First AR Build Questions

[Two Tone]

This is why I joined this forum, to get advice on how to choose a barrel and bolt carrier group for my first AR build (actually two builds, doing one for the wife).

What I have so far:

Anderson lowers, consecutively-serial numbered.
Plan to get these engraved with our first names and date of marriage.

Aero Precision upper receivers.

Rock River Arms lower parts kits with National Match two-stage trigger.

Magpul ACS stocks.

ERGO pistol grips.

What I want: Nitride or chromed bolt and carrier. Phosphate looks a bit harder to clean.

Cerokoted, stainless steel, or nitride coated barrels.

Both rifles for hunting deer in wooded areas with possibility of shooting across a big field.

Wife: thinking 16 inch lightweight barrel for her. Not into fluting as I think those might be more trouble to clean if dropped into the mud on a fall. Wife is short and small-stature.

Me: thinking 20 inch barrel, medium heavy or light weight (M4 extension?). Just like for the wife it's for hunting in the woods. May not need 20 inches.....open to 18 inches but desire longer than 16 inches.

Currently looking at:

Wilson Combat (but hate the flutes)

Alexander Arms Incursion (but they require their phosphated bolt)

Lilja Barrels. Allows use of Aero Precision nitride bolt. Con: out-of-stock.

McGowan Barrels.....haven't emailed them yet but like their offerings.

These will be home builds..........so.........advice on which barrel length and maker? Things to look out for?

[michael1778]

I've been thinking about setting aside the 18" mid-length gas barrel I have (possibly with too large a gas port) and going with a Wilson Combat 18" in rifle gas. They should be soft shooting and more than accurate enough.

As to your concerns about external cleaning of flutes, I have a fluted 22" 6mm AR (Predator) barrel that I found had been badly stored by my wife while we were separated. It was covered in find clay cat litter dust. Wiped it down with a microfiber cloth and it was good to go. I do not think it will be the issue you appear to believe.

Given today's disrupted supply chains, I encourage you to snag a pair of the Wilson Combat 18 inchers (or whatever quality barrels are in stock) and don't look back. Don't be such a flute hater, my friend. I wish the Monster barrels were in stock from SixFive but alas, not to be.

[michael1778]

Maybe these for your BCGs? Price seems good for the described blemishes.
https://www.grendelhunter.com/product/gr...etic-blem/

[LRRPF52]

Welcome to the forum!

For rifle builds or selection, it makes sense to start with the barrel, then pressure containment parts, action, receivers, fire control, aiming solutions/optics/mount, then furniture.

Barrel:
Barrel will determine weight, muzzle velocity, and most of your accuracy.

Since your stated intent is to have 2 lighter hunting rifles for you and your wife, I think you’re on the right track for lengths and overall build approach.

For limited open terrain and heavy woods, 14.5” - 20” barrels work.

A 16” MLGS or 18” MLGS/ILGS/RLGS will work well for your wife, depending on how short she is.

My wife is tall, but she still thinks my lightweight AR-15s are heavy when she holds them. It really comes down to their comfort and how they interface with the rifle.

I have a 16” Lilja WASP Grendel that is really light and sounds perfect for what you’re looking for, but they only made them when we did the initial Forum Group Buy with Lilja.

That overall 16” Grendel build with MI 12” free float tube, standard M4-ish receiver set, B5 SOPMOD stock, is 6.3lbs empty without any optics. If I had used 2A Balios Lite receivers and handguard, I could drop that weight down closer to 5lbs.

The 16” AA Incursion barrel is 1.99lbs, while the 11.5” Grendel AA barrel is 1.36lbs. My experience with the Incursions is that they are very light.

All 6.5 Grendel barrels should come with an M4 extension, which helps with feeding the larger diameter cartridge.

If you get a fluted barrel and it’s Cerakoted, it won’t matter anyway.

For your wife’s build, I think it pays to have it fit to her. Too light might be harder for her to shoot though, so there is a balance point.

