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Old 10-15-2019, 12:20 PM
Buck91 Buck91 is offline
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Default AR gas system vs bbl length



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How much of an effect does gas system length have on velocity as opposed to barrel length in an AR platform? There are lots of tests out there, for example, of 5.56 and .223 ammo from various bbl lengths but most of them are using either all the same gas system or no gas system at all (bolt guns and cutting down the bbl).

For example, if one has a 16" carbine and a 16" midlength, would you expect any appreciable difference in .223 velocities? What about a mid vs rifle length 18 inch bbl?

Similarly, when looking at .300blk for a hunting load there are many carbine length 16 inch options. Would this have any effect on unsuppressed supers? I'm not talking about action function, simply considering velocity differences.
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Old 10-15-2019, 02:22 PM
ajole ajole is offline
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I think it would be negligible, there's just not that much gas being diverted from pushing the bullet, regardless of tube length.
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Old 10-15-2019, 02:30 PM
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The longer gas systems are supposed to be softer shooting, less recoil.
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Old 10-15-2019, 04:14 PM
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It's negligible at best.
If you are thinking about getting a 300 blackout gun with a shorter barrel you should get one with a pistol length gas system. The carbine length gas systems have a shorter dwell time and can lead to poor cycling of the action. Meaning, the shorter distance between the gas port and end of barrel allows less gasses to cycle the action and can cause failures. This has not been the case with 556 guns.
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Old 10-15-2019, 04:46 PM
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I would be more concerned with cycling the action with a short barrel than bullet speed.
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Old 10-15-2019, 06:05 PM
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no cycling issues with a 7 1/2 barrel 5.56 ar pistol and a Franklin binary trigger. yes I have lost velocity but that isnt what it was purchased for.
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Old 10-15-2019, 10:04 PM
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I have a 10.3, pistol gas system.
Works like a charm, suppressed or not.

Longer barrels do yield some increase in velocity for supers, but it's pretty negligent. The round was designed for shorter barrels.
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Old 10-16-2019, 07:56 AM
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The OP is asking if a longer gas system decreases velocity. My experience says no. By the time the gas system even starts moving, the bullet's left the barrel.

My carbine and mid length shoot identical velocities. Barrel length naturally makes a difference as people have been stating.
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Old 10-18-2019, 09:02 AM
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Been a while since I looked into this topic, but I do remember some. The main variable is how much longer is the barrel compared to the gas system. The greater this difference, theoretically the more velocity you lose to friction. As soon as the propellant gas passes the gas port in the barrel, it loses its "push" due to now working to cycle the action. Therefore, a 20" barrel with a carbine gas system would have the most velocity loss (though you'll never see this setup).

For the most part, your gas system length is going to match your barrel length to negate any loss in velocity. However, the main contributing factor in my experience is your specific ammo (powder, bullet type, weight, etc.) To that end, it's worth testing different types of ammo to see what works best for you and your gun. The same ammo may not work well for different guns. For example, an old bolt action I had worked fine on Remington UMC for punching paper, but my newer bolt action (Remington, of all things) locks up when I try to run UMC, requiring me to knock the bolt open with a mallet. It's awful, but then it throws Hornaday Black like a champ.
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