14.5 or 14.7 Reliability with Mid-Length Gas System


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Lou McGopher
February 2, 2012, 01:12 PM
I'm thinking of getting a MLGS 14.5 or 14.7 complete upper from PSA or DSA. I've had a few people recommend them to me. But I've also seen several complaints about short-stroking or extraction problems with lower-powered loads, although I've read the carbine length gas system was originally for 10-12" barrels. I'm wondering what experiences THR members with this setup have had using lighter loads. I don't want to buy one if manufacturers haven't quite figured out how to make them work right. Poll above. Discuss below. Thank you!

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C-grunt
February 2, 2012, 01:17 PM
From what I have read it is a smooth shooting setup but pretty much requires you to use full powered .223 or 5.56.

Z-Michigan
February 2, 2012, 02:25 PM
From what I have read it is a smooth shooting setup but pretty much requires you to use full powered .223 or 5.56.

I've read the same thing and it seems to be about the "common wisdom" now for this arrangement.

The 14.5" is not overgassed with a carbine length gas system, unlike the 16" where it's less than ideal. That's not to say that a 14.5" midlength is a bad idea, just that it's aiming for a fairly small niche.

243winxb
February 2, 2012, 03:11 PM
I've read the carbine length gas system was originally for 10-12" barrels. In 1979 Colt M16A1 carbines were 14 1/2"

wnycollector
February 2, 2012, 04:33 PM
From what I have read it is a smooth shooting setup but pretty much requires you to use full powered .223 or 5.56.

I have a BCM 14.5" middy and it's a very smooth shooting little carbine. I have put ~2500 rounds through it over the past 18 months. Of that 2500 rounds only ~500 rounds have been full power (IMI M193). The other 2K have been a mix of Brown and Silver Bear 55 and 62gr FMJ and WPA 55gr FMJ. I have never had a single incident where there was a FTF or FTE. As with everything YMMV.

dmancornell
February 2, 2012, 04:41 PM
Sample size of 1, my DD 14.5" middy has digested 2k rounds of PMC and S&B .223 ammo with no issue.

Lou McGopher
February 2, 2012, 10:42 PM
IDK that I would use Wolf in it. Brown/Silver Bear sounds better... But if other people don't have problems using Wolf in it, that's a good sign.

Tirod
February 3, 2012, 11:42 AM
As a SBR requiring BATF approval, it's a niche gun. With a pinned flash hider to make the NFA, there's no point in bothering.

Not that some don't have the need, but it wasn't explained why a 14.5 would be the preferred barrel length to choose. Since there have been some legitimate question whether the reduced range is appropriate in open country, it's a compromising feature for overall use.

M4's in vehicles or as a PDW for non combatants are valid, as an LEO duty gun, not so much, for civilian use, have significant power and range limitations for sporting or hunting purposes - in general. Three gunners don't seem to have bothered, even with most shots on short range situations. Out to 200 is about it, yet they trend to 16 18" barrels.

For all that, carbine gas on 14.5, with full power ammo the way it is designed to be used, it about the only way to get it. From there, a bit of tuning is ok, but too many tinker with it rather than just use the correct ammunition - which is where most of the complaints come from.

The specifics of the design use the one ammo it's designed for - full power military loads. If the budget and ballistics fit, then it's an appropriate choice. Often, it's just to own one.

Destructo6
February 3, 2012, 01:36 PM
Jim Sullivan, in a SAR article, stated that the M16 DI system needs abouy 7" of barrel in front of the gas port to be reliable.

The M16 series was set up that way with a rifle length gas system and the M4 series is such with a carbine gas system.

Anything less and reliability can be expected to suffer.

JustinJ
February 3, 2012, 02:20 PM
Do all 14.5 barrels on the market have the same sized gas port? If not this would likely explain variances in reliability with "under powered" ammo.

goon
February 3, 2012, 02:42 PM
I've been doing some reading and although I've never even held a 14.5 inch Midlength, I've read that by switching to a lighter buffer you can often get marginal powered ammo to cycle properly.

If you like the extra sight radius of a midlength but want the reliability of a carbine gas system in that barrel length, you might consider one of the Dissipator set ups that PSA is making.

Lou McGopher
February 3, 2012, 02:42 PM
As a SBR requiring BATF approval, it's a niche gun. With a pinned flash hider to make the NFA, there's no point in bothering.

Not that some don't have the need, but it wasn't explained why a 14.5 would be the preferred barrel length to choose.

It'd be a bit shorter than a 16" barrel with a flash hider. And many owners of the 14.5 mids report it to be lower recoil, aiding in followup shots.

Still, it's much easier to find quality, competitively priced 16" mids and 14.5" carbines. I am thinking the 14.5" mid isn't worth the hassle and risk.

243winxb
February 3, 2012, 03:04 PM
http://www.brownells.com/.aspx/pid=7592/Product/AR-15-M16-ADJUSTABLE-GAS-BLOCK The gas port pressure curve is a critical part of internal ballistics for cartridges used in gas operated firearms. Gas operated weapons are generally tailored to a narrow range of powder burning rates and characteristics. If the port pressure is too low the weapon will fail to function and if to high the weapon may function too forcefully or rapidly causing extraction or cycling problems. When using the fast H4198, the pressure peaks very fast and is done producing pressure sooner than your slow powders. With such a wide range of bullet weights from 40gr to 80gr, matching the gas port location and size is critical. If the gas port was moved closer to the chamber and drilled larger, H4198 would work. Quote from > http://www.thehighroad.org/showthread.php?t=502784

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