dist1646
Ultimate Member
Just got back to this thread. I can't say exactly how but, it works. The rifles I have bedded cut my verticle dispersion by almost half at 600. That's a significant reduction.
Lapping and Bedding an AR Upper
- Thread starter IndispensableDestiny
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Just got back to this thread. I can't say exactly how but, it works. The rifles I have bedded cut my verticle dispersion by almost half at 600. That's a significant reduction.
clandestine
AR-15 Savant
Dist1646 is correct. When there is play between the upper and lower it will cause some inconsistencies with optics.
Magnumite
Ultimate Member
Recoil begins upon ignition. Where ever barrel vibration points the upper, thst's where the bullet goes.
Would love to revisit this question, particularly the bedding part. Is it worthwhile for an AR308 long range build? Is Loctite 620 still recommended? What is the proper procedure? Thanks everyone.
Saw this video and starting wondering. Skip to 1:35.
https://www.youtube.com/watch?v=Mpu-aZ3N1Ps
Saw this video and starting wondering. Skip to 1:35.
https://www.youtube.com/watch?v=Mpu-aZ3N1Ps
clandestine
AR-15 Savant
He did a great job with that video. IMO yes truing and bedding the barrel is a positive thing. There is no negatives in my opinion if its done right. I have not used the Indian Gasket Sealer so I will have to try it. I am always open to learning new things.
I do know that the assumption about loctite for bedding is incorrect in regards to Loctite #620. I have customers with barrels with tens of thousands of rounds and I have torn the guns down wth no indication that the loctite has cracked, weakened, or broken down. He also uses blue loctite for the gas block set screws, thats inferior IMO. Rocksett is the right product for this job.
That gun is alo a precision rig and he dimples the barrel and uses a set screw model. Pinning and Dimpling can induce stress on a good barrel. For a precision build a clamp on gas block add the least amount of stress to the barrel.
Loctite is bad for many areas of an AR but for Gas Key FLats and Barrel Bedding, its a good application.
He touches on some great points in the video about torque and even covers headspace. Great stuff but he does neglect to use a torque wrench onthe GB Set Screws and the Tensioning Bolts of the Rail. It is important to torque those parts to keep distortion to a minimum and to keep an even load on the bolts.
Here is how I would assemble that Upper:
SLR Clamp On Gas Block (9-11 Inch# MAX)
PTG .308 Lapping Tool
Loctite 620 for Bedding
Areoshell 64 for the Barrel Nut Threads and the MFG FT# suggestions for the Nut
Muzzle Device Rocksetted to 25-30FT# MAXIMUM
Matched/Polished Feed Ramps and Reburr Barrel Extension
omegared24
Ultimate Member
With so many manufacturers in the business it is extremely beneficial to check things like this and correct. Everyone may use top of the line raw forgings but the finish is what matters. I have been given an odd look on many occasions when I ask that question.
My go to uppers have been professionally assembled and checked.
Thanks for the great write up Clandestine! I'll be doing those things on my next build, but I don't think I can use the lapping tool since I have "enhanced" type uppers from Aero and Mega. Do you agree?
https://aeroprecisionusa.com/m5e1-enhanced-upper-receiver.html
http://www.megaarms.com/maten/upper-receivers/mkm-maten-keymod/
clandestine
AR-15 Savant
I have lapped ones that look like the ones you listed. I can't say for sure if those particular uppers will work with the lapping tools as I dont have notes to the contrary.
If you are unsure you can send just the upper receivers to me and I can check and lap them for you if the tools work.
I can also lap AR15 Uppers in my lathe if necessary but it takes a LOT of setup time in the 4 jaw. I don't have a jig to do .308 type AR Uppers in the lathe.
