Questions about my first AR build???

[customcutter]

I bought a blem Spikes lower at least 5 years ago, and bought a RRA NM 2 stage trigger and LPK. I bought it with the intention of building a Grendel, but have never been able to find an upper or barrel/bolt combo at the gun shows or found them in stock online.

I had found and saved an article on the Snipershide forum years ago about building an accurate AR, but the link no longer works. If anyone has any good links or post on accuracy build tips please post them. The only thing I've found in 2 days of searching is mostly barrel, ammo, and shooter ability related. I did find one post on another forum that talked about rigidity of the upper and making sure that the upper was "square" to the bore and a link to tool on Brownells for the tool and how to lap the upper til it was square.

I plan on building a hunting rifle with good accuracy on a budget. Yes I know, accuracy and budget don't belong in the same sentence, but hoping it can be done.

Parts so far are the Spikes Lower, RRA NM 2 stage trigger and LPK. I have ordered an 18" Liberty barrel and bolt.

Planning on ordering a Diamondhead USA VRS "T" 13.5" rail. I like the engineering of the system and appears very rigid. I am also considering the VLTOR MUR upper with forward assist. What other uppers should I look at considering rigidity/beefiness of the upper.

Looking for recommendations for the rest of the build based on a budget.

thanks,
CC

[XcountryRider]

The only difference for building a Grendel and any other AR is the amount of torque you put on the barrel when you screw it on. Its close to 60lbs vs the 30 some lbs for a 223. Thats basically it. So any youtube videos will be helpful it does not need to be specifically for building a grendel.

[customcutter]

XCR,

Thanks for that info. I had read that the torgue specs on the 5.56 were from 30-80#'s. Also have read that the lower that value was that the less "torque or distortion" that was imparted to the upper, and therefore the better the accuracy. That was also another thing I liked about the Diamondhead hand guard, not having to line up the gas tube with notches on the nut. I also watched a couple of youtube video's, one by a competent gunsmith (some others I wasn't so impressed with). It seems like a pretty straight forward assembly, compared to head spacing a bolt action.

Edit: Just found some more info when I did a search for barrel nut torque. Migh help someone else also.

http://www.65grendel.com/forum/showthrea...rel+torque

[Drifter]

The only difference for building a Grendel and any other AR is the amount of torque you put on the barrel when you screw it on. Its close to 60lbs vs the 30 some lbs for a 223. Thats basically it.

Perhaps I missed the memo, but I've never noticed where a handguard manufacturer recommended a different barrel nut torque based on cartridge. Can you share any additional information?

If anyone has any good links or post on accuracy build tips please post them.

Link: http://bulletin.accurateshooter.com/2011...s-answers/

[customcutter]

Drifter,

thanks I have that one on my favorites now for easy reference. Not sure I agree with every thing there, but some things worth addressing for sure.

CC

[XcountryRider]

http://www.youtube.com/watch?v=uOurwaQ3J2Q

[customcutter]

XCR,

I watched both videos on the build. I know he was using a plastic/rubber malet to drive the barrel into the receiver, but I couldn't help but cringe. Seemed funny that he mentioned talking with Bill Alexander and torquing to 60#, and used locktite on the barrel extension to bed it to the receiver, but didn't use it on the threads? IIRC I read where Bill said they use locktite on the extension and the threads?

I've probably read close to 500 post in the last couple of days. Seems that everything from 30-120# has been done, and some are locktiting the barrel extension to receiver, some are not. Some are locktiting the barrel nut threads and some are using anti-seize compounds. I'm thinkng 60#'s sounds reasonable and I'll be triple torquing the nut. I'll do a little more research before deciding on locktiting the threads or anti-seize??? I'll also be checking the receiver to make sure it is square to the bore, and lapping if necessary before assembly.

thanks,
CC

[LRRPF52]

You do not want to go over 80 ft-lbs. Per Bill Alexander, if you are installing a heavy barrel and are looking for the most accuracy, then bedding the extension makes a lot of sense.

