CAR15 to a XM177

[tommy.duncan]

I want to cut the barrel and weld a 5.5" flash suppressor. What do I have to do to compensate for the shorter barrel. Do I just cut the barrel, lathe it down and thread it for the suppressor? Do I have to change for the gas chamber? Please help!!

 

[dfariswheel]

Much depends on the gas port in the barrel.
You may need to switch to a heavier H1 or H2 buffer, probably not as much as an H3.

One possibility to think over is that you loose a lot going to the shorter barrel and the barrel and flash hider is still going to be 16" long.
As an option, why not buy a "slip-over" flash hider that telescopes over the barrel and looks like a XM.
This looks very much like an XM but you still have the superior 16" barrel.

Here's my old Pre-Bushmaster with a custom made telescoping flash hider.

 

[BBBBill]

dfariswheel's idea make much more sense. You will avoid lots of potential problems doing it his way.

 

[rcmodel]

+1

It makes absolutely no sense to cut a 16" AR barrel shorter then it already is, just to make it look like something else.

The 5.56 NATO/.223 Rem lives and dies on high velocity.

Cut the barrel to make it look more trick?

Might as well paint it hot pink while you are at it!!

And barrels shorter then the 14.4" M4 are known to cause all kinds of gas system problems, hard slam-bang cycling beating the gun up, harder more abrupt recoil, or not cycling at all..

rc

 

[tommy.duncan]

WOW!!!
Hasn't anyone ever customized a car or anything??
I have several full size and carbine ar's, including different calibers. I have (get this) 0 that's right ZERO XM177's.
And, The AR15 I built my wife has pink furniture!!
No need to be an asshat.

 

[BBBBill]

Sorry you think that we are being "asshats", but the facts are that you are treading into territory that will likely lead to a malfunctioning gun. There's a ton of historical evidence to support that if you care to do the research. The government had a lot of problems with the XM series before they got them to run reasonably well. Over the last 40+ years I've seen lots of aftermarket clones that would not run reliably because the manufacturers did not have the gov't data and did do their due diligence. The suggestion by dfariswheel to use a slip over design flash hider will save you ever so much money and grief. If you have the money, time and patience to work it out, have at it.

 

[Al Thompson]

Nobody is being an asshat. Two guys who have literally decades of experience are trying to help you out.

 

[tommy.duncan]

My "asshat" comment was due the "make it look trick and paint it hot pink" comments. I am looking for a SBR in the AR15 platform. I don't know of a manufacturer that sells an XM. I was wondering if one could be made. I was asking a question I didn't have an answer for, that's why I asked someone with experience, a simple that is difficult, or that will lead to some problems would have been enough. The false flash suppressor is a good idea, but it is not what I was looking to add to my arsenal. I have put several posts on here and I have received several good answers, that is why I asked the question here. I have been shooting for over 30 of my 43 years on this planet, I don't have all the answers.

 

[Billy Shears]

Take a look here: http://beta.ar15.com/archive/topic.html?b=3&f=123&t=608850

Scroll down and you'll see a carbine I built using a slightly modified Bushmaster slipover flash hider (had to have the wrench flats added), and a repro grenade ring that I bought off of gunbroker.com. The result is a pretty good external copy of a USAF GAU5-5/A. The upper receiver is a Colt and the lower is a Nodak Spud. You can, of course, put together one with the forward assist if you'd prefer an army XM-177 clone.

I'd highly recommend using the method I did. The slipover flash hider will give you the appearance you are looking for, but beneath it you will still have a 15 inch barrel, and with the flash hider welded in place, it's long enough to avoid becoming an NFA firearm. The longer barrel will give you better ballistics and reliability. You'd gain nothing from cutting the barrel to 11.5 inches and welding on a flash hider; the appearance would be the same as mine, but the performance would be inferior.

I'd recommend browsing the retro forum at AR15.com. You'll find all sorts of useful and interesting information if you want to build a retro rifle or carbine. Some of the people over there have made some pretty impressive retro rifles, even repros of the earliest prototypse ARs.