Last edited:
Doco Overboard
Ultimate Member
Enjoyed reading this and i think that there are a lot of little things that can be done to improve functionality which is part of the enjoyment of owning a particular type of weapon. With that being said I'm wondering how lapping the face on a design like that is entirely beneficial without being certain the threads have been cut square to the rest of the receiver. Im asking a question not giving a condemnation for the pro's verses the cons because I don't know if the threads are cut before or after heat treating for warpage or maybe its just that heat treating doesn't effect aluminum the same way during the manufacturing process. It just seems like there is a lot hanging out there on an AR upper. Im just not that familiar with the entire circumference of the front ring needing lapped to square it up, sometimes its only a portion. some one mentioned in an earlier post the process was like an m700 but part of blueprinting is makeing sure the bore is aligned with the center line of the bolt and lugs and recoil lug etc but chasing the threads sometimes means the old barrel cant be used becuase the thread fit is lost so a new barrel is usually cut to fit. Just trying to understand the benefits of the ops efforts and someone else mentioned an improvement in vertical stringing so ther has to be some benefit. Thanks.
clandestine
AR-15 Savant
You can paint the crush surface of the barrel extension with layout fluid and tighten the barrel nut. Even load will remove the layout fluid evenly if the threads are true enough to avoid problems. I can measure thread runout of the threads in relation to the bore with my lathe and a runout indicator, but they are rarely out of spec in my gauging.
An untrue Upper Face can cause irons and prics to run out of adjustment, it can cause free float rails to sit incorrectly, and it can also put uneven load on the Bolt Lugs when a round is chambered.
Doco Overboard
Ultimate Member
Thanks I can see how lapping that extension makes for a good fit and makes sense to eliminate vibration an uneven stress at the front of the receiver. I just have a hard time visualizing how if those threads are off stacked up against tolerances in the bolt fit to lugs they could ever be square to the machining inside the receiver unless that is the benefit for the lugs squaring themselves in the extension and by not being "fixed" to the receiver themselves. I'm guessing this is why there is inherent accuracy to the design and why its so important. I would think the lapping would just be part of a well fit rig and assembly what could it hurt? I would probably at the very least check the fit and lap as necessary for a routine build. One day Im going to get out of the stone age and collect some AR stuff to mess around with. Thanks again for the reply.
DutchV
Ultimate Member
- Jul 8, 2012
- 4,722
Aero says their enhanced uppers don't need to be lapped.
I have lapped a bunch and all were off at least a little tiny bit. Essentially it is the front face of the upper receiver, where the barrel band mates against the upper. It may only be a little, on the order of a thousandth or less, but that is a critical mating surface that plays a big part in the accuracy and alignment of the barrel to the upper. I have heard of many that had 'sight off to one side' issues to get the rifle on target and this will normally correct that, get your sight centered again and shoot better as a result.
I won't build an AR, 7.62's included, without lapping the upper receiver and bedding the barrel when needed.
I won't build an AR, 7.62's included, without lapping the upper receiver and bedding the barrel when needed.
They can't be, from what I see. You are kind of stuck with that, though the design appears to be solid, you are still at the mercy of their word on that.. I guess time and builds will tell.
Just thought I would pop in here to say that my Aero Precision enhanced upper has performed well. I am not sure about their marketing claims, but it definitely made assembly easy, and it seems solid. My only real issue with it is lack of information on rail compatibility. They used to (maybe still do) make vague claims that rails besides theirs were compatible, but I never found any solid data. Overall my sample of 1 works well for what I use it for. I have a Vortex SPARC AR on it as well as diamondhead BUIS on there permanently now, but I had a 1-6 and cheap PA 4-14 FFP on it to stretch its legs a bit, and it has always been under 1 MOA at 100 yards if I do my part (16" Faxon Gunner barrel + a seekins bcg . . . Checked for proper headspace). Never had to mess with windage to zero any of the optics/sights to the scope and never had any POI shifts, so I can't imagine it being badly off. Again, this is a sample of 1 and I'm only speaking to overall upper quality, not taking a stance on whether it needs lapping and bedding. I have no particular dog in the fight when it comes to lapping and bedding AR uppers, though I believe that it can certainly help to squeeze the most out of the rifle and solve some problems. Enjoying reading this thread, though. Thanks to all who have shared their experiences.They can't be, from what I see. You are kind of stuck with that, though the design appears to be solid, you are still at the mercy of their word on that.. I guess time and builds will tell.
So, after measuring, the PTG tool will NOT work in either Aero or Mega enhanced type uppers. PTG tool is 1.5" and the upper opening is around 1.37". PTG offered to custom make the tool for me for an additional $20 so it will fit. Not sure if it's worth it at this point or just trust the quality machining of Aero and Mega...
clandestine
AR-15 Savant
Sounds like I need to modify one of mine so they will work.
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