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Posted: 12/28/2005 4:36:30 AM EDT
I'm considering cutting a 20" HBAR barrel down to 18" and having the barrel re-profiled (gov't profile).

I'll be using the rifle length gas system and the standard rifle buffer tube and buffer. Are there any issues I should be aware of with this set up (reliability, etc)?

Let's see some pics of 18" barrels with rifle length gas systems

Link Posted: 12/28/2005 5:17:02 AM EDT
[Last Edit: 12/29/2005 9:40:58 PM EDT by CK]
Here's my standard looking rig with a 18 inch SPR barrel and DCM float tube that was built by WOA -

Link Posted: 12/28/2005 5:23:32 AM EDT
When I started my SPR project over year ago I was thinking about this same problem. I contacted ADCO and they forwarded my email to Mr Holliger who obviously has lots of experience with SPR barrels.
Mr Holliger told they are using .106" gas ports on their barrels.

I decided to start with tad bit smaller drill. It´s easier to drill bigger gas port than try to make it smaller.
After phosphatizing process I drilled .102" gas ports on each barrel and they were ready to testing. I had few failures to eject during first 50 round test session on each barrel but reason for this was only in chambers I did not polish.
After that I have had couple of short strokes with IMI M855 Ball, bolt doesn´t lock back but takes fresh round from magazine, so the gas port should be opened little more.
However, this same problem has occured with my 20" Gov´t Profile Bushmaster. Rifle is on box stock condition except KAC M5 RAS, go figure...

Maybe SPR gas port should be opened a tad more but since it works just fine with Sierra 77gr handloads and rifle was build purely for precision I´m not going to fix it.







MN
Link Posted: 12/28/2005 5:59:21 AM EDT
[Last Edit: 12/28/2005 5:59:58 AM EDT by C4iGrant]
Link Posted: 12/28/2005 6:00:52 AM EDT
Kurts Kustom does fabulous work. see www.KurtsKustomFirearms.citymax.com
He has modified a whole bunch of ARs for me.
Link Posted: 12/28/2005 6:04:32 AM EDT
M4A2.....Bother those are sweet looking. You gave me an idea. Damn You.
Link Posted: 12/28/2005 7:17:39 AM EDT
Jeff,
I have a 16" barrel using the rifle length gas system. The gas port had to be opened up a bit to 0.110 (an increase of 0.016") but she runs fine. I'd think with the 18" you might be able to get by w/o tweaking the port.
Link Posted: 12/28/2005 7:31:13 AM EDT

Originally Posted By Forest:
Jeff,
I have a 16" barrel using the rifle length gas system. The gas port had to be opened up a bit to 0.110 (an increase of 0.016") but she runs fine. I'd think with the 18" you might be able to get by w/o tweaking the port.



<--trying to learn

Is it the problem of the gas traveling the length of the rifle gas tube? Or...?

Why would you need to open it up as small as above?
Link Posted: 12/28/2005 7:41:07 AM EDT

Originally Posted By chromeluv:

Is it the problem of the gas traveling the length of the rifle gas tube? Or...?


Lack of dwell time. (time bullet is in the barrel between the gas port and the muzzle) A lower dwell time reduces the amount of gas that is channeled back to the bolt carrier.



Why would you need to open it up as small as above?



It needs to be opened up to get enough gas back to the BCG to operate the rifle. Remember the gas is pretty high pressure so a small increase in the diameter results in alot more gas going back.
Link Posted: 12/28/2005 7:50:28 AM EDT
[Last Edit: 12/28/2005 7:51:07 AM EDT by chromeluv]

Originally Posted By Forest:

Originally Posted By chromeluv:

Is it the problem of the gas traveling the length of the rifle gas tube? Or...?


Lack of dwell time. (time bullet is in the barrel between the gas port and the muzzle) A lower dwell time reduces the amount of gas that is channeled back to the bolt carrier.



Why would you need to open it up as small as above?



It needs to be opened up to get enough gas back to the BCG to operate the rifle. Remember the gas is pretty high pressure so a small increase in the diameter results in alot more gas going back.



Forrest,
thanks for making that simple.
Is it a safe to say all/most 18inch between 20inch barrels with rifle gas locations, will need their gas ports widended?
Link Posted: 12/28/2005 7:56:24 AM EDT

Originally Posted By chromeluv:
Is it a safe to say all/most 18inch between 20inch barrels with rifle gas locations, will need their gas ports widended?



