Barrel play in upper receiver

[R.D.]

I just removed my barrel in anticipation of receiving a LT 7.0 foreend. There is a noticeable amount of play in the barrel to upper receiver when the barrel nut is loosened. It is to the point of being able to rattle in the receiver . Is this acceptable? Although I have taken a armorer course I can't recall the specs. The other barrels I have removed all were much tighter than this one. This is the same LMT upper that I received that did not have a roll pin in the gas tube FWIW.

[C4IGrant]

Originally Posted by R.D.

I just removed my barrel in anticipation of receiving a LT 7.0 foreend. There is a noticeable amount of play in the barrel to upper receiver when the barrel nut is loosened. It is to the point of being able to rattle in the receiver . Is this acceptable? Although I have taken a armorer course I can't recall the specs. The other barrels I have removed all were much tighter than this one. This is the same LMT upper that I received that did not have a roll pin in the gas tube FWIW.

You generally want a tight fit between your barrel and receiver. When I do custom builds, I fit the barrel into the receiver so it is nice and tight.


C4

[K.L. Davis]

the prints call for an unfinished bore of 1.00 -0/+0.006

the last inch, where the barrel fits, is stepped down to 1.00 -0/+0.002

[R.D.]

Thanks for the guick responses Grant and K.L. .

[coldblue]

It sounds like you have a barrel extension the small side and an upper on the big end. If you are unable to select alternative parts, I'd use green locktite to improve the "cyclinder" fit. You will get some degree of "compression" when you torque the conventional barrel nut, but not enough to take up the loose fit you describe.
I have even epoxied undersized barrels to uppers on match rifles with heavy barrels because I never expect to wear those barrels out. This gives me the confidence I need when shooting that I am the only element in the equation that can cause a shot to print outside an otherwise tight group.

[R.D.]

Thanks for the advice ColdBlue but I returned that upper group for a refund as the managment of the place I got it from and I did not see eye to eye on the problem .I did order another LMT upper from G&R and that one is much tighter in receiver to barrel extention fit.

[UPSguy]

Originally Posted by C4IGrant

You generally want a tight fit between your barrel and receiver. When I do custom builds, I fit the barrel into the receiver so it is nice and tight.


C4

By fit do you mean you try various uppers with various barrels, or do you have another means?

[C4IGrant]

Originally Posted by UPSguy

By fit do you mean you try various uppers with various barrels, or do you have another means?

No. I build up the barrel extension to get a tight fit into the receiver.



C4

[Bill Alexander]

Barrel extension Dia - 0.9975/0.9995 typical for general production, ovality to 0.001 or better. Surface finish should be 16RMS or better. This latter spec is not always observed but is essential for a truely consistent rifle. This is not defined as small groups rather the rifle must be capable of maintaining a very consistent POI/POA across a wide enviromental range and time.

Receiver Dia - 1.002/1.005 as finished, again for general production, ovality is not defined but typically runs 0.001/0.002. This prior dimension is probably the hardest to control as the anodizing process adds thickness which is difficult to control. Again to chase the consistency demon the reciever can be adjusted down to 0.9980/1.001. and the barrel then sweated into place. Adding a little loctite 2440 in the joint during assembly ensures a true 100% contact surface against the smooth barrel extension but this is not a good long term substitute for a tight fit.

For home builds 0.000/0.003 is an acceptable clearance remembering that a 0.000 clearance will demand that the parts are heated for assembly, so this looks very tight.

Bill Alexander