Home Forums Hunting & Shooting Gunsmithing Enlarging Win M70 Mag box?

Sooner or later you will have problems. If your willing to except that have at it.

Most guys are not aware, but except for one exception all the Winchester mag boxes are the same basic dimension and that dimension is taylored for a 375 length round. The feed rails are also all identical to my knowledge. To make the dimension work with a -06 based round Winchester pinched in the top of the box slightly, then added a spacer to compensate for the box being to wide at the rear. When you remove this spacer on a -06 mag box, the box is too wide at the rear.
If your rifle is chambered in 300 win mag, 338 win mag, or 7mm rem mag the spacer can be removed and a 7mm stw follower used with good results. Of course these rounds have the same head diameter as the H&H.

I wouldn't use a .375 box with any 06 based case as the stack is wrong..

If you want a longer magazine that will work then send the gun to Dennis Olson, Plains, Mt. and tell him what you want and he will weld up your magazine to fit your cases and throat and you want to seat bullets out..You might gain about 100 FPS or more with the long throat as you can seat bullets out enough to gain about 4 or more grs. of powder at the same pressure..I do this with all my 7x57s but I don't use the IMP case.

Most factory guns have longer throats than magazines and that is problematic to some folks that are into that sort of thing..

Another option is the 7mm magnum rechamber if your looking for more juice.

Yep and once you remove the spacer form a -06 based round you end up with a 375 H&H mag box with the rails the top part of the box pinched in slightly.

Just cut the spacer out of the back, and spot weld the box together; it is no trick. Try the cartridges with the OAL you want, and see if the will function. If so, great-you are done. If not, then you start by shortening the bolt stop. That is an easy amateur-level repair as well.

So what you are saying BWalker is that if you are using a magnum cartridge (in my case a .300 win) you can remove the spacer and put in a 7mm STW follower to avoid any problems. Correct?

If so, do you also need to change the extractor blade and bolt stop as well to compensate for the extra length available? If so will the 375H&H parts work, or did you go with 7STW specific parts?

I assume this is the place your talking about Western Gun Parts

You wouldn't happen to have the numbers on hand would you? I'll be getting the same parts (extractor blade and bolt stop for the 375 h&h). I'll have to look into the STW follower though

I put the spacer wall back on my box for added support, so what the shells rest on is the same width of wall that they were on originally. The thickness of the spacer is about .060" without the extensions that i cut off, so I was'nt giveing up to much lenght on my box.
Elmer