If you are installing a lighter profile barrel that is shorter, like 18" or less and medium contour, he said he has seen no need for it (bedding). On a budget, there are a number of things you can do to drop the price down, and it's a buyer's market right now, so there are a lot of deals to be had on uppers, lowers, carriers & BCG's (5.56), LPK's, furniture, etc.

[customcutter]

LRRPF52,

Hoping to stay in the 50-60# range. Several things I liked about the Diamondhead handguard. The proprietary nut that doesn't have to align the gas tube with a slot or hole in the nut. The tight tolerances and rigidity. Also it looks good and should be very comfortable in the hand. I know I'll pay extra for that but I think it's worth it.

I'll be using an 18" Liberty barrel, so if I have a tight fit between the upper and barrel I'll fore go the locktiting on the barrel extension. Any thoughts on locktiting or anti-seizing the threads? I read Bills comment in one thread and IIRC he stated that the locktite kept the threads from galling, which is the primary purpose of the anti-seize???

thanks,
CC

[LRRPF52]

Bill doesn't like white lithium grease because it rots, and has a foul stench to it when it does.

I like some type of grease on the threads to prevent galling, but I also am using Cerakoted uppers most of the time that I have done myself.

More importantly, I like a nice blended barrel extension and feed ramps. I also lap the bolt to the lugs, radius the ejector, and do some other things to reduce brass abuse. I made a cut Grendel case with an internal spring to lap the lugs so there is evenly distributed load from the bolt lugs to the extension teeth. It's a common practice for custom rifle builders.

[Tedward]

LRRPF52,

Hoping to stay in the 50-60# range. Several things I liked about the Diamondhead handguard. The proprietary nut that doesn't have to align the gas tube with a slot or hole in the nut. The tight tolerances and rigidity. Also it looks good and should be very comfortable in the hand. I know I'll pay extra for that but I think it's worth it.

I'll be using an 18" Liberty barrel, so if I have a tight fit between the upper and barrel I'll fore go the locktiting on the barrel extension. Any thoughts on locktiting or anti-seizing the threads? I read Bills comment in one thread and IIRC he stated that the locktite kept the threads from galling, which is the primary purpose of the anti-seize???

thanks,
CC

I like the Diamond heads too and the barrel nut works great. I have one on a Grendel with the 16" Barrel. I found this place that was the best price at the time. This is a 10.25" with my 16" but your 18" Barrel might look good with a 13.5".
[ATTACH=CONFIG]4246[/ATTACH]

US GUN SOURCE out of stock today but just keep watching. Changes weekly.
http://www.usgunsource.com/grips-pads-st...ating.html

[customcutter]

I've been searching for info or procedure on lapping the lugs on AR bolt. I haven't found anything on this site from 2 days of searching. I just did a quick search on google and found a few articles where others are asking about the procedure.

Does anyone have a link? Also wouldn't this change the headspacing on the barrel bolt combo???

thanks,
CC

[LRRPF52]

I pulled this up in a few seconds:

[video=youtube;Cor-K6bZpZ0]http://www.youtube.com/watch?v=Cor-K6bZpZ0[/video]

The concept is the same for the AR15/AR10, however, you can fabricate your own lapping tool by cutting a culled Grendel case in half, place a spring in it, remove your ejector from the bolt, then lap the bolt to the extension by cycling the charge handle back and forth. When I do it, I make sure the CH latch does not slide over the latch notch on the upper to reduce wear there (steel vs. aluminum).

These are common gunsmithing techniques, and pretty standard on NRA hi-power rifles.

[NugginFutz]

The concept is the same for the AR15/AR10, however, you can fabricate your own lapping tool by cutting a culled Grendel case in half, place a spring in it, remove your ejector from the bolt, then lap the bolt to the extension by cycling the charge handle back and forth. When I do it, I make sure the CH latch does not slide over the latch notch on the upper to reduce wear there (steel vs. aluminum).

