Question: Tight Fit With An LMT MRP Piston Upper

[FMJ556]

Hi,
I have been having the toughest time putting an LMT MRP piston upper
on a lower. The fit is extremely tight.
I have tried it on two lowers and both had the same issue. It seems to
me that the LMT upper has these two small "bumps" on the mating
edges where it meets the lower receiver just forward of the magwell.
I haven't seen these on other AR uppers.

Can anyone who has an LMT upper confirm this, i.e is this a standard
LMT "feature" or do I have some kind of odd machining flaw. It seems
too symmetric as it is on both edges of the upper in the same spot to
be a flaw. My guess is that it is machined in to ensure a tight fit with
their own lowers, but can be a problem with other company lowers.
Thanks.

[Bill Bryant]

Don't let TK know you started a thread with anything in it about upper/lower fit. :rolleyes:

[Agile53]

FMJ556 looking forward to any feedback you get as
I had/have the same issues mating my MRP piston
upper to my Defender lower. Bought these NIB direct
from LMT last year & added a 12.5" drop-in barrel w/
piston assembly from LMT this year.
Will be interested to see what we can find out here.

[Iraqgunz]

Why? His post has ZERO to do with your idiotic post. We are talking about a true failure of them to mate up as opposed to someone worrying about a little wobble.


Don't let TK know you started a thread with anything in it about upper/lower fit. :rolleyes:

[Jay Cunningham]

Don't let TK know you started a thread with anything in it about upper/lower fit. :rolleyes:

Bill Bryant, please check your PMs.

[FMJ556]

Sorry, I didn't mean to upset anyone with this topic.
For anyone interested I did find something over on AR15.com (http://www.ar15.com/forums/topic.html?b=3&f=118&t=456313).
It seems my theory was confirmed, LMT does intentionally
machine in these raised spots on the upper receiver.
LMT's advice is to file it down !!. More of a hassle than a
help in my opinion.

[Byron]

I had those bumps on my LMT MRP Piston upper. The fit on any of my lowers was so tight that it required me to use a freakin' punch to disassemble the weapon :rolleyes:

A couple minutes with a file and I got it squared away no problem. Now it fits any lower normally.

[lawusmc0844]

I finally got my MRP piston upper after a 7-8 month backorder. I tried it on my Daniel Defense lower and it just would not secure. It fit on my Kaiser Defense lower, but it was a very tight fit. I emailed Ryan Johnson of LMT about this and this was his reply...


...The CQB receiver itself is designed to have a very tight fit to the lower in which its mounted. So I am not surprised of the difficulty with mounting it on the Daniel Defense or Kaiser lower halves. It would also have a tight fit on an LMT lower…this is so once mounted on a lower the upper and lower have a rock solid fit.



Please let me know if you have any other questions or concerns.



Thank you,



Ryan Johnson

Sales Representative

Lewis Machine & Tool Co.

1305 West 11th Street

Milan, IL 61264

Phone: 309.732.9527

Fax: 309.787.2636

Email: johnsonr@lewismachine.net

[eternal24k]

I like the idea of having two "bumps" which the user can file to get the preferred fitting.