6.8 SPC Forums banner
21 - 40 of 46 Posts

·
Registered
Joined
·
1,869 Posts
If someone claims the uppers they use never need lapping so they don't bother doing it I think the obvious question is " How do they know it is square if they don't check it with a proper fitting lapping tool . I have seen barrels shoot straight that were in uppers that were not square . Also if the extension fits loosely in the upper and is torqued down into an off square upper the bolt lugs will not square up where as if the extension fits tight they may square up even though the nut is not putting even pressure the circumference of the barrel . In other words , you can't tell by how one shoots if the upper is square or not .

Sent from my LM-K920 using Tapatalk
 

·
Registered
Joined
·
650 Posts
Here is something (or 2) to consider;

The body of the 'squaring' lap spins in the carrier bore. If there is any clearance between the bore and the body, the lapping surface can wobble, be pulled of square, chatter, etc. leaving the face of the extension mating surface less than perfectly flat and also less than perfectly square.

If the bore for the extension is not perfectly in line with the carrier bore, the the squaring lap will actually 'lap' the face of the extension bore off square with the bore for the extension and produce the exact opposite of the intended result.

I watched several videos of people using the squaring lap. I did not see a single video where anyone lubed the lap body and carrier bore. I wonder how much anodizing was removed by running things dry.
100% True I always use a home made arbor and cleaned the face up on my lathe
 

·
Registered
Joined
·
1,869 Posts
I think there is a lot of confusion about what is being accomplished by lapping. If the face is going to be squared with the bore the tool will have to be tight in the bore as the amount of clearance will be amplified in the amount the face is off . If all you are trying to do is insure the face is flat you could do that with a piece of 400 grit and a flat pane of glass .

Sent from my LM-K920 using Tapatalk
 

·
Premium Member
Joined
·
18,655 Posts
Here is something (or 2) to consider;

The body of the 'squaring' lap spins in the carrier bore. If there is any clearance between the bore and the body, the lapping surface can wobble, be pulled of square, chatter, etc. leaving the face of the extension mating surface less than perfectly flat and also less than perfectly square.

If the bore for the extension is not perfectly in line with the carrier bore, the the squaring lap will actually 'lap' the face of the extension bore off square with the bore for the extension and produce the exact opposite of the intended result.

I watched several videos of people using the squaring lap. I did not see a single video where anyone lubed the lap body and carrier bore. I wonder how much anodizing was removed by running things dry.
It's the same hole straight through, they don't drill the back half then spin it around and drill the little front section.
 

·
Premium Member
Joined
·
18,655 Posts
I haven't built uppers as part of the business since 2012 but before that every upper was squared on a lathe. Out of thousands most were off .002" across the 1" threads even the Mega. 2 clicks on the CNC is what it took to clean them up. The thing is the Mega bores fit tight to the extension and would have been held straight with the bore with only part of the extension flange touching the face of the receiver.
I still think if the extension fits tight in the bore of the receiver you don't really need to lap it but it sure does not hurt anything.
There are 2 camps of builders out there, the ones that do everything they can to make their rifles as accurate as possible and the ones that slap everything together chanting "it'll be fine". Obviously the same crowd that builds auto engines without checking the deck and head for a flat plane.
 

·
Registered
Joined
·
15 Posts
THIS is why you "face" or true an AR upper. EVERY upper I have come across has needed some trueing. Even Seekins and Aero Precision. I am not talking about disassembling an ultra high end rifle from a manufacturer that shoots under MOA. I am talking stripped receivers or upper build kits. If you do this a NEW scope will likely zero for windage in less than a quarter turn. This is one of those CAN'T hurt MIGHT help steps. Why would you not do it?
 

Attachments

·
Registered
Joined
·
2,596 Posts
THIS is why you "face" or true an AR upper. EVERY upper I have come across has needed some trueing. Even Seekins and Aero Precision. I am not talking about disassembling an ultra high end rifle from a manufacturer that shoots under MOA. I am talking stripped receivers or upper build kits. If you do this a NEW scope will likely zero for windage in less than a quarter turn. This is one of those CAN'T hurt MIGHT help steps. Why would you not do it?
When building from scratch, why not do it??!?? Leave behind any lingering wish you HAD after it’s assembled.

I usually go until about 1/4 of the face remains.
 

·
Registered
Joined
·
15 Posts
Probably an even better reason to true, is ensuring bolt lugs share the load as evenly as possible. I personally have never broken a bolt. I cant say trueing is the reason, maybe I have never pushed the limits of a Grendel bolt.
 

