Baffled?

[Time Killer]

So, my BIL shoots a 300 RUM. I shoot a 6.5-284. We generally always go to the range together. Both of our rifles are threaded to shoot suppressed. My suppressor is the 338 variety so that I can use it on any weapon. I have no problems on my rifle. On his there are baffle strikes near the end of the suppressor on every shot.
I take it off and put if on my other buddy's rifle (.308) and he has no trouble, shoots clean. Put it back on the RUM and it strikes again.
So, its obvious to me that his threads are off....right?
I take the rifle to our smith. He puts it on the dial indicator and says its within tolerance.
At this point I am left with 2 other thoughts: My smith is full of bs or he has a pressure problem.
He is shooting an Obermeyer undersized bore. Could this have anything to do with it?? Has anyone experienced this?

 

[MTBULLET]

check the crown

 

[benchracer]

I wonder if it could be a bullet stability/yaw issue. Is your BIL shooting light bullets in a fast twist or heavy bullets in a slow twist? Either situation could conceivably cause some bullet yaw, which might account for the strikes.

 

[Time Killer]

He's shooting 210 Bergers in a 1:11 twist. Sound right?

 

[6.5x47hunter]

11tw should be fine.

check the crown

change seating debth

try another bullet as gun may not like the Berger? (unlikely)

if you're running them at max payload? slow them down?

i assume you are running retumbo- H1000 or similar burn rate powder?

 

[Time Killer]

Thanks for all the advice.
Yes, Retumbo and close to max load.
What should I be looking for in the crown?
FYI, with suppressor off this rifle is 1/4-1/2 moa at 3145 fps.
I just kicks like a mule and sounds like cannon... haha

 

[benchracer]

He's shooting 210 Bergers in a 1:11 twist. Sound right?

Sounds perfect. That pretty much blows my theory up. I think I need an emoticon for headscratching...

 

[mrultramag]

Inside diameter of the brake? They are supposed to be a certain amount larger than the bore size. But....that still doesn't explain why the 308 shoots thru it just fine...hmmm

 

[IdahoCTD]

It depends on how your smith is checking the bore to threads. Some barrels are like a jump rope inside. So while they are turned on centers in the middle of the barrel the bore is way off. With a barrel such as this the threads could be within a few thou to the bore but the bore is actually pointing in a different direction. I recently chambered a barrel and dialed in roughly a 1" section of the bore for straightness where the pilot of the reamer was to finish cutting the chamber. The crown end of the barrel was off .134" at 22" long and it was turned on centers at 27" long. A barrel like that could easily experience a bullet strike over the length of a silencer.

 

[6.5x47hunter]

slow it down!

 

[6.5x47hunter]

at 3145 fps.
I just kicks like a mule and sounds like cannon... haha

slow it down below 3100, you're likely disrupting the flight at the crown with turbulence. i switched to H1000 and use @ 1gr less per same velocity as Retumbo.

if you need more speed than that get a 30-378 and a longer pipe.