mounting an M203....Help!!!

**norshon3** · 05-09-08, 07:14

I just spent some bucks (to me!) on an original LMT 40mm M203 and custom 37mm barrel to make it ATF legal w/o a DD transfer.....anyway I can't mount the sucker and am frustrated....Help....

okay here are the specs.

1) LMT 10.5" MK18 SBR upper.
pic. http://www.rainierarms.com/?page=sho...product_id=383
2) LMT M203 "standard model" ....
pic. http://www.autoweapons.com/photos07/nov/lmtgl.html

* It would seem the thickness of the barrel on the LMT upper, limits the ease of the 203' just snapping around the barrel. Should I be looking at taking the front sight off?

Hope this makes a bit of since.....

Ooops....I have a new flashider that has a 203' mounting bracket on the hider' itself.

**M4Guru** · 05-09-08, 07:40

There is a flat cut out on colt M4 heavy barrels for the M203 to slide around right before the barrel nut. I have not seen this on a MK18 since it is too short to mount a 203 on because the front bracket is out past the muzzle anyways. A different, rail mount 203 is available that can be made to work with some FF tubes. Or you can buy a stand alone stock for the model you have.

So, more importantly, once you get it around the barrel nut, what is a standard M203 gonna clamp onto at the front? The flash hider?

**sinister** · 05-09-08, 08:22

I gotta ask why?

AAI and LMT make the Pic rail Product Improved 203 that takes advantage of a free-float rail system.

**norshon3** · 05-09-08, 08:41

I am completely open to any and all suggestions / ideas....

I am not familiar with any new devices that allow easy mounting, so please feel free to make suggestions and point me to certain products related to the piece I have in hand.

I know LMT makes a new 203' that has the rail attached for easy mounting BUT as I already have the device in hand, I just want to make it work....

Thank you.

**erh** · 05-09-08, 15:18

Your simplest solution is gonna be to install a longer M4 profiled barrel..
The "Flat cut-out" as mentioned above are what you need, as well as the forward
mounting area which you presently will NOT have...

Good luck Sir..!

(Admittedly, I catch myself wondering why as well..?!?)

E!

**M4Guru** · 05-09-08, 16:15

As was said above, your upper and 203 are not compatible with one another. Here are the options:

1. Buy a new 203 with a rail mount and a FF tube to put it on. This will be really spendy all over again.

2. Buy a stand-alone adapter for the 203, therefore keeping your 10.5 upper and you can carry the 203 like an M79. This would by my preferred option since I hate the 203 with a passion and want to keep it off my gun.

3. Buy a 14.5" or 16" barrel/upper with 203 cuts.

**norshon3** · 05-09-08, 20:34

Okay....take a look at this interesting pic.

http://i32.tinypic.com/akaeky.jpg

I am bound and determined to make this work....call me stubborn....I have the mounting issue worked out. The flash hider that has the extra space on the unit will work (I have been told/assured) in regard to the end of the 203' receiver as secured to the end.

The issue I am having now seems an easy one BUT before I start "beating" on it, I need some advice:

* When I remove the handguards and am looking at the bare barrel underneath, it would seem the barrel is "too thick" to simply "snap" the 203' receiver (the "ears") on the barrel.....is this common on say the "standard M4" ? Does it take a little "tap" with a rubber hammer to mate the 2 pieces OR is the barrel on the 14.5" thinner on some units?

Thank you.

**M4Guru** · 05-09-08, 20:51

There is a flat on each side milled out of the barrel between the FSB and barrel nut, about 2 inches long. This allows the 203 to go around the barrel. I have 6 MK18 uppers at work. 4 are like yours and 2 have the flats. I don't know the rationale behind this.

The next part is important: IF YOU TAP IT ON THERE YOU WILL **** IT UP PERMANENTLY. The barrel steel and more malleable 203 receiver will have a pissing contest and the barrel will win.

You need to accept that your choices do not work together and do it the right way. Just cause some SEAL or SF guy did it does not make it right. Ask me how I know that wrapping the mounting bracket around the FH is a bad idea...