I am getting tumbling rounds, not every round.  Maybe 1 out of 20 sometimes slightly more, sometimes less.  It only happens with either wolf 55gr or silver bear.  Didn't have a problem with 62gr wolf or 55gr nato.  

This is with a 7.5 CMG upper 1/7 twist.  

I have Miculek brake that I am a little nervous to use

any thoughts on what it might be?

Could the twist rate be to fast causing the light bullet to pull apart, or is the light bullet not being stabalized?

After researching this myself I have learned that the 1/7 twist is best for short barrels.  

Lighter bullets will be more stable and be less likely to tumble.  

7" barrels willnot stabalize bullets reliably.

This is what I have learned!  If I am washed up please correct me!  

Fargo

I never had a problem with M193 55gr ball in my CMMG 10.3", but the Wolf 55gr ball would key hole quite frequently at 25 yards.. Like you, I also found the 62gr Wolf to work just fine.

1/7 likes heavier ammo, stick to what doesn't key hole and you are fine.

By the way, don't ya just love CMMG's stuff? Good barrels, and excellent service.

ETA:

7" barrel will stabilize the right bullets just fine...

I have been very happy with my CMMG, they were very nice and very fast to deal with. I recommend them to everyone I talk to about ARs