·
Registered
Joined
·
15 Posts
In the early 90's I never did this. I recall seeing the tool referenced in the Brownells catalog. I looked at it, read the description, and thought, this must be a tool for salvaging an out of spec upper. But being a perfectionist I ordered one. I tried it on the first upper, it was not square. So then I did another, it was not perfect either. Next thing you now I got a floor full of disassembled uppers. I made a note of which ones took the most effort to square. Yes every single upper needed to be re zero'd. The ones that took the most effort also took the most adjustment to re-zero, and in all cases the turret was returned to a point closer to factory zero. I now do EVERY one I get. I did a Seekins Billet upper, even it was not perfect. I ended up selling it before I built it. The guy who bought it asked if I had done that. I said yep. He said he had wondered if it was worth the effort. He eventually got it built. He put a new scope on it, and called me just to tell me it only took a handful of clicks to dial in the windage. I told him that has been my experience also.
 

·
Registered
Joined
·
441 Posts
Discussion Starter · #33 ·
Got the tool, disassembled my 6.8 and squared the (Anderson) reciever. Sadly, I have been unable to test it to see if it made any major difference. So stinking hot, it's probably going to be this fall, or at least cooler temps before I venture forth! LOL!
I learned a LOT from the first few AR I assembled.
ALWAYS scrub (and I mean SCRUB!) the chamber before assembly.
Lube the threads (very little) before installing the barrel nut.
True up receiver before installing barrel.
Torque barrel nut to 35 ft/lbs.
Wait 5 minutes.
Back off barrel nut and torque to 35 ft/lbs again.
Wait 5 minutes.
Back off barrel nut and torque to 45 ft/lbs and align notches for gas tube.
Does the torque, release, torque, release, torque make a big difference?
I dunno...but it sure soothes my OCD thinking I've stressed and relieved the nut and threads a couple of times.
 

·
Registered
Joined
·
672 Posts
Got the tool, disassembled my 6.8 and squared the (Anderson) reciever. Sadly, I have been unable to test it to see if it made any major difference. So stinking hot, it's probably going to be this fall, or at least cooler temps before I venture forth! LOL!
I learned a LOT from the first few AR I assembled.
ALWAYS scrub (and I mean SCRUB!) the chamber before assembly.
Lube the threads (very little) before installing the barrel nut.
True up receiver before installing barrel.
Torque barrel nut to 35 ft/lbs.
Wait 5 minutes.
Back off barrel nut and torque to 35 ft/lbs again.
Wait 5 minutes.
Back off barrel nut and torque to 45 ft/lbs and align notches for gas tube.
Does the torque, release, torque, release, torque make a big difference?
I dunno...but it sure soothes my OCD thinking I've stressed and relieved the nut and threads a couple of times.
I doubt the torque release repeat does any type of stress relief. I can see a benefit in that it irons all the miniscule hills and valleys of the mating surfaces so that a higher percentage of surface area is in contact.

I do a similar process with quick detach scope mounts. Usually mount, dismount and adjust tension of the clamping system at least ten times before zeroing the scope. The the mount to rail contact pattern becomes well establish and repeatable.
 

·
Registered
Joined
·
1,869 Posts
I doubt the torque release repeat does any type of stress relief. I can see a benefit in that it irons all the miniscule hills and valleys of the mating surfaces so that a higher percentage of surface area is in contact.

I do a similar process with quick detach scope mounts. Usually mount, dismount and adjust tension of the clamping system at least ten times before zeroing the scope. The the mount to rail contact pattern becomes well establish and repeatable.
Agreed , the waiting a given time for stress relief is only needed when using torque to yield / stretch bolts .

Sent from my LM-K920 using Tapatalk
 

·
Registered
Joined
·
1,869 Posts
What if 35lbs and an aligned gas tube doesn't happen??
It didn't , that is why he went to 45 lbs . I often see people get all goofy when talking about how precise the torque has to be on barrel nuts and wonder if they realize how wide the margin is . Anywhere between goodn snug and goodntite is ok with 40-60 being my preferred range . I personally would use shims to stay in that range if need be but none of my uppers need nut- tube alignment . That said I have never known of a nut torqued to 35 backing off or 80 stripping threads or trashing an upper .

Sent from my LM-K920 using Tapatalk
 

·
Registered
I got guns, you got guns, we all got guns! Free to the bone, please do not f**k with me.
Joined
·
3,726 Posts
ok now i'm interested... I dunno anything about this but does it help with accuracy?
 

·
Premium Member
Joined
·
1,302 Posts
ok now i'm interested... I dunno anything about this but does it help with accuracy?
Squaring an upper would if it needed it, if you don't know if it needs it then do it anyway, it only makes sense.
 
21 - 40 of 46 Posts
Top