dreadpirate Wrote:Have to be careful yes. I heated the barrel bolt and did not torch the aluminum upper directly.
[EDIT] At what temp for annealing aluminum? 800 deg F? Don't think I got it that hot.
I read 650deg F depending on what type of alloy you have. 6061 T6 or 7075 T6. I also read that alloys of aluminium change grain structure at even lower temperatures than the main element because they are a combination of elements ('eutectic'). I don't know enough to be definitive and there are different temperatures quoted on different internet sites, but I do know that unlike brass aluminium alloy does not change colour as it changes property, and of course the receiver will be anodised or Ceracoated anyway. Some barrel nuts are alloys also. Point is, we can't be certain of what the exact temperature will be with a torch, or what flame heating is doing to that area. Messing with the grain strength of such a critical area of the gun could be robbing Peter to pay Paul. What I mean is, trying to increase accuracy by introducing glue and then heating it might not be such a good idea.
That said, your glue will be flowing/liquid as you apply it and before hardening anyway... so why heat it?
I hear what you are saying, implying it is not a big deal, but I think it is. Heating the receiver and barrel nut with a naked flame hoping the metal properties remain the same is wishful thinking. Applying glue to the interface between the receiver face and barrel extension journal does not make sense to me. Applying glue however to fill any tiny void between the barrel extension and receiver (evidenced by slop) does make sense, perfect sense in fact.
I suppose it also depends on the quality of parts you end up with, and are prepared to tolerate. Top quality 7075 billet receivers by companies like Mega Arms will never need glue (or you return them for a replacement/refund). Lower end, non-MILSPEC forged 6061 receivers are more likely to be out of spec. But then, they are also cheap so can be replaced, instead of trying to fix sloppy tolerances with glue...Just saying.
I know I'm playing Devil's Advocate here and wish you well with your builds. I guess I need to work through all the reasons for doing this in my own mind. A beautiful group by the way - excellent shooting.