How far can the barrel of an AR15 flex? First build

[Abrams07]

Built my first AR15, mostly seemed to go well but a couple things came up and I'm not sure if I should take it to a gunsmith to check it out.

I think my first mistake was starting with a polymer lower.

For the buffer tube, it bent a lot before the castlenut got anywhere near 40 ftlbs so I just tightened it reasonably well, staked it, and all seems well. Didnt want the whole thing snapping in half. Some existing web posts suggest this is fine but I'm also noticing that my takedown pin is really stuck most of the time. I greased it and moved it in and out a lot and it moves okay but as soon as I put the upper receiver down it basically takes a punch and a good push to get it in or out (no hammer).

Should I be concerned about the takedown pin doing that? Is it possible the detent is poking out too far from a possibly poorly cut plastic lower, or would it be something else like the pin itself?

Now for the main question. When I was swapping the flash suppressor out for a compensator, it came off without much fuss but with the installation, I had to put a lot of muscle into it to get it timed right. The upper was secure so-so in a clam vice block but I was mostly using my hand to keep the barrel and everything in place (pretty easy) but for a moment I let my hand off and the wrench flexed the barrel quite far. Basically to the edge of the free float rail for a brief moment. It returned to the center of the free float rail after I realized what just happened. It looks straight. Looks center. Can't tell anything happened when looking at it but it freaked my out seeing it bend so far so quick.

Is it possible I jacked up the barrel nut or the barrel extension by doing that? or if everything looks good and straight, all is well?

Was enjoyable, looking forward to the next one. Definetly getting a Geissele Reaction Rod and a metal lower for the next one but I hope I didn't jack up my current rifle. Thanks guys.

[alexisjohnson]

the pins being tight isn't an issue per se...they should loosen up over time but there shouldn't be any flex in the other parts....

[17+1]

[AR-15 Rep]

The take down pin being tight could mean the lower is off by a little, and that could be off at the pivot pin, the deck height, or the takedown pin hole is off by just a little bit. You can run it and see if there is a problem, but chances are it will be ok. Barrel flex, no... but something flexed from what you said so I would check the feed ramps from barrel to receiver, make sure the bolt carrier slides nice and easy. Remember there is just a pin in the barrel extension that times the barrel to upper receiver, the receiver is aluminium, the pin and barrel are steel. Timing issue with flash hider, I am sure there are many posts about tricks etc

[Barang]

I have one lower (AP) that I have to use mallet to push it out.
I have another lower (AP) that I have to tap it with punch to push it out.
They are now loose enough where I can push them out without mallet or punch.

When working installing/replacing muzzle brake; I clamp the barrel not the receiver or the barrel ext. That just me but others have effective way of doing it.

[reverser]

If you grab the end of your stock and twist it, does the buffer tube twist? If not, you're fine. Your stock should stay properly aligned. If it doesn't stay properly aligned, fix it. You don't want it to work loose and have the buffer retainer pop out on you.

Do you have calipers to measure your takedown pin? What's the diameter? I would probably try another pin first. If you suspect the detent remove it and try it without it. If you suspect the lower, run the pin JUST through the lower. If you suspect the upper, run the pin just through the upper. If you suspect the holes are the correct size but just misaligned, then just modify the pin and forget it. Don't mess with the holes - I don't want to see a new thread about how you ruined your lower with a file.

The barrel flex you're talking about... if you are pulling the muzzle toward the hand guard perpendicular to the barrel axis it is normal. They will bend toward each other. You shouldn't be able to bend them all the way toward each other and they should return to their original position, but yeah, they move. Is your barrel extension all the way in? When you tightened the barrel nut, did you follow the part of the directions where they said to tighten and loosen a few times before torquing down? It is hard to explain - it should flex but there shouldn't be any play (rattle?) in there.

And yeah, don't rely on a vise block on the upper when installing a muzzle device. You can shear off the barrel extension index pin or mangle the upper where the pin fits. You're fine if your gas port is aligned though.

When are you going to shoot it? Pics?

[FeuerFrei]

Use a barrel vice to do barrel work. Including R&R muzzle fobs.
You can use a 1/4" drill bit to correct the TD pin problem. It should never require tools to move that pin. People live with this because they don't bother to check it prior to assembly. Fix it by removing the safety switch and running the 1/4" drill bit through the upper & lower TD pin hole when upper/lower are closed to true up the alignment. Turning it by hand usually works well enough.
No need to chuck it in a drill.

Sent using a long string and 2 Dixie cups

[blackrat]

If you're going to be doing a decent amount of AR work a bev block is a nice addition to your tool set. The part that works with an upper secures via the barrel lugs so you get a nice solid grip without having to worry about tweaking anything.

[Califpatriot]

I have an Aero M5 where the builder used the wrong pivot pin and marred the finish trying to hammer them in. It was rough at first, but with a liberal application of Hoppe's and use, works properly. An Anderson AR-15 I built has a takedown pin that took forever to get to open easily, but again, with Hoppe's and use, works properly.

[bfoosh006]

Next time... and frankly this time , since I would back off all that torque at the last place a fired bullet see's...

Use these to properly time your brake.

https://www.brownells.com/rifle-parts/barrel-parts/rifle-barrel-hardware/washers/shim-kit-for-mounting-flash-hiders-5-56mm-1-2-28--sku100023663-103512-195597.aspx?cm_mmc=cse-_-Itwine-_-shopzilla-_-100-023-663&utm_medium=cse&utm_source=connexity&utm_campaign=itwine&utm_content=100-023-663