.300 RUM Internal mag questions...

[jrhammo08sxt]

Building a .300 RUM based on a stainless large shank action. What I am wondering is will the .300 Remington Ultra Mag round work fine in a .338 Lapua AI mag? If so, I am going to go with DBM from Pacific Tool and Gauge. If not, guess I will have to stick to internal. My question then would be is the internal box longer than any other Savage 110 based long action? My semi-educated guess would be it is the same size...
Any info on this subject is greatly appreciated!!

[sharpshooter]

RUM mag boxes are .220" longer than a standard magnum box. They have been discontinued for some time.

[jrhammo08sxt]

I found some aftermarket options for detachable mags at accurate mag.com...