Barrel Installation question

[strongisland]

When installing a barrel into the upper receiver I noticed a very small amount of play between the barrel extension indexing pin and the notch in the upper receiver. To describe the amount of play imagine you taking a firm grip on the barrel and attempting to wiggle it within the notch. Again the movement was very minimal but non the less it was present. My main concern is although the M4 feed ramps line up between the barrel extension and upper after torquing down the barrel nut this small amount of play will leave a not so perfect alignment of the feed ramps. It doesn’t appear to pose a problem with function because there was a very small amount of movement to began with. Is this normal and if not what fixes are there if any to secure a barrel to an upper with NO movement between the pin and notch? This is my second build and on the first one the fit was really tight. Everything lined up perfectly.

Thanks in advance

[bkb0000]

pretty common… the only time you need to take any corrective action is if it’s bad enough to cant your FSB out of tollerance. from your description, it should be fine.

[C4IGrant]

@strongisland

When installing a barrel into the upper receiver I noticed a very small amount of play between the barrel extension indexing pin and the notch in the upper receiver. To describe the amount of play imagine you taking a firm grip on the barrel and attempting to wiggle it within the notch. Again the movement was very minimal but non the less it was present. My main concern is although the M4 feed ramps line up between the barrel extension and upper after torquing down the barrel nut this small amount of play will leave a not so perfect alignment of the feed ramps. It doesn’t appear to pose a problem with function because there was a very small amount of movement to began with. Is this normal and if not what fixes are there if any to secure a barrel to an upper with NO movement between the pin and notch? This is my second build and on the first one the fit was really tight. Everything lined up perfectly.

Thanks in advance

The alignment pin on the barrel extension should fit easily into the slot in the upper receiver. Play should be very minimal. If you can rock it back and fourth, you might want to change out upper receivers.

C4

[strongisland]

play was or is very minimal with the fit. just wondering if that is to be expected. I know some things will mate-up better than others but to have a peace of mind figured I would post here. On another note what if the wiggle room was more than minimal movement? Other then scrapping the upper what corrective measure could one do to line things up?

Thanks again

[bkb0000]

theres a few options… shim it; have an assistant torque against the FSB while you tighten the bbl nut; use two vices to block the barrel and receiver at the same time, probably a few others that aren’t coming to mind. but if you don’t already have the tools or time, you can always sell the receiver for a small loss and buy a new one for $80 all over the place. they cheap, dawg.

[strongisland]

@bkb0000

theres a few options… shim it; have an assistant torque against the FSB while you tighten the bbl nut; use two vices to block the barrel and receiver at the same time, probably a few others that aren’t coming to mind. but if you don’t already have the tools or time, you can always sell the receiver for a small loss and buy a new one for $80 all over the place. they cheap, dawg.

Roger That