What goes into an accurate AR upper?

ammo, barrel, trigger, optic. in that order. at least for me.

Send your upper to Compass Lake Engineering https://compasslake.com/product-category-hide/barrels/ and Frank will install the barrel that fits your price range. The chambering job will be done right, no oval chambers! Talk to Frank about the primary bullets you will be using. I shot match 69's, 75's, and 80's, and my barrel was a 1:8 something with a Wylde chamber. If the bolt is new, he may use it, assuming the lugs are true, but if the bolt was used, like mine, he used a new good quality bolt.

After that, what you use for irons or optics is up to you. I did have Frank install one of his scope bases, so I could put optics on top.

Incidentally, a good custom barrel will shoot wonderfully. I have had outstanding experiences with Douglas, Wilson barrels. I had a Kreiger installed, and while it is a great barrel, Kriegers are tight. I had to cut my loads by 1.5 to 2.0 grains to reduce primer piercing. That could be an issue if you have ammo cans of ammunition loaded up.

I recommend, not loading ammunition that will not be shot within the year. Gunpowder deteriorates and causes case neck and body splits. If I knew that, I would not have made completed ammunition and had the stuff still around.



someone else's surprise!

I live in SW New Mexico and have never seen any of that.

M

Barrel is the most critical thing, whether upper or lower. Free floating handrail is also important. Tight receiver-to-extension fit or shimming during assembly is also critical.

Barrel: Proof, Bartlein turned by Craddock, Shilen, or Krieger.

Nothing else in the upper is critical.

Correct headspacing.
The only way you are going to know is with head space gauges.

Shooter skil, barrel choice, twist rate, free floating, ammo, optics , trigger, then everything else.
I have an Ar with a 1/7 chrome vanadium Checkmate barrel, free floated, that will shoot 1/2 moa groups at 300rds with Hornady Black 75gr bthp, $200 scope, Tapco stock, Anderson lower with stock milspec 6lb trigger. It out shoots my higher end Ar's and gets laughed at by some of my friends with Daniel Defense and high dollar custom builds, ...until I shoot with them. The barrel is the backbone of this performance, but without good ammo and skill, the rest is bandaids.

What goes into an accurate AR upper?

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Ammunition. What does “accurate” mean to you as far as caliber, group size, number of shots and distance?

Even the cheapest of junk AR uppers I have shot do better than the old “pie plate” rifles my ancestors used, effectively. So quantification might help answer your question. Knowing what your expectations are.

I got a 6.5 Grendel upper off @LoonWulf awhile back, IIRC it’s a Saturn barrel from Brownells.

It has shot 3 SMK’s under MOA at 300 yards with a number of shooters behind it.

brewer12345 said:

Sub MOA with something like 6.5 Grendel. I can shoot and I can hand load if factory stuff isn't what the rifle likes.

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6 ARC in a Proof barrel. Factory stuff will HIGHLY likely be sub-MOA, and handloads make it even easier. Feed it some 105 Hybrids or 103/108 ELD’s and it’ll shoot itty bitty.

Get a heavy enough barrel (and light enough stock) such that your rifle balances forward of the front pivot pin by about 3-4”, and it’ll be a ridiculously capable rifle.

brewer12345 said:

What does it take to build an accurate AR upper? I imagine a high end barrel helps. What else is important?

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Care and attention to detail...

And love, can't forget love.

I have put together 2 Del-Tons that were sub moa with factory ammo. In addition to the above posts, the upper receiver must be in spec and fit together properly and the bolt must be in spec and lock up properly and not have drag from not fitting the BCG properly like a PSA I had. A quality AR should be MOA or better with quality ammo. A really good barrel is most critical, a free floating handguard is also an improvement as mentioned.

A Great barrel greatly improves your odds of the barrel liking a lot of different loads ( this includes a well made chamber ) ..., tight upper to barrel extension fit, ...free float tube, ...nothing allowed to even possibly make contact with the gas block ,... proper gas tube to gas key interface ( no binding / a smooth easy fit ),... great assm. practices,.... snug upper to lower fit ( think of that as the "bedding" of an AR15 )

I've put several together that shoot sub MOA with good ammo with cheap Aero, Anderson and PSA uppers/BCGs and generic gas blocks, tubes and handguards.

I start by lapping the front of the upper then check barrel to upper fit using 1000th shims next heat the upper (toaster oven at 300 for 30min) and freeze the barrel (overnight), install shim or shims on barrel and install in upper, tighten barrel nut (I like ~45ft lbs), free float handguard.
Triggers I have polished stock ones on a glass pain, paper sack and toothpaste using lower weight springs and a set screw through the handle to take up slack they are surprisingly smooth but not as smooth as a good drop in, AERO lowers have a set screw to tighten the upper to lower fit.
I like both the 6.5 Grendel and the 6 ARC but there are a lot of calibers that will help you get sub moa.
Good luck with your search

From the vast majority of what I’ve read supreme accuracy is as simple as a BCA of any configuration and a can of M855. I hear this magic is “MOA all day” out to 600 yards...”when you do your part”.

Barrel barrel barrel. Ammo ammo ammo. Practice practice practice. Insert “good” before each of those. I own no bleeding edge accurate ARs but if I did it would be dumb luck for what I spend. MOA yes, one tiny hole no. Maybe I should try one of those BCAs...

Never had to lap an upper to achieve sub-moa accuracy.

lysanderxiii said:

Never had to lap an upper to achieve sub-moa accuracy.

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Still, it’s inexpensive enough, particularly for multiple builds, and the basis for doing so is sound. I’ve lapped the last several and found no unexpected negative effect.

I've lapped my last 3 builds, only took a few minutes.

I've only done one precision AR15 build, my others were with "OK" barrels (Faxon's and Larue's) and shoot sub MOA with some load tinkering. My one precision rig has a White Oak Amory barrel with a matched bolt. I lapped the receiver and "bedded" the barrel extension into the upper using Loctite. It is easily a 1/2 MOA rifle with decent loads, it will run with my bolt guns out to 600yds with 77 grn OTMs. The WOA barrel comes with an oversized gas block journal, but instead of turning it down, I use a small hone to open my SLR AGB up to fit.

All of my builds have Geissele SSA-Es in them except for the SPR build, that has a SD-E trigger.

lysanderxiii said:

Never had to lap an upper to achieve sub-moa accuracy.

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Sure is nice to be able to set tube-block alignment without shims AND with a regulated torque target though.

1. Barrel
2. Ammunition
Everything else (in AR platform) just gets you minuscule, incremental improvements.

twarr1 said:

1. Barrel
2. Ammunition
Everything else (in AR platform) just gets you minuscule, incremental improvements.

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Trigger and total rifle weight are pretty huge contributors - as well as float tube (vs clamshell) aren’t minuscule. When you can push your barrel around because your handguard bears on the barrel, or when a heavy trigger means it’s easier to move your entire rifle over a fulcrum than break the sear, accuracy suffers considerably.

3. Trigger