I was at my dealer picking up my new Gemtech HALO suppressor, when he offered to do a quick alignment check with a .223 caliber rod with the suppressor mounted on the various uppers I had brought along.

Well, we did not discover any alignment issues but we did discover that the rod would not fit into my 16" CMMG M4 carbine upper.  The rod passed easily into the bore of a 16" Colt barrel and a 16" GTS Recon barrel.

I believe the CMMG barrel is chrome lined, but so is the colt barrel.  The CMMG barrel
has seen moderate use (less than 2,000 rounds) and does not show any signs of pressure issues with Lake City, UMC, SA or Guat.

This barrel has been 100% reliable, and I have shot 2-3" groups at 100yd with Lake City M193.  While this is not the magical MOA that everybody else gets, it seemed adequate for a short range gun that normally wears an Aimpoint.

Does anybody have any thoughts on the matter?  My dealer has never had a barrel in his shop that would not accept the rod.  Should I look for a new barrel, or is this no big deal?

Thanks

I thought bore Diamiter was suppost to be .219"

Anyways Have you noticed any excessive copper fouling?

I do not want to sound stupid, but what would excessive copper fouling look like?

I clean the bore with CLP and a bore snake.  I have never noticed anything out of the ordinary compared with cleaning my other uppers.

I am not exactly sure of the diameter of the rod used.  Needless to say, it fit in the other barrels and not in the CMMG.

BTW:  CMMG has caught this thread and contacted me to see if I want to send them the upper for a look see.  Impressive.