Calguns.net  

Home My iTrader Join the NRA Donate to CGSSA Sponsors CGN Google Search
CA Semiauto Ban(AW)ID Flowchart CA Handgun Ban ID Flowchart CA Shotgun Ban ID Flowchart
Go Back   Calguns.net > INTERESTS AND ACTIVITIES > Gunsmithing & How To
Register FAQ Members List Calendar Mark Forums Read

Gunsmithing & How To Pro, Amateur & WECSOG and Tutorials, Guides & OLL Build Instructions

Reply
 
Thread Tools Display Modes
  #1  
Old 07-17-2013, 10:22 PM
repoman1984's Avatar
repoman1984 repoman1984 is online now
Senior Member
 
Join Date: Jun 2009
Location: West Los Angeles
Posts: 814
iTrader: 12 / 100%
Default Cutting a 16" AR barrel to pistol length?

To be clear I'm talking about a freash unmated 16" approximately upper and a freash out of the mill pistol lower so no legal debate please : ).


Lets say I take a 16" upper and cut it RIGHT after the front sight, file it square, crown it with a ball bearing and some grinding paste. Will it cycle? is accuracy going out the window?
__________________
If you want to stop me from enjoying life you'd better bring an anti-aircraft gun, a mac truck and a deity that takes requests.
-Repoman1984
Reply With Quote
  #2  
Old 07-17-2013, 10:31 PM
NoNOS67's Avatar
NoNOS67 NoNOS67 is offline
Senior Member
 
Join Date: Aug 2008
Location: San Diego, CA
Posts: 2,162
iTrader: 25 / 100%
Default

Might not be enough barrel after the gas block.

Last edited by NoNOS67; 07-17-2013 at 10:35 PM..
Reply With Quote
  #3  
Old 07-17-2013, 10:37 PM
repoman1984's Avatar
repoman1984 repoman1984 is online now
Senior Member
 
Join Date: Jun 2009
Location: West Los Angeles
Posts: 814
iTrader: 12 / 100%
Default

Is there some kind of formula on this? The shorty uppers I see have 2" and a flash hider.
__________________
If you want to stop me from enjoying life you'd better bring an anti-aircraft gun, a mac truck and a deity that takes requests.
-Repoman1984
Reply With Quote
  #4  
Old 07-17-2013, 10:45 PM
hermosabeach's Avatar
hermosabeach hermosabeach is offline
Calguns Addict
 
Join Date: Feb 2009
Posts: 9,262
iTrader: 7 / 100%
Default

In general you want a faster twist rate for shorter barrels.

1:9 twist in an 20-24" will stabalize most weights
The M4 with the 14 1/2" uses the 1:7 twist

I would look at the factory pistol uppers and the twist rate to see how your barrel compares to see if it will stabalize the round.
__________________
Reply With Quote
  #5  
Old 07-17-2013, 10:46 PM
NoNOS67's Avatar
NoNOS67 NoNOS67 is offline
Senior Member
 
Join Date: Aug 2008
Location: San Diego, CA
Posts: 2,162
iTrader: 25 / 100%
Default

I know I saw the numbers somewhere here...

Haven't finished building my pistol yet, but have heard they can be a bit temperamental. Aside from wanting to use what your already have, is there any reason you don't just but a pistol upper?
Reply With Quote
  #6  
Old 07-17-2013, 10:50 PM
repoman1984's Avatar
repoman1984 repoman1984 is online now
Senior Member
 
Join Date: Jun 2009
Location: West Los Angeles
Posts: 814
iTrader: 12 / 100%
Default

Quote:
Originally Posted by NoNOS67 View Post
I know I saw the numbers somewhere here...

Haven't finished building my pistol yet, but have heard they can be a bit temperamental. Aside from wanting to use what your already have, is there any reason you don't just but a pistol upper?
To be honest not really been planning a pistol build for a LONG time the thought of finding a cheap used carbine upper and making a project of it crossed my mind.
__________________
If you want to stop me from enjoying life you'd better bring an anti-aircraft gun, a mac truck and a deity that takes requests.
-Repoman1984
Reply With Quote
  #7  
Old 07-18-2013, 12:07 AM
ar15barrels's Avatar
ar15barrels ar15barrels is offline
I need a LIFE!!
 
