I have everything I need to build an XM177E1 clone except the bare 10" lightweight .625 barrel.  It's my understanding that no one makes a barrel like that, so everyone starts with something else and has a smith modify it to spec.  I planned on starting with a BCM lightweight 11.5" barrel (This One) and having a local shop cut it to 10", open the gas port to .09ish, and pin on my Colt M16A1 take-off front sight (taper pin holes already drilled).  Will my plan work?  Any issues cutting a lightweight barrel and pinning a previously used front sight?  What barrels have you guys started with, and who did your work?  Thanks.

I used a Double Star 16" chrome lined pencil barrel. Since I was using a fake moderator I wasn't concerned about the barrel being the exact length because I could cut the thread as long as I wanted and hide the length inside the moderator. In fact, I left mine at 11 or 12 inches and it looks just fine. I cut and threaded the barrel myself. The barrel already had the front sight installed and unless you have a jig to index the front sight to the barrel, using a pre-drilled sight base is going to be next to impossible to mount properly. There are shops that can do it. I have a jig I use that I can mount to my drill press or a milling machine. With a pre-drilled sight base it's not just a matter of running a drill bit into the hole and drilling through. You start with an end mill because of the round contour of the barrel inside the hole. Then you need the proper taper reamer for the taper pins unless you use straight pins.  

Don't drill the gas hole until you test fire the gun. If you need to open it up there should be enough room to move the sight base out of the way to do it even with the moderator welded on, depending on your overall barrel length. I left my gas hole alone and found it operated flawlessly the way it was.

Also remember that if you cut your barrel all the assembled parts need to have a finished overall length of 16" unless you're building an SBR. Cutting the barrel to 10" and using the fake moderators or long flash suppressors, which are usually 5" long, will leave you an inch short. That's the main reason I left my barrel longer than 10" as mine isn't an SBR. With the moderator pinned and welded I got the entire assembly right about 16.25" in length.

I was going to comment on the gas port when I read your post. In the "old days", a .090+ port size was common. It doesn't need to be that big though. With the advent of the Colt Mk18 and its' developements, it was found that .070+_ would work. There are many more buffer weights to play with today, along with different buffer springs, which has led to smaller ports being workable.

Specialized Armament sells one.

http://www.specializedarmament.com/products/Barrel_Front_Sight_Assembly_10_Special_Purpose_Lightweight-1007-289.html

JT distributing has lighweight 10.5" barrels. I used one of their 11.5" barrels for a retro build.

10.5" lightweight barrel

You're new around here, aren't you?



Oops, my bad. I mistook specialized armament for someone else. Yes, aside from the extreme high prices, specialized armament is good to go. The option of chopping another make and sending it to one of our retro brothers, John Thomas, or others is the way to go IMO. Sorry for the late night snafu.

Other than being kinda pricy, whats the deal?

Ken carries top-notch stuff. Pricey but very high quality.

Take a look at J&T distributing, that's where I bought mine.
Comes with the front sight base already installed.
The barrels listed are not chrome lined but you can add the chrome lining as an option, I did.
I bought the 14.5 inch chrome lined and had it cut down and a Brick moderator pinned on to make it 16 inches, so I didn't have to deal with SBR.
Send the barrel to John Thomas for the modifications, HE DID MINE AND IT TURNED OUT ABSOLUTELY BEAUTIFUL!!!

Yes it did.

If you can find a used Colt 11.5 and cut it down you may not need to open the gas port, mine works perfectly but I am also running a Colt Moderator on it.

Lots of great advice.  Thank you all.