Posted: 3/14/2011 4:15:37 PM EDT
| I am building a 9mm upper off of your 9mm A1 upper. The Rock River barrel nut I have seems to "bottom out" on the reciver when I hand tighten it but the barrel still has some play in it. This is the first upper I am building and I was wondering if this is normal. It looks like when I tighten the nut down it will mash the reciver! Is there different length barrel nut I should be using? Is there a difference between an A1 and A2 barrel nut or are they the same thing? Thanks for the help! |
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I have never taken a Rock River 9mm barrel off a receiver to see if there is a difference in their shank dimensions.
However, Colt pattern barrels have a spacer washer that goes between the barrel shoulder and the front of the receiver. Perhaps this is missing? It should all go together and tighten down no problem. Are you using a standard steel barrel nut, or some after market aluminum deal for a free float tube? The dimension from the front of the threaded shank to the flat face of the receiver should be around .455" +/- .002". Here's what the 635U looks like with a barrel installed and a mil-spec nut tightened down. If yours doesn't look like this your barrel nut may be cut wrong. 
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