Join Date: Jan 2006
Location: Van Nuys
Posts: 38,059
iTrader: 88 / 100%
Default

Quote:
Originally Posted by repoman1984 View Post
Lets say I take a 16" upper and cut it RIGHT after the front sight, file it square, crown it with a ball bearing and some grinding paste. Will it cycle?
The short answer is NO.

It generally takes 3" of barrel beyond a carbine gas system gas port to run reliably.
A carbine gassed barrel cut at the front of the FSB would end up with about 1.7" past the gas port.
__________________
Randall Rausch

AR work: www.ar15barrels.com
Bolt actions: www.700barrels.com
Foreign Semi Autos: www.akbarrels.com
Glock, XD and M&P pistols, Benelli and Remington shotguns: barrel, sight, trigger and receiver work.
Most work performed while-you-wait, evening and weekend appointments available.
Founding member of the CAPRC
Reply With Quote
  #8  
Old 07-18-2013, 12:12 AM
repoman1984's Avatar
repoman1984 repoman1984 is online now
Senior Member
 
Join Date: Jun 2009
Location: West Los Angeles
Posts: 814
iTrader: 12 / 100%
Default

Quote:
Originally Posted by ar15barrels View Post
The short answer is NO.

It generally takes 3" of barrel beyond a carbine gas system gas port to run reliably.
A carbine gassed barrel cut at the front of the FSB would end up with about 1.7" past the gas port.
What do I end up with if I chop 3.5" past the gas port?
__________________
If you want to stop me from enjoying life you'd better bring an anti-aircraft gun, a mac truck and a deity that takes requests.
-Repoman1984
Reply With Quote
  #9  
Old 07-18-2013, 10:30 PM
ar15barrels's Avatar
ar15barrels ar15barrels is offline
I need a LIFE!!
 
Join Date: Jan 2006
Location: Van Nuys
Posts: 38,059
iTrader: 88 / 100%
Default

Quote:
Originally Posted by repoman1984 View Post
What do I end up with if I chop 3.5" past the gas port?
11.3"
__________________
Randall Rausch

AR work: www.ar15barrels.com
Bolt actions: www.700barrels.com
Foreign Semi Autos: www.akbarrels.com
Glock, XD and M&P pistols, Benelli and Remington shotguns: barrel, sight, trigger and receiver work.
Most work performed while-you-wait, evening and weekend appointments available.
Founding member of the CAPRC
Reply With Quote
  #10  
Old 07-20-2013, 11:34 PM
Seesm's Avatar
Seesm Seesm is offline
Calguns Addict
 
Join Date: Nov 2008
Posts: 7,921
iTrader: 50 / 100%
Default

You can play with gas port sizes to make it cycle right.
__________________
Machining, Fabrication, Welding (All metals), Mini 14 / Mini 30 Magazine locks, AR15/M16/AR10 Sling loop plates, Muzzle brakes, Motorcycle parts, Bobcat tractor work.

DefenseIndustries.US
Auburn, CA
Reply With Quote
  #11  
Old 07-21-2013, 10:22 AM
ar15barrels's Avatar
ar15barrels ar15barrels is offline
I need a LIFE!!
 
Join Date: Jan 2006
Location: Van Nuys
Posts: 38,059
iTrader: 88 / 100%
Default

Quote:
Originally Posted by Seesm View Post
You can play with gas port sizes to make it cycle right.
Not when you get to only 1.5" of barrel past the gas port which is what you have if you cut flush to the FSB.

