M-70 ultra mag action


Active Member
Oct 4, 2004
Hello all, Just a short question. I am looking for a M-70 action to build a 300H&H. I have located a M-70 in 300 RUM but am wondering if the magazine lips on the reciver have been opened up wider for the fatter RUM case? Is this is the case I think I will still buy it to build a 338 RUM. Thanks, Nathan

First off welcome to LRH!!

I have not built a rifle chambered in a full length standard belted magnum using an action designed for the RUM rounds at least not with the M70 action.

I have used a Rem 700 action that was originally a 375 RUM to build a 257 STW adn it worked like it was made for it.

I ordered a replacement mag box for the STW size case but found the original RUM box actually feed rounds better. This is probably due to the wider feed lips and the slightly wider RUM mag box allowed the STW case to get under more lip.

Anyway, if you can just take some dummy 300 H&H rounds and see if they will feed well out of the action.

THe very shallow shoulder on the H&H may cause problems with shoulder binding and you may have to get replacement mag box for this round but they are available.

The biggest thing is to see if the feed rails will actually hoid the rounds in the box, especially the second and third as the top rounds are stripped off the top.

Also see that there is not major case body binding as the rounds feed up the mag as well. If there is this may be fixed with the narrower mag box but it may also increase the tendancy for a round to jump past the feed rails when the round above it is cycled.

Just try it with some dummies and see what it does as is, may work fine, may not. I will say if it does not feed properly, it can be hell or impossible to get it to do so. Its easy to take the rails down, pretty hard to add to them.

Try it and let us know what you find.

Like I said, this conversion seems to work pretty well in the M700 action but can not say for sure on the M70.

Good Shooting!!!

Kirby Allen(50)
Nathan, you've got my curiosity, your rifle is chambered for .300ultramag. You'd like to chamber it for a .300H&H, but would settle for a .338ultra. Care to explain?
AJ300MAG, I can explain! I am looking to build another 300 H&H because it is my favorite cartridge. If the RUM action will not work I will just build it into a 338 RUM and find another action for the H&H. Also I have a 32 inch 338 Mike Rock blank I have been sitting on. Wanted to build a Lapua but am waiting for Olympic Arms to put out more ultramag actions, they seem to out for awhile? I did buy the M-70 this morning and will pick up tonight. Nathan
The lips do not hold the 300H&H cartridges very well. Only about 1/4 of the case contacts the lip causing the case to pop out very easy. Also when loaded with 2or 3 rounds in the mag it will not feed properly. Maybe a different box would help? Nathan

The larger box for the RUM rounds should allow to much of the feed lips to contact the H&H round.

Sounds like to me the follower is not pushing the first round over far enough.

You may need to get the new box as well as the correct follower for the H&H class rounds.

Remember taking an action for a larger round and chambering it for a smaller round can always cause problems.

Good SHooting!!!

Kirby Allen(50)
I removed a box and follower from another H&H of mine and it worked better. But the ultra box and H&H follower works even better. Thanks Kirby. Nathan
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