Bit of a Quandary

C

Calibre

New member
I have been gunsmithing for 35 years. My work consists mainly of restoration on pre-1960's era machineguns. As favors for friends and neighbors I will work on their hunting guns and competition guns. (No benchrest.)

Anyway, I re-barreled my neighbors Remington 788 a few months ago so he could use 125 gr. bullets. Used an M-852 Manson reamer for a shorter throat and tighter case dimensions. Everything went well. Test fired with some military surplus ammo. Other than one sticky case, all chambered and extracted okay.

Told my neighbor to start his reloads 5 grs. lighter than with his factory barrel. (43 grs. 3031) His first round through the gun blew the primer out of the case. I have since switched him over to IMR4895, as that is what I have experience with in my high power competition guns. Started him out with 40.0 grs. of powder with a 125 gr. bullet. (Nosler I think) Showed signs of excessive pressure so we dropped down to 39 grs. Same thing ... sticky cases, a couple of blown primers and flattened primers. Made it down to 36 grs. of 4895 and sticky cases and excessive pressures pretty much disappeared except for the occasional blown primer. Case extraction, even on the ones with blown primers, is fine at 36 and 36.5 grs.

I have been reloading since 1977 for handguns and rifles with absolutely no problems and currently shoot about 15,000 rounds a year of my reloads for the different disciplines I engage in and this has got me stumped.

Have also tried a couple types of powder and 4 different types of primers and every different combination does the same thing. Starting loads from different manuals seem to produce higher than normal pressures.

First few rounds shoot great and all seems fine ... then it happens. As we continued to shoot, about one third of his cases keep blowing out primers while the rest of the cases look normal. Have tried Federal cases, Remington cases, several different once fired military cases ... nothing seems normal about this haunted gun.

Have gone so far as to slug the bore and all that checks out fine.

This has me stymied. In all my years I have never run across this type of situation. Has anybody here ever heard of this type of thing and a possible solution for it?

Thanks in advance for your help!!
 
Some things come to mind;

788's are plagued with bolt compression due to the rear locking lugs which can make good case maintenance/resizing a challenge and,

this can cause the unwary to over-size cases.

Many custom reamers are cut quite short.

It sounds like you might be crimping at your casemouths....

Trim some cases back, 'WAYY back, like lop 50thou off the case mouths and see if the problem goes away. If this solves your short-term problem than it's time to move on to the next series of challenges.....
 
BTW, the reason "over-sizing cases" is relevant is because this is what causes cases to grow in length. ALL case growth is the result of the resizing cycle.
 
I had the opportunity to measure some of his cases this morning. Seems as though he was taught that the cases had to measure to exactly maximum case length. (2.015") He was also taught that you size and deprime the case(s), trim, then tumble and that tumbling can beat up a case so you resize the cases again. Thus, pulling the expander ball through the case a second time. He's a good neighbor and helps my tired old butt out quite a lot, so I'll spare him a berating.
 
Don't count on what the customer tells you

Calibre said:
I have been gunsmithing for 35 years. My work consists mainly of restoration on pre-1960's era machineguns. As favors for friends and neighbors I will work on their hunting guns and competition guns. (No benchrest.)

Anyway, I re-barreled my neighbors Remington 788 a few months ago so he could use 125 gr. bullets. Used an M-852 Manson reamer for a shorter throat and tighter case dimensions. Everything went well. Test fired with some military surplus ammo. Other than one sticky case, all chambered and extracted okay.

Told my neighbor to start his reloads 5 grs. lighter than with his factory barrel. (43 grs. 3031) His first round through the gun blew the primer out of the case. I have since switched him over to IMR4895, as that is what I have experience with in my high power competition guns. Started him out with 40.0 grs. of powder with a 125 gr. bullet. (Nosler I think) Showed signs of excessive pressure so we dropped down to 39 grs. Same thing ... sticky cases, a couple of blown primers and flattened primers. Made it down to 36 grs. of 4895 and sticky cases and excessive pressures pretty much disappeared except for the occasional blown primer. Case extraction, even on the ones with blown primers, is fine at 36 and 36.5 grs.

I have been reloading since 1977 for handguns and rifles with absolutely no problems and currently shoot about 15,000 rounds a year of my reloads for the different disciplines I engage in and this has got me stumped.

Have also tried a couple types of powder and 4 different types of primers and every different combination does the same thing. Starting loads from different manuals seem to produce higher than normal pressures.

First few rounds shoot great and all seems fine ... then it happens. As we continued to shoot, about one third of his cases keep blowing out primers while the rest of the cases look normal. Have tried Federal cases, Remington cases, several different once fired military cases ... nothing seems normal about this haunted gun.

Have gone so far as to slug the bore and all that checks out fine.

This has me stymied. In all my years I have never run across this type of situation. Has anybody here ever heard of this type of thing and a possible solution for it?

Thanks in advance for your help!!
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I mean that respectfully. Until you reload several yourself, with your own known good equipment and are sure what powder and what charge is in the cartridge, I wouldn't think it's a problem with the rifle. Sounds like too much of some particular powder to cause such a dangerous condition. I am no gunsmith though.
 
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