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+--- Thread: Questions about my first AR build??? (/showthread.php?tid=6766)
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Questions about my first AR build??? - Tedward - 11-25-2013
All this talk about squaring up the extension to the upper is really deceptive. If the extension is installed on the barrel by the barrel maker that should be square. Then you put the barrel into the upper and when the barrel nut is snugged then torqued, it presses the extension flat against the upper receiver. There is no adjustment. If you find it off by the method LRRPF52 (Midway) said with the dykem to see the contact points, then using the compound is just to smooth and make it contact evenly.
Is that all your talking about doing? Mate the surfaces of the back side of the bolt lugs to the barrel extension with the lapping compound?
Questions about my first AR build??? - customcutter - 11-25-2013
Tedward Wrote:All this talk about squaring up the extension to the upper is really deceptive. If the extension is installed on the barrel by the barrel maker that should be square. Then you put the barrel into the upper and when the barrel nut is snugged then torqued, it presses the extension flat against the upper receiver. There is no adjustment. If you find it off by the method LRRPF52 (Midway) said with the dykem to see the contact points, then using the compound is just to smooth and make it contact evenly.
Is that all your talking about doing? Mate the surfaces of the back side of the bolt lugs to the barrel extension with the lapping compound?
The procedure that LRRPF52 and Midway were talking about is to lap the bolt to the lugs inside the barrel extension.
Squaring the upper receiver to the barrel extension is another matter. The uppers are not always square to the bore. Brownells sells a lapping tool that can be used to square it up and make sure you have 100% contact around the upper receiver to the barrel extension. Then you get into, is the barrel nut machined square, are the threads on the upper machined square, etc, etc. It would be similar to "blue printing" a bolt action receiver. An awful lot of work to chase that last 1/4" of accuracy. Maybe worth it in National Competition, but not a hunting rifle.
I don't have a jig, or know of anyone that has one. I do have a large surface plate and machinist squares, so I'll check it that way. If necessary I can turn a jig on my lathe and lap the upper, but from what I've read the VLTOR's are machined pretty well.
Questions about my first AR build??? - customcutter - 11-25-2013
Any thoughts on this BCG and Supplier? Maybe I'm looking in the wrong places but looks like any decent BCG is $130-150??? Seems like it would be worth the extra $50?
https://www.primaryarms.com/WMD-Guns-NiB-X-NiBH-X-Complete-Bolt-Carrier-Group-p/nibxbcg-0002.htm
Questions about my first AR build??? - NugginFutz - 11-25-2013
customcutter Wrote:The procedure that LRRPF52 and Midway were talking about is to lap the bolt to the lugs inside the barrel extension.
Squaring the upper receiver to the barrel extension is another matter. The uppers are not always square to the bore. Brownells sells a lapping tool that can be used to square it up and make sure you have 100% contact around the upper receiver to the barrel extension. Then you get into, is the barrel nut machined square, are the threads on the upper machined square, etc, etc. It would be similar to "blue printing" a bolt action receiver. An awful lot of work to chase that last 1/4" of accuracy. Maybe worth it in National Competition, but not a hunting rifle.
I don't have a jig, or know of anyone that has one. I do have a large surface plate and machinist squares, so I'll check it that way. If necessary I can turn a jig on my lathe and lap the upper, but from what I've read the VLTOR's are machined pretty well.
What he said.
Because some of my rifles do shoot for that last 1/4", I find the effort worth while. Just not explicitly for a hunting rifle, as CC says.
Questions about my first AR build??? - NugginFutz - 11-25-2013
customcutter Wrote:Any thoughts on this BCG and Supplier? Maybe I'm looking in the wrong places but looks like any decent BCG is $130-150??? Seems like it would be worth the extra $50?
https://www.primaryarms.com/WMD-Guns-NiB-X-NiBH-X-Complete-Bolt-Carrier-Group-p/nibxbcg-0002.htm
I've only heard about PA (most of it good), but have never used any of their stuff.
The first thing about your selection that jumped out at me was that this seems to be a 5.56 bolt, not a Grendel bolt.
Questions about my first AR build??? - LRRPF52 - 11-25-2013
Most production rifles don't have evenly bearing bolt lugs. This is true of hunting rifles, as well as AR15's. You can check any of your rifles with Dykem and confirm this for yourself. It's simply a product of slapping production guns together on an assembly line where cost benefit analysis doesn't warrant ensuring 100% contact between the bolt lugs and their recesses or barrel extension.
My leaning is towards the durability of the system, then accuracy. Since we're dealing with a bolt geometry in the AR15 that was designed around the .222 Remington in as light of a gun as possible, there isn't a lot of bolt lug mass to begin with.
Yes, the barrel manufacturers "should" ensure that the barrel extensions are true to the barrel, and they "should" ensure that the bore is concentric to the OD, and they "should" ensure that the barrel breech end threads are true and concentric to the bore. Unfortunately, these are all very rare to find on a production rifle.
Same with receivers. Notice that NugginFutz stated that half of his AR15 receivers were not true on the face? Everything should be true off of the center of the bore. The more parts that are true and concentric to the bore's center, the more balanced and accurate the system will be from both a longevity and accuracy standpoint.
If the receiver face is not true, it will cant the barrel off to one direction, so that the bolt lugs only engage on one side. This configuration will in fact break bolts, shearing lugs off in very few rounds. On the billet receivers made by well-renowned companies like LAR, Seekins, and Mega Machine, you have a much higher standard of QC when it comes to the receiver face being trued to the bolt carrier raceway.
In the bolt gun world, this is why precision billet actions are so popular with accuracy nazi's. Why spend all the time trying to un-suck a Remington 700 action, when you can just get a top-end CNC billet receiver from GAP, Surgeon, Templar, etc.
Questions about my first AR build??? - customcutter - 11-25-2013
NugginFutz Wrote:The first thing about your selection that jumped out at me was that this seems to be a 5.56 bolt, not a Grendel bolt.
Yes, I was thinking I could use the bolt carrier for the Grendel build, and have a spare bolt for my Rem R-15. But, that kinda defeats the purpose of the NiB treatment???
Newbie question, would the spare bolt (NiB) have to be head spaced to the R-15? Or a new bolt headspaced for any AR, or are the machining tolerances tight enough that it doesn't matter which bolt is used?
I know bolts should be properly headspaced on Grendels, but didn't know if that was due to different bolt configurations, specs, type 1, type 2, etc, before the Grendel went SAAMI.