Wht would cause shrinking primer pockets?

[Grant]

On my 45-100 brass the primer pockets keep shrinking. Never had that happen before, had some expand but never shrink. The brass is starline. Grant

[13Echo]

Never heard of that but I have had slight variation in primer diameters from brand to brand or even lot to lot that resulted in hard seating.

Jerry Liles

[JSnover]

I don't have any idea but I sure would like to hear the answers for this one. Are they only shrinking after they've been resized a few times or are the pockets tight every time? What kind of dies are you using? Small base dies are cut to a tighter tolerance but they shouldn't cause anything like that to happen.

[montana_charlie]

As Obama spends more and more of our money, none of our pockets need to be as big as before. I guess your primer pockets are just getting on the bandwagon...

Do you know the pockets are smaller because you measured them...or because of the way it feels when you seat primers?
How long (how many reloads) have they been shrinking?

CM

[Grant]

On new brass they seat perfectly then with each reload they get tighter. I clean the pockets good with the proper pocket cleaner. Guess Ill drop by Bufallo Arms and get a pocket uniformer. I hate straining muscle to seat primers. RCBS dies are used and trying a Lyman sizerto see what happens there. Thanx Grant

[BPCR Bill]

How do you clean your primer pockets? Do you use the standard cleaners, or a primer pocket uniformer? I use the Lyman pocket uniformer. It's dimensions stay the same regardless. If the pockets are indeed getting smaller after firing, the uniformer will be difficult to insert. If that's not the case, then you have variances in primer cup dimensions. Starline brass has a rep for being to hard, and that won't flow easily under pressure. If your brass is too soft, or chamber pressures are significantly higher, primer pockets tend to get too big. Been there, done that.

Regards,
Bill

[montana_charlie]

Do you know the pockets are smaller because you measured them...or because of the way it feels when you seat primers?
On new brass they seat perfectly then with each reload they get tighter.
I hate straining muscle to seat primers.

If you have some unfired cases of the same brand, measure the pockets.

Measure the diameter and the depth...just to cover all of the bases.

Put the ID jaws of a dial caliper in a 'shrunken' pocket. Spread the jaws as far as you can, and lock the caliper in that position with the thumbscrew.
Pull the jaws out gently so you don't disturb their spacing, and try them in a 'new' pocket.
They should fall right in if your observations are correct.

If they are at all snug in that new pocket, you have something else going on...like maybe your cases are not quite properly aligned with the ram when you try to seat primers.
CM

[swheeler]

Taking a guess here based on personal experience with the 6.5 Carcano grafs brass and Lee shell holder. I was getting tight primer seating because the Lee shell holder was just barely catching the rim on the case, when I pulled the expander through the neck the cartridge head was being deformed causing tight primer pockets. If I very carefully lubed the heck out of the inside of the case neck it would help with the problem and most primers would seat normal. I finally CURED the problem for good(after pulling the rim off a couple cases)by buying an RCBS shell holder that fit into the extractor groove on the head closer(one for 35 rem). Now I don't know if this would be happening to you with the straight walled case when you withdraw it from the sizing die, but possible I would guess, lots of case wall to resist, hang on while withdrawing from the sizer die. If it is happening I would think you would/might/possiblely also notice tight closing when you chamber a cartridge , because of the deformed rim. Make sure your die is clean and cases are well lubed, check shell holder fit to brass rim.

[RMulhern]

Take a 45 degree chamfer tool and chamfer the top edges of the primer pockets! If you're using Federal primers....THEY'RE HARDER than any other primer! As to the usage of lube on your case necks and pulling the expander button back through the neck....USE POWDERED GRAPHITE!! And if you're using the average 'run of the mill' seating method such as an RCBS tool that has the multiple primer holder of plastic....ascertain that the ram is aligned within the tool for if not and it's off to one side....this is a PITA!! Sinclair International makes a primer seating tool that eliminates this PITA!!

[swheeler]

I threw the powdered graphite in the garbage 20 years ago, you can't beat lube on a neck brush, but I like to tumble after sizing for all my single stage loading.

[JSnover]

Take a 45 degree chamfer tool and chamfer the top edges of the primer pockets! If you're using Federal primers....THEY'RE HARDER than any other primer!

I wondered about that; if the case heads are work-hardening or if the primer cups are harder it might make someone think their pockets were shrinking.