Does the AR upper receiver matter?

[FishinGuns]

Hah funny story/coincidence: I JUST built an upper with a VLTOR MUR and URX4.

I’m sitting on three currently that I’m dragging my feet on, as I still need glass for two of the three.

 

[MontanaMan]

They’re not available stripped, but I think the BCM Mk2 forged upper is the best of both worlds here.

^I guarantee you it’ll fit tighter than a VTLOR MUR, at 1/3 the price too. I love VLTOR MUR uppers, but never has one that’s passed through my hands been even remotely as tight as an undersized BCM.

Not quite accurate.................the BCM Mk2 is listed at around $125, but not at all available other than as a complete barreled upper group, but you can find Vltor 1a uppers for around $165-170 when they are available, so the BCM is nowhere near 1/3 the price of a Vltor.

MM

 

[TheOE800]

Not quite accurate.................the BCM Mk2 is listed at around $125, but not at all available other than as a complete barreled upper group, but you can find Vltor 1a uppers for around $165-170 when they are available, so the BCM is nowhere near 1/3 the price of a Vltor.

MM

In context I was speaking about BCM blem uppers, which were available until a few weeks ago for $60; which is precisely 1/3rd the $180 retail of the MUR-1A.

Moving on to the BCM Mk2, it WAS available stripped I think at the initial run in January or February. Since then it hasn’t been sold stripped, but yes it has been available as a complete URG since then.

I’m sitting on three currently that I’m dragging my feet on, as I still need glass for two of the three.

I feel you there. I’m waiting on a Vortex Gen3 for said upper and have two or three other uppers lacking glass at the moment.

 

[Push]

There are a number of rail systems including some of the best like gisessle that will not work with the mk2.

BCM makes the best forged uppers. Hands down no question. 95% is the quality of machining and consistency. It’s a staple of many precision Builds and unless you are hanging a giant barrel, the added stiffness of billet is Not worth it. A forging will always be a stronger receiver, all things being equal.

Vltor are forged uppers.

 

[Constructor]

If you feel the top tier Upper is affordable, you should buy it and build on it with no hesitation.

Otherwise, squaring the receiver face, and bedding the barrel extension are good ideas. Neither is necessary to proper function; but many (myself included) consider it beneficial to accuracy.

Squaring can be done at home prior to assembly; a kit is utilized in conjunction with a hand drill, lower speed is better. I use standard coarse valve grinding compound as my abrasive, and I clean it up thoroughly afterward.

Barrel extension bedding is typically described as using Permanent (Red) Loc-Tite. I've done both of these processes, and had no problems in the process. I allowed the assembly to cure overnight. There are several varieties of Red Loc-Tite; and I assume someone will be along eventually to add that info after my post.

I performed the barrel nut seating three times to peen in the receiver threads. The nut I used had a hex profile, and I used a crowfoot wrench attachment on my ancient automotive Torque wrench to attain a final torque of 60 Ft Lb. The nut was lubed with anti-seize compound.

I was troubled by the idea that the permanent Loc-Tite would prevent me from removing the barrel. I haven't tried it and likely won't. But I also concluded that there might be an option here.

If I do this again, I will start by applying release agent to the barrel extension where it would come in content with the Loc-Tite. Let it dry completely before proceeding further. It may have no effect beyond allaying my unnecessary caution.

These were my base components, 15".

Greg

What happens when you heat red loctite, it turns to liquid. What happens when you heat block loctite, nothing. We have been using blue since the late 80s when there were only 3 people building AR high power rifles.

 

[Choid]

What do you think about using the blue gel permatex loctite. Seems like that, brushed on to the barrel extension, might have the best properties for bedding. Like bedding a stock with epoxy in consistency.

 

[RScott]

I’m looking to do a few upper builds, with top tier handguards, and Krieger barrels.

Assuming the upper receiver is mil spec, from Anderson to Noveske/BCM - will the upper receiver matter for group size or anything else?

Yes they matter. A sloppy barrel fitment will lend to poor accuracy. I much prefer a jp/bcm upper that makes use of a reduced diameter to seat the barrel. These typically will require thermal fitment of the barrel to the upper locking them snuggly together.

 

[drewthebrave]

Lots of variables at play here. I like BCM upper receivers because they generally have an interference fit with most barrels. I've had some barrels that had an interference fit with a standard milspec upper, and I've had some barrels that had a *slightly* sloppy fit even in multiple BCM upper receivers. Some barrel manufacturers intentionally oversize the barrel extensions to achieve a tight fit in a milspec upper - these might be unusually difficult to install into a BCM upper. With the state of manufacturing in 2021, it may make sense to buy few different uppers so that you have a few options on-hand to see what works best with your particular barrel extension.

I liked recommending BCM blemished uppers because at $60 they were a smoking deal - but now that they're $90, it's not quite the slam dunk deal it used to be (though I'd take a $90 BCM Blem over most other "new" milspec receivers). I've heard good things about VLTOR, Wilson Combat billet, Precision Firearms and JP uppers - but you will pay quite a bit more for those than the BCM. It might just make sense to true the face of a milspec upper, then bed the barrel with some shim-stock & Loc-tite to take up the slop.

 

[DavidAR10]

I frackin' love this bar.

Legos, esoteric parts, torque wrench - no torque wrench, twist spring loaded dial vs split beam torque wrench
{yes, split beam is the only correct answer if using one},
just da-da-damn yada...

