AR assembly techniques.

[Jmedic_]

I have currently built a few uppers/lowers at this point, but by no means consider myself to be an expert/armorer. And, I'm always interested in hearing/seeing how others go about their builds and the techniques, insights, etc. So, recently I was watching somebody build a BCM 9" .300/blk upper (however, the video is now gone for some reason). This video was of particular interest since I'm about to build my BCM 11.5 upper. Anyway, in the video, the guy building it used compressed air to clean any particles, dust, or debris that may have been in the barrel nut, feed ramps, and receiver threads. How critical or important is this? This guy was the only person I've ever seen do this, and he was pretty adamant about how important of a step it was (I do have a compressor and can utilize this technique if it's beneficial). In the same sort of vein, is soaking threads of various parts in acetone critical/required or pointless? The acetone cleaning I have seen in quite a few videos, but not in all of them. Sorry for the long winded post!

[RobertTheTexan]

I don’t soak my parts in acetone. Wasn’t even aware that was done. In the video, were all the parts brand new? If so, then I think the only time I would use compressed air was if I was lapping my upper receiver or some other activity that left metal particles that could come into contact with threads or threaded surfaces. I do clean the threads on the upper and wipe down the inside threads on the barrel nut before applying aeroshell.
I’m not an expert either, but that’s the way I do it.
I think if I let my OCD run wild I could see myself using my air compressor to blow out whatever particles, real or imaginary.


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[joeg26er]

I've built one upper and lower
It was pretty easy
All the videos I researched most made a point of proper torque
Proper degrease then regrease or loctite as appropriate any threads
The most difficult for me was installing the trigger
It kept uncocking

[Jmedic_]

I don’t soak my parts in acetone. Wasn’t even aware that was done. In the video, were all the parts brand new? If so, then I think the only time I would use compressed air was if I was lapping my upper receiver or some other activity that left metal particles that could come into contact with threads or threaded surfaces. I do clean the threads on the upper and wipe down the inside threads on the barrel nut before applying aeroshell.
I’m not an expert either, but that’s the way I do it.
I think if I let my OCD run wild I could see myself using my air compressor to blow out whatever particles, real or imaginary.


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Yup! Brand new right out of the packaging. The guy was saying basically if any little bits of debris get into those areas they could really mess with the function of the rifle. And maybe "soak" wasn't a good word. For instance, Surefire put out a muzzle device installation video a few years ago. And the guy in the video poured acetone on the muzzle threads and barrel thread, cleaned with a Q-tip until the Q-tips had no visible anything on them, then he proceeded to install the muzzle device. It seems like a good practice, but it doesn't seem to be the "standard"?

[SomeOtherGuy]

Not an expert. I have never used compressed air or acetone. If a part appears to have dirt or production grit I clean it with something compatible with its ultimate use - typically gun CLP for parts that will have CLP or grease on them, or water-based spray degreaser for parts that will be dry in use, or are getting painted.

Again, not an expert.

I think compressed air is massively over-used though. It's the absolute best way to put your contaminated grit or oily residue into the shop air, so it can slowly settle on EVERYTHING in the shop and make a much bigger mess. If there's enough grit that you can't wipe it away or blow it with your breath, try a shop-vac.

[Jmedic_]

I've built one upper and lower
It was pretty easy
All the videos I researched most made a point of proper torque
Proper degrease then regrease or loctite as appropriate any threads
The most difficult for me was installing the trigger
It kept uncocking

Yes, torquing is definitely important and yes triggers can be a pain in the ass haha. You never cleaned your threads with acetone before installing or used compressed air?

[Todd.K]

Yup! Brand new right out of the packaging. The guy was saying basically if any little bits of debris get into those areas they could really mess with the function of the rifle. And maybe "soak" wasn't a good word. For instance, Surefire put out a muzzle device installation video a few years ago. And the guy in the video poured acetone on the muzzle threads and barrel thread, cleaned with a Q-tip until the Q-tips had no visible anything on them, then he proceeded to install the muzzle device. It seems like a good practice, but it doesn't seem to be the "standard"?

Threads for a silencer mount need to be cleaned completely with solvent. Same for anything getting thread locker.

The biggest mistake I see is failing to torque the barrel nut to max, then loosen several times before final torque setting.

[Jmedic_]

Threads for a silencer mount need to be cleaned completely with solvent. Same for anything getting thread locker.

The biggest mistake I see is failing to torque the barrel nut to max, then loosen several times before final torque setting.

Yup, I don't think I've ever seen somebody not do that. Who knows what people do in the privacy of their own garage, though.

[joeg26er]

Yes forgot to mention the breaking in and seasoning of torque on the barrel nut is very important

Second to the trigger assembly clocking the barrel nut was also a bit of a pain

[556Cliff]

Threads for a silencer mount need to be cleaned completely with solvent. Same for anything getting thread locker.

The biggest mistake I see is failing to torque the barrel nut to max, then loosen several times before final torque setting.

Who goes to the maximum (80 foot pound) torque spec for the tighten/tighten/loosen routine?

The tighten/loosen routine is supposed to be done with the minimum (30 foot pound) torque spec, not the maximum.


Also, I have always hosed down every metal part with CRC non chlorinated brake cleaner and then I use an air compressor to dry the parts prior to assembly.

All plastic parts get hand washed with hot/warm soapy water and then they get the air compressor.

Yes, my skin will crawl if I happen to see someone skip these steps.