View Full Version : fitting an upper to a lower?

February 20, 2009, 20:06
I just bought my first FAL kit and receiver (entreprise arms type 3 receiver). I put the pivot pin in and tried to latch the upper to the lower and the lower will not latch at all. I tore down the lower and removed the butt stock and dove in to the frame locker. I removed all that to get a better look. It seems that the lip of the frame locker is too low to go over the nub on the upper. What's the best way to correct this? Should I order a new frame lock and see if mine is out of spec / bad? Or are there a few key places on the LOWER that I should file down to help the upper pivot in place a little lower. It looks like I have < 1/2 a cm from being completely against the lower as far as it can go. that might be enough to get the frame lock to engage the upper. Thoughts?

February 20, 2009, 21:43
how far did you take it down? I feel I would have to take off ~ 1cm of material to make this work. Would that compromise the integrity of the nub on the receiver? Or should I grind the frame locker and raise that, although I'd be worried about getting the angle wrong or compromising the integrity of that part. It's only $10 for a new one, so if that's the easiest fix I'd love to buy one and fit that one.

February 20, 2009, 23:55
Check out this thread:


It seems like you may be having the same problem.

If you have to take off a centimeter of material, then something seem seriously amiss, or you have misdiagnosed the problem.

I would make sure you know why it is not latching. For example in my case the upper reciever lug was hitting the lower receiver crossbar. This prevented it from closing, and it was no where near inline. By removing a sliver off the lower receiver crossbar the two closed properly. (see picture in the other thread)

February 21, 2009, 00:32
Ok, I flour'd up the lower and wetted the lug, it is NOT bottoming out. To give some reference, the frame locker slides ever so slightly over the end of the uppers lug, so it's not THAT much that it's off. the front of the upper is not hitting the cross piece of the lower either.

Is there a SOP to fix this? Should I get a new frame locking nub for the lower and file that to fit (or hope it fits), or should I take some height off the length of the lower receiver (I don't know if that could be a problem or not).

February 23, 2009, 04:57
just a bump. muttman

February 23, 2009, 09:39
So are you saying the the frame locking plunger does slightly ride over the receiver locking lug but just not enough for solid engagement?

L Haney
February 23, 2009, 20:17
Have you tried it with the locking plunger REMOVED? Does it bang all the way down then? Make sure what is causing the problem before you remove metal from anything. This was mentioned above, it's great advice.


February 23, 2009, 22:08
I tried it with the frame locker out and it does not bang on the bottom. With a little force downward the frame locker will lock up on the upper receivers lug by a hair, but not engage the lug fully.

I'm going to try a new frame locker before going any further. If that fails I will remove some metal along the length of the lower. If that horribly fails I'll get a US made lower (with the added bonus of a compliance part).

February 25, 2009, 13:29
have you looked over at gun plumbers reiver of the enterprise reciver. he talks about the fit of upper to lower in his review. muttman

L Haney
February 25, 2009, 18:04
Originally posted by bcass
I tried it with the frame locker out and it does not bang on the bottom. SNIP

I made a suggestion I can tell was not clear, my apologies. What I intended to get across was if the locking plunger/cam- the spring loaded wedge at the rear of the lower is removed completely, will the upper pivot down until the rear of the upper is completely flush with the vertical face at the rear of the lower? Or is there still a gap between the upper and lower at the rear? If the upper "pinches" into the vertical face at the rear of the lower, the upper is possibly just a smidge too long. If it does close completely, it is the fit of the locking lug and the plunger that is likely at fault.

February 25, 2009, 18:28
There is a slight gap between the back of the upper and lower at the rear (between the sight base and upper).

February 25, 2009, 18:30
Originally posted by muttman
have you looked over at gun plumbers reiver of the enterprise reciver. he talks about the fit of upper to lower in his review. muttman

Do you have a link to it? The lastest review I could find were in '07, I have a receiver from the Jan-Feb '09 batch that just went out.

February 25, 2009, 19:04
You have to go to arizona response systems website under NOTES. I looked under reviews myself on falfiles and then thought about the website.

February 26, 2009, 10:16
here you go

all most at the bottom of the page.
yes it is from 07-08 time, it should still give you a idea of what is/ could be wroung and how to fix it. my intrest in this post is I have one on the way and now the drops are forming on my brow :eek: after reading your post.


February 26, 2009, 10:38
Don't go read my posts about feed ramps then :(

I eventually found the review, thanks! I'm placing an order for parts next week so i can trouble shoot the locker. I had a friend who has built a FAL or two say he's had to remove a little material with a file from along the top of the lower to allow the upper to seat a little deeper. I can't time the barrel yet either because it came with a stub on it, and since this is my first built / FAL I don't have a gas nut wrench.

February 26, 2009, 11:09
try a bottle oper for a gas wrench. muttman