BTW,
MUR-1A for my small frame AR builds.

 

[TimK]

You can ask your barrel guy to fit a +0.001" barrel extension. It'll require heating the upper to get it together, but it eliminates all slop. I've done it a couple of times to duplicate JP's thermal fit, and it works perfectly.

 

[vinniedelpino]

I just used loctite 648 retaining compound to bond a criterion barrel to an upper with fantastic results. This is a different compound that what you'd find at your local hardware store and runs about $15.

I'll never get the barrel off of the upper, but who cares? Stripped uppers are cheap. There's zero play, it's an extremely strong anaerobic bond with high temperature resistance and it's a laser now. I didn't have to mess with shim stock either and it added about 20 seconds to the assembly of the upper.

 

[308pirate]

All mil spec means is that they follow guidelines with materials and tolerance

It means a lot more than that if they truly follow the M16 technical data package

Technical specifications are not guidelines, they are requirements. Tolerances are useless without the nominal dimensions they control.

 

[Ape_Factory]

You know what feels worse? Buying a V7 slickside upper and realizing it’s just an Anderson with the rails machined.

Please tell me you're completely joking about this. And you're referring to the ones being sold currently?

I've bought two of the "lesser" uppers w/forward assist (I think they call it the M4) and both were interference fit with what to me, looks like a higher quality, smoother finish than my ADM lower they mate to. Is all their hype about the aluminum alloy being used just that, hype? Or are these made to their specifications by Anderson?

I actually contacted them on the need to lap the receiver and was told to absolutely not do that as they're trued from the factory. Both builds are sub-MOA

I'll be quite pissed if it's a standard Anderson upper with the only change being the logo and machined rail (and a 200% markup). I get there are only a few places which actually make the uppers but if additional precision machining is done, I'm ok with that. If not well....eff me.

 

[RUTGERS95]

I’m looking to do a few upper builds, with top tier handguards, and Krieger barrels.

Assuming the upper receiver is mil spec, from Anderson to Noveske/BCM - will the upper receiver matter for group size or anything else?

no it does not, if there was any difference or improvement from one to the other in 'any' area, it would not be material and negligible at best. Buy what you like

 

[RUTGERS95]

Please tell me you're completely joking about this. And you're referring to the ones being sold currently?

I've bought two of the "lesser" uppers w/forward assist (I think they call it the M4) and both were interference fit with what to me, looks like a higher quality, smoother finish than my ADM lower they mate to. Is all their hype about the aluminum alloy being used just that, hype? Or are these made to their specifications by Anderson?

I actually contacted them on the need to lap the receiver and was told to absolutely not do that as they're trued from the factory. Both builds are sub-MOA

I'll be quite pissed if it's a standard Anderson upper with the only change being the logo and machined rail (and a 200% markup). I get there are only a few places which actually make the uppers but if additional precision machining is done, I'm ok with that. If not well....eff me.

get ready to be pi$$ed

 

[TheOE800]

Please tell me you're completely joking about this. And you're referring to the ones being sold currently?

I've bought two of the "lesser" uppers w/forward assist (I think they call it the M4) and both were interference fit with what to me, looks like a higher quality, smoother finish than my ADM lower they mate to. Is all their hype about the aluminum alloy being used just that, hype? Or are these made to their specifications by Anderson?

I actually contacted them on the need to lap the receiver and was told to absolutely not do that as they're trued from the factory. Both builds are sub-MOA

I'll be quite pissed if it's a standard Anderson upper with the only change being the logo and machined rail (and a 200% markup). I get there are only a few places which actually make the uppers but if additional precision machining is done, I'm ok with that. If not well....eff me.

get ready to be pi$$ed

Not joking, but it was many years ago. Both the $55 Anderson Sport and $150 V7 lightweight uppers had the exact same machining flaw in the ejection port. I mean exactly the same size, in exactly the same place.

 

[Ape_Factory]

Not joking, but it was many years ago. Both the $55 Anderson Sport and $150 V7 lightweight uppers had the exact same machining flaw in the ejection port. I mean exactly the same size, in exactly the same place.

Well damn. Have to say I'm happy with both VSeven uppers and I'm sure they contract them out to someone, either billet or forged to their specs, with their materials specification. I may have to give an Anderson upper a go if I ever decide to build something else and save a hundred and change.

 

[bfoosh006]

All of this. A high quality upper is expensive because of QC. You're paying for that meticulous consistency which cost a lot of money on a mass produced product.

The variation of tolerance of different manufacturers is too vast: barrel extension vs. Upper Inner diameter.

From my experience, permanent bedding works better than shim. When I bedded my AR barrel, I'd see random "consistency" of upper inner diameter. Sometime they're tight in the front toward index pin. Sometime they're tight toward the back toward feed ramp.

The last time I bought a Noveske Gen1 upper was when John was still alive. Not sure about their quality now. I'd assume that it's still good to go.

If you have a Noveske rail then I would get a matching Noveske upper. It costs may be $20 more than the new BCM upper. Choose which roll mark you prefers.

Either way, you wont be disappointed. Lots of good recommendation in this thread.

IMHO , this as well.

You bought a great barrel... buy a great respected upper. For the same reason you bought a Krieger. QC.

Lower cost uppers can and do work well, but they tend to be far more hit or miss.