I've got one in 30-06, and I'm wondering if the heavier caliber actions are strong enough for that caliber?

s

Socrates,
I have a friend with an Interarms based on the 98 Mauser action in .375 H&H. I would think that it should be strong enough for the .450 Ackley. I am unfamiliar with the smaller caliber Interarms actions.

You can put anything in a MK-X action that will fit, and not worry about it!

Using the magnum Mark X action (375 length, opened up at the back), it should work for the 416 Rem, 450 Lott, Watts, Ackley, etc. Siderails and feedramp might need some work.

I think I would start with a short magnum Mk X action (ie: 7mm Rem Mag, etc) and then open up the rear of the action. I believe that the 375 Mk X has some of the front of the action removed from the factory. Now, I'm not saying it will fail, obviously there are thousands of these rifles out there, I just like a little more margin to play with. Plus a short mag Mk X will be a lot cheaper then a 375. Yes, the box and rails will need work, but usually not a lot. FWIW - Dan