Heat shielding is a big one for me. I have long arms and having the barrel shrouded out to the muzzle device is a great advantage operationally.
Don't - stay true to M4 design
General accuracy overall
Accuracy reasons: I use slings and bipods
Additional length for equipment placement
Additional length for shooting mechanics
As close to muzzle as possible for barricade use
Aesthetics
Other (note in post)
Heat shielding is a big one for me. I have long arms and having the barrel shrouded out to the muzzle device is a great advantage operationally.
I like to free float any carbine that I intend on using for 400+ meters. You can get 600ish meters from a 14.5-16" non free floated, but I've found the accuracy is much better with a milspec barrel and a free float system. Rifles length always benefit from free floating significantly aiding precision.
I don't sweat the length of the forend on a CQB setup because most of the time it's not practical to set your carbine on a barrier (berm, wall, corner, window, hood) like you would in a 3gun competition. Because in a real gunfight doing so gets you killed.
It's important to stand behind cover and give yourself enough distance so that when enemy fire hits the wall or hood it gives enough time and english so the ricochet and debris cast from it go over your head versus into it. It's not as commonly known but it's a good way to die or get a medal for getting shot in the face. To this day I see tacticool instructors still barricading up.
For those who are unfamiliar, you should stand 6 feet behind a hood or so behind a wall if you're coming over the top while you slice canted from left or right.
Hope this helps. Precision rifles require more real estate for bipods and the long heavy barrel, and peripherals. If you watch a sniper he will not barricade his rifle in a firefight, he will hold it from 6+ feet behind cover. Same rule applies. When sniping from a nest, it's also good practice to be well behind cover to minimize your silhouette.
Last edited by Core781; 06-08-18 at 23:16. Reason: spell
THIS^^
Depends on it's intended purpose, you will get a small accuracy advantage with an FF, but in the real world you won't be shooting match ammo. Light mounting positions is also a plus, but not as much as you may think. If you have a surefire light, have a buddy walk around a corner with it on, and in an aiming position.(please do this with an unloaded firearm) and see how long it takes for you, and what advantage that would give you...
My .02; additional length rail helps prevent branding my leg after extended fire and transitioning to handgun.
My 15” rail gives me plenty of mounting options, plenty of room to place my support hand wherever I want, and the effects of free floating don’t hurt either. Plus my magnesium KMR is crazy lightweight.
My full float handguards are all 12" - 13" in length. Plenty of room for all the accessories I could ever want, and usually cheaper than their 15" counterparts.
As close to the muzzle device as I can get, for one reason alone: my visual accommodation issues dictate putting the BUIS front sight as far forward as possible. Front blades placed farther back become vague suggestions about where to aim.
Having a full-length "heat shield" is appreciated, as is reduction of barrel shadow from the weaponlight, but those are not particularly important to me.
toc.
Maybe I am the odd ball out, but I don't really see the need to go past 13" on a 16" barrel. I do use a 15" to test looks and protect the barrel on a more precision oriented AR that I use in run and gun and prone, but for general purpose/HD on LW barrels, 13" takes the cake for me. Looks kinda funny too having a 16" skinny barrel hiding behind a 15".
Edit: the poll didn't mention ergos. I think ergos is the most important for me. I love wrapping my hand around those rounder slimmer ID FF rails - the MK 14 and MCMR just feel fantastic and help me control the rifle.
Last edited by beschatten; 06-11-18 at 07:23.
A 6920 is more than enough rifle for 99% of shooters dealing with 99% of shots taken with an AR-15. A friend of mine can shred 3-gun courses with a 6920, and makes dudes with multi-thousand dollar rifles look like boys playing with twenty-twos. The indian, not the arrow. That said, maximizing the platform, when you have the luxury of doing so, makes a lot of sense. If you have the money to buy, and/or the time & inclination to build, you are confronted with making a series of choices, that of gas system and rail being two of the more significant ones.
For me, gas system is a an engineering choice first and foremost. I prefer the longest gas system that I can get in the rifle while maintaining long enough dwell time to reliably cycle the weapon. Typically, that is only a couple of inches of barrel beyond the gas port. From what I can tell from reading a vast amount of other people's experience with the topic (I don't own 30 rifles of varying stripe), when the amount of barrel beyond the gas port drops to below two inches or so, the rifle can get squirrely depending on ammo, gas port size, etc. That said, a 7.5 inch carbine gas system lets a rifle get down to that mk18 10.3 barrel length and still reliably cycle the weapon.
As to non NFA rifles, be it a 14.5 pin&weld or a 16+, a carbine gas system leaves so much barrel beyond the gas port--and especially in the early, hot/high pressure section of the barrel--that the port pressures are significantly higher than what is required to cycle the weapon. Mid-length gas systems on non NFA rifles with barrels under 18" (which should have a rifle length, probably) allows for better operating conditions for the weapon.
Next, free floating gives you a ton of extra room to mount garbage on the rifle. Such long rails also allow you to grip farther out towards the muzzle, which aids in controlling recoil and, for me, driving the muzzle from target to target. They also allow for the attachment of bipods, which is crucial to milking maximum accuracy out of the rifle at longer ranges. The same friend as mentioned above is able to make on-demand sub-moa hits with a 556 rifle out to and beyond 600 yards.
I am not sure if he could do that with a stock, non-free floated 6920, but then again, you never know till you try...
When I bought a new rifle, I didn't have restrictions from an agency regarding what I could have. And so, I bought mid-gas in a 16" barrel. At the time of my purchase, I could have gotten a plastic handguard and FSB (though these were significantly rarer in manufactured complete rifles then). But, as I had control over the whole process, I ended up with a Troy Alpha rail installed on the rifle from the factory. So, factory free-float mid length gas.
I am putting together a 14.5 rifle now--which rifle will be getting a thread in the Custom Builds section whenever I get the damned Geiselle rail (ordered 05/25, still "processing")--and again faced the same questions. I could have just bought a 6920 and moved on with my life. Instead, I decided that I wanted to waste a bunch of time and money learning how to do armorer level work on the AR-15 platform, and fully assemble my own rifle. Given that I had complete control of the variables, and that my barrel length was 14.5, it made no sense to get carbine gas. Mid length, as stated above, makes for a better operating system. Next, I could have easily just gotten a magpul handguard, but since I had complete control over the variables, I'd gone with a low-pro gas block, and ordered a gucci-ass G rail. The end result will be a rifle that has nearly all of the slack taken out of the system: the only variable left will be me.
Last edited by noonesshowmonkey; 06-11-18 at 08:57.
Nice, informative post, IMHO. Plenty of excellent points.
Patriotism means to stand by the country. It does not mean to stand by the President... - Theodore Roosevelt, Lincoln and Free Speech, Metropolitan Magazine, Volume 47, Number 6, May 1918.
Every Communist must grasp the truth. Political power grows out of the barrel of a gun. Our principle is that the Party commands the gun, and the gun must never be allowed to command the Party Mao Zedong, 6 November, 1938 - speech to the Communist Patry of China's sixth Central Committee
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