Longevity, Accuracy Tips for the AR15

[LRRPF52]

There has been a lot of talk lately about bolts breaking, accuracy, home builds, etc.

Many of us have already learned the hard way that slapping parts together that look like any other high-end AR15 doesn't always equal an accurate or reliable gun. I honestly have always had reliable guns because I have a bit of experience sourcing components, and maybe there has been some luck involved too.

But what about when we start getting into other calibers like the 6.5 Grendel? Can we just slap parts together and realistically expect consistently sub-MOA, 100% reliable guns?

Nope. Now I'm guilty of being a bargain shopper, but I steer clear of parts that aren't from sources I know well. I have bought many blem uppers, with the understanding that I don't care about their cosmetic appearance, as long as they are 7075 with a Type III hard coat anodizing, because they are getting Cerakoted anyway.

But what about accuracy? Are all uppers created equal?



No they are not. This one had only about 25% face engagement with my upper receiver lapping tool, where you could clearly see the light through many areas on the receiver face when abutted with the tool. I had a high-end barrel installed in it, and it shot 1.5 MOA or worse, with unpredictable grouping. See the black area; that used to extend all the way down to the other side. The black is now in contact with the tool, and I have a trued face.

I was thinking of using it for one of my Lilja barrel uppers, so I lapped the receiver face after pulling the .223 Wylde barrel. This is the tool set-up in the upper that you use to true the receiver face, along with lapping compound.



For those of you who are thinking that dropping your Lilja, Krieger, Bartlein, and other high-end barrels into a blem reject upper is going to deliver sub-MOA performance, you are rolling the dice unnecessarily. There are some great companies who make beautiful billet uppers that they ensure are true. Not only will this provide a foundation for the most accuracy potential from your barrel, but it will prevent uneven stress on the bolt lugs in the barrel extension, which is a known breaker of bolts in any caliber.

If you are doing a lightweight or heavy gun, you might want to check this for yourself, or have an experienced AR15 smith do the work for you.

[cory]

Where can we find the tool you have in your drill?

[Klem]

Is this the one?


$27 (with discount) at Brownells

http://www.brownells.com/gunsmith-tools-supplies/rifle-tools/receiver-tools/ar-15-m16-upper-receiver-lapping-tool-prod20220.aspx

[LRRPF52]

That's it. Midway has it on sale for less I think.

[Klem]

That's it. Midway has it on sale for less I think.

Here's a related question...

What are your thoughts on gluing the barrel extension into the receiver?

I have never done it and makes me cringe to think about it but have read some who believe in it. I have an open mind to anything that might improve accuracy so welcome your thoughts.

[NugginFutz]

With respect to the Upper Receiver Lapping tool, it should be noted that this tool has a precise fit. It needs to be caressed into place, and should not be forced, in any way. A little light lube on the pilot is a must. I've read a few reviews (MidwayUSA?) where some have said that it wouldn't slide into their uppers, so this leads me to think that either their uppers weren't to spec, or they had attempted to man-handle the tool into place. The main point, though, is that it is a precision fit, and it is quite easy to bind it up.

One should also be very careful to take it in very small steps, checking progress at frequent intervals. Obviously, you cannot replace lost material.

Klem: if you can afford to give me another month, or two, I can give you my impressions on the one barrel I bedded with Loctite Blue. It is a low end AR-Stoner 5.56 H-Bar, paired with a DPMS upper. This was the first build where I experienced what I consider a sloppy fit (barrel deflection amounted to approximately .5 degrees before torquing the nut). I had similar misgivings as yours but, after weighing the pros and cons, I went ahead and tried it. With an Aimpoint H1 micro, it is hitting 4" steel at 200 yards with no trouble, so accuracy seems to be decent enough. I intend to run a few hundred rounds before I break it down. At that time, I'll know the answer to the question that has been nagging me since I bedded the barrel. I have a bottle of propane standing by, just in case.

Either way it goes, I really don't count it as a great risk, considering the minimal investment I have in the barrel and upper.

[keystone183]

Great info. In addition to this, what would you suggest as the most important steps to ensure a home build is set up to get the most accuracy possible out of the barrel? As far as build goes anyhow. Not talking quality trigger or glass, but construction tips. Thanks!

[Klem]

Fair enough, I'll look forward to hearing more later then.

My thoughts are that unlike say a Rem700 where the bolt lugs are part of the receiver, and so the mating and squaring of the barrel with the receiver is critical, an AR barrel comes complete with barrel extension already mated and hopefully squared. So, a solid link between the barrel and the upper is important for the sight system sitting on the top, and in general holding all together, but not like a bolt gun.

