Had a M70 in 375 H&H come in for a bolt replacement.
Customers complaint was that the firing pin hit the primer offset.
Well I finally figured out what was wrong. Somebody had over ground and polished the feed ramp to the point that there was no support left for the bolt to rest on in the closed position.
The front of the bolt would move .019" from side to side, and .008" up and down.

The front ring would accept a .704 plug and the bolt measured .691 to .692 in diameter just behind the locking lugs.

The area left on the feed ramp to support the bolt was about .030" front to rear and only .080" wide. It had been polished out of round, this allowed the bolt to just move around depending on the extractor tension on the case head.

SO GUYS when you redo the feed ramps on any bolt rifle you need to leave a large enough area to SUPPORT the bolt in the closed position.
And do not over poilsh this area.

Jim Wisner
Custom Metalsmith

Every time I see a post on here with someone asking how to “polish and slick up†an action I cringe...and even more so after reading some of the suggestions.

IMHO, before anyone even starts to think about polishing and/or removing metal from the working parts of a weapon they should be forced to learn the basic mechanics and design of that weapon to know what effects their “polishing and slicking up†are going to have.

Amen brother! I remember the pre-'64 that came in the shop one day, it was a 300 win mag rechambered to 300 Wby. The guy that did the comversion must have had a tough time getting it to feed because he had ground the feed ramp so far there was no bottom bolt lug engagement left in the action. I told the owner to take it out and bury it before someone got hurt.

You can always take a wee bit more off but it is pure HELL to put it back. I wish that I had a dollar for every action that I've seen ruined by bubba grinding & polishing the feed ramp. I have yet to determine wheather it is due to ignorance or shear stupidity!

Jim, what was the solution, or was there one?

Red

I have a post 64 that was like that new. I bought it in 1985 or 86. There is a relief groove behind the lugs and the top of the feed ramp is to low. The front of the bolt just kinda flops around in there. It is a 264 WM and it shoots well enough for a hunting rifle but it aggravates me because it just isn't right. The primer strikes are all off center. I have another 70's vintage model 70 in 243 and the front of the bolt is much better supported when I put the magnum bolt into it. So I guess the factory could get carried away when they opened the feed ramp too.

quote:

I've seen ruined by bubba grinding & polishing the feed ramp.

Which is why I think some of the best advice on gunsmithing that circulates around the Internet is hide the damned dremel and forget about it!