Cutting 11.5" Barrel To 10.5"

[Joeywhat]

First off, search function seems to be broken, it won't let me search...

I'm looking to start a pistol AR build. Here in the great state of Michigan SBR's are verboten, so this will have to do. Roughly planning on a 10.5" barrel, normal length receiver extension, all high quality stuff. Want this thing to run like a top.

I was going to go with BCM because they are quality and are priced right. Probably is it doesn't look like they have 10.5" barrels. Is it wise to cut down either an 11.5 or 12.5" barrel to 10.5", or should I get a different brand?

My concern is that with the short barrel the gas system may not be set up the same for the 10.5/11.5/etc. Swapping buffers is easy but I don't care to have to screw with the gas port or anything. If this is NOT a good idea, what is a good complete (no BCG, handguards OK) upper for a comparable price to BCM's offerings?

FWIW this will most likely have a KX3 on the end, if it makes a difference.

[Col_Crocs]

For the same quality, DD has 10.3 hammer forged barrels.
Noveske has 10.5 full uppers in different configs, including one with the KX3 package. higher Spec'd barrels but higher priced as well.
http://www.rainierarms.com/?page=sho...uppers_noveske

If I may ask, why a 10.5 over an 11.5?

[superchi]

Just curious why you'd want to cut down the 1" from a 11.5" upper?

It's reported that 11.5" rifles run much more reliably than 10.5", there's a review and explanation of it over on arfcom by Bravo Company USA:

Q: Why BCM chose the 11.5" SBR over the 10.5"

I get this question a lot. It is a good one. When we spec our program we can build anything we would like, so we sat down and looked at the pros and cons.

First Statement: I know a good 10.5" SBR can run very well. I personally own a semi MK18 type and it runs great. No problems.

A: Dwell time.
Dwell time is the time that your gas operated weapon maintains pressure to continue the cycling of the weapon. It primarily exsists from the time the bullet passes the gas port in the barrel to the time the bullet exits the muzzle. When you pull the trigger and fire the weapon the movement of the bolt carrier group unlocks the bolt, extracts, and ejects the spent casing. Then it cocks the weapon, feeds, chambers the next round, and then locks again. One of the thing that can make SBRs finicky is the dwell time (or lack of).

The 11.5" carbine is approximately 4% longer weapon than its' 10.5" counterpart, but this extra inch gives the barrel a 40% increase in length for dwell time. IMHO, this is an excellent trade off. This additional dwell time (all other things being equal) will allow the carbine to be more forgiving to different ammo types, extremes in air temperature, weak or worn extractor springs, worn extractors, buffer weights, etc.

Last Statement: For those folks who have a 10.5" that works very well, I would reply; me too. (see first statement)

If I had to "go to war" with a AR15 Carbine, I would grab the BCM 11.5".
The BCM 11.5" Runs Like a Dream.

Hope this info helps,
Paul

Instead of cutting down an upper, check out factory built 10.5"/10.3" uppers from reputable companies like Noveske, LMT, and CMMG (CMMG offers the 10.3"). LMT uppers are usually sold without BCGs and handguards at similar prices to BCM uppers, where from what I see Noveske and CMMG sell only complete uppers.

In regards to the Noveske KX3 flash suppressors, they supposedly improve cycling in SBR uppers by increasing backpressure. There are also claims that they mitigate recoil. It's also fairly long and fairly heavy for a muzzle device. What's your reason for wanting one? Reliability? Looks? Fireball flash signature?

I personally have a 10.5" LMT SBR that runs just fine with a M16 carrier, H buffer, unaltered gas system, and a AAC Blackout flash hider.

[Joeywhat]

Overall length, and cosmetics.

If it comes to it I'll just order an 11.5 and keep it stock if it's all I can get in that price range.

Basically I'm going to run a 13" rail, which should be just about even with a 10.5" barrel and KX3. Another reason I'd rather have a cut down 11.5" is so that I can have the barrel cut right where I need to, so the pig is just a hair past the end of the rail.

I guess what I really need to know is if the gas port hole is the same on 10.5 and 11.5 barrels. Is the ONLY difference the extra inch in length?

[Joeywhat]

Just curious why you'd want to cut down the 1" from a 11.5" upper?

It's reported that 11.5" rifles run much more reliably than 10.5", there's a review and explanation of it over on arfcom by Bravo Company USA:



Instead of cutting down an upper, check out factory built 10.5"/10.3" uppers from reputable companies like Noveske, LMT, and CMMG (CMMG offers the 10.3"). LMT uppers are usually sold without BCGs and handguards at similar prices to BCM uppers, where from what I see Noveske and CMMG sell only complete uppers.