I'm thinking if the fit is sloppy prior to torquing-up the barrel nut, or as '52' is showing in the first photo, not square, then some sort of filler material could mitigate the potential for inaccuracy. Perhaps your Locktite, or even two-part metal epoxy like JB Weld or Devcon. Unlike stock bedding however the potential for glue starvation is pretty high with tight fits squeezing it back out so I am unsure how much support it would give the interface after you torque up the barrel nut.

[bwaites]

Great info. In addition to this, what would you suggest as the most important steps to ensure a home build is set up to get the most accuracy possible out of the barrel? As far as build goes anyhow. Not talking quality trigger or glass, but construction tips. Thanks!

Have a pro build it! Lol! Even the guys who build their own often rely on guys like John Holliger at White Oak to build the guns they really count on in competition.

[Sojorboy]

LRRFP52 - There are some great companies who make beautiful billet uppers that they ensure are true.

Would u mind sharing a few company names u would suggest are great companies for a quality build ?

Thank you

[Klem]

Great info. In addition to this, what would you suggest as the most important steps to ensure a home build is set up to get the most accuracy possible out of the barrel? As far as build goes anyhow. Not talking quality trigger or glass, but construction tips. Thanks!

Having shot F Class/Target Rifle for a few years I can say that the general consensus among shooters is that all things being equal 80% of the guns accuracy is in the barrel. One local gunsmith who is also the National F Class champion buys barrels in for his customers (mainly Krieger) and spins them in his lathe looking for shadows, indicating a barrel that was not reamed true at the factory. No doubt he keeps the best and sells the rest to people like me in a massive conflict-of-interest. Similarly consistent with another story from a Bench Rest gunsmith who was telling me the world's best shooters will organise for ten barrels for the season, and discard eight as not being good enough for competition. A particularly good barrel is called a 'hummer' where I shoot, and is only screwed on for competition to save its finite life (assuming you have a vise and action wrench). Good gunsmithing is important and having an Olympic grade barrel manufacturer like Lilja is a must, but out of all the 50 barrels he is selling us, some will be better than others, and no-one will ever know why.

I have also noticed what we call 'The Golden Age' of barrels. After a few rounds of initial seasoning new barrels are at their best for about 300rds, then slowly deteriorate to a point where the group size exceeds your definition of accurate. Most committed shooters over here buy a barrel a year, which could be around 3,000rds before discarding. For 6mm barrels that can mean they are given or sold to a gunsmith who cuts them down to a hunting length, re-crowns, and sells them to roo shooters. My point is that as long as you have a good scope, trigger, loads etc the accuracy of the system is predicated on the barrel, and it is perishable.

I would say good barrel, scope, trigger and ammo...Followed by plenty of practise. If you are like me you never have enough time to practise, and while concentrating on building carefully with reputable parts is certainly important, it's not a proxy for practise.

OK, that said, I use high-speed/high-pressure moly grease for the barrel extension/upper join. Castrol make it for high-end performance cars. I also use a Davidson barrel vise when torquing, so the barrel is held rigid and takes the stress. Clamp the barrel as close as possible to where the torquing is going to happen. If you use those clam-shell type AR upper holders you risk stressing the upper when torquing. Seating the gas block. You need to line-up the holes exactly and that means measuring to see whether you need to sit the block the equivalent distance forward of the shoulder as the old clamshell forestocks would take. I think the newer clamping type blocks are superior to the older grub screw types. Pay particular attention to how the bolt carrier mates with the gas tube, so there is no run-out. I seal the carrier key against the carrier with Silastic (gasket seal) to prevent gas leakage. This assumes you are building the bolt carrier from scratch and not buying ready-made. Also assumes you are not installing a piston gas system like an Adams Arms. You can stengthen the extractor claw with a tiny o ring around the spring, or a commercial D-fender.

I have heard of people going to some lengths to eliminate the wobble between upper and lower with bedding the join. I reckon a rubber wedge does just as well.

Lastly, I'm going out on a limb here to suggest you might consider not using a muzzle device at all. Pay particular attention to the crown and protect it religiously from damage and crud. If you screw on a muzzle device it tends to build crud quicker than not and this will affect accuracy. Consider having the barrel re-crowned if at all in doubt down the track, it's not a big job. You can even buy a hand crown reamer from Pacific Tool and Gauge with it's own pilot guide and do it yourself.

That said, an AR frame will never be as accurate as the Stolle Panda, BAT action, heavy Palmer type 6mm bench-rest, bolt action specials. It's a semi-auto Assault Rifle and that keeps it in perspective for me.

[Klem]

One more thing while I am on a roll...

Get yourself a torque screwdriver for things like the screws on your rings. Having them all at exactly the same lbs aids accuracy.

I'd better shut up.

