Primer Pocket Uniforming

[bill123]

Has any testing been done that shows uniforming primer pockets has any effect on velocity spread or precision?

 

[Mikecr]

I doubt it.
I had a firing pin slip under it's set screw once that led me to striking tests. What I saw through adjustment of pin protrusion from bolt face, was a coming into and out of best precision.
It was very similar to results of bullet seating testing.
This testing was from a standard primer seating, which had primers preloaded to 4thou crush in standard pocket depths(as uniformed with the fixed Sinclair tool). The seating was with an indicated K&M, and my headspace is always set to 1thou bump.
Through prior testing I've found that different primer brands perform better with either 2, 4, or 5thou of crush(CCIs requiring the most, Rems the least).

I currently have a headspace issue with a pistol that causes accuracy and reliability failures where ammo rim thickness varies by too much. This seems just a few thou to problem, so the gun's striking must be on a hairy edge of function.

 

[bill123]

I doubt it.
I had a firing pin slip under it's set screw once that led me to striking tests. What I saw through adjustment of pin protrusion from bolt face, was a coming into and out of best precision.
It was very similar to results of bullet seating testing.
This testing was from a standard primer seating, which had primers preloaded to 4thou crush in standard pocket depths(as uniformed with the fixed Sinclair tool). The seating was with an indicated K&M, and my headspace is always set to 1thou bump.
Through prior testing I've found that different primer brands perform better with either 2, 4, or 5thou of crush(CCIs requiring the most, Rems the least).

I currently have a headspace issue with a pistol that causes accuracy and reliability failures where ammo rim thickness varies by too much. This seems just a few thou to problem, so the gun's striking must be on a hairy edge of function.

Just so I'm clear. You don't think that there has been any testing done or you don't think uniforming makes a difference?
Thanks for the reply

 

[Gunpoor]

I tried primer pocket uniforming for a while and it just didn't make any difference at all. When I say no difference, I mean no group opening up or closing up, no difference in velocity, but I did find that there was a difference in the time it took to load ammo. JMHO

 

[Mikecr]

Just so I'm clear. You don't think that there has been any testing done or you don't think uniforming makes a difference?

I don't think there has been any testing done -that has been published (just local).

Uniforming can't hurt, and depending on your seating system and the brass itself(of course), it could make a big difference. For instance, let's say you seat primers to flush with the casehead. Then varying depths of pocket could certainly mean the firing pin would have to finish primer seating. Even beyond the affect of this to primer function, it could be thought of in terms of variable striking, or variable lock time, or variable striking force. Any are well known to degrade results.

I seat to a given crush in same depth pockets. Since primers themselves vary in height, I have this variance to manage. I do so by tossing primers departing from mean by more than +/- a couple thou.
Also, none of this reaches all the way to misfires. I'm talking about accuracy, and not reliability.

 

[bill123]

I don't think there has been any testing done -that has been published (just local).

I seat to a given crush in same depth pockets. Since primers themselves vary in height, I have this variance to manage. I do so by tossing primers departing from mean by more than +/- a couple thou.
Also, none of this reaches all the way to misfires. I'm talking about accuracy, and not reliability.

I meant more local testing.
So you measure each primer? What kind of mv/ precision results have you noticed?

 

[Gene]

I am reading Glen Zediker's book "Handloading for Competition". He has a long chapter on this subject and he opines that each primer pocket must be the same depth; primer must not protrude above the case head; and primer residue must be removed after each firing. And most important, all three anvil legs must bottom.

 

[AZShooter]

I uniform pockets for the consistency it might yield with primers in same position. I haven't taken the time to do comparisons. To me doing all I can to make each case the same as another is the goal.

Some Norma brass, I have encountered in recent years, has to have the pockets uniformed as the primers are very close to protruding from the case head.

There is another benefit, when you go to clean up the primer pocket after firing, the uniformer will remove the residue much better than the primer pocket wire brush.

 

[bill123]

I uniform pockets for the consistency it might yield with primers in same position. I haven't taken the time to do comparisons. To me doing all I can to make each case the same as another is the goal.

Some Norma brass, I have encountered in recent years, has to have the pockets uniformed as the primers are very close to protruding from the case head.

There is another benefit, when you go to clean up the primer pocket after firing, the uniformer will remove the residue much better than the primer pocket wire brush.

I Typically uniform w/a Sinclair fixed uniformed that becomes my PP cleaner as well. It does a great job. I was just wondering if there was any evidence that it had a measurable effect, or that I was doing it for the sake of uniformity that didn't really matter. Just trying to be more efficient w my time.

 

[Mikecr]

So you measure each primer? What kind of mv/ precision results have you noticed?

Yes, I measure every primer.
The indicated K&M primer seater makes easy work of all measures there. It simultaneously allows for zeroing out each primer to each pocket with measure indicated. So while my pockets are same depth, any indicated deviation is my primer height itself. Where that get's high, I just grab a different primer & toss the offending. Then I zero primer to pocket and seat to desired crush, again as indicated. Every one the same.

The first thing you learn using this tool is that consistent seating could not be done by feel.
It actually has to be measured to be known.

I also use my Sinclair uniformer for pocket cleaning.

 

[bigedp51]

I uniform my primer pockets and if you did you would see a lot of variation in primer pocket depth. Meaning when uniforming very little may be removed from one case and on the next case you keep reaming and thinking you will never hit bottom.

I do this religiously with all my cases fired in my AR15 rifles and M1 Garand. Also the military print shows that the primers should be .006 below flush for 5.56 and .008 below flush for 7.62.

I drink too much coffee and have chronologically gifted eyes to see any accuracy difference. But it makes me feel better knowing I'm making high quality brass with uniformed primer pockets and flash holes.

On the flip side of this and you do not prep the brass you can blame your fliers on the case not being uniformed.

Below, 7.62 Lake City and commercial contract 7.62 ammo has the primer .008 below flush.

 

[Kansaswoodguy]

I don't bother with uniforming primer pockets and have no issues shooting sub MOA consistently. I would love to see imperical data derived from a rail gun in a windless shooting environment showing the percent change in group size of uniformed primer pockets, powder charges weighed versus thrown, concentricity and a few other variables that we obsess over in this hobby.

 

[Mikecr]

If your efforts are no better than sub-moa, you haven't even begun to obsess in this endeavor.