AR upper receiver lapping - Page 2

MarkCO · April 5, 2023, 03:33 PM

Quote:

Originally Posted by Shadow9mm

and Final Pass

I see nicks and grooves on the raw receiver face. You have successfully made your receiver worse than it was.

Shadow9mm · April 5, 2023, 05:15 PM

maybe maybe not. Based on the removal patters i had a bit of a high spot at the bottom. while the surface may have some small grooves in it, it is also now flat. it may be an even trade.

I did also notice some wear marks/grooves in the bar itself after lapping this upper. so that's not great. Im calling it at this point. I only used the 600 grit on my colt upper. it looked much cleaner. But based on this upper and the way the tool looks, its getting returned.

HiBC · April 5, 2023, 08:24 PM

It looks like a steel tool. Steel is harder than aluminum. The way lapping works,the grit embeds in the softer material . Its the harder material that gets cut.
Interesting. Thanks.
Did it get dry? A little galling maybe?

I'm not criticizing. I'm trying to learn from what I see.

MarkCo's comments are interesting,too.

Shadow9mm · April 5, 2023, 09:19 PM

Quote:

Originally Posted by HiBC

It looks like a steel tool. Steel is harder than aluminum. The way lapping works,the grit embeds in the softer material . Its the harder material that gets cut.
Interesting. Thanks.
Did it get dry? A little galling maybe?

I'm not criticizing. I'm trying to learn from what I see.

MarkCo's comments are interesting,too.

Im trying to learn too, no worries. Just keep in mind im no expert. Just sharing what im doing in the hopes i get some good advice and others can learn from my experience.

steel tool. Did not get dry as best i can tell. The lapping compound was kind of a thick paste. Had to mix it up. Had separated. Looked like it had grease or petroleum jelly in it from the consistency. I worked in about 10 second passes. Applied fresh compound each time. Im wondering if the 320 grit was too coarse. Also i think wheeler uses silicon carbide, which can embed. Apparently there are non embedding lapping compounds, which i would consider if i was looking to try this again.

tangolima · May 21, 2023, 03:30 AM

Found some 0.01" soft lead strips (originally for fish sinker). Cut a thin strip and used that as gasket / crush washer under the barrel shoulder. While I was at it, I applied blue loctite to the barrel shank. Torqued the nut back to proper timing. Torque went up by about 10lbf-ft. Will see whether it will help. Probably not much as it is a very cheap upper. Once a while, when everything is perfect, it did shoot sub moa 10-round groups, with peep sight mind you. Hopefully with the mod, such delighting moments happen with more regularity.

The idea is similar to lapping. The soft lead conforms to the harder steel and aluminum so that the force is even all around.

-TL

Sent from my SM-N960U using Tapatalk

stagpanther · May 21, 2023, 05:54 AM

I pull barrels quite a bit off of well-used rifles, I've found that the area around the chamber and the extension where it fits into the receiver is a cauldron of high-pressure heated gas which mixes with combustion residue and residual cleaning solvent--it's going to find a way into any joint. The other thing about lapping that I became nervous about it was that I was unsure of how it might affect headspacing and lug lock-ups--I suspect that even minute depth changes could make a difference. The extension pin slot may or may not also be affected--I had a barrel once that absolutely refused to work with any bolt and I eventually figured out the extension pin was slightly out of clock with the gas port and lugs. I'm not saying it's a bad thing you shouldn't do--but I suspect that it's not as straightforward as blueprinting a bolt action receiver. I'd like to hear from an industry expert to weigh in on this. My opinion about any receiver to barrel mating that involves shims is that is inherently going to cause problems sooner or later--always has on any rifle I've used them on.

tangolima · May 21, 2023, 11:01 AM

Headspacing is in the barrel extension. Lapping / shimming should not affect headspacing. It does change the location of the lock lugs by a few thous. Between the bolt and bolt carrier there is about 1/4" margin built in the design to delay the locking / unlocking. A few thous change shouldn't be problem. Lapping / shimming is perpendicular to the pin slot. It doesn't change that either.

I prefer shimming (actually not quite shimming in normal sense) to lapping for a few reasons. I generally don't want to remove metal from parts if I don't have to. Shimming is reversible. Spending money to buy another tool is another reason.

There was a bit of residue on the barrel shank. When I wriggle the barrel I could feel a slight slop there. The loctite hopefully will fill that.

Will shoot some group to see how it works.

-TL

Sent from my SM-N960U using Tapatalk

April 5, 2023, 08:24 PM	#28
HiBC Senior Member Join Date: November 13, 2006 Posts: 8,295	It looks like a steel tool. Steel is harder than aluminum. The way lapping works,the grit embeds in the softer material . Its the harder material that gets cut. Interesting. Thanks. Did it get dry? A little galling maybe? I'm not criticizing. I'm trying to learn from what I see. MarkCo's comments are interesting,too. Last edited by HiBC; April 5, 2023 at 08:33 PM.

May 21, 2023, 05:54 AM	#31
stagpanther Senior Member Join Date: March 2, 2014 Posts: 11,887	I pull barrels quite a bit off of well-used rifles, I've found that the area around the chamber and the extension where it fits into the receiver is a cauldron of high-pressure heated gas which mixes with combustion residue and residual cleaning solvent--it's going to find a way into any joint. The other thing about lapping that I became nervous about it was that I was unsure of how it might affect headspacing and lug lock-ups--I suspect that even minute depth changes could make a difference. The extension pin slot may or may not also be affected--I had a barrel once that absolutely refused to work with any bolt and I eventually figured out the extension pin was slightly out of clock with the gas port and lugs. I'm not saying it's a bad thing you shouldn't do--but I suspect that it's not as straightforward as blueprinting a bolt action receiver. I'd like to hear from an industry expert to weigh in on this. My opinion about any receiver to barrel mating that involves shims is that is inherently going to cause problems sooner or later--always has on any rifle I've used them on. __________________ "Everyone speaks gun."--Robert O'Neill *I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!* Last edited by stagpanther; May 21, 2023 at 06:00 AM.

May 21, 2023, 03:30 AM	#30
tangolima Senior Member Join Date: September 28, 2013 Posts: 3,873	Found some 0.01" soft lead strips (originally for fish sinker). Cut a thin strip and used that as gasket / crush washer under the barrel shoulder. While I was at it, I applied blue loctite to the barrel shank. Torqued the nut back to proper timing. Torque went up by about 10lbf-ft. Will see whether it will help. Probably not much as it is a very cheap upper. Once a while, when everything is perfect, it did shoot sub moa 10-round groups, with peep sight mind you. Hopefully with the mod, such delighting moments happen with more regularity. The idea is similar to lapping. The soft lead conforms to the harder steel and aluminum so that the force is even all around. -TL Sent from my SM-N960U using Tapatalk

May 21, 2023, 11:01 AM	#32
tangolima Senior Member Join Date: September 28, 2013 Posts: 3,873	Headspacing is in the barrel extension. Lapping / shimming should not affect headspacing. It does change the location of the lock lugs by a few thous. Between the bolt and bolt carrier there is about 1/4" margin built in the design to delay the locking / unlocking. A few thous change shouldn't be problem. Lapping / shimming is perpendicular to the pin slot. It doesn't change that either. I prefer shimming (actually not quite shimming in normal sense) to lapping for a few reasons. I generally don't want to remove metal from parts if I don't have to. Shimming is reversible. Spending money to buy another tool is another reason. There was a bit of residue on the barrel shank. When I wriggle the barrel I could feel a slight slop there. The loctite hopefully will fill that. Will shoot some group to see how it works. -TL Sent from my SM-N960U using Tapatalk