Sinclair, and my home made version of the same tools just aren't as accurate as the soot method...but at least the Sinclair, Hornady, and my home made version all give similar results. The soot is just more accurate for me as "feel" has less to do with it.

Thanks very much! This is precisely why I asked the question here. I'm just surprised that I never thought to check that.

[noone]

Just to let you all know, the bullets were jamming into the lands. When I checked using my soot method, the lands were clearly visible on the bullets when the C.O.A.L. was 2.260. By shortening the C.O.A.L. I got rid of the issue. I guess it is better to have a short throat than an extra long, or shot out one.

Thanks very much to all who responded.

I only have about 100 rounds left of the old lot of ammo, so when I go to the next loading (about 500-600 rounds) I expect my accuracy to improve. But, of course, I will have to work up loads again. Over time, as I shot up the ammo, I have been neck turning all the cases as the necks were causing runout problems. Next time, all the cases will get annealed...

[LRRPF52]

With being jammed into the lands, your start pressure was peaking over max then. Great that you identified this and posted back. I never asked what chamber you have, which is usually one of my first questions.