Assembled My First Upper: Mistakes and Lessons Learned

[DMW1116]

This began as a $30 blem stripped lower from PSA. The lower was finished with a PSA B5 Systems lower build kit. It went together without a hitch.

Enter the upper. This started as a BCM blem stripped upper. I found a good deal on a Roscoe mid-length 16” barrel with a front sight pinned gas block added by the distributor. The BCG, front sling swivel, front sight detent and spring, birdcage, gas tube etc were all from DS Arms. They added the front sight gas block also.

First lesson is check your stuff before you start. The extractor had a narrow groove and wouldn’t extract. DS Arms sent a new one so I swapped out the guts and put it back in the bolt.

First mistake was trying to heat fit the receiver and barrel with a hair dryer. That resulted in a half stuck barrel which required a Mapp gas torch to remove and reinstall.

Second mistake was trying to use the barrel nut to pull the receiver onto the barrel. Bad idea. The receiver twisted and the index pin was off. When one has a heat fitted receiver, use real heat. A hair dryer just gave enough confidence to get in trouble.

In cleaning up the mess above I ended up removing the dust cover and reinstalling it. It went about as well as can be expected. I dropped the spring and had to find it.

When installing the barrel, I found the barrel nut was tighter than I expected. I tightened it with an armorers tool then got my torque wrench. I moved the nut enough for the gas tube guide to fit properly and was at 50 ft-lbs already. Minimum is 30 as I understand but I think I’m still in range. I used a Wheeler upper vice block and the insert with a gas tube guide rod.

I also ruined the first gas tube roll pin. Fortunately DS Arms included a spare. The sling swivel installation is also pretty ugly, but it isn’t going anywhere. If I get annoyed with it, I’ll put a new rivet in place.

I still need to put the hand guard on but I need to get one of the delta ring tools. I can’t get them on properly with just my hands. I went to great effort to get the proper tools, mostly by just being patient until the tools were in hand.

My first lower was pretty rough too, so I am not surprised. This was the third, so lowers I feel pretty comfortable assembling. Upper lab are where the fire is, so I waited to get into one of those. I won’t get to test it until next weekend but function testing has me hopeful. Ultimately I’d like an M4 style rifle with backup sights and a fixed 3-4 power optic. For now it will have to do with just backup irons. I

 

[AlexanderA]

You were trying too hard. I wouldn't have bothered with heat fitting the barrel.

 

[DMW1116]

What other options were there? It wasn’t fitting without heat or lapping the inside of the receiver.

 

[Okie_Poke]

I learn something every time I assemble one or swap out parts. I try to avoid having to learn the same thing twice, but "use the correct tool the first time" is a lesson the rears it's head again and again. I hope you've got it sorted out and the rifle performs like you were hoping/expecting.

 

[DMW1116]

It’s together, except the hand guards. The bolt cycles, dry fires no problem, fits the lower, etc. I cleaned the barrel and oiled it inside and out. The front sight pin was a little finicky but I have that worked out now too.

I checked the inside and the barrel fits the upper at the feed ramps just about perfectly. I kinda wish I’d gotten the Midwest URR instead of the vice block but it’s 4x the cost. If I planned to build more than one more it would be worth it.

I checked head space twice and it’s clear. I thought lining up the snap ring, weld spring, delta ring, and barrel nut would be rough but there was more room to work in there than I thought.

 

[DMW1116]

Obligatory pictures. It has an MBUS rear sight installed. Sight picture is nice and it’s lighter than my 16” PSA with its aluminum flat top rail and scope.

 

[gotboostvr]

You were trying too hard. I wouldn't have bothered with heat fitting the barrel.

Some BCM uppers are tight enough heat is needed. They're marketed as such.

My buddy just uses the gas stove in his kitchen.

 

[AlexanderA]

What other options were there? It wasn’t fitting without heat or lapping the inside of the receiver.

Some BCM uppers are tight enough heat is needed. They're marketed as such.

In my experience assembling uppers, this has never been needed. But then again, I was using standard parts.

The AR is meant to be modular. If you stray from in-spec parts, you can expect problems. I doubt that marginal "performance" gains outweigh interchangeability.

 

[jmorris]

What other options were there? It wasn’t fitting without heat or lapping the inside of the receiver.

Lapping is a process of rubbing two things together with an abrasive between them. If you are lapping for a smooth fit and its not smooth yet, you are simply not done yet.

Forcing things together that don't fit together isn't the answer, unless, "how do i make this even more difficult?", was the question.

 

[DMW1116]

I assume BCM knows more about their receivers than I do. They said in the packaging heating may be necessary and they undersize it slightly on purpose. I haven’t built an upper with anyone else’s receiver, but it seems like they’re one of the few to do that.

 

[Charlie98]

They said in the packaging heating may be necessary and they undersize it slightly on purpose.

I would have avoided it specifically because of that. Just my .02 worth.

 

[Demi-human]

I would have specifically bought it because of that. Just saying.

I had to heat an upper to fit a rim-fire barrel. It out shoots all but my bedded Savage FV/SR, as far as rimfires go. It might help it was a Beyer barrel.

And now we can talk about glueing them in, and the thick walled MURs, too.
As many ways to skin them as there are cats, I think…

 

[gotboostvr]

I would have avoided it specifically because of that. Just my .02 worth.

I would have specifically bought it because of that. Just saying.

Ah, the duality of man.

I can see both sides of the argument, and could find room in my gun safe for either.

