Begara B14

[SSG Graybush]

So, I wasn't specific enough. My thought was I have a 300rum and I know the 26nosler is just a shortened version. The 300rum will can't be pushed down into the magazine. If I put a pice of brass in from the bottom it will feed up when the bolt is worked. I'm assuming that would mean the feed rails need to be opened?

It takes about 10 minutes to open up the feed rails with a bastard file, go slow a couple strokes a side and open it till a peice of brass just barely slips through it. And you'll need a rum follower and mag box if doing a bld style rifle. I just did this to a 300 wm to make a 33 Nos. Wyatt's has the follower and box. Dalton at Wyatts talked me into doing it and it's super ez. Without the right follower and box it will bind, and rds will pop up.
edit- my Remington 700 LA bdl wouldn't allow the 33 nos case to pass through. It was a few thou too narrow for a 33 Nos case. A rum case might feed up through, but I doubt a fat Nosler case would. You need a peice of 26 Nos brass to check opening to open feed rails.