View Full Version : Can you cut down a M4 config barrel to 11.5"?
Since I don't have access to my guns at this moment, I can't take a measurement & answer myself.
Is there enough material on the M4 conf barrels to allow cutting to 11.5"?
I didn't know if the cut for the 203 would allow for this.
I want a quality mil spec barrel & am tired of waiting on possible solutions nor do I want to pay $400+ for a new Colt barrel. I have run into some Colt M4 barrels with welded FH's & including chop & rethreading would be less than $300.
I'm open to suggestions.
M4 cut barrels work best at 12.5". That puts the FH just in front of the 203 cut.
You might be able to get it cut to 11.5, but it'd look weird as hell.
http://img.photobucket.com/albums/v204/kenc3/DSCN0813.jpg
This is actually slightly less than 11.5", something like 11.3" or so. haven't measured it precisely.
The original MK18(CQBR) is a cut down M4 barrel to 10.3in so yes it can be done but you will have to open up the gas port to .069-.071. The 12.5in I believe comes from the fact the that it will give you 5in of dwell time and that is considered to be the minimum and still have a large operational envelop for reliable function. I know you can get the short ones to run guys do it all the time but even the MK18 can have trouble in colder weather. The more dwell time will also allow for use of a larger variety of ammo as well.
Yeah. Someone here posted that LMT had cut several of their 14.5s down to 12.5 for his unit. They ran good with no port modifications.
You aren't saving money buy cutting down a M4 barrel over buying a factory 11.5" outright.
You aren't saving money buy cutting down a M4 barrel over buying a factory 11.5" outright.
Only if I can get the barrel in the low $200 range. I have a line on a complete Colt Commando upper & I think im going that route. Im just getting tired of waiting for what seems to never be available or priced thru the roof.
Only if I can get the barrel in the low $200 range. I have a line on a complete Colt Commando upper & I think im going that route. Im just getting tired of waiting for what seems to never be available or priced thru the roof.
It is better to buy a factory barrel at any price range.
You start with a $350 Colt M4 barrel.
You chop this and thread for ~$100 and do any gas port work/refinishing.
Now you are up to $450 in this project. You are left with a cut down barrel that is worth $125 at the most.
So you are basically out ~$300.
The only time when you need to be modifying a barrel is for a custom length.
We shoot some ICE/Customs ar's last year and they had there barrels cut down. They went from a AUG to Colts with cut down barrels. I was told that they could only get 55bt to stablize out of them every thing else keyholed.
Dave
I was told that they could only get 55bt to stablize out of them every thing else keyholed.
Barrel length wouldn't have anything to do with that. Twist rate or a poor job of barrel chop might though.
Are the gas holes the same size?
I just bought a complete Colt Commando upper. Just have to wait for it to come in.
Are the gas holes the same size?
Nope... There's a specific size that corresponds to a barrel length range.
Does anyone have a chart for this? Ive heard of such charts but have never actually seen one myself.
Dano also brings up a great point and one that is mostly over looked by most people doing the short barrel thing and that is external ballistics. The majority of ammo is below fragmentation velocity right out of the muzzle of the 10.5in guns. Some of the smaller specialty units have realized this and now have ammo tailored for short barrels with projectiles that will perform at the lower velocities. The ammo industry is responding to the need but will be awhile before it is widely available.
Consider the range you intend to engage targets and make sure your rifle/ammo combo will so the job.
[QUOTE=Dano5326;207490]I started using 12-12.5" 5-6 years ago and find the 12.5" the most user friendly length for:
-comprimise between external ballistics and portability
-as Grinch stated will work with most any ammo you pick up.. even the weak civi crap, unlike the 10"rs
-runs a little cleaner than a 14.5
-a little more burn length making it more can friendly
-I prefer 2 more inches out front to strike with, vs a 10"
-one can still use legacy m203's, and/or if using another 40mm I prefer the m4 barrel to project a little bit, unlike on 10"rs
-USGI 14.5" are readily available just need a SOLID shop to chop & thread.
_______________________________________________
Not to thread jack I am considering moding a 14.5 to a 12.5 can anyone tell me if the gas port had to be opened up and if so to what size?
thanks
As others have stated it can/has been done. Just make sure you have someone do it that understands the need to open up your gas port , and if you plan on using a suppressor make sure they thread it right, using a lathe and single point thread tool!
K.L. Davis
08-24-08, 23:15
Barrel length wouldn't have anything to do with that. Twist rate or a poor job of barrel chop might though.
While it may not have much effect in the stated instance, barrel length does have an effect on stability -- bullet stability is a function of how fast the bullet is spinning (and other factors), the rate of spin is measured in RPMs and is determined by:
twist rate and,
velocity <== which is effected by barrel length.
Velocity is also a consideration when calculating drag/BC...
Every formula I know to calculate the proper RoT needs the velocity of the round (Greenhill uses a K factor, but even that is 150 or 180, based again on velocity).
