I know the recommended total overall length for the 300 RUM is 3.600 in, but is it ok to have them at 3.606in? They chamber in my rifle without being marked by the rifling. Should I sink the bullets a little to be safe?

A 300RUM has so much freebore, you can probably go up to 3.77" and not touch the rifling. So what I do is load as far as I can and still fit the shell in the gun. Which is 3.63". Believe it or not, your velocity/pressure will probably go down some by going from the standard 3.57" (factory) to 3.63".

I load my 300ultramags to 3.670".

I load 180 BTs to 3.678". That's the longest that will fit in the mag and I have plenty of freebore.

Dad gone, whey are all these 700 actions different by that much. I believe you guys when you say that 3.678" will fit in your mag. I just see the mags so much different. At 3.63", I am at the limit.