Parts affecting accuracy??

Originally Posted By: steve garrettI bought one of those tools. the thing I don't like about them is the friction it causes inside the upper. So add lube you might think. the problem its too easy to get the lube mixed in with the lapping compound. I didn't like how it was working. the better option would be just send the thing to mike.

mike, I appreciate your comments here lately. I would be interested in your thoughts between barrel extension fit to upper fit, have you seen any difference if the barrel extension isn't fitting that tightly when its inserted into the upper? are you just using blue locktite on your extension when putting these together?



I feel the fit between the barrel-extension and upper is crucial. The AR-15 was never meant to do what we are doing with it. It was originally designed as a weapon of war, and accuracy just wasn't all that important. It had a spindly, light barrel hanging out of the upper receiver. Now, we are hanging great, big bull barrels 24" long off of the end of the receiver, and expecting fine accuracy.

These barrels are supported by a smooth, hard surface 1" in diameter and about 1" long. If you imagine how much leverage that long heavy barrel has, you will see why I "bed" the extension in loc-tite. The thread-locker is not used as a "glue" but as a bedding compound, leaving the barrel-extension now where to move. The upper and barrel-extension, for all intents and purposes, become one-piece.
 
Originally Posted By: steve garrettI bought one of those tools. the thing I don't like about them is the friction it causes inside the upper. So add lube you might think. the problem its too easy to get the lube mixed in with the lapping compound.



ya that was something i've always been extra careful about.

but thats why the instructions i followed also stressed that every time you pull the lapping bar out you wipe out *ALL* the extra lapping compound off both the upper and the lapping bar.

it makes a mess of things, but its worth the effort to preserve as much of the inner annodizing as you can i guess.
 
I'd easily believe the lapping mandrels don't yield perfection, but in my makeshift tests, it's better than they left the factory. BUT... I don't have a great way to eliminate slop. I mounted the receiver on the lapping mandrel, turned it between live centers on my woodworking lathe, and used an indicator on a makeshift mount... I've always wanted to put it on a proper lathe with a better fitting spindle...
 
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Originally Posted By: dtechOriginally Posted By: steve garrettI bought one of those tools. the thing I don't like about them is the friction it causes inside the upper. So add lube you might think. the problem its too easy to get the lube mixed in with the lapping compound. I didn't like how it was working. the better option would be just send the thing to mike.

mike, I appreciate your comments here lately. I would be interested in your thoughts between barrel extension fit to upper fit, have you seen any difference if the barrel extension isn't fitting that tightly when its inserted into the upper? are you just using blue locktite on your extension when putting these together?



I feel the fit between the barrel-extension and upper is crucial. The AR-15 was never meant to do what we are doing with it. It was originally designed as a weapon of war, and accuracy just wasn't all that important. It had a spindly, light barrel hanging out of the upper receiver. Now, we are hanging great, big bull barrels 24" long off of the end of the receiver, and expecting fine accuracy.

These barrels are supported by a smooth, hard surface 1" in diameter and about 1" long. If you imagine how much leverage that long heavy barrel has, you will see why I "bed" the extension in loc-tite. The thread-locker is not used as a "glue" but as a bedding compound, leaving the barrel-extension now where to move. The upper and barrel-extension, for all intents and purposes, become one-piece.

I agree!

I took some flak this summer from a guy about this kind of fitting. I had a buddy out to my shop to build his first AR, and in practice, I had him shim and glue his barrel to his upper. At a public range (serves me right), my buddy described that shimming and bedding process, and the "experienced AR builder" began berating the process as voodoo and a waste of time. Of course, he was shooting shotgun pattern groups at 50yrds with the AR he had brought, and we were punching bug holes at 100 with the rifles I'd built that way, so I didn't worry much about his "experienced" opinion. I do use stainless steel shim stock when I can to help center the extension, but do epoxy on both sides.
 
My Brownells lapper(?) and lapping compound should be here tomorrow. In anticipation I stripped my upper down over my lunch break. I can't believe I didn't check the receiver face before assembling it initially. I think I could tell that it isn't square by applying black sharpie to the face then using the flat edge of a speed-square to make contact all the way around. The sharpie was rubbed off in some areas but definitely not in a few spots. It will be interesting to see just how much it needs. Getting this upper trued, assembled, and re-sighted it by this weekend's coyote hunt will be fun.

Also my Trijicon Accupower 3-9x40 MOA reticle scope came in. It's nice but honestly I think I'm going to keep my Trijicon Accupoint 3-9x40 mildot reticle on this upper. I might send the Accupower back and order the 2.5-10x model.
 
How much slop on the barrel extension is acceptable? Reason I ask is while my son and I both have AR's already, he is building a higher end AR, and wants me to help him. Most of the parts are here, and I checked the fit of the barrel to the billet upper, and it slid in easy. Dug out some .001 shim stock I had, and it wouldn't quite go in. Guessing the total clearance at .001 to .0015 and thinking that the .001 shim may work if we warmed up the upper. If not, I have found some .0005 stainless shim stock on the internet, but not sure how easy that would be to work with. I would prefer not to use Loctite, but will if need be. I guess I'm thinking I should try the .001 shim stock with heating the upper, and if that doesn't work, see if I can get the .0005 shim stock to work, or should we leave well enough alone.
 
