I'm in the process of trading for a short action Remington 700 to install a Wyatt's 0.0125" longer magazine box, with side openings for the front of the shoulders.

Need a fixture to hold the action straight with either top or bottom up/down with relation to bed of mill to open the back 1/8" on bottom, and to move rail shoulders forward one RCH.

Anyone make such a fixture?

Thanks,

I recently opened a 700 L/A for a Wyatts box, doing the 300 PRC.
I screwed my picatinny rail to the receiver then laid the whole thing in a 6 inch Kurt vise upside down.
The rail enables registration of the round receiver in the vise, super simple, effective, 15 minutes done.

The same can be accomplished using and old Leopold 1 piece base.
Care should be taken on vise clamp force.

I suppose one could clamp on the rail, but not as rigid as down in the vise.

Two matched v-blocks on parallels in a vice with the v-block U clamps holding the receiver down. Indicate off the cutouts on the bottom of the receiver to level, square, and locate. A carbide end mill will do the business with less fuss. Finally, creep up on your numbers checking for fit as you go because magazine boxes are only sheet steel bent around a mandrel, and can go a couple thou one way or another.

Webfeet, thank you for that advice. I marked the bottom metal by scribing around the box into some Dykem (I used to use blue, but now I use Red). Found a 3/16" carbide end mill. A local machinist will do the cutting. I can't stand up very well any more, so I gave my mill and lathe away.

Thanks again.