AR-15 Stripped Lower Prep?

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bfro5482

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In my research for my first AR build, I have seen people preparing their lowers by running drill bits (by hand) through the detent and pin holes.

I totally understand the need to inspect for burrs, machining chips or finish build up and addressing issues if something is noticed.

Doing it to just do it doesn’t seem right.

I also think the need would be based on the quality of the lower you are using. I’m starting with an Aero Precision M4E1.

Thoughts??
 
It’s not really “doing it just to do it”. As you noted, it is removing any burrs that might be left over from the machining process (which are sometimes difficult to see) and if you’re using the right drill bit size it ensures that the pin holes are in spec. Nothing sucks more than getting half way through the assembly process only to find that your lower is out of spec and you have to strip everything to send it off to get fixed.

Is it absolutely necessary? No. But it’s quick and easy insurance. I’ve had a couple of lowers come in out of spec and it’s a pain to deal with if you’ve already got roll pins in there.

With the way the gun industry has been the last couple of years, I wouldn’t put it past any company to occasionally have a QA issue.
 
I've assembled eight lowers and never done anything other than wipe the bare lower down before starting.
 
entropy said:
Even with Anderson lowers I've never had an issue with any of the detent or pin holes.
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Same also for Anderson stripped lowers and Spikes Tactical/S&W M&P15/Frontier Armory (Joe Bob Outfitters) stripped 9mm lowers.

bfro5482 said:
In my research for my first AR build, I have seen people preparing their lowers by running drill bits (by hand) through the detent and pin holes ... Doing it to just do it doesn’t seem right.

Thoughts??
Click to expand...
I found few drops of oil along the detent pin channel and around the pins help with break in and ease of pins sliding in the receiver holes. Makes pushing out the pins so much easier.

That's essentially the only prep I have done for the stripped lowers. I also oil the bolt gas rings to prep the BCG for the assembly.
 
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It’s a totally unneeded step 99.9% of the time. I’ve built AR’s using stripped lowers from Spikes Tactical, Anderson, Aero, Blacks Creek and High Standard and none of them required drilling or reaming of any hole. I would think you are more likely to damage the lower if that drill caught an edge or you got even slightly off center.
 
Maybe just do what I've done on other things.
Take a drill bit of the appropriate size... and flip it around. Use the smooth portion as a gauge. This will tell you if there's a burr or anything out of spec that you need to deal with.
A lot of the time, just a bit of a push will knock it out. If you need more, I still suggest a reamer, but at least you'll have the right drill bit on hand if you need it.
 
I did nothing to mine. Not even oil, since once assembled it went straight to my paint booth.

If you're using an Anderson bolt catch. The large chunks that sit in the lowers slot, might need beveled and ground down a bit.

Larue upper lugs may need stoned down a bit. Very tight.
 
Never heard of such a thing...I've used Stags, Spike's Tactical, Grizzleys and Andersons and never seen a single need to do this. I also don't understand lower/upper fit with gaps; all mine look tight and don't rattle....chalk it up to good component selection I guess.
 
berettaprofessor said:
I also don't understand lower/upper fit with gaps; all mine look tight and don't rattle....chalk it up to good component selection I guess.
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I think some on gun forums like to perpetuate decades old information/experience. Sure, in the Army during the 80s, Vietnam era M16s we shot were well worn and rattled and some ARs in the 90s showed air gap even when new.

But fast forward to 2021, most recent ARs, and PCCs I have assembled using different brand components produced tighter/tight upper to lower receiver fit with almost no air gap and no rattle, even with cheaper Anderson lowers.

I recently built several ARs using these build kits and upper to Anderson lower fit has been snug tight - https://www.22mods4all.com/ar-15-223-5-56/builder-kit/?sort=priceasc
 
entropy said:
Why would you want a striped lower?
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Darn. Beat me to it.

bfro5482 said:
I totally understand the need to inspect for burrs. . . Doing it to just do it doesn’t seem right.
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So you totally understand the purpose of inspection, and you believe the person doing the inspection does not understand the purpose of inspection. Eh?

Rolling a bit through the pin holes is inspection, as is running a bolt up the grip bolt hole. In all the PSA Blem lowers I've helped friends with, the worst issue I ever found with slightly tight grip bolt threads.

I also give them a spritz of relatively heavy oil and let it soak into the parkerizing.
 
I typically pin gauge holes quickly, then lap anything which needs to allow a pin to move. It takes extra time, and isn’t a significant influence on rifle performance, but it’s not much time and it offers a bit of peace of mind for me.
 
You want pins to fit tight, I’ve done 4 builds and never had a pin hang up or bind. Lightly lube and gently tap into place.
If you have a problem, hand turn the proper drill bit to remove any burrs.
 
I have run into a couple problems with Anderson lowers with burrs, namely in the detent holes. Would I consider this mandatory prep work? Nah. But if you put in the detent or the spring and have binding then it would need to be done. I haven't used Aero lowers but have heard good things about their quality. So I doubt you will have to do this at all.
 
Step one: build the lower
Step two: if needed prep the lower, if not continues step one.

note, don’t overthink it, just build it and if any issues arises fix it and move on, more often than not there’s no reason to do so.
 
herrwalther said:
I have run into a couple problems with Anderson lowers with burrs, namely in the detent holes. Would I consider this mandatory prep work? Nah. But if you put in the detent or the spring and have binding then it would need to be done. I haven't used Aero lowers but have heard good things about their quality. So I doubt you will have to do this at all.
Click to expand...

Me too, the rear detent hole. The 1st one drove me a little crazy, after that I now just check 1st. Now the guns I've put together with Aero lowers haven't had any issues. They're really my favorite lower & upper to work with.
 
Drills aren't precise. A reamer would be much more precise way of enlarging holes and gauge pins would be better for checking hole sizes.

I've built a few ARs from striped lowers and have never had a problem with badly sized holes or burrs. OTOH, I haven't made a habit of buying the absolute cheapest lowers either.

The only prep I typically do is to coat the hidden areas of the lower (places that aren't exposed on a assembled unit) with Boeshield T9. But I am kinda paranoid about hidden corrosion.

BSW
 
I’ve never had to do any debuting or anything before assembling lowers. I would only recommend it if I actually found a burr or something that might impede assembly. Aero makes super nice receivers and parts so I’d imagine that you will have no issues with your M4E1.
 
Have never done that to any of my builds.
But I guess if you buy quality lowers you don't expect to have issues. I have numerous guns from 4 different manufacturers. No issues with any of them being "out of spec". Aero Precision, New Frontier, Spikes Tactical and Quentin Defense
 
I've never prepped an AR15 lower. I purchased budget lowers and boutique lowers and they are all similar in that you just put the parts in the right holes. Just make sure your AR lower is milspec or claims to be milspec and you should be good to go.
 
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