This is a new build I finished last night. Both the upper and lower are Aero. My first issue was the rear takedown pin is very stubborn. I need a punch of some type to get it out, not ideal. I don’t know if that’s related but it’s an issue. The real issue is the charging handle won’t clear the end plate (no name mil-spec CH I believe cause that’s what I had on hand). Seems odd that these most basic parts aren’t functioning together.



Is there a bigger issue that I’m unaware of that is causing this?

I have a couple of BCMs on order but I won’t see those for a week or so.

I can grind either the end plate or the CH but not if that’s going to be a Bandai’s to a bigger issue.

First, is your castle nut loose? Hard to tell for sure from the photo, but it looks like it could be.

Next, your end plate should be effectively flush with the castle nut. Again, hard to tell exactly from that angle, but yours looks like it protrudes above it.

This is how it should look, from the side. Note how tight the nut is to the plate, and how they're basically flush across the top and below the "lip" of the lower receiver's vertical portion.


I'd start with loosening the castle nut a little bit (if it isn't already loose), then seeing if you can push the end plate down a bit before retightening the castle nut. That may be enough to get the plate out of the way.

If that's not it, then it appears that either the end plate is out of spec or it's just a tolerance stacking issue. Try replacing the end plate, or if you don't want to bother with that then file down the top of the end plate a bit before reinstalling it.


The tight rear takedown pin isn't necessary an issue. I've had them be really tight on some brand new builds, before wearing in after the first range trip and cleaning, resulting in them being able to be pushed out by hand as usual.

Could be stacking tolerances in an unlucky combination, or could be your end plate is wonky size wise. Seeing how much it sticks out above the nut, I'd lean that way.

Quick/easy test:

Go fetch a CH from another AR.
Put it into this one.
See what happens.

I agree with Rogue. That plate shouldn't be that high. Did you assemble the lower or did it come that way? I have had a couple Aero guns and never had a problem with them. The rear take down pin being tight seems to be the norm with them. Mine were too.

This message has been edited. Last edited by: patw,

Castle nut is tight with 3 uugga wuuggas. It’s not staked.

The end plate was a pretty snug fit too so I doubt there’s any room for that kind of movement but I’ll reassess.

I built the lower. Not my first but the first in a number of years and the first that didn’t run 100%, let alone at all. I’m pretty certain it’s an out of spec end plate but I’ll confirm tonight. It just blows my mind that something that basic can be out of spec like that, but who knows, more shit shipped in from China or who knows where. I’ve spread my lunch money around to so many places lately it’s hard to remember where I got these but I think MAS.

It’s a nice little rifle pistol. The weather has improved greatly and I hope to put some freedom down range tomorrow. I’m lucky to be able to do that out my back door.

I’ve never seen a tight castle but with a gap, maybe the photo is playing tricks on the perception but it looks like there is a fairly sizable gap there. Not sure that is contributing to the problem but how would you stake it?

I would just buy a new and plate and castle nut, or dremel the end plate a tiny bit if that doesn’t bother you.

quote:

Originally posted by OttoSig:
I’ve never seen a tight castle but with a gap, maybe the photo is playing tricks on the perception but it looks like there is a fairly sizable gap there.

It definitely appears that way in the photo.

Is the end plate reversed? Maybe the tab is not in the right spot or not fully seated?

Can we get a profile or side shot of it? Might help. Unless they are all aero it could be stacked tolerances. If your end plate is from a different maker, it may be out of spec and either way definitely shouldn't be that high. That picture is definitely making it look like the end plate and castle nut are gapped.

Usually there is a depression on the rear face of the lower, and a matching raised feature on the bottom of the end plate that fits in the depression and helps align the end plate vertically. We need a picture like the one RogueJSK posted that shows the fit of the plate against the rear of the lower.

Concerning the rear takedown pin, do you have to slam the Upper down for it to close on the lower before pushing in the takedown pin? If so, the buffer tube is turned in too far.

It doesn’t appear to be any more gapped than RogueJSK’s which is none.

I’m pretty certain it’s oriented correctly. The sling mount only goes in one way and that’s facing to the rear.

Going to go pop it in the vice and take it apart. Hopefully find another end plate, that or take some off the top.

New end plate (and a new detention spring ) much better.



It’s hardly worth the effort for what they cost but now I have to dig up where I got those endplates.

The finished product, well almost.

Don’t buy your generic end plates from MAS Defence. I’ve had very good luck with them on many things in the past. The one on the top was the offender. The one on the bottom came with my SBA3 brace.



And Mark, I turned in the buffer tube one less turn and it still held. I didn’t have to slam it but I did need to squeeze it to get the pin pushed in. Goes together marginally better now. The pin is still tight but we’ll see if I can loosen that up tomorrow.

quote:

Originally posted by BRL:
(and a new detention spring )

hahaha!

Non Colt parts,SAWSALES is your friend.Specialized armament warehouse.Built MANY M16s and Ar15s since the early 80s.Use quality Mil spec parts. Good luck.

I just skimmed, what about ‘commercial’ verses ‘mil-spec’, possible?

I should post that MAS Defense took care of the issue. Though one came in my box with the SBA3 Brace and the other was loose, both on the same order, they said both of the end plates were theirs, were the same exact part and there should have been no reason for the difference. One was just out of spec.

They sent me a new one and an RMA for the defective unit. I'm glad they took care of it promptly. Up until this point they'd provided very good service. They even called me when he taped my box of parts up getting ready to ship letting me know it was going out the door on my initial order. Unlike Brownell's when I received a Law folder with 2 missing parts, finally had to call them after they ignored my email, told me they'd give me gift card when I returned it and I could order another which by the way was not $80 more than what I paid for the other. Instead of sending me a new unit or getting me the parts, they told me to call Law and plead my case with them, something I felt they should be taking care of. As a salesperson myself, I can't imagine having my customer call Kubota because there is a couple of essential parts missing on their new tractor. <Rant Off>

At the time of this particular build I'd only built 3 other rifles so I though maybe I'd run into some type of issue or mistake I made ordering. Kind of like me ordering a M4E1 handguard for a M4E1 ENHANCED upper receiver

Aero lowers have a set screw under the takedown pin whose purpose is to apply pressure to the rear takedown lug and stop rattle. (At least, mine do.)

Take the grip off and hit it with an Allen wrench. If that's your issue, should make an immediate difference.