Just got my bcm upper in yesterday same as above WAY more slop in the upper to lower fit than any of my aero uppers.
- Thread starter JustBC
- Start date
hmmm. Learning stuff here. Working on parts for my take on an SPR build.
Liked the looks of the Aero uppers and really like their M4E1 lowers. MSTN even showed a build he did with and Aero set and parts from a subsidiary of V7 that was very accurate and saved a good bit of coin over a billet set.
Then one guy says the BCM uppers are the best. Another says they are sloppy. Have a BCM upper on an Aero lower and there is no slop what so ever. Snugger than a Scotsman's wallet. That is without messing with the tensioning screw.....
Think I am just gonna have to build off the aero lower and BCM upper I have and see how it goes..... I can tear down and use a thick walled upper if needed.
I might like my receivers like I like my women, with a little more where it counts.......
Liked the looks of the Aero uppers and really like their M4E1 lowers. MSTN even showed a build he did with and Aero set and parts from a subsidiary of V7 that was very accurate and saved a good bit of coin over a billet set.
Then one guy says the BCM uppers are the best. Another says they are sloppy. Have a BCM upper on an Aero lower and there is no slop what so ever. Snugger than a Scotsman's wallet. That is without messing with the tensioning screw.....
Think I am just gonna have to build off the aero lower and BCM upper I have and see how it goes..... I can tear down and use a thick walled upper if needed.
I might like my receivers like I like my women, with a little more where it counts.......
Lapping/facing an Upper is simplicity itself. Takes a few dollars, a hand drill, and about five minutes.
The equipment. The gear for the 308/AR-10 costs about a buck more.
Is this necessary. Hell, I don't know, but it's quick, affordable; and if there was a concern before, there's very likely none afterward. I do it, and am in the early stage process of testing accuracy before and after.
Greg
The equipment. The gear for the 308/AR-10 costs about a buck more.
Is this necessary. Hell, I don't know, but it's quick, affordable; and if there was a concern before, there's very likely none afterward. I do it, and am in the early stage process of testing accuracy before and after.
Greg
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Can you describe how your thermofit process?
It's not my process...its the design of the bcm upper with an undersized barrel tenon port. You need to heat up the upper with a heat gun, slide your barrel in and it will shrink tight around the barrel extension. It won't slide in without doing this, making for a nice, tight barrel to receiver fit
While I do it a a matter or course, I really doubt that the receiver face lapping alone will make a discernible difference unless the said receiver is far worse than any I've ever seen & I think bedding / thermo fitting has a more significant impact.
YMMV
Now bedding would be an entirely different process. That is where one uses 609/620 on the barrel tenon before inserting into their loose/sloppy fitting upper receiver.
Warming the aluminum upper about 100F (from 70F ambient to 170F, Ouch 
) will expand the bore about 0.0012".
Chilling a Stainless barrel (I stand mine upright in the freezer) about 70 degrees F, close to zero F, will shrink the barrel by about 0.0006".
You can get ALMOST 0.002" extra clearance by this method.
To bed AND thermal fit,
I mask off the extension, and spray a fairly even coat of high temp rattle can paint. Shooting for about a 1 to 2 mil thickness (2 to 4 mil diameter increase). I then use fine emery paper to thin to close to a 2 mil diameter increase (about a mil of paint).
Maintaining an even coating is pretty easy with only a mil of paint.
Let it cure well before sanding and then chilling.
This paint has a very high compression strength, doesn't crack or creep, or corrode.
I've previously posted pic so I won't bother.
) will expand the bore about 0.0012".Chilling a Stainless barrel (I stand mine upright in the freezer) about 70 degrees F, close to zero F, will shrink the barrel by about 0.0006".
You can get ALMOST 0.002" extra clearance by this method.
To bed AND thermal fit,
I mask off the extension, and spray a fairly even coat of high temp rattle can paint. Shooting for about a 1 to 2 mil thickness (2 to 4 mil diameter increase). I then use fine emery paper to thin to close to a 2 mil diameter increase (about a mil of paint).
Maintaining an even coating is pretty easy with only a mil of paint.
Let it cure well before sanding and then chilling.
This paint has a very high compression strength, doesn't crack or creep, or corrode.
I've previously posted pic so I won't bother.
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Bed, don't bed.....had to make sure i wasn't on AR15 . com............. Ive done both and didn't see any difference, but if it gives you confidence in your equipment do it.