BCG
The most important things about the Bolt Carrier Group are:

Proper 6.5 Grendel bolt that will fit and interface with your barrel extension. Pretty much everyone on the market is making Grendel compatible bolts with the correct face depth of .136”, but they should be 2.810” long if you plan to use a standard firing pin. If dealing with a reputable company, they will provide matching bolts to the barrels they are turning and installing barrel extensions on.

Carriers: The carriers need a proper inner dimensional series of steps to have an efficient gas seal with the bolt. This is far more important than what coating they have on them.



If those parts don’t seal well together, the gas system will leak and not provide sufficient internal gas expansion to initiate carrier movement in the cycle of operations.

The only way to measure if they are right is to have the armorer’s gauges, or send them to have someone with gauges perform a diagnosis for you.

The carrier key needs to be fastened correctly and securely, with proper bore diameter and flange on the opening to the gas tube flange, which inserts into it when the BCG is in battery.

It also makes sense to have a hard, tough surface inside the bolt bore that will last, and the Mil-Std hard-chromed treatment is the most tested, proven approach to that dating back to the late 1950s.

Gas block/Gas Tube
The gas block and gas tube need to be securely and properly installed and aligned with multiple critical data points.

If your gas block is not securely fit (interference fit is the best-requires a jig or lots of pounding), gas will leak from around the block/journal interface and not provide the sufficient amount of gas needed to cycle the action.

The gas tube needs to be tightly fit in the block with no leakage as well, then aligned with the carrier key so they don’t clip. Clipping will wear down the flange, which will again cause short-stroking of the action.

Receivers
Upper receiver needs to have a square face, correct inner diameter raceway and extension tunnel, and mate with the lower properly. Mil-Std calls for a dry film lubricant to be baked into the raceway to help suspend lubricant and maintain lubricity for the bolt carrier rails. I use a tool to check and true my upper receiver faces so a mechanical true zero of the barrel to the upper can be achieved. Angled surfaces are caused by the anodizing process on some uppers, so they need to be trued.

The lower receiver needs to mate with the upper, pin locations need to be correct, and the magazine catch especially needs to be at the correct height. These dimensions are pretty uniform and standardized with reputable companies in the industry, so they typically aren’t a problem with recognized brands.

Fire Control Group and LPK
You mentioned using RRA 2-stage triggers. Those will probably be fine for your hunting uses, but when shot in a high round count, the surfaces on them are known to wear out, which is why Geissele became a thing. I’m not sure where RRA stands nowadays, if they changed any processes or metallurgy, but that’s one thing to note about them.

LPKs seem like they should all be the same, but they aren’t. Mil-Std LPKs include inspected parts, cadmium-plated detents, US-made everything including springs, so a lot of the after-market LPK stuff was trash from the 1990s-2010s. I’ve seen improvements in that space since suppliers became more aware of the TDP, but it can be hit-and-miss.

You will also want correct buffers and action springs, with Mil-Spec RETs, lock rings, and end plates for the ACS stocks. ACS is a bit heavy, really good for AR-10 carbines or 20” AR-15 rifles.

Optics/Mounts
This will be the biggest expense outside of the rifle, often more than the rifle. For brush/woods and sometimes open hills, a good 1-4 or 1-6 Low Power Variable Optic works great, but a Red Dot does really well in the woods too.

Mounts are best to stay with Made in US or Europe. Tons of good companies out there in that space with more and more innovation each year.

My mounts consist of LaRue, ADM, and NightForce. I have a few off brand ones that I never bought, ended up in my shop somehow, but they are garbage.

For handguards, lightweight free-float units with solid mating to the upper are all you need. The less frills, the better for a hunter.

Let me know when you get your barrel and we can talk through the inspection, prep, and upper receiver assembly process using accuracy and reliability-enhancing techniques. You can search for those here on the forum in the meantime with the Custom Search Engine found in “Announcements”.

Welcome aboard

[Two Tone]

Just what I was hoping for: GREAT INFO!

