I would highly highly suggest watching Brownells' video on lapping your upper receiver. It is also important to make sure that if you do this to check that the shoulder on the threads is perpendicular to the bore of the receiver.
After the first run, you had lapping compound on the tool where it contacts the bore of the receiver. An effective way to increase the diameter of the receiver and wear out the anodizing. Oil works better on that part of the tool.
Short answer: You by a quality barrel from a reputable supplier and hope for the best. Longer answer but certainly not the 100% complete long answer: The thing is, Barrel extensions and barrels are often fine being lathe turned part. The worst that can happen is dishing of the perpendicular faces and unwanted taper to the cylindrical faces. The thing that makes receiver different, even from reputable manufactures, is that they are milled parts that have uneven material removal. Internal stresses can cause distortion of machined faces when material that would otherwise be resisting the opposing internal stresses is removed.
Bingo • I knew if I scrolled down far enough someone else had to ask. Purchasing cheap uppers isn’t recommended. I saw the bulge in the mating surface. That’s the foundation of cascading failure. A drill press and a method of guaranteeing perpendicularity ± .0001” isn’t unreasonable. If you can’t establish a control, your best bet is to purchase an upper receiver from a reputable manufacturer. And, you still have to inspect it.
Why would he do that? Its an AR and thus the headspace is set by the bolt and barrel extension relative to the chamber. Unlike a manual bolt action rifle (like say a Rem 700), the upper receiver of an AR platform has ZERO to do with headspace. This is why often times, barrel manufactures will offer the option to by matched bolt and barrel combo's.
Assuming the face was not square and flat (as measured with a precision instrument) I damn sure wouldn’t allow you to use a hand drill on one of my upper receivers. Your time would be better spent doing some 5S activities.
Nope, not on an AR platform rifle. The headspace of such rifles is dictated by the bolt, barrel, and barrel extension relationship. The upper receiver has zero to do with that relationship, unlike a regular bolt action rifle like say a Rem 700. This is why many AR barrel manufactures will offer matched bolt and barrel combo for higher end barrels.
I am an SDI grad myself! Something I have found that helps accuracy after the lapping process, is using a little green loctight on the inside of the receiver where the barrel extension slides in. I tried this on my LR build during school and it improved the accuracy very well.
Observation: For any mated surfaces ... If you are going to "TRUE" one side of a mated pair, you need to know (or make sure) the other side is also "TRUE". If you're going to TRUE the receiver, you also need a method to TRUE the "Stop Ring" on that barrel.
The number of people who do things just to do them and feel good about them without understanding what is going on... Trying to get a precision anything using an electric drill motor by hand in a plastic block you tossed in a vice? Don't do this.Theres no way you're going to achieve concentricity with this setup You could be just as accurate with a sanding block and 800 grit sandpaper to flatten the face evenly.
The mandrill has the entire shaft to track inside the upper receiver. And even if the lapping surface isn't completely perfect, because it's spinning its still lapping evenly. With hand sanding you'd have to make sure your receiver is perfectly level, and then also make sure your sanding block and hand is perfectly level.
_"Theres no way you're going to achieve concentricity with this setup"_ Ummm, it would be wise to have an understanding of what words like "concentricity" means before posting comments using them and making yourself look foolish. Nothing about this process has anything to do with "concentricity", it is about perpendicularity and things can (and often are) eccentric (i.e., not concentric) while still being perpendicular. The whole point of this process is in part, about ensuring that the barrel extension mating face is as close to perpendicular as possible to the bolt carrier bore but really, its about getting as much surface to surface contact as possible between the barrel extension mating face and receiver face. Now is this the "best method", no but it still works fine for all but the most precision oriented builds.
Some dykem or sharpie marker will help you to see the high and low spots a lot easier.
I would highly highly suggest watching Brownells' video on lapping your upper receiver. It is also important to make sure that if you do this to check that the shoulder on the threads is perpendicular to the bore of the receiver.
After the first run, you had lapping compound on the tool where it contacts the bore of the receiver. An effective way to increase the diameter of the receiver and wear out the anodizing. Oil works better on that part of the tool.
Suggestion… use a sharply marker to color the portion of the part you are truing so that you can have a much better visual indicator of your progress.
You should put some oil on the mandroll when you put it in the receiver.
Is the lapping compound aluminum oxide ? That's what I use in my shop ...just curious
i use valve lapping compound .
How do you address an uneven surface on the mating face of the barrel ring?
Those barrel extensions are machined as such that it is nearly impossible for that face to not be perpendicular to the cylinder.
