I am not sure. I know the RUM has some freebore built in on purpose. According to reamer vendors I talked to, they said that is the spec for thier reamers. It is a safety factor and a way for the RUM to compete with the Weatherbys in speed. There is a guy on the accuratereloading forum AJ300, that had his 300RUM special built to where there was no freebore but could reach the rifleing and still fit in his magizines. He said basically, the manuals had to be thrown out when he did this due to pressures building. It also shows this on quickload software. He did show me groups that showed the gun to be a tackdriver however. And he seems to be able to find accurate loads out of most all bullets. Where I have to pick and choose bullets.

I have no problem with the RUM's having freebore in them, as long as its consistent. Problem is when I measure the differences I did, that shows very sloppy workmanship. For me to reach the rifling on my 300RUM custom, I have to load out to 3.84". Which unless you use a 200gr accubond or long bullet, you can't do and have sufficent grip.

but with my 308Win browning Medallion I can reach the rifling and still be within SAAMI specs, but it doesn't fit in my clip.