I have a .375 H&H Interarms Whitworth with a Gentry 3-position safety. Was plagued with misfires with one reduced load and always chalked it up to the load -- now I have misfires with a full-power load. If I try the cartridge again it will often go off. I don't think it's the primers, since I use the same ones in several other rifles without a problem.



Firing pin protrusion is good and headspace is correct. The inside of the bolt is clean.



I'm thinking the firing pin spring may be weak but could use advice or other opinions/tests to run. I suppose I could swap in the spring from my other Mark X?

All sorts of possibilities... maybe the cocking piece is dragging on a burr or other protrusion/misalignment in the Gentry bolt shroud? Maybe the trigger engagement is out of whack and the cocking piece is dragging there? Also, check the headspace. Maybe its a little too much.

Out of the zillion posibilities, here's a few more pretty basic ones...



1. It appears you handload for your .375. Are your primers seated all the way to the bottom of the primer pocket, by FEEL? If not they should be. A primer not all the way to the bottom of the pocket may be seated completely by the first firing pin strike, but not fired. The second strike may then fire it.



2. Your rifle may have correct headspace, but do your handloads? Get a Wilson .375 cartridge headspace gauge and check your resized cases in it after you have run them through your dies in preparation for priming and powder....



3. Does your bolt handle go all the way down when you close the action? If not, relieve whatever is necessary to make it do so.



4. If you have a Gentry safety, do you also have an after-market firing pin? If it is lighter than the original one (as some "speed-lock" substitutes are) then you may have lost sufficient momentum to reliably fire your cartridges. Cure for that is to either go back to the heavier original, reliable, striker, or to check around to see if you can find primers with a more easily indented cup, such as Federal's often seem to be...



5. Almost forgot...maybe something (like some steel wool or a tiny piece of a patch?) got inside your bolt body when you had it apart installing the gentry safety? Disassemble bolt and check for anything which could be softening the blow of the striker on the cartridge primer.



Good luck. Is no doubt some really simple, very small, thing...often the very hardest to identify, but very easy to cure once discovered.



AC

I had the safety installed by Gentry -- cost the same as buying it retail. I will call them to ask for anything I should double-check. I think that's the most likely prospect.

The firing pin and spring are original and the bolt closes all the way.

Cartridge headspace shouldn't be an issue with a belted case, should it?

Finally, primers -- I'm not 100% sure (the box is at home) but I think I used Federal 215M for the last batch. I seat them the same way I seat for all my other rifles (i.e. with an RCBS hand priming tool), which all work fine.

Yes, you can have too deep of a belt recess just like you can cut the shoulder too deep on a beltless round. Unless the rifle was known to be 100% reliable before the safety installation; headspace is a possibilty.

Sometimes the fates can line up against you with a maximum (but allowable) headspace condition and a lot of brass that just meet minmum (but allowable) belt length and the combined tolerances cause the equivalent of too much headspace. Brass belt dimensions are often all over the place, even from lot to lot of the same brand.

I believe Gentry recommends installing a stronger firing pin spring when installing one of their safeties on a Mark X. I'd contact Gentry and ask what weight spring they recommend, install it and see if the problem goes away.

A couple of years ago I happened to acquire about 8 or 10 brand-new Mark-X actions in there original boxes. The papers with each put there proof test date as Late 1970's to early 1980's. In examining these I discovered that every one of them had an extremely slow-soft muddy if you will firing pin fall. This was after I had cleaned all the mud, grease, and assorted debris out of the bolt. The repair involved stoning burrs off the cocking piece and firing pin AND replacing the firing pin spring. In measuring the spring force in a tester I discovered that the factory spring had about 20% less force than a standard mauser spring. As suggested by others a WOLFF spring fixed that.
Good Luck Jerry

Years ago I had a head space problem develope, just in front of the web the cases were starting to bulge so took the rifle to a gunsmith who discovered the barrel was loose, no iron sights and had undone nearly half a turn. was not a mark x but same could happen to most rifles.