Thanks, Kino
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Thanks, Kino
I have no idea what you mean by the cologne thread or why you can't seem to understand what I said. I was referring to the claim being made about cutting/crowning and the opening of the gas port. I also never said it was something I would do. In fact, aside from your misguided attempt to make it look as if I was being contradictory I have oft stated I would buy a good barrel rather than cut one down.
Cutting, crowning, threading, and re-porting a barrel is child's play to any capable gunsmith. In fact, machining 4xxx series steel is a treat. If the barrel at 16" is no longer of value to the owner then it is all gain. You would likely loose the value of the machine work when trying to sell a used barrel. I would proceed.
If I misreprented what you said it was unintentional. Needless to say your initial statement to me was less than complimentary yet I was still only relaying what I thought was the truth regarding a semi-complicated decision, not looking for drama.
All I would ask at this point is if you perceive the stated modifications to be so risk-free (as do most in this thread apparently) then why advise against such modifications if it's less expensive to make them with a capable gunsmith instead of just buying new? Keep in mind that it actually wasn't your post that formed my initial opinion, but when I found the thread I was looking for there you were also advising against.
MistWolf is a knowledgable guy and I wasn't looking to derail his thread. Was just trying to help and apparently it backfired. Hopefully at least some more detailed knowledge of the scenario was passed on to our fellow members.
Here is the M4 profile from Randall's site.
Add .75" to the lengths shown for actual measurements to account for the bolt face to shoulder dimension.
If you cut it at 10.625", the FH shoulder is at 10.000"
The total bbl length is 10.625+.750=11.375"
http://www.ar15barrels.com/tech/m4a1.jpg
http://www.ar15barrels.com/tech/ar15bolt-extension.gif
Here is the other option for a 12.75" bbl, the FH shoulder is at 11.375"
http://img822.imageshack.us/img822/8980/adco1.jpg
The answer to your question is yes. If your goal is to cut it short enough to eliminate the notch, it could be made between 10 & 11.3 inches.
I had a 6920 barrel cut to an even 10 inches several months ago. The gas port was left alone to use as a mostly suppressed SBR. It's soft shooting w/ not much gas to the face while using my Surefire 212.
The combination of 10in barrel w/ 9in handguard makes a seemless transition from handguard to can. I haven't noticed a decrease in accuracy after the chop.
Here is a thread on the same question.
https://www.m4carbine.net/showthread.php?t=18155
If it's just cut and threaded at 11.5", you will still see some of the taper unless more machine work is done. Rguns sold cut-down Colt M4 barrels as Commando barrels in the past. It was pretty obvious.
I got one years ago and had Adco cut it to 10.3" and open the gas port to make a MK18 upper. Don't shoot it that much, but it's worked fine.
I thought the first CQBR/MK18 barrels were made by cutting down M4 barrels?
ETA: I posted a pic of the 11.5" barrel, before it was cut to 10.3", in the thread linked above.
FWIW, ADCO's charge for this job is quite inexpensive. Last week I sent them a DD M4 barrel that I wasn't using anymore to get this done.
Cut, crown, thread, and gas port modification was only $65.