BRAAIJR, going from 14.5 - 12.5 you should be able to leave the port alone. I've done so several times. Going shorter still will require some additional porting.
While it may not have much effect in the stated instance, barrel length does have an effect on stability -- bullet stability is a function of how fast the bullet is spinning (and other factors), the rate of spin is measured in RPMs and is determined by:
twist rate and,
velocity <== which is effected by barrel length.
Velocity is also a consideration when calculating drag/BC...
Every formula I know to calculate the proper RoT needs the velocity of the round (Greenhill uses a K factor, but even that is 150 or 180, based again on velocity).
The reason I don't give too much consideration to length is my unscientific observations of M856 tracer out of the Colt commando barrel. That bullet is about as long as anything out there. This is limited experience for sure.... but I've fired 856 out to where the trace burns out. And you can see that the round stays stable from an 11.5" barrel..... much more so than a 20" barrel with 1/9 twist.
I'd like to try a 10.5" barrel just for the hell of it.
K.L. Davis
08-25-08, 10:25
...And you can see that the round stays stable from an 11.5" barrel.....
Like I said, in the topic of this thread, the effect of barrel length probably has zero effect, but barrel length can not be dismissed as having *no* effect...
...just saying.
BRAAIJR, going from 14.5 - 12.5 you should be able to leave the port alone. I've done so several times. Going shorter still will require some additional porting.
Can you recommend a good Barrel Shop to do the cutting? Looking for a shop with a good turn around time?
Can you recommend a good Barrel Shop to do the cutting? Looking for a shop with a good turn around time?
I give mine to a local gunsmith/machinist & he's takes anywhere from 2 weeks to a few months depending on workload.
Just got my Colt Commando upper. As new condition complete w/b&bc assembly.
Can't complain about the price either.$525 to my door!
Just got my Colt Commando upper. As new condition complete w/b&bc assembly.
Can't complain about the price either.$525 to my door!
That's the exception. That's almost half the market price of a new condition Colt commando upper.
Just a short update.
Last week I went to shoot it using a used standard contract b/bc assembly & was having it short stroke & dbl feed. Today I put the Colt assembly back in & same thing. I pulled the extractor & the spring had a blue buffer. After replacing the extractor spring with a gold spring & black buffer, the gun now rocks. It Didn't skip a beat with about 350 rds of grungy old quat surplus.
Wanted to add that I'm also running a H buffer.
Does anyone have any pics of a M4 barrel shortened to 12.5 in the manner described? I have seen the pics of the shortening of the barrel Vltor did for their flash suppressor that incorporates the mounting shoulder for the M203 into it's rear dimension.
I am curious what this would look like leaving enough shoulder on the barrel itself for a standard A2 bird cage flash suppressor and still be able to mount the 203, preferably with the quick detach latch.
IPSC_GUY
SIERRA II ALPHA
Robb Jensen
01-19-09, 22:03
Does anyone have any pics of a M4 barrel shortened to 12.5 in the manner described? I have seen the pics of the shortening of the barrel Vltor did for their flash suppressor that incorporates the mounting shoulder for the M203 into it's rear dimension.
I am curious what this would look like leaving enough shoulder on the barrel itself for a standard A2 bird cage flash suppressor and still be able to mount the 203, preferably with the quick detach latch.
IPSC_GUY
SIERRA II ALPHA
My 12.5" SBR, a customer of mine gave me a 200 round old 14.5" Bushmaster barrel that he messed up the threads on and I had it cut to 12.5" and rethreaded.
Early on with a VLTOR flash hider.
http://img.photobucket.com/albums/v408/gotm4/gunpics/e3958dad.jpg
Currently.
http://img.photobucket.com/albums/v408/gotm4/gunpics/IMG_6022.jpg
http://img.photobucket.com/albums/v408/gotm4/brownSBR002.jpg
COOL ! ! ! That is what I was looking for. About how much shoulder did you leave 1/4 of an inch or so?
IPSC_GUY
SIERRA II ALPHA
Robb Jensen
01-21-09, 07:47
COOL ! ! ! That is what I was looking for. About how much shoulder did you leave 1/4 of an inch or so?
IPSC_GUY
SIERRA II ALPHA
Just eyeballing it it's about 3/16" or so.
My 12.5" SBR, a customer of mine gave me a 200 round old 14.5" Bushmaster barrel that he messed up the threads on and I had it cut to 12.5" and rethreaded.
How do you like that Bushmaster barrel? Have you shot it enough to formulate an opinion on it?
Robb Jensen
01-21-09, 13:18
How do you like that Bushmaster barrel? Have you shot it enough to formulate an opinion on it?
It's working out fine, shoots reliably and is pretty accurate. The balance is nice. I do wish it was a faster twist so that I could utilize my stash of 75gr and 77gr ammo.
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