Some reloading manuals have a Rate-of-Twist chart in the reference section in the back. Speer and Sierra come to mind...
According to my Sierra manual, the Ruger #1 in 6mm has a 1~10" twist... In fact all Remington's listed have the 1~9" with the exception of the 40-X which has a 1~10".
If I were you, I'd pull the barrel and measure the twist. I have found that depending on when Ruger manufactured the rifles, twist can vary... My buddy had #1 in .257 Robts and couldn't figure out why it wouldn't shoot heavy bullets.... He measured the twist and found it had a 1~14" twist.
I measured mine and it's 1~10"...
To measure the twist, I put the rifle in a gun vise. Take a SS cleaning rod, and fit a snug fitting brush to it. Best to tighten the brush tight, so it won't unscrew when you are pulling it.
Insert the rod a few inches down the bore. I mark the rod with a line around it at the muzzle with a permanent marker. Use a ruler and put a mark well back lengthwise on the top of the rod so you can tell when it turns one full and complete turn. Push or pull the rod until it completes exactly one turn, then mark the rod again at the muzzle. Remove the rod and measure with a ruler between your two marks: That is the rate of twist. I usually do it 3 or 4 times to make sure I didn't get a false reading....
Once you've done it a couple of times, it's quite easy. Then you have no doubt what you have... Be aware that surprises can and do happen. I've seen factory 7mm Rem barrels with 1~9", 1~9.25", and 1~9.5" twist. And have even heard of folks who've had them 1~10". I once had a custom 7x57 Mauser that had a 1~12". Thus, I don't always believe the charts...
Hope that helps...
GH
