• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

Getting a Win mod 70 to feed a longer cartridge?

So I just got a Winchester model 70 XTR in .257AI. The magazine box has a spacer in it to limit the OAL of the cartridge so heavier, higher BC bullets get stuffed deep in the case and has to make a big jump to the lands.
I am thinking the way for me to correct this is to install a 7x57 magazine box and a new breach bolt stop. Is there anything else that might need to be done?


Obsessed Member
Staff member
Forum Supporter
2019 Supporter
Might work with nothing more than your planned parts swaps, but I'm thinking it will take a bit of tweaking and fiddling to get it just right so it feeds reliably, since there is about .296" diffence in the OAL , with the 7x57 of course being the longer of the two.
You may find you still need a spacer block in the mag, just one not quite as thick.
Youi might try just milling down the spacer in the existing magazine for starters.
In Idaho now and will be getting the 7x57 magazine box when I get back. I will put that in and the see what I need to do with the bolt stop.

So today I got the 7X57 magazine box. Took about 30 seconds with the file to slightly shave it for the fit. Measured the difference between the two spacers and cut off that much off of the bolt stop. Tomorrow going to grind the bolt stop to smooth it out and match the shape of the original's end. Then I will slap it back together and see if any other tweaking is needed. This should work.
A couple minutes with the dremel on the bolt stop, touched up with bluing pen, and slapped together. Loaded magazine up with some "dummy" cartridges I had to set my dies with, and she appears to function flawlessly.
This ended up being a very simple, yet very worthwhile modification.


Obsessed Member
Staff member
Forum Supporter
2019 Supporter
Nice work!
Like I said, a little tweaking, a little fiddling and you have it running.

Be sure to work the bolt with those dummy cartridges briskly a dozen or more times, do it like a grizzly was charging you and you needed to empty the mag into it.

If it feeds a full magazine like that, 5 or 6 times (load the dummies into it in a different order each time) then you can be reasonably sure it will function correctly with live ammo, then go test it with your hand loads and some factory ammo to be sure, in a life or death situation you don't want to be "hoping" it is going to run.

I suspect it will do so just fine, but it pays to be careful.

On another note regarding such modifications to firearms by the owner, if you think that you might ever sell the gun, I would keep the original magazine with it now, and acquire a new, factory original dimension bolt stop for it, and put those in it BEFORE selling it.

Sell it with the parts you modified in a bag, and tell the new owner that it is back in factory original condition, but can be easily modified to feed the cartridge it is chambered for with a longer OAL if desired, by installing these two parts, at THEIR discretion. Tell them it ran fine with those parts for years or XX rounds, but that you are not a professional gunsmith and that they might want to have one check it out before using it with the modified parts installed.

If you don't do that, and I strongly advise that you do, at least be sure to include a note with it describing what modifications have been made to it and that the buyer is assuming all risks from the moment of purchase on, to help limit your liability for the changes made to the gun should something go wrong and some ambulance chaser try to blame you for it.

Trust me, this CAN HAPPEN. Have seen it many times, and been the expert witness in a number of court cases such as this, both for the non pro gunsmith who modified and sold it, and for the new owner who got hurt because some kitchen table hack modified something in a way that was not readily apparent to the new owner, and that the seller failed to disclose he had done.

Since you are not a professional , licensed gunsmith with liability insurance, you need to protect yourself in this manner. Now, not later.

You might want to store a letter with the gun describing the changes you made, so should you die unexpectedly and your estate sells it, it will limit the liability to the estate for any failures in the hands of the new owners. Keep the original Magazine and an original bolt stop with the gun too, and clearly marked as to what they are, and what gun they go with.
Ran into this one in a court case once as well.

Sad state of affairs when we have to jump through all these hoops, but better to do so than risk losing everything you have worked for.