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+--- Thread: Accuracy fixed. (/showthread.php?tid=13337)
Accuracy fixed. - Bigs28 - 07-10-2017
Brian if your inserting it in the same direction as my post 36 then your not doing anything wrong. If it doesn't fit, then it doesn't fit. Mine was snug going in but it went in no problem. Contact Pacific tool and tell them the lapping tool doesn't fit and see what they say.
Accuracy fixed. - just_john - 07-10-2017
I have gotten uppers that had been ceracoated and the internals were not masked before applyign the coating. The result was that the inside diamater was reduced to almost "too small" with excess material. If yours is ceracoated, the tool may not be the problem.
Accuracy fixed. - Lastrites - 07-10-2017
Bigs28 Wrote:I did mine verticle but basically just like this with a couple paper towels.
https://youtu.be/Wgw6MhO83Fg
Put the barrel in vertical, cleaned the dripping stuff and put on the barrel nut to hold in place for 24 hours.
What I noticed with his liberal application of blue, most comes off when he slid the barrel in the receiver, seems to me an thin application of blue in the receiver and on the ext. would be better. That said, while he wiped blue off the threads it didn't appear he used any grease on threads prior to torquing the nut so it's likely that nut with be a pain to remove if that day ever comes as there has to be some lock-tite on the threading.
Personally a barrel fit such as that really should have a shim as that fit is what I'd call sloppy.
Accuracy fixed. - Bigs28 - 07-10-2017
I used the barrel nut to hold in place for 24 hours. Then removed added grease and torqued back on.
Accuracy fixed. - brian y - 07-11-2017
just_john Wrote:I have gotten uppers that had been ceracoated and the internals were not masked before applyign the coating. The result was that the inside diamater was reduced to almost "too small" with excess material. If yours is ceracoated, the tool may not be the problem.These are hard coat anodized but you can see from the pics the tool goes in when inserted from the other end and sticks when inserted in the proper end;
I do not know if you can tell from the second photo but it seems there is too much material and it is butting up to it and stopping the tool from going in, and before anyone asks this is not how I was planning on using the tool, I just put it in the vise this way to take the pics lol.
![[Image: IMG_0397_zpsrtjwighu.jpg]](http://smg.photobucket.com/user/steelheadr99/media/IMG_0397_zpsrtjwighu.jpg.html)
![[Image: IMG_0398_zpsux2babhr.jpg]](http://smg.photobucket.com/user/steelheadr99/media/IMG_0398_zpsux2babhr.jpg.html)
Accuracy fixed. - dreadpirate - 07-14-2017
This is the result of (1) lapping the receiver, (2) bedding with Loctite 620, and (3) polishing the feed ramps. 5 shots at 100 yards. I'll take it.
![[Image: LKr6XL8.jpg]](http://i.imgur.com/LKr6XL8.jpg)
Accuracy fixed. - Klem - 07-14-2017
just_john Wrote:Klem, there is no issue with a little loctite on the face of the receiver. The point of lapping and loctiting is to facilitate a "single piece of metal" barrel thru receiver. If there is a little loctite on the face ( after cleaning off the excess), when the barrel nut is torqued down, it just helps to insure that there is no slack anywhere between the barrel and receiver. If there is any space or gap anywhere in this transitional area, there is opportunity for movement at ignition which creates an upredictable shot to shot variation. Just remember that if a little loctite is a good thing, a lot of it isn't!
Thanks for replying but I remain unconvinced that glue between the receiver face and barrel extension increases accuracy. If you go to the effort of shaving minute angles of metal off the receiver face to square it why then let glue or any other substance in between that carefully machined interface? If there is slop between the extension and receiver then by all means try and fill it with something that hardens (and does not flow when heated). But the receiver face and the extension journal needs to be intimate.
I am aware quite a few people don't care about the excess glue squeezing onto the shoulder but I imagine your guns would be even more accurate if you could somehow get the glue to where it is needed, and keep it from where it is not.
Accuracy fixed. - dreadpirate - 07-14-2017
Klem Wrote:I am aware quite a few people don't care about the excess glue squeezing onto the shoulder but I imagine your guns would be even more accurate if you could somehow get the glue to where it is needed, and keep it from where it is not.
Easy - heat the barrel nut with a torch so the Loctite flows out and settles in the gaps after you have it assembled. Use Loctite 620 which should not liquefy under normal shooting temperatures.
Accuracy fixed. - Klem - 07-15-2017
dreadpirate Wrote:Easy - heat the barrel nut with a torch so the Loctite flows out and settles in the gaps after you have it assembled. Use Loctite 620 which should not liquefy under normal shooting temperatures.
Heat it with a torch? To be clear, you mean a naked flame? No, heating aluminium brings with it the potential of annealing. There has to be a better way.