Perhaps a piston system could work with that little barrel past the port, but a DI system won't.
__________________
Randall Rausch

AR work: www.ar15barrels.com
Bolt actions: www.700barrels.com
Foreign Semi Autos: www.akbarrels.com
Glock, XD and M&P pistols, Benelli and Remington shotguns: barrel, sight, trigger and receiver work.
Most work performed while-you-wait, evening and weekend appointments available.
Founding member of the CAPRC
Reply With Quote
  #12  
Old 07-21-2013, 10:54 AM
SOAR79 SOAR79 is offline
Veteran Member
 
Join Date: Jan 2013
Location: LA,IE,SD
Posts: 2,987
iTrader: 3 / 100%
Default

i've wondered about this as well. While looking for pistol length barrels i've noticed that they are wayyyyy pricier
Reply With Quote
  #13  
Old 07-21-2013, 12:19 PM
big ron's Avatar
big ron big ron is offline
Senior Member
 
Join Date: Jan 2010
Location: rancho cucamonga, ca.
Posts: 778
iTrader: 48 / 100%
Default

I have one that's 2 1/2" from center of gas port to the end of the barrel, with a YHM flip up sight and a bird cage flash hider. so about 3 1/2" from center of gas port to the end of the FH. runs like a champ, I have run cheap and good ammo
__________________
"I pledge allegiance to the Flag of the United States of America and to the Republic for which it stands, one nation, indivisible, with liberty and justice for all."
Reply With Quote
  #14  
Old 07-22-2013, 10:35 AM
OffGrid's Avatar
OffGrid OffGrid is offline
Member
 
Join Date: Feb 2009
Location: San Migetto-CentralCoast
Posts: 274
iTrader: 0 / 0%
Default

I will have to go measure my pistols.

My 7.5 is definitely pistol length gas but I am pretty sure both of my 10.5 are carbine length gas and they run any and everything I put in them. Took some tuning but they are GTG now.

My first 10.5 is a YHM 1/9 barrel i've had for about a year and a half and the newer one i've only had a short while but both are running good.

Decent accuracy as well. In addition to some movable stands for shorter distances I have 6 & 10 steel plates and a steel body silhouettes set up at 100 yards and can tear up the 6 all day long with just a red dot. Not bad for 7.5 and 10.5 barrels if you ask me.

Yes I run heavier buffers and the BCM extractor upgrades.
Reply With Quote
  #15  
Old 07-23-2013, 2:44 PM
OffGrid's Avatar
OffGrid OffGrid is offline
Member
 
Join Date: Feb 2009
Location: San Migetto-CentralCoast
Posts: 274
iTrader: 0 / 0%
Default

Finally checked. The YHM is 2&3/4" from gas port to end of threads.
Reply With Quote
  #16  
Old 07-26-2013, 1:25 PM
repoman1984's Avatar
repoman1984 repoman1984 is online now
Senior Member
 
Join Date: Jun 2009
Location: West Los Angeles
Posts: 814
iTrader: 12 / 100%
Default

OK question part 2: a 9mm AR is strait blowback so barrel length would have very little effect on reliably cycling as long as its not ridiculously short say less than 5"? Am I correct?
__________________
If you want to stop me from enjoying life you'd better bring an anti-aircraft gun, a mac truck and a deity that takes requests.
-Repoman1984
Reply With Quote
  #17  
Old 07-26-2013, 3:11 PM
ar15barrels's Avatar
ar15barrels ar15barrels is offline
I need a LIFE!!
 
Join Date: Jan 2006
Location: Van Nuys
Posts: 38,059
iTrader: 88 / 100%
Default

Quote:
Originally Posted by repoman1984 View Post
OK question part 2: a 9mm AR is strait blowback so barrel length would have very little effect on reliably cycling as long as its not ridiculously short say less than 5"? Am I correct?
Correct.
5" is fine.

I have not seen any sold that were shorter than 5", but a 3" should run fine too.
__________________
Randall Rausch

AR work: www.ar15barrels.com
Bolt actions: www.700barrels.com
Foreign Semi Autos: www.akbarrels.com
Glock, XD and M&P pistols, Benelli and Remington shotguns: barrel, sight, trigger and receiver work.
Most work performed while-you-wait, evening and weekend appointments available.
Founding member of the CAPRC
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump



All times are GMT -8. The time now is 11:25 PM.




Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2016, vBulletin Solutions, Inc.
Proudly hosted by GeoVario the Premier 2A host.
Calguns.net, the 'Calguns' name and all associated variants and logos are ® Trademark and © Copyright 2002-2016, Calguns.net an Incorporated Company All Rights Reserved.