[customcutter]

LRRFP52,

Thanks for your thoughts on this. I've read an awful lot the past month waiting on parts for my build. Barrels seem to be the largest contributor to accuracy along with good triggers. I've seen several threads on the upper being square to the line of bore, and also think that can be a contributing factor to broken bolts, along with hot loads, and poor fits on the bolt to barrel extension. I guess I'll be checking my upper first and then lapping the bolt second. I'm hoping that the fit is tight enough on the upper to barrel extension that I don't have to worry with bedding with locktite. If it's a loose fit I may try it first for accuracy and then bed it afterwards if accuracy is not accecptable for my hunting needs.

thanks again,
CC

[cory]

One more thing while I am on a roll...

Get yourself a torque screwdriver for things like the screws on your rings. Having them all at exactly the same lbs aids accuracy.

I'd better shut up.

IMHO don't waste your money on a torque screw driver. Buy a 1/4 torque wrench. You can use a 1/4 socket with a phillips bit in it or an allan socket to torque the screws in your mount. You'll get more use out of a good torque wrench than a torque screw driver, outside of your rifles.

[LRRPF52]

Buying Billet vs. Truing Yourself
As far as buying versus truing your own receiver face, JP, LaRue, Seekins Precision, Mega Machine, and Precision Firearms come to mind as excellent billet sets. I still will check every upper to see that the face is true, but unless you are an anal-retentive machinist, one of the most critical arrangement of parts is totally out of your hands with the AR15: The barrel extension and barrel mating.

OCD
I have a friend who will let a lathe spin with dial indicators on it for 45 minutes before he even thinks about cutting threads on a barrel. Most of the barrel extensions on the AR15 market are mass-produced units meant for volume, not precision. Furthermore, most AR15 barrel makers simply are not going to take the time to ensure that the threads are perfectly true to the center of the barrel's bore, which is not straight in a lot of rack-grade barrels anyway.

Everything really works outwards from the bore center, and the high-end barrels will have a true, straight hole drilled through them in top-end steel, then rifled nicely by a gifted machine craftsman. Some companies that make top-end barrel blanks will totally louse up the profiling and chambering if you let them, because it isn't a core competency for them.

If you hand an AR15 barrel job over to a comfortably OCD machinist or smith, who worships at the throne of having everything centered, trued, and concentric, the attachment of a top-quality barrel extension to a top-quality barrel blank that he has profiled will make a difference in the accuracy potential of the barrel/BE.

At the moment of ignition and peak pressure burn, the real force of the recoiling energy on the chamber and bolt is driven rearward against the receiver face, from the barrel extension flange, so support there is more important than support around the extension, but I still love a fit where the extension is very tight after ensuring the receiver face is true. + 1 for using lubricant in the pilot that inserts snugly into the carrier tunnel/raceway. These lapping tools have no movement off of true once they are inside the upper, so they need a nice thin oil in there.

Tempered Fits
Some companies use a tempered fit of the extension into the upper, like Mega and JP, where the tolerances are such that the upper won't let the barrel extension fit into it without thermal contrast between the parts, and that gives you a super-tight fit that is probably superior to bedding a sloppy mating.

Accuracy Lessons From BR and F-Class
Klem makes a number of really good points that indicate a strong F-class and benchrest train of thought, where we have really pushed the capacity of the custom industry to improve accuracy potential in barrels, receivers, and bolts. The same principles apply to the AR15 in many ways, which is where a lot of the tricks come from for accurizing the Black Rifle.

Realistic Accuracy Expectations for AR15
Most Grendel shooters are not under the illusion that they will be winning benchrest competitions against BAT machine actions with Kriegers and the 6mm PPC, but we will take all the accuracy we can get in the AR15, whether it means the difference in our confidence level as we cleanly break the trigger with the center of our crosshairs on the heart of a trophy beast, or on a small steel plate at a match.

Here are some other basic tools I use for smithing the AR15:



As to the D-Fender and enhanced silicon extractor buffers, you can over-tension bigtime in my experience with these units, so just check the extractor to ejector balance in your particular bolt. These were really meant for aiding harsh extraction in the military CLGS commando variants, where port pressure is high with 5.56 NATO loads, and the case fights to be pulled before it has rebounded back to memory as the extractor tries to pry it from the chamber. This is especially true with the 10.5" guns, suppressed.

The Grendel barrel length and gas system configurations where this is more likely to be an issue are:

* 10.5"/CLGS with a large port
* 18"/MLGS with a port larger than .076"
* 20"/MLGS (Saber actually cranked out a bunch of these for some reason)
* 28"/RLGS

We generally fight these guns with buffer and carrier weight, and then an increased power recoil spring.