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#6183330 - 02/16/12 12:27 PM Re: Gas piston vs. gas impingement [Re: tex_n_cal]
XL5 Offline
Campfire Regular

Registered: 06/14/11
Posts: 645
Loc: East of the Sun, West of the M...
All gas operated guns have to poop somewhere.

Direct Impingement poops where it eats, but it's in a location that at least is convenient to clean up after. All else being equal, the DI system probably will fail to function due to accumulation of poop after fewer rounds fired than an OpRod (gas piston) system.

Typically you have to remove the OR gun's handguards to clean up its poop, which is more involved than breaking down the DI gun to access its breech. But that's an action that typically is needed far less frequently than cleaning the poop from a DI gun. I haven't heard a credible real-world field report on them yet but there are a couple of piston ARs and piston conversions for ARs that advertise they are "self-cleaning."

The bolt in a DI gun gets much hotter in operation than the bolt in an OR gun, too hot to handle, which can be a deal-breaker if for some reason you might need to do emergency maintenance on the bolt (probably not very likely).

The OR system necessarily puts reciprocating mass outside the centerline of the bore, which potentially can negatively impact accuracy.

The OR system has additional parts, additional weight, additional complexity, additional manufacturing costs and additional potential single points of failure.

The OR system also will spray hot poop over whatever happens to be near the gas block when it releases the gas. This might be you hands or gloves or whatever you have hanging on your accessory rails. In the real world, the OR gun's hot poop has been known to overheat handguards.

OR platforms are fussier than DI about gas port tuning if you try to run them suppressed.

If you've heard the nightmare stories and have qualms about the DI platform's reliability, check out this video. It's an M-4, being fired full auto as fast as the operator can change mags:



At around 400 shots fired, the handguard begins to catch fire. At about 420, one round cooks off. Except for that one cook-off (and the bit about catching fire), the carbine functions normally until its gas tube melts after firing 810 rounds (27x30) in just over four minutes. That's about 190 RPM in a platform with a recommended sustained rate of fire of 12-15 RPM.

Originally Posted By: tex_n_cal
I think Stoner pretty well knew what he was doing, when he went to DI. You obviously avoid the piston rattling next to the barrel.

Stoner wasn't married to DI. He built the Armalite AR-18 as a piston-operated advancement on the AR-16.

EDIT:
If my media tag for the video isn't working, it's here.


Edited by XL5 (02/16/12 12:33 PM)
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#6184196 - 02/16/12 03:43 PM Re: Gas piston vs. gas impingement [Re: XL5]
TWR Online   content
Campfire Tracker

Registered: 11/21/06
Posts: 5071
I wonder how much him selling the rights to the M-16 and it's DI operating system to Colt, had to do with the divorce???

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#6184466 - 02/16/12 04:43 PM Re: Gas piston vs. gas impingement [Re: XL5]
jimmyp Offline
Campfire 'Bwana

Registered: 11/28/03
Posts: 10098
Loc: Georgia
Nice video.

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#6184735 - 02/16/12 05:36 PM Re: Gas piston vs. gas impingement [Re: XL5]
JohnBurns Offline
Campfire Guide

Registered: 09/17/09
Posts: 2527
Loc: Wyoming
Originally Posted By: XL5
The bolt in a DI gun gets much hotter in operation than the bolt in an OR gun, too hot to handle, which can be a deal-breaker if for some reason you might need to do emergency maintenance on the bolt (probably not very likely).

Originally Posted By: tex_n_cal
I think Stoner pretty well knew what he was doing, when he went to DI. You obviously avoid the piston rattling next to the barrel.

Stoner wasn't married to DI. He built the Armalite AR-18 as a piston-operated advancement on the AR-16.

EDIT:
If my media tag for the video isn't working, it's here.


I have pulled the BCG from my DI AR after some pretty long strings of fire and it was never too hot to handle while the barrel would blister skin.

The video shows how well the DI AR works and also shows how poorly most in the firearms industry shoot. As the video goes you can actually see the shooter improve his reloads and become more efficient at keeping the gun running.

I am always amazed at how well designed the ergos are on the AR-15 and it seems possible (based on the AR-18) that Stoner got somewhat lucky with the AR-10 and AR-15 in this respect.

This really is why all the other pretenders like the SCAR have such an uphill battle in the Carbine Improvement program. If the contenders keep the inline recoil then it is just another AR and if they try and drop the stock to look different then the gun will never shoot with the AR in the hands of someone who has the slightest clue.
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#6185064 - 02/16/12 06:40 PM Re: Gas piston vs. gas impingement [Re: JohnBurns]
rost495 Offline
Campfire Oracle

Registered: 01/05/05
Posts: 32783
Loc: La Grange, TX
We used to practice rattle battle as a team quite a bit, and I did it at home because I wanted to be proficient.

600 yards could get upwards of 40 plus hits on a silhouette(with irons) in 50 seconds from prone. That of course included 1-2 mag changes.

I'd shoot that time and again. I still never had any melting or fire issues etc... which confirms a lot of what John says here. Still no reason to go piston.
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#6185181 - 02/16/12 06:58 PM Re: Gas piston vs. gas impingement [Re: rost495]
Ruger280 Offline
Campfire Regular

Registered: 02/20/07
Posts: 559
Loc: Little Elm, TX
Nice video. I wonder how much longer if any the gas tube would have lasted in a rifle length?
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#6188593 - 02/17/12 05:11 PM Re: Gas piston vs. gas impingement [Re: Ruger280]
Reloder28 Offline
Campfire Outfitter

Registered: 03/09/06
Posts: 8227
Loc: Deer Park, Tx
I am impressed with the input here & thankful.
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#6189857 - 02/18/12 03:59 AM Re: Gas piston vs. gas impingement [Re: Reloder28]
MichiganScott Offline
Campfire Ranger

Registered: 03/17/06
Posts: 1968
Loc: God's Country
http://www.thefirearmblog.com/blog/2010/06/09/a-clean-wouldnt-hurt/

Pictures of an DI AR-15 after 16,000 rounds of Wolfe ammo without cleaning, just lube every 1000 rounds. May be dirty, but it still fired.

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#6189877 - 02/18/12 04:24 AM Re: Gas piston vs. gas impingement [Re: MichiganScott]
jimmyp Offline
Campfire 'Bwana

Registered: 11/28/03
Posts: 10098
Loc: Georgia
Wonder what lubricant he was using?

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#6190442 - 02/18/12 08:13 AM Re: Gas piston vs. gas impingement [Re: Reloder28]
Mackay_Sagebrush Offline
Campfire Guide

Registered: 07/03/07
Posts: 4076
Originally Posted By: Reloder28
I am impressed with the input here & thankful.


Reloader,

I have been very fortunate to have been given the opportunity by Uncle Sam to be cross trained as an armorer on a whole host of weapons systems, including the M4/M16 series, as well as be the guy in the field carrying it.

I can tell you from spending many hours inside of many defense manufacturers factories acting like a sponge, that I have zero problem carrying a Colt M4 into battle,. The DI system M4/M16 series has served me well in some pretty lousy places, in some pretty austere conditions and has never let me down.
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