In regards to the Noveske KX3 flash suppressors, they supposedly improve cycling in SBR uppers by increasing backpressure. There are also claims that they mitigate recoil. It's also fairly long and fairly heavy for a muzzle device. What's your reason for wanting one? Reliability? Looks? Fireball flash signature?

I personally have a 10.5" LMT SBR that runs just fine with a M16 carrier, H buffer, unaltered gas system, and a AAC Blackout flash hider.

My previous post explains most of it...going with the pig mainly for noise, and as a basic flash hider. Having fired a full auto 10.5" AR indoors with an A2 hider, I really want something to help with the blast. I realize it's nothing like a suppressor (also illegal here...) but anything that helps. I also figured it would help the short upper run a little better. Don't really care how it looks, it's a fightin' gun. Function is king here...so if there is no way I can get a 10.5" gun that runs, I'll go with something else.

[superchi]

It's probably safe to assume that the gas port will not be sized exactly the same between different manufacturers and lengths of barrels. Given that, you will still probably be able to achieve reliable function by playing with the buffer weights if you stick with a quality built upper.

The KX3 seems like the ticket for you as the way it handles backpressure and gas as well as its weight may help in mitigating recoil and maintaining controllability during sustained SA or FA fire.

[gunny]

Just curious why you'd want to cut down the 1" from a 11.5" upper?

It's reported that 11.5" rifles run much more reliably than 10.5", there's a review and explanation of it over on arfcom by Bravo Company USA:



Instead of cutting down an upper, check out factory built 10.5"/10.3" uppers from reputable companies like Noveske, LMT, and CMMG (CMMG offers the 10.3"). LMT uppers are usually sold without BCGs and handguards at similar prices to BCM uppers, where from what I see Noveske and CMMG sell only complete uppers.

In regards to the Noveske KX3 flash suppressors, they supposedly improve cycling in SBR uppers by increasing backpressure. There are also claims that they mitigate recoil. It's also fairly long and fairly heavy for a muzzle device. What's your reason for wanting one? Reliability? Looks? Fireball flash signature?

I personally have a 10.5" LMT SBR that runs just fine with a M16 carrier, H buffer, unaltered gas system, and a AAC Blackout flash hider.

I would highly recommend the DD 10.3 over the CMMG 10.3. CMMG is hit or miss on QC & CS. I wouldn't rate CMMG as very reputable when compared to companies like BCM, DD, KAC, Colt, Sabre, etc.

[Joeywhat]

Any other input here?

The more I mull it over and run the measurements, the more I'm thinking an 11.5" barrel with the KX3 and 13" rail would actually work just fine. Looks like a 10.5" barrel would put the KX3 inside the tube...bad juju IMO.

I'm still interested in whether or not this would work, though. I might also consider a Levang comp which seems to be a lot shorter...although I'm not sure if it will be as effective as the KX3.

[one]

You really probably want to pass on this idea. It's not worth it to cut down an inch of barrel.

I run an LMT CQBR upper and as I understand it they modify the gas hole in those to get them to run reliably. You'd probably have to do the same to your gun.

All of the other reasons cited in this thread are totally valid.

[sparky-kb]

I'm bumping this thread because I've recently had the same idea as the OP. Interested to know if the chop ever occurred and how it worked.

I was originally going to get an LMT 10.5 upper and possibly have the .071 gas port opened up a smidge if it needed it in order to run a broader variety of ammo. I've since read that LMT hasn't been know for their threads being very concentric. Also found out that BCM 11.5s have a gas port about the size I was going to open the LMT up to if needed.

The BCM 11.5 gas port is supposed to be .076 from what I've read. That is a number I've heard aids 10.5s reliability with varying ammo without completely over gassing. I do have access to some suppressors but it will be shot mostly unsuppressed for now. Potentially more suppressor use down the road once I get my own.

All that got me thinking about buying a BCM 11.5 (cheaper than the LMT) and having it chopped by a good Smith to ensure the threads are good to go and have my Mk18 RIS installed while it's there.

Gas port would be a bit larger to aid reliability. Threads known to be concentric for suppressor use. Rail installed All of that in one visit to the gunsmith and potentially solving some issues I've read about with LMTs. The issues I'm referring to are bad thread jobs and being picky with any ammo other than hot 5.56 spec.

My main concern is making sure my threads are concentric. No room to re cut a LMT 10.5 if they aren't. Gas port changes are a secondary concern as I wouldn't really know if any changes were needed until doing some shooting with the LMT. Going larger off the bat would be more of a proactive approach.

Any reason that wouldn't work?

Edited to add: Reason I'm set on 10.5 is that I put 10.5 for barrel length when I sent in my paperwork. I don't want to have to change it plus this is my first SBR and I've already got a couple of pinned 14.5s so I want to go as short as I reliably can.