Quote Originally Posted by Nate View Post
My first attempt at installing a new Douglas barrel on an old receiver has gone very well except that my gas cylinder will NOT fit. It is so tight on the splines that tapping with a block of wood is useless. What has gone wrong here?

I don't think anything is "wrong" per se, but have you measured the barrel OD on the old barrel at the splines v.s the OD of the new barrel?

A new Douglas barrel may be slightly oversize in OD to allow the tightest possible fit of the gas cylinder to prevent sight movement once mounted.

I think your problem is actually a good one. I would carefully measure the two OD's and then file or stone or both to get a nice tight fit on the barrel splines.

When I rebarreled my DCM M1icon back in the early 90's the replacement barrel (a custom one by one of the big mfg's) was super tight. I just filed and stoned and filed and stone until I got a near perfect fit.

That M1 is still a tackdriver.