Get a midlength. I really see no reason for the CAR length gas system on a 16" rifle. The only reason the CAR exists is for 14.5" barrels.
CAR = 14.5"
MID = 16"
RIFLE = 18"+
Sorry, but I don't exactly agree with that. The midlength gas system was designed for use with the 18 inch barrels for the spr project (designated marksman).
The reason the gas port was moved forward (creating a midlength gas port) was because it was intended for use on a longer barrel and if they'd left the gas port where it is on a 14.5 or 16 inch Car barrel, there would be excess pressure stemming from the longer barrel causing too much dwell time with the gasses in the barrel & op system and would've resulted in too hard of extraction and in turn would run more risk of failures to extract and eject and broken and split cases upon extraction.
I've heard the midlength was created to aid in extraction, though from what I can remember of the SPR project was created to be used with an 18 inch barrel so it would function correctly.
Someone then had a brain fart and decided to try it on a 16 inch barrel, though the car length system wasn't a design flaw in 14.5 or 16 inch barrels or even the car length operating system altogether, but when using a longer barrel without moving the gas port, there's just too much pressure by adding space towards the muzzle without moving the gas port to match the barrel length.
I can't say the midlength on a 16 inch barrel is overall the worse thing that could've happened, but I do think that it also has it's drawbacks. And will be more prone to stoppages because the pressure curve is shorter when using a midlength system on a 16 inch barrel because when the bullet exits the barrel (and is closer to the gas port) there won't be as much back pressure pushing back on the bolt carrier to cycle. It's the same reason some folks have trouble with some SBR's.
It's the sudden drop in pressure after the bullet passes the gas port and exits the barrel sooner without allowing for enough back pressure to reach the bolt carrier to cycle as intended.
Once the bullet passes the gas port and leaves the muzzle, the pressure in the barrel drops almost all at once.
If the rifle is dirty, or has weakening springs and such, expect it to have short strokes and stovepipes because there's not as much pressure reaching the carrier if you're comparing apples with a car length op system placement of the gas port.
A good way to explain it is, the bullet is a cork with a lot of pressure pushing it down the bore. The gas doesn't move into the gas tube until the bullet moves past the gas port.
If the bullet stays in the barrel longer after passing the gas port, there will be more pressure on the op system and blowing back into the reciever. And the oppsosite if the gas port is closer to the muzzle (not as much pressure pushing back on the carrier--the case of midlength tubes on 16 inch barrels).
For what it's worth, on super short 7 inch and 8.5 inch SBR and pistol barrels, the gas port and tube is even shorter than a car length version. It's the same basic principle. It had to be moved to match the barrel length.
OK, back on topic, copy and paste from wikipedia concerning the development of the midlength gas system. Here's a couple of links that makes mention of it, but not any technical data.
United States Army Squad Designated Marksman Rifle - Wikipedia, the free encyclopedia
United States Army Squad Designated Marksman Rifle
Variants
The
82nd Airborne Division examined an alternate version, based on the
M4 Carbine.
The barrel was to have been an 18-inch long fluted Douglas barrel with 1:8 twist. A mid-length gas system was to be used, along with the Daniel Defense M4Rail 9.0 handguard. This effort never went beyond the staffing process.
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United States Navy Mark 12 Mod X Special Purpose Rifle - Wikipedia, the free encyclopedia
A
Mk12 Mod 0 Special Purpose Rifle in the hands of a United States Army Special Forces soldier.Type
Sniper rifle/
designated marksman riflePlace of origin
United StatesService historyIn service2002–presentWars
Operation Enduring Freedom,
Operation Iraqi FreedomSpecificationsWeight10 lb. (Fully loaded, w/ Heavy Barrel, Optic & 30 Rounds)Length37.5 Inches
Barrel length18 Inches
United StatesService historyIn service2002–presentWarsOperation Enduring Freedom, Operation Iraqi FreedomSpecificationsWeight10 lb. (Fully loaded, w/ Heavy Barrel, Optic & 30 Rounds)Length37.5 Inches Barrel length18 Inches
