uniforming primer pockets?

[Curt]

Are uniforming primer pockets with a tool like Sinclairs a must for a AR service rifle?

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[P. Greaney]

I believe the rationale for uniforming primer pockets is that it provides for the uniform seating of the primer and ensures that the primer does not protrude above the base of the cartridge case.
The first reason ensures that the primer does not move forward when struck by the firing pin as it is seated firmly in the pocket and the second reason ensures that the primer does not protrude boyond the base of the cartridge case and you do not get a "slam fire" when the bolt moves into battery.

I don't believe it is necessary, but consider that I just spent several days uniforming the primer pockets of three thousand cartridge cases with the Sinclair tool chucked into a hand drill.
I don't know any serious high power competitor who doesn't uniform primer pockets of the ammunition that they reload and use in competition.

[Mudcat]

I don't know any serious high power competitor who doesn't uniform primer pockets of the ammunition that they reload and use in competition.

Dang....I wonder how I made it as far as I have and have never uniformed a primer pocket! Must be lucky I guess....or not a serious high power competitor.

John

[MEHavey]

I started uniforming when I began getting high primers in S&W500 brass a while back. (So high I had trouble getting them out of the shell holder on occasion.) That made me more sensitive to the fact that more brass seemed to producing more high primers as a rule of late. `Don't know when except the pocket corners don't seem as cleanly swaged "...as in the old days."

When I started reloading for both the AR and the Garand it just became do-it-everytime.

[Curt]

I am trying to get my WSR primers to exist in my R-P brass and Win brass. I had been uniforming the pockets but i think that is is adding to my problem ever so slightly. I have backed my load down 6/10's of a grain and I have stopped losing primers but still have significant push back of the primers.I ordered a chronograph to see what these things are really doing.I am close to a full grain under max load for a 77 SMK. I put a primed case in my rifle yesterday to test a new firing pin, I placed the muzzle against a folded towel on the floor as to not scare the dog and the primer backed out almost completely.
The down side is I would have better luck at winning the lottery than finding other brands of small rifle primer to try. I am sitting on 10K wsr's I bought at Perry last year and have about 2K each once fired R-P and Win brass I bought from the local police range.Now my salary got cut and my budget is shot so I am just hoping this works for the season. I am out of patience and funds.

[MEHavey]

>
> "...but still have significant push back of the primers....."
>

That sounds like a headspace issue, not a primer/seating problem.

>
> I put a primed case in my rifle yesterday to test a new firing pin, I placed
> the muzzle against a folded towel on the floor as to not scare the dog and
> the primer backed out almost completely.
>

"...almost completely..." ? Heavy duty.... headspace, either the rifle or (more likely) your sizing die setup relative to your rifle's working headspace. The amount that the primer is backing out is a measure of the excessive room your case has relative to the bolt face after the firing pin kicked it forward. I'm (kinda) surprised it fired at all if that's the case.

[P. Greaney]

Dang....I wonder how I made it as far as I have and have never uniformed a primer pocket! Must be lucky I guess....or not a serious high power competitor.

John

I would imagine that you made it as far as you have by shooting instead of spending time uniforming primer pockets. I would further speculate that luck did indeed play a part, albeit a minor one. As to how serious you are about the sport, based on what I have read of what you have posted in the past, I would regard you as devoted to it.
Last, I don't know you.

[Curt]

Actually the chamber is very tight.About alot tighter than my other AR's were.I am bumping the shoulder back about .003

[limazulu]

Are uniforming primer pockets with a tool like Sinclairs a must for a AR service rifle?

I never used one, at first. You need a relatively clean primer pocket for the primers to seat well. I used a small dental pick but I have a bad neck and that didn't help matters as build up would be harder for me to remove after several reloads (even using the pick). I used the primer pocket uniformer in a drill and it saved my neck and cleaned up the pocket like new. I don't reuse it on a case except after about three reloads so with six reloads on a case I've used it twice (I use the pick inbetween).

[MEHavey]

For the primers to be doing as you suggest, the chamber's got to have enough (spare) room in it for the primers to back out a lot. Otherwise the cases are literally "boxed" in between the bolt-face and chamber shoulder, ...with nowhere to go.

Primers do always back out slightly (the headspace allowance) upon ignition, but then get slammed back flush as pressure expansion stretches the case head back against the bolt face. Low pressure loads that don't stretch the heavier base web thickness of the case enough will leave that primer (slightly) raised by the amount of normal headspace gap clearance (or less).

But that you can fire a primer-only case and get the primer to back out *that much* says there's a lot of (extra) room somewhere.