To the OP, you have an outstanding barrel, good luck whichever way you go.
To the OP, you have an outstanding barrel, good luck whichever way you go.
Revisiting this post after all these years.... The upper was an Aero. They are not as tight as some but I already had it. If I had a top shelf upper I probably wouldn't bother. In the end it was a fun project and kept me out of trouble for a couple evenings.
If the vendor offers decent customer service, ask them first. I recently did a lightweight AR15 build and contacted the vendor of my upper. They said to absolutely NOT do this as it was trued at the factory and wasn't needed. Had to freeze the barrel overnight and heat up the upper for them to fit together. We'll see how it shoots. I have high hopes.
Kinda wanted to circle back to one of the first posts, where someone mentioned using a release agent on the barrel extension so that the Loctite would adhere to the receiver, but not the extension.
Has anyone else here tried that method?
Has anyone else here tried that method?
Wouldn’t you want the loctite to adhere to the extension and not the receiver? If you pull the barrel, it should be because it’s toast. The upper receiver should last much longer than a barrel. I’d want the crud coming out with the barrel and new loctite on the replacement barrel. Less cleaning of the upper receiver tenon, seems ideal to me.
We have been using blue loctite since the late 80s. There is no need to use a release agent, we just take a wood dowel and tap the barrel out.
Someone made a comment that the company selling uppers told them not to true/square they are square from the factory. That tells me who ever said that has never checked one to see. Most receivers are milled on a pallet system with 16 receivers mounted side ways on a tower. The tower/pallet clips onto the table of the mill. There is play in the pallet system. I check them and square them on a $110,000 quad axis lathe where the receiver spins upon the bore. I have squared thousands of receivers from 2009-2017 almost every one was off .002" across a 1" receiver bore. I don't use the "tools" they sell but they work.
One thing I will say is IF the extension is a tight fit squaring the receiver will not matter. The bore ID and extension OD will hold the barrel/lugs square with the bore.
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Just my 2 cents... I Loctite ( 620 ) and lap the receiver face on all mine. Very little effort, for the improvements.
That said... that is only part of the "formula" ( lack of a better word ) for more consistent precision.
I am a fan of a snug upper to lower fit as well... That allows me to "wield" the AR more consistently off the bench as well.
Zero possible contact between the gas block and free float tube, smooth consistent gas tube to gas key interface...
Many more things IMHO...
Bottom line for me, "True and Glue" done properly... ( quality tools and paying attention ) has produced satisfying results.
FWIW... every upper I have lapped, has been out of true to various degrees. BCM, PSA, Aero, Rainer Arms, Armalite, Spikes, SanTan, Cross machine & Tool, SOLGW... etc.
That is not to say the machining is out of wack... I suspect it has more to do with the anodizing.
My typical results show more consistent grouping at the very least. And less heat shifting .
Some of the barrels precision have improved significantly over groups prior to the "True n Glue".
NOTE: not with every ammo tried... but the ones that did improve, were well worth the effort involved.
Shimming and a Thermo Fit, basically are doing the same thing as the proper Loctite... probably , a better long term job ( how long I don't know )
"If" True n Glue was the perfect , complete answer for great AR precision... we all would be doing it.
But, as mentioned earlier... IMHO, it is part of the puzzle for better AR precision.
That said... that is only part of the "formula" ( lack of a better word ) for more consistent precision.
I am a fan of a snug upper to lower fit as well... That allows me to "wield" the AR more consistently off the bench as well.
Zero possible contact between the gas block and free float tube, smooth consistent gas tube to gas key interface...
Many more things IMHO...
Bottom line for me, "True and Glue" done properly... ( quality tools and paying attention ) has produced satisfying results.
FWIW... every upper I have lapped, has been out of true to various degrees. BCM, PSA, Aero, Rainer Arms, Armalite, Spikes, SanTan, Cross machine & Tool, SOLGW... etc.
That is not to say the machining is out of wack... I suspect it has more to do with the anodizing.
My typical results show more consistent grouping at the very least. And less heat shifting .
Some of the barrels precision have improved significantly over groups prior to the "True n Glue".
NOTE: not with every ammo tried... but the ones that did improve, were well worth the effort involved.
Shimming and a Thermo Fit, basically are doing the same thing as the proper Loctite... probably , a better long term job ( how long I don't know )
"If" True n Glue was the perfect , complete answer for great AR precision... we all would be doing it.
But, as mentioned earlier... IMHO, it is part of the puzzle for better AR precision.