These are common gunsmithing techniques, and pretty standard on NRA hi-power rifles.

You mean something like this?
[ATTACH=CONFIG]4249[/ATTACH]

What type of spring did you select?

[LRRPF52]

That is perfect. I also used my chamfer/de-burr tool to chamfer the edges at the cut, so that it wouldn't have any sharp edges to combine with carbon or lapping compound and screw up my chamber. I only place a small amount of lapping compound on the lugs, since that is the only area being lapped.

I think I used an M16A2 rear sight spring. You do need to remove the ejector from the bolt, and I have the Brownell's AR15 tool for that-makes it an easy job.

[customcutter]

LRRPF2,

Thanks for the link. Yes I'm familiar with "blue printing" a bolt action even though I haven't done it. I probably won't do it with the Grendel, but I will put a little dykem on the lugs just to see how much contact I have. The main reason I probably won't do it is I don't want to mess with the headspacing on the bolt/barrel combo. I've read several threads on the subject now, I'm not sure how much it does for accuracy. However, I am convinced that it can be a contributing factor to broken bolts.

Nugginfutz,

Thanks for the diagram. As they say a picture is worth a thousand words. I'm not sure why, but I was visualizing using the spring and the back half of the case.

thanks,
CC

[LRRPF52]

AR15 head spacing is sloppy by design. There's no way the mass and inertia of the bolt carrier group can generate enough force to deal with variance in shoulder location like the camming action of a turn-bolt Mauser. So precise shoulder locations aren't an issue, and have to be under-sized to feed in a gas gun. There's no way you're going to affect headspace with lapping, unless you use heavy grit media, and go to town on it for hours after ingesting some serious amphetamines.

You don't need to blue print as far as receiver face is concerned, unless it's obviously out of spec, which will break bolts all day long. Some smiths start from scratch, and will true the barrel extension, all the faces, and go super-anal on it, and end up with a gun that shoots sub-1/2 minute consistently. There is a lot of work involved in getting that extra 1/4" that most people won't bother with.

[NugginFutz]

My understanding of the reason behind lapping the locking lugs is as follows:
The primary purpose is to increase the bearing surfaces of the lugs. This ensures the load encountered during firing is evenly distributed. The secondary reason, but the one most desired, is the potential for improved accuracy. There seems to be a perception that the Grendel is a bolt breaker, but I think that the reputation is more anecdotal than factual. Regardless, I can see the practical application of lapping the 6.5G bolt's locking lugs, if for nothing else, than to evenly distribute the force loads across all the lugs, thus reducing the possibility of any one fracturing.

What I am uncertain of, however, is the accumulated wear of the the barrel adaptor. If, for example, you have more than one bolt, do you lap them all? And, if so, does that translate into unwarranted wear of the barrel adaptor (manifesting as additional headspace)? It seems to me that there is a distinct possibility of overthinking this.

[customcutter]

I think the main areas I'm going to concentrate on are the squareness of the upper and the fit of the barrel extension to the upper. I won't be punching paper for that last 1/4". It will be a hunting rifle that I can hopefully get to shoot sub MOA. To start with I'll assemble without bedding the barrel extension and I'll use anti-sieze on the barrel nut. If accuracy isn't there I'll back up and start over.

[NugginFutz]

I think the main areas I'm going to concentrate on are the squareness of the upper and the fit of the barrel extension to the upper. I won't be punching paper for that last 1/4". It will be a hunting rifle that I can hopefully get to shoot sub MOA. To start with I'll assemble without bedding the barrel extension and I'll use anti-sieze on the barrel nut. If accuracy isn't there I'll back up and start over.

A very sensible, organized approach. If you know anyone with an upper receiver lapping tool, it may be worth offering a 6-pack for the use of it. Half of my uppers, when checked, were not square (some a little, one a bit more). By lapping them, I at least had the peace of mind that squared receivers were not going to be an issue. Mind you, now, some of mine are bench riders, and others are mud guns. I treat then all the same, though, in case I ever interchange parts.