Carbine vs mid-length gas systems has been a hot topic for quite a while. Why not just use an adjustable gas system like the FN/FAL. It would adjust carbine gas pressure to mid-length levels.
Of course it would give one less reason to buy or build another rifle or upper assembly. GeezerD :big_boss:
Because barrel length and gas port location play a roll, too.
You can’t really just restrict gas flow on a carbine, and expect it to perform like a mid length.
I understand about gas port location and size,barrel dwell time,and reciprocating mass as they relate to the firing cycle. On the FN/FAL it is used to compensate for ammo of differing pressure. For example, allowing it to use machine gun ammo without putting excessive stress on the rifles action. The FAL was used by a lot of different countries with differing ammo specs. It just seems to me it would help reduce stress in the AR system. However, these days folks are trying to make the AR into something it was never meant to be.
GeezerD :big_boss:
It seems much cheaper to have no moving parts and a mid length over an adjustable block on a carbine. You are still afforded some room to tweak with a mid length as well.
1 - You can get adjustable gas blocks. (JP, or a Switchblock but the SB is for suppressor hosts.)
2 - In a DI gun it makes more sense just to change the gas port size. But once again, this is a better thing for suppressor hosts, as it doesn’t change dwell time. In a DI type gun the gas port being moved forward does more towards making the system smoother than an adjustable port does.
3 - Adjustable gas tubes are stupid, they aren’t hard to find, but there is a reason nobody reputable uses one on SHTF, or fighting gun.
Here’s a test.
Get two rifles. Both 14.5’'. One carbine, one midlength. Buy an adjustable gas block.
Shoot the carbine in standard configuration, then with the adjustable block with the gas port size tuned down. Shoot it again. Made a little difference. Shoot the midlength in standard configuration. A lot smoother, huh?
Gas port regulators aren’t the magic bullet. Port location from the muzzle end of the barrel is the key timing element. It’s an optimum distance for most barrel lengths. The 16" with carbine is the exception, as it’s longer - which means the bolt cycle starts earlier, when barrel pressures are higher. It’s subjected to higher pressures longer.
Hydraulic law shows that playing with the port size won’t change the onset of pressure, only slightly delays the peak, and cannot reduce it. About the only way to do that is choke it down so much the bullet would leave the barrel first and dump gas.
Military ammo is loaded to deliver a set pressure for the gas port location, not like civilian ammo, which varies bullet weight and pressures for different loads. That’s why civilian firearms have so many gas compensating mechanisms - shotguns especially. It’s a problem shooting light and heavy loads, same for the AR. The military doesn’t tolerate it, and requires the load to develop the correct pressures. Hence, no adjustable gas blocks. Milspec ammo for a milspec action. It’s not always about part dimensions, it’s about dynamic reliability.
Change the port location, change the port size, change the ammo max pressure loading, so many variables outside the operating window exist it’s no wonder the white box stuff acts up.
It really comes down to using the proper ammo, not buying cheap ammo that won’t work reliably. Just because some troops have to ride in HMMV’s doesn’t mean we need folding stocks - it’s the HMMV. It was never intended to be used for the job. Neither is white box ammo. Changing the gun to suit isn’t the answer, it’s just accommodating a cheap shortcut.
Why accomodate the wrong ammo when it won’t be used when the SHTF? Because that’s what the gun is really for, cheap plinking.
As stated… moving the port down gets you thousands of PSI lower port pressure and more time for the chamber pressure to drop which makes extraction less of a fight.
I guess I didn’t explain the FAL gas system benifits clearly. The FAL gas system exhausts a portion of the gas to the outside resulting in lower pressure at the bolt carrier which will somewhat slow down the bolt unlocking sequence and it could be further retarded by increasing the reciprocating mass. This would be of particular value on SBRs.
GeezerD :big_boss:
That’s it sir.
why would i want that? the more the better :sarcastic:
ha but yeah adjustable gas systems could be an advantage in some ways i spose. i just like the simplicity of the non-adjustable DI…
We know the dwell time is less on a mid length, and as such, less gas is directed into the tube. Also, with the tube being longer, there is more room for gas to expand. If you account for the difference in gas volume increasing the diameter of a carbine gas tube so that it had the same volume as a mid length tube would result in identical performance