I have heard of using Indian engine gasket sealer instead of loctite to fill the voids on the extension, has anyone here ever tried that? Seems like a viable option but you guys have much more experience than I do with precision AR builds
Permatex form-a gasket- #1, the kind that gets hard will work but it is tougher to get apart than loctite blue.
What do you think works best?
The Permatex probably makes a more rigid connection but again pain to get the barrel out.
I used that instead of loctite when I trued/bedded my two of my uppers. I haven't tried pulling my barrel yet so I can't comment on that. One of the rifles I trued/bedded I had shot a good bit before and knew what it was capable of accuracy wise. After bedding and truing it definitely became more consistent and can shoot groups in the .3's on occasion. Ultimately, I think it's effectiveness(or ineffectiveness) it based on how well your parts interface. My parts weren't exactly a tight fit and I was getting a slight wandering zero range trip to range trip. It has alleviated both those issues for me. The other AR I bedded is sub-MOA shooter too so that doesn't hurt either. I'm a believer.
Would you mind touching on this one a little more?
Are you aiming for no tick? Are you adjusting the gas tube? Not a whole lot out there on this subject, but I think it has something to do with it all, after true-n-glue.
Thanks in advance!
I second this question because there is enough clearance in the upper for the BCG that no matter how you adjust it, if the carrier is riding higher it may slightly contact the gas tube if you’ve adjusted it to not do so when riding lower. I always make sure mine slide on with minimal friction with the upper oriented properly and gravity keeping the bcg lowered then upside down so it’s somewhere in the middle. Cycling it is very unlikely to be in one of these two states with the buffer spring driving it forward, so I’m unsure how you could make it no contact.
That’s how I go about it and think of it, I haven’t really tried to adjust anything though, to see if it made much difference.
I also don’t get to shoot long range on a regular basis with 3 & 2yr olds, and a rather stout fishing appetite...
At the very least... polish the entrance to the gas key, with a conical felt polishing head ( on a dremel ) and some polishing rouge. Nothing crazy mirror like... just smooth it up.
https://www.thefreelibrary.com/Gas+...lignment+in+the+AR-15+leads+to...-a0364199086
https://www.thefreelibrary.com/Gas+...e+never-ending+saga+continues....-a0540679188
My apologizes, I may have not written that out properly ( better at mechanics than "grammar" )
I meant, no contact between the gas block on the barrel and free float tube.... you really want the barrels whip to not be effected by anything except itself.... no Mlok / KMod screws touching the GB , and ample clearance around the GB at the ID of the handguard
And I meant..... smooth interface between the gas tube and the gas key... minimize any binding at the gas key
See the above links.
Click the "Gas Tube Bender" and it has some images and description of how to adjust.
FWIW.... here is my results from a OEM Factory built PA65 upper... to a "Match Oriented, self re-assembled" 6.5CM .... as always... YMMV.
I used all the easy tricks I could.
I am pretty ham-handed... so if I can do this, anyone with a good basic mechanic aptitude... can as well... pay attention to even the small details.
https://www.ar15.com/forums/industr...-again-UPDATED-with-Tn-G-results-/301-285762/
I did the same tricks to a PA 10 Upper with a 22" 6.5CM Criterion barrel... my profile pic ( at the link ) shows my best Cherry picked 10rd group.
( Yes I am proud of the group... and I threw the flier.... 10rd groups that tiny , made me screw up.... I can show you all another nice 10rd group in .308 that I did the same thing too.... Lol )
Watch the Criterion Barrel videos on Accurizing the AR15.... https://criterionbarrels.com/media/accurizing-the-ar-15-video-series/?v=00dc5da36527
I used all the easy tricks I could.
I am pretty ham-handed... so if I can do this, anyone with a good basic mechanic aptitude... can as well... pay attention to even the small details.
https://www.ar15.com/forums/industr...-again-UPDATED-with-Tn-G-results-/301-285762/
I did the same tricks to a PA 10 Upper with a 22" 6.5CM Criterion barrel... my profile pic ( at the link ) shows my best Cherry picked 10rd group.
( Yes I am proud of the group... and I threw the flier.... 10rd groups that tiny , made me screw up.... I can show you all another nice 10rd group in .308 that I did the same thing too.... Lol )
Watch the Criterion Barrel videos on Accurizing the AR15.... https://criterionbarrels.com/media/accurizing-the-ar-15-video-series/?v=00dc5da36527