Why don't you coat the inside of the receiver with glue and not the outside of the barrel extension? Then as the two parts are brought together it pushes the excess in the opposite direction of the face. Hopefully the receiver face and shoulder remains clean. It would be a little more fiddly cleaning the excess but there's enough access into the receiver to do this.
Screw the barrel nut on and leave it vertical with the barrel pointing down. Gravity keeps the liquid glue right up to but not on the face as it hardens.
Accuracy fixed. - dreadpirate - 07-15-2017
Klem Wrote:Heat it with a torch? To be clear, you mean a naked flame? No, heating aluminum brings with it the potential of annealing. There has to be a better way.
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.
Accuracy fixed. - dreadpirate - 07-15-2017
Here is a better shot of the group.
![[Image: STZx9WN.jpg]](http://i.imgur.com/STZx9WN.jpg)
Accuracy fixed. - Klem - 07-15-2017
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.
Accuracy fixed. - LWP - 07-15-2017
This would be the method that I would use (IMO) if I were to use loctite. Agreeing not to have any Loctite between the face of the receiver and barrel barrel extension makes good since to me.
Accuracy fixed. - LWP - 07-15-2017
I would think that if one did want to apply Loctite inside the receiver first and then install the barrel extension, screwing the barrel nut on to the proper torque specs and leaving it vertical with the barrel pointing down would let gravity do its thing. Keeping the liquid glue right up to, but not on the face as it hardens would be easy and smart as well.
Accuracy fixed. - bj139 - 07-16-2017
Klem Wrote:Thanks for replying but I remain unconvinced that glue between the receiver face and barrel extension increases accuracy. If you go to the effort of shaving minute angles of metal off the receiver face to square it why then let glue or any other substance in between that carefully machined interface? If there is slop between the extension and receiver then by all means try and fill it with something that hardens (and does not flow when heated). But the receiver face and the extension journal needs to be intimate.I imagine you would have to lap the barrel shoulder as well to get the accuracy you envision. The loctite just fills in the tiny gaps which will always be there no matter how well you lap. Think about creating an airtight seal between 2 metal surfaces.
I am aware quite a few people don't care about the excess glue squeezing onto the shoulder but I imagine your guns would be even more accurate if you could somehow get the glue to where it is needed, and keep it from where it is not.
Accuracy fixed. - Sticks - 07-16-2017
I would hope that the barrel receiver extension would be true, not require lapping.
Lapping a receiver however has been proven again and again that it is a benefit.
Bedding the barrel extension into the receiver by whatever means has also proven to be a benifit - though I agree with Klem that any bedding material that requires heat should be avoided. Heat and slow cool on Aluminum and Aluminum alloys makes them harder - pushing brittle depending on the original properties and how much heat was applied.
I'd stick with the tried and true blue locktite applied in a thin layer in both the receiver and on the barrel extension, taking care to not push excess into the internals of the receiver, and keeping it off the threads. Install the barrel nut with aluminum or nickel antisieze (prevent dissimilar metal electrolysis), torque to spec and clock if needed for gas tube, let sit for 24 hours until cured.
Accuracy fixed. - dreadpirate - 07-16-2017
Klem et al - fair enough; perhaps the heat treatment is not worth the side effects. The armorer I was working with seemed to think it would "set" the Loctite 620 in place. Heating or not; I still think the bedding and lapping are worth it. My question is should this ALWAYS be done when assembling an upper, or or only done if you are having accuracy issues? The reason I started done this road is (1) this was my first upper assembly and I wanted a pro to double check my work, and (2) the rifle was shooting 2" groups at 100 yards.
Accuracy fixed. - dreadpirate - 07-16-2017
Here's another thing to think about; even if you don't apply heat to the Loctite initially. If you want to change the barrel, you will have to heat the Loctite to, what?, like 400 deg F to get it loose? Guess it depends on which Loctite you use. But you MUST use a Loctite that will not melt during normal shooting. My point is; once you go down the path of Loctite, you will have to apply heat at some point in the future to remove the barrel, right?
Accuracy fixed. - dreadpirate - 07-16-2017
Here's what Loctite says:
"TYPICAL CURING PERFORMANCE
Product 3620 has been specifically developed to cure at lower
temperatures and/or shorter times than standard products.
Recommended conditions for curing are exposure to heat
around 100°C, (typically 90-120 sec. @ 100°C). Rate of cure
and final strength will depend on the residence time at the cure
temperature."
So you are supposed to heat it to 220 deg F, not 400 deg F. Hopefully that's what I did
Accuracy fixed. - LWP - 07-16-2017
So now I'm curious, what temp does the barrel extension and chamber heat up to with an ambient temp of 95* shooting 10 shots at lets say in 20 seconds produce? Or, how many shots can be fired before the temp gets high enough to start to melt the blue loctite?