Not sure what you are trying to say here.

20" barrells cut to 16" will need their port opened up to operate reliably with a wide variety of ammo and temperture conditions. Some people do get by w/o opening the port using only M193 (military pressure) and in warmer climates.

At 18" I'm thinking you could get by based on the increase in dwell time. But that's a guess. I'd say cut then test before playing with the gas port size.
Link Posted: 12/28/2005 8:03:00 AM EDT

Originally Posted By Forest:

Originally Posted By chromeluv:
Is it a safe to say all/most 18inch between 20inch barrels with rifle gas locations, will need their gas ports widended?



Not sure what you are trying to say here.

20" barrells cut to 16" will need their port opened up to operate reliably with a wide variety of ammo and temperture conditions. Some people do get by w/o opening the port using only M193 (military pressure) and in warmer climates.

At 18" I'm thinking you could get by based on the increase in dwell time. But that's a guess. I'd say cut then test before playing with the gas port size.



Reason I asked, I got in on an ABS carbon fiber wrapped barrel,it is 18standard, then add the FH on the front, increases its size to just be approx just below 20inch. I know the FH has no determining factor on the gas movement up the gas tube but that is why I put between 18-20 to see if I needed to 'learn' some mroe

Link Posted: 12/28/2005 8:56:10 AM EDT

Originally Posted By chromeluv:
Reason I asked, I got in on an ABS carbon fiber wrapped barrel,it is 18standard, then add the FH on the front, increases its size to just be approx just below 20inch. I know the FH has no determining factor on the gas movement up the gas tube but that is why I put between 18-20 to see if I needed to 'learn' some mroe




Two points here.
1) Flash Supressors are not included in this discussion because they don't add to the dwell time.

2) You are ordering a custom barrel - the 'smith should know how large to drill the gas port to get reliable operation. Jeff's comment is more on cutting down a 20" to 18" - so you're changing part of the equation. You are having a barrel built for 18" from the get-go that is very different.
Link Posted: 12/28/2005 9:14:54 AM EDT
Nice pics gents. Keep them coming!


The project that I have in mind is taking a AR15A2 HBAR, having the barrel reprofiled close to gov't profile under the handguards and having the barrel cut down to 18".

I'll be running an A2 stock (rifle buffer and buffer tube).

Link Posted: 12/28/2005 9:17:32 AM EDT
Like this (only the barrel will stick out 2" more)?

Link Posted: 12/28/2005 9:29:53 AM EDT
Link Posted: 12/28/2005 9:33:22 AM EDT

Originally Posted By BRONZ:
M4A2.....Bother those are sweet looking. You gave me an idea. Damn You.



Pleasure is all mine...

MN
Link Posted: 12/28/2005 9:38:48 AM EDT

Originally Posted By USMC03:
Nice pics gents. Keep them coming!


The project that I have in mind is taking a AR15A2 HBAR, having the barrel reprofiled close to gov't profile under the handguards and having the barrel cut down to 18".

I'll be running an A2 stock (rifle buffer and buffer tube).



I forgot to mention I´m using heavy steel buffers (5.54- 5.76 oz) on my builds, so with standard rifle buffer (5.15 oz)your shortened should run fine.

MN
Link Posted: 12/28/2005 11:37:48 AM EDT
I have a barrel coming that was a 20" govt. profile cut to 18". Seller says with port at .090 it is reliable with nato spec and S&B. will find out how it runs once it gets here. Will go on a collapsible stock with standard carbine buffer.

Nick
Link Posted: 12/28/2005 3:39:43 PM EDT
I cut down a 20" HBAR myself to 18", it ran fine with no mods to the port. My SPR sports an 18" barrel from CLE, no idea on the port size, but it runs fine w/ 77 GR BH SMK's (never tried M193 in it )
Link Posted: 12/28/2005 3:52:21 PM EDT
I hate it when Grant shows a pic of that rifle Everytime he does that, I have to hide my CC. GRANT STOP IT !
Link Posted: 12/28/2005 3:57:54 PM EDT

Originally Posted By bsbg:
I cut down a 20" HBAR myself to 18", it ran fine with no mods to the port. My SPR sports an 18" barrel from CLE, no idea on the port size, but it runs fine w/ 77 GR BH SMK's (never tried M193 in it )



No pics?!?!? You have let me down bsbg



Link Posted: 12/28/2005 4:31:59 PM EDT

Originally Posted By USMC03:

No pics?!?!? You have let me down bsbg






I lost the pics of the chop job in a hard drive episode, but managed to find this on for you:



Link Posted: 12/28/2005 4:34:13 PM EDT
Link Posted: 12/28/2005 5:36:26 PM EDT
[Last Edit: 12/28/2005 5:45:14 PM EDT by ALAN308]



Link Posted: 12/28/2005 5:40:54 PM EDT



Adco built RRA 18" upper with standard gas port
Link Posted: 12/28/2005 9:08:05 PM EDT
[Last Edit: 12/29/2005 5:39:43 PM EDT by mr_h]
i have a bushy 20" gov barrel cut back to 18" . it ran fine with full pressure ammo but on a cool AZ winter day and winchester white box q3131 it short stroked a few times. i opened the gas port to .090" and the problem went away. that was using a carbine stock and an H buffer.

here is a WOA SPR barrel that eats everything thrown at it,,


here's the bushy that was cut back to 18",,
Link Posted: 12/29/2005 8:12:01 AM EDT
I have to say, IMHO, the 18 ooks better than the 20". This coming from a guy who's other AR is a 14.5" HBAR...seems I like the slightly shorters.

Nick
Link Posted: 12/29/2005 8:39:36 AM EDT
Link Posted: 12/31/2005 1:34:21 AM EDT
Had a 20" Gov't profile cut to 17" with no gas port work done for a truck gun build. Running a standard buffer in a collapsible stock. FA CMT BCG. Functioned fine with XM193 and Q3131A. Bolt would lock back. Tried Federal American Eagle 55gr, Winchester 55gr white box(from Walmart not nato pressure stuff), and BH 52 gr SP- wouldn't lock the bolt back. This was at appproximately 55 deg. So colder weather would only be worse. Glad I didn't get a chance to try it in colder weather. I might have been disheartened. I need to pull it apart and open up the gas port. The AE lot I have is pretty weak, so if it will work with that then it should be GTG.
Link Posted: 12/31/2005 3:56:00 AM EDT
Link Posted: 12/31/2005 5:30:11 AM EDT
Graeat looking stick Grant. I was considering something like that for my next build. Only in 6.8.
Link Posted: 12/31/2005 7:02:15 AM EDT
Link Posted: 1/1/2006 9:52:30 PM EDT
Link Posted: 1/21/2006 5:15:57 AM EDT
tag
Link Posted: 1/21/2006 5:21:15 AM EDT
[Last Edit: 1/21/2006 5:25:30 AM EDT by dennysguns]
Link Posted: 1/26/2006 12:27:40 AM EDT
Here's my baby. It's my main competition/teaching rifle. The optic on it in this picture is old. I run a TA-11 w/ JPoint for 3-Gun and a TA01NSN w/ JPoint for teaching.



SPC Richard A. White, Senior Medic
249th MP Detachment (EACF)
Camp Humphreys, ROK
Link Posted: 1/26/2006 2:41:16 AM EDT
Mine is oh-so-plain, but I like it like that....



It's a Bushy, turned back to muzzle diameter under the HG's, and has an Izzy brake (opened up on the muzzle). Very light and handy.
Link Posted: 1/26/2006 3:27:52 AM EDT
[Last Edit: 1/26/2006 3:30:27 AM EDT by peasant]
My rifle (sorry no pic) has a Bushmaster 20" chrome lined cut to 18" w/o opening the gas port. NO problems with any ammo I've tried in temps down to 30 degrees. With a float tube and A2 FH it shoots 3/4 MOA-honest. Yesterday it shot WELL under 2" with Win Varmint 45 gr. at 275 yds! I am absolutely sold on the 18" barrel length. VERY handy. Still heavy but I'm afraid to have it reprofiled to gov spec because I don't want to jeopardize it's accuracy. I presently have 250 rounds thru it and am monitoring it for any accuracy loss due to flaking of the chrome at the muzzle. If it goes to 1000 rnds. and holds I figure I'm good.
Link Posted: 1/26/2006 5:34:17 AM EDT
My 20" DPMS stainless barrel, cut back to 18" & reprofiled to .750 under the handguards. Points and shoots almost like a carbine with the lightweight carbon fiber tube, but softer and flatter feeling with the extra barrel length (and the Benney Cooley comp doesn't hurt either). Tryiing to get a TA11 for it to finsh it off. Got a Weaver GS 1.5-6X on there now.

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