What about the barrels shoulder mating surface how to we know its perpendicular to the barrels center line?
Short answer:
You by a quality barrel from a reputable supplier and hope for the best.
Longer answer but certainly not the 100% complete long answer:
The thing is, Barrel extensions and barrels are often fine being lathe turned part. The worst that can happen is dishing of the perpendicular faces and unwanted taper to the cylindrical faces.
The thing that makes receiver different, even from reputable manufactures, is that they are milled parts that have uneven material removal. Internal stresses can cause distortion of machined faces when material that would otherwise be resisting the opposing internal stresses is removed.
This is basically want you want to do for a legit SPR build. It's a basic part of accurizing the rifle.
Made me cringe, no oil on the guide and to high of speed.
Do you grind until all of the color is gone from the face of the receiver?
Sooooo your gonna check headspace now right
Bingo • I knew if I scrolled down far enough someone else had to ask. Purchasing cheap uppers isn’t recommended. I saw the bulge in the mating surface. That’s the foundation of cascading failure. A drill press and a method of guaranteeing perpendicularity ± .0001” isn’t unreasonable. If you can’t establish a control, your best bet is to purchase an upper receiver from a reputable manufacturer. And, you still have to inspect it.
Headspace is not affected by this, but it's good you're thinking about it!
Why would he do that? Its an AR and thus the headspace is set by the bolt and barrel extension relative to the chamber. Unlike a manual bolt action rifle (like say a Rem 700), the upper receiver of an AR platform has ZERO to do with headspace. This is why often times, barrel manufactures will offer the option to by matched bolt and barrel combo's.
A little tip us to color the reciever end with sharpie and then it's super obvious when your flush
Assuming the face was not square and flat (as measured with a precision instrument) I damn sure wouldn’t allow you to use a hand drill on one of my upper receivers. Your time would be better spent doing some 5S activities.
Wouldn't this change the headspace?
Nope, not on an AR platform rifle. The headspace of such rifles is dictated by the bolt, barrel, and barrel extension relationship. The upper receiver has zero to do with that relationship, unlike a regular bolt action rifle like say a Rem 700. This is why many AR barrel manufactures will offer matched bolt and barrel combo for higher end barrels.
@@CJ-ty8sv Thank you for your answer!
I am an SDI grad myself! Something I have found that helps accuracy after the lapping process, is using a little green loctight on the inside of the receiver where the barrel extension slides in. I tried this on my LR build during school and it improved the accuracy very well.
Observation: For any mated surfaces ... If you are going to "TRUE" one side of a mated pair, you need to know (or make sure) the other side is also "TRUE". If you're going to TRUE the receiver, you also need a method to TRUE the "Stop Ring" on that barrel.
Hit it with a sharpie to see how much you’ve actually removed next time.
Thank you for the video; going to help a lot. May 22nd, looking forward to school and learning.
There are so many things wrong in this video.......
Like?
Thank you for the awesome video I love sdi
This is dumb and not needed if your upper receiver was produced this millennia.
Did you not see the bump on the receiver
What’s dumb is you saying it’s dumb, Dummy
Can't wait to start my school, I start June 19
Can't recommend this method. Please look elsewhere folks
nothign wrong with it. I have done dozens.
The number of people who do things just to do them and feel good about them without understanding what is going on...
Trying to get a precision anything using an electric drill motor by hand in a plastic block you tossed in a vice?
Don't do this.Theres no way you're going to achieve concentricity with this setup
You could be just as accurate with a sanding block and 800 grit sandpaper to flatten the face evenly.
So how should be done then? What is the closest to perfect method in your mind?
The mandrill has the entire shaft to track inside the upper receiver. And even if the lapping surface isn't completely perfect, because it's spinning its still lapping evenly.
With hand sanding you'd have to make sure your receiver is perfectly level, and then also make sure your sanding block and hand is perfectly level.
Wrong lol
_"Theres no way you're going to achieve concentricity with this setup"_
Ummm, it would be wise to have an understanding of what words like "concentricity" means before posting comments using them and making yourself look foolish.
Nothing about this process has anything to do with "concentricity", it is about perpendicularity and things can (and often are) eccentric (i.e., not concentric) while still being perpendicular. The whole point of this process is in part, about ensuring that the barrel extension mating face is as close to perpendicular as possible to the bolt carrier bore but really, its about getting as much surface to surface contact as possible between the barrel extension mating face and receiver face.
Now is this the "best method", no but it still works fine for all but the most precision oriented builds.
Let me guess...
The next video will be on feed ramp issues. 🤦♂️