Thanks a ton guys.

So RRA NM trigger group may not be the best? :eek:

Looked over the Wilson Combat barrels.......very slick! Love the markings too.

So concerning the parts I have......looks good so far?

[Fodderwing]

Just what I was hoping for: GREAT INFO!

Thanks a ton guys.

So RRA NM trigger group may not be the best? :eek:

Looked over the Wilson Combat barrels.......very slick! Love the markings too.

So concerning the parts I have......looks good so far?

What volume of shooting do you plan on? I have multiple RRA 2 stage triggers that work great. It seems to me it would require some serious volume to wear one out.

But, buy what you feel comfortable with, it is your money.

[Two Tone]

I put a RRA two-stage into my S&W M&P 15 then loaned it to a friend. He fired at least 1000 rounds though it (I gave him a can of 7N6) and the trigger is as good as the day I put it in.

These will be hunting rifles and with today's prices, probably not get shot much at all!

Sorta decided on the Wilson Combat barrel. Will try to order one soon.

[Two Tone]

How's hive opinions on this M-Lok upper?

Also, how great is this upper build video?

https://www.midwestindustriesinc.com/pro...-crm14.htm

[LRRPF52]

Just what I was hoping for: GREAT INFO!

Thanks a ton guys.

So RRA NM trigger group may not be the best? :eek:

Looked over the Wilson Combat barrels.......very slick! Love the markings too.

So concerning the parts I have......looks good so far?

For your stated purposes, I don’t see you running into issues with the RRA 2-stage triggers. Guys and gals who ran into problems with them were shooting 10,000+ rounds per year training for and competing in High Power matches. Sometimes the critical sear surfaces would wear out and cause safety or inconsistent performance.

This is why Bill Geissele developed his 2-stage trigger, where the materials science and metallurgy he used addressed those types of problems to make a long-lasting match trigger with a full power hammer spring.

Other competition manufacturers were using lower power hammer springs, which would fail to activate military primers in colder temperatures, so especially the Army Marksmanship Unit and other competitive teams were looking for tough trigger/sear alloys with hammers driven by full power hammer springs.

I’m not sure you would feel the difference if you got behind them and compared.

[LRRPF52]

How's hive opinions on this M-Lok upper?

Also, how great is this upper build video?

https://www.midwestindustriesinc.com/pro...-crm14.htm

I like the MI handguards and have used many of them.

There are a few things I would mention with the assembly video that I recommend not doing, but it is overall a decent video.

1st: Isolate the barrel itself when doing any type of muzzle device work. That means the barrel is clamped, not the upper or a barrel extension insert rod like he used when he removed the muzzle device.

2nd: Barrel nut torque can be anywhere from 35-80ft-lbs, doesn’t have to be a specific number. Since there nut doesn’t have Armorer wrench teeth on it that have to be timed with the gas tube, as long as you’re 35ft-lbs or more, you’re fine. For accuracy related to barrel nut torque, the AMU did studies across large samples of rifles and found that the 20” government profile barrels shot better with higher torque, whereas the heavy competition profiles barrels shot better with lower torque values. Something to do with resonant harmonics that balance out like that.

3rd: Gas tube alignment needs to be trouble-shot with the upper upside-down and your stripped carrier inside so you can find where it won’t clip the carrier key. After you’ve measured the correct axial port location relationship between the block and the gas port, you will know where you need to place the gas block to have port alignment. I bed my gas blocks to seal off the gas system, but I prefer interference fit if I can get it. Most gas blocks are built to slip-on for the DIY-er, which isn’t helpful for the gas system because it promotes leakage.

Their basic approach is OK though for installing their product. Big thing is to remember the torque plate that fits inside the gap at the bottom of the handguard.

I also apply their supplied Blue locking compound onto the knurled surface of the barrel nut to prevent the handguard from slipping forward when shot with a bipod. They used to have smooth OD barrel nuts that would allow that to happen.

I also make sure the receiver face is square before letting the barrel go near the upper.