Originally Posted By: muskyHow much slop on the barrel extension is acceptable? Reason I ask is while my son and I both have AR's already, he is building a higher end AR, and wants me to help him. Most of the parts are here, and I checked the fit of the barrel to the billet upper, and it slid in easy. Dug out some .001 shim stock I had, and it wouldn't quite go in. Guessing the total clearance at .001 to .0015 and thinking that the .001 shim may work if we warmed up the upper. If not, I have found some .0005 stainless shim stock on the internet, but not sure how easy that would be to work with. I would prefer not to use Loctite, but will if need be. I guess I'm thinking I should try the .001 shim stock with heating the upper, and if that doesn't work, see if I can get the .0005 shim stock to work, or should we leave well enough alone.

Where I really prefer a tight fit, the AR platform is actually quite forgiving as far as non-concentricity. The bolt can float a certain degree in all directions without killing accuracy. This point is actually what makes the AR platform so easy to make accurate. If you have only a tiny bit of non-concentricity between the bolt-raceway and the bore in a bolt-action rifle, you won’t have fine accuracy.

All that said, if you coat the barrel-extension in blue Lock-Tite, the surface-tension of the Lock-Tite will center the extension plenty close enough for fine accuracy.
 
How do the receiver threads come into play? If you square the front of the upper but the threads are not true then the nut will only contact one side of the barrel when tightened. What affect does this have and how can it be corrected?
 
Originally Posted By: Broken ClayHow do the receiver threads come into play? If you square the front of the upper but the threads are not true then the nut will only contact one side of the barrel when tightened. What affect does this have and how can it be corrected?

The threads on the receiver are the week part of the receiver. When the front of the receiver is not square, and the barrel-nut is torqued, the receiver threads and the thin area of the receiver that encompasses the barrel-extension distort to conform, but the barrel is left misaligned with the bolt raceway. When the receiver-face is squared, but the receiver threads are not perpendicular to the bolt-raceway, when the barrel-nut is torqued, the threads distort slightly and the extension is held firmly against the receiver face.
 
Originally Posted By: wormydog1724My Brownells lapper(?) and lapping compound should be here tomorrow. In anticipation I stripped my upper down over my lunch break. I can't believe I didn't check the receiver face before assembling it initially. I think I could tell that it isn't square by applying black sharpie to the face then using the flat edge of a speed-square to make contact all the way around. The sharpie was rubbed off in some areas but definitely not in a few spots. It will be interesting to see just how much it needs. Getting this upper trued, assembled, and re-sighted it by this weekend's coyote hunt will be fun.



cant wait to see the result!

remember - only remove just enough material for a square face. if you end up taking too much off you'll have to shim to get a proper torque with the barrel nut to get the alignment right for gas tube clearance - with a milspec style barrel nut anyway.
 
Plant.One brought up a good point: Taking too much off of the front of the receiver.

Yes, whenever you take material off of the face of the receiver, you are going to change the timing with your barrel-nut. It may be to your advantage.... or it may not. The one thing it will always do is change how far back in the receiver the barrel extension sits. Even removing just a few thousandths of an inch creates a misalignment between the feed-ramps in the receiver and those in the barrel-extension. You wouldn’t think this would be a big deal, but..... it will absolutely kill the feeding of hollow-point bullets. I use a Dremmel to alter the very bottom of the ramps on the barrel-extension, leaving no “lip” for the bullet tips to catch on.

We don’t like shims. If we end up working on a customer’s upper and we can’t quite get the barrel-nut to time-up, we put the barrel-nut in the lathe and take a small amount of material off of the clamping surface of the nut.

The point brought up by Broken Clay opens up another situation you may not have realized. When you torque up an unsquare receiver, the torque-band is quite broad, in other words, the amount of movement in the barrel-nut from first contact with the barrel-extension until you have sufficient torque may be 15 degrees, allowing you some choice as to the hole you stop at. This torque-band is long because you are distorting the threads in order to pull the extension down onto an unsquare receiver. It’s much like compressing a split lock-washer. When the receiver is square, your torque-band is going to be VERY short, and may not offer even one hole that will line-up.

This is the EXACT reason that we designed our own float-tube/barrel nut. Our nut is a two-piece unit that allows you perfect timing with perfect torque every time, on any receiver. No more trips to the lathe!
 
This is something I have thought of. The barrel nut isn't* an issue because I'm using a Midwest Industries LWM G3 handguard. The barrel nut is so small it goes under the gas tube so there's no timing necessary.

As to the feedramp alignment, that's been a fear of mine. I snapped a picture looking inside the receiver and it looks like there should be a little bit of room before I take too much off and the barrel extension ramps are in too far. That will be something I'll be watching carefully.

*I don't think I can take too much off as to where my barrel nut bottoms out on the receiver before getting the extension tight. I didn't really look closely before I took it all apart, but it seems like there was enough room that I would have to really be aggressive to have that issue, then I'd be way past having issues with the barrel feedramps.
 
Well I got it lapped and back together. I won't know the results until this weekend probably. I got it pretty well flat and smooth then put the barrel back in and torqued the barrel nut to spec. It took quite a bit of lapping until I was happy with it. The feed ramps in the upper and barrel extension still look good to me. It might just be my mind playing tricks but the barrel looks a bit more centered with the handguard. I know that's probably not even able to be seen without measuring, but I'd like to think I did some good with it.
This Wilson Combat barrel showed flashes of greatness before but seems to throw a round here and there. Hopefully now it will truly shoot lights out all the time.
 
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