If I were building a rifle and trying to accurize it as much as possible, it'd probably be my first choice. I may do just that in the near future.

For my general purpose carbines, that can't seem to stay in one configuration for any amount of time, and ~1.5MOA is acceptable, there's nothing wrong with standard tolerance barrel fit.

 

[Charlie98]

If I were building a rifle and trying to accurize it as much as possible, it'd probably be my first choice. I may do just that in the near future.

For my general purpose carbines, that can't seem to stay in one configuration for any amount of time, and ~1.5MOA is acceptable, there's nothing wrong with standard tolerance barrel fit.

That was my general thought. The OP's purpose for his upper was a general purpose rifle. I'm not saying it didn't work... obviously it did... but I wonder to what end? He's going to have the dickens if and when he decides to change barrels.

I built an 'accurate' AR last year... I just used a generic (PSA) upper and a little bedding compound. It shoots better than I can.... but to each his own.

 

[gotboostvr]

That was my general thought. The OP's purpose for his upper was a general purpose rifle. I'm not saying it didn't work... obviously it did... but I wonder to what end? He's going to have the dickens if and when he decides to change barrels.

I built an 'accurate' AR last year... I just used a generic (PSA) upper and a little bedding compound. It shoots better than I can.... but to each his own.

I think the heat fit uppers sound like a easier solution than bedding or epoxying, but if I already had a spare standard upper on hand, I'd probably bed that instead of buying a heat fit one.

 

[Charlie98]

I think the heat fit uppers sound like a easier solution than bedding or epoxying,

My concern is the tolerances. OP said the barrel nut went on reluctantly. The phrase '10 pounds of sausage into a 5 pound case' comes to mind... but I would defer to BCM. I would assume some of their rifles are built the same way, and they are known to have good build quality.

 

[gotboostvr]

My concern is the tolerances. OP said the barrel nut went on reluctantly. The phrase '10 pounds of sausage into a 5 pound case' comes to mind... but I would defer to BCM. I would assume some of their rifles are built the same way, and they are known to have good build quality.

He also admitted he didn't use enough heat. Using the barrel nut to seat the barrel might have contributed. And 50ft/lbs is in spec, I belive it's 30-80 depending where the gas tube holes line up.

A buddy of mine built, I think 4 uppers on those BCM's, and used a gas stove, not a hair dryer, and slipped the barrels right in. He thought it was a real slick solution.

 

[Lo-Profile]

I've never had to heat a upper to install a barrel in my 12 builds. Uppers we're Aero Precision or Spikes. Always added antiseize to the upper receiver, some were tight, if needed I used a wooden mallet and they went in. Add antiseize to the barrel nut threads as well.

 

[DMW1116]

The barrel nut was never a problem other than I tried to use it for something it wasn’t intended to do, namely pull the barrel into the receiver. The barrel was a tight fit into the receiver but BCM said it would be. The purpose of this was to build my first upper and end up with an M4ish rifle. So far it seems successful on both counts. Would I build on another BCM upper? So far I see no reason to avoid them. Would I do things differently? Absolutely. Test firing this weekend may change my mind though.

 

[DMW1116]

There was plenty of anti seize on everything. There has to be some on the barrel nut and receiver threads.

Seriously, after getting everything apart and cleaning up, I reapplied anti seize to the threads and the barrel nut tightened up no trouble.

 

[Charlie98]

Test firing this weekend may change my mind though.

Let us know how it does!

 

[DMW1116]

I check a few things every time I get it out. The PSA EPT Trigger seems better than I thought it would be. It’s heavier than the 2-stage triggers on my more target oriented rifles but it’s crisp and virtually creep free.

I am a fan of the Magpul MBUS sights. The sight picture is good and I’ve shot with them to 200 yards. I may replace the one on it now with the newer version. This one came off my DMR after I mounted the new scope.

The safety is solid, trigger is good, head space is good, and the bolt moves freely within the upper. The new extractor hooks case rims solidly. It sounds a little rough. I’ve oiled it twice and will again before shooting, but the phosphate finish on the BCG soaks it up like a sponge. The anodized finish of the upper seems to as well.

I don’t see any reason why it wouldn’t work, but I won’t know for sure until I test fire it. I’m planning to start with some 5.56 American Eagle and Fiochi 223, then move to some full power hand loads. If those work I’ll move to my 22 Hornet +P practice loads. They’re downloaded to about 2500 fps with SW Tactical Rifle and are quite pleasant to shoot.

 

[DMW1116]

I don’t want to say all is well, but it shot great with no malfunctions. It groups about the same as my A4 copy when shot with iron sights.

There might be an issue with the buffer spring though. It seems awfully short and has some sort of dried grease or paint in it that flaked off and got into the parts around the buffer retainer pin and back of the BCG.

 

[DMW1116]

I turned the buffer spring around and ran some test loads through it. Then cooked up a 55 grain M193 load with CFE 223. I tried a couple other older hand loads and haven’t had a hiccup yet. I need to decide on an optic. Looking hard at a fixed 3x-4x type.

 

[gotboostvr]

I turned the buffer spring around and ran some test loads through it. Then cooked up a 55 grain M193 load with CFE 223. I tried a couple other older hand loads and haven’t had a hiccup yet. I need to decide on an optic. Looking hard at a fixed 3x-4x type.

I really like the Primary Arms micro prisms, they're not just "good for the money" they're just good.

An ACOG is objectively better in a few ways, but the PA micros have a few tricks up their sleeves, like an adjustable eye piece, incredibly lightweight and a very adaptable mounting system.