Preimer pocket prep

[jmason]

When uniforming primer pockets for large rifle cases; what depth should they be uniformed to?

 

[AJ Peacock]

The uniformer should automatically stop at the correct depth, as it will have a shoulder on it. There is a SAAMI spec, but I can't remember what it is.

AJ

 

[Winchester 69]

Re: Primer pocket prep

SAAMI spec for large rifle primer depth is 0.132 maximum, 0.125 minimum.
.

 

[jmason]

So the set screw in this thing is must be for changing the blade when it gets dull.

I measured it and it falls in the upper 3/4 of the spec. I also just tried it on a few cases and I'm a little shocked at the amount of material it takes out as well as the differing amounts between cases. Thanks for the help!

 

[jmason]

Update

I just noticed I misspelled "primer".

Report:

I made a couple cases a little too uniform! The primers fall back out! Might be from some high pressure loading before. That's not the first time that's happened. I measured the blade (it protrudes less than sammi max) so I know it can't cut more than the saami depth out but a few primers look low. Hopefully I don't get misfires.

Is it the general consensus that if the primer stays seated that all is well?

 

[Winchester 69]

Re: Primer pocket prep

So the set screw in this thing is must be for changing the blade when it gets dull.

And for re-setting the cutting depth when it self-adjusts. RCBS?
.

 

[Quarter Round]

Re: Update

Your primer uniforming tool will remove excess brass and square the bottom of the pocket. The primers will be seated uniformly below the base and flush against the bottom of the pocket. It should not cause loose primer pockets, but that is usually attributed to high pressure as you stated and or soft brass.

 

[jmason]

Re: Primer pocket prep

And for re-setting the cutting depth when it self-adjusts. RCBS?
.

Yep. RCBS. I have it bottomed out. My thought was the pressure on the tool is always downward (have trim mate) so it should stay there. Unless.......

Charles

I guess the misfire concern came from seeing the primers below the base of the brass. I'm suprised primers don't get peirced when you don't uniform the pockets. The primers appear lower to the naked eye. I did notice before doing this that some primers didn't seem to sink the entire way in before.

 

[Winchester 69]

Re: Primer pocket prep

The benefit of uniforming the primer pockets is that the primers seat completely.

Pierced primers are caused by excessive clearance between the firing pin and its bore in the bolt. The metal is extruded into the gap.
.

 

[anachronism]

Most primer pockets are swaged with a tool that's slightly tapered. It has to be tapered to allow the tool to be removed easily. When we uniform primer pockets with a reamer, we take that taper out. My experience has been that this could decrease primer pocket life a bit because primers in factory pockets seem to seal more towards the bottom of the pocket, in this tapered area. Most primers that I bothered to measure (I was bored) had a slight taper in the opposite direction and were larger at the mouth of the primer. I know this is really hard to follow, but think of two cones one slightly smaller than the other, placed mouth to mouth. One mouth will fit inside the other, then go a short distance before it can go no further. Hopefully, I'm not too tired right now to explain this coherently. I'm sure I'll get flamed anyway...

 

[jmason]

makes sense to me. by the way I had no misfires.....