User Panel
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 |
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Kurts Kustom does fabulous work. see www.KurtsKustomFirearms.citymax.com
He has modified a whole bunch of ARs for me. |
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M4A2.....Bother those are sweet looking. You gave me an idea. Damn You.
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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. |
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<--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? |
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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.
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. |
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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? |
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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. |
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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 |
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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. |
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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). |
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Yes |
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Pleasure is all mine... MN |
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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 |
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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 |
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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 )
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I hate it when Grant shows a pic of that rifle Everytime he does that, I have to hide my CC. GRANT STOP IT !
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No pics?!?!? You have let me down bsbg |
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To make it even better (or worse) it is now sporting the new Tango Down Bipod. C4 |
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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 |
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Here is my gas systems page showing different length barrels and gas systems drawn to scale.
The bottom text explains some about how gas systems work and what to do when you are using a non-standard setup. |
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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.
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Graeat looking stick Grant. I was considering something like that for my next build. Only in 6.8.
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Thanks. C4 |
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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.
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