Re: 7mm rechamber
Like shortgrass said options will depend upon magazine length but I have REBARRELED several win mags and they are essentially the same. The bolt face is .532" and without bolt work you can rebarrel to:
6.5 rem mag - my favorite and have done 2 from 300 win mags, there is lots of room to have it reamed so you can seat those long 6.5 bullets way out and get out of the bullet taking up case capacity
264 win mag
300 win mag (mag length may be critical since the 300 win mag case is longer than the other win mags)
338 win mag
338 RUM - I rebarreled a 338 win mag into one but I had a long magazine. The case head is only a couple of thousandths larger and I needed no bolt face work or rail work
375 Ruger - this caliber is designed to fit in a 3.4" action and has more case capacity than a 375 H&H. I rebarreled a 264 win mag into one without a hitch
458 win mag?
There are probably more.
What kind of gun and how long is the magazine
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