Posted on 09/27/2018 5:40:09 AM PDT by w1n1
Wasn’t the ArmaLite rifle designed originally with a 20 inch barrel? And is it true that the 20 inch barrel complimented the round which was designed to fire from the ArmaLite
“Wasn’t the ArmaLite rifle designed originally with a 20 inch barrel? And is it true that the 20 inch barrel complimented the round which was designed to fire from the ArmaLite” [Clutch Martin, post 21]
Which ArmaLite Rifle?
There were several.
If you refer to the arm that became the US-issue M16 & M4 rifles, from which the semi-only “AR-15” series of rifles was eventually derived, the answer is yes and no.
The “original” was ArmaLite’s AR-10, a rifle chambering 7.62x51mm NATO, designed by a team led by Eugene Stoner. It appeared too late to gain serious attention in the US military’s drawn-out search for a replacement for the M1 Garand.
Stoner left ArmaLite; the company licensed manufacture of the AR-10 to Artillerie Inrichtigen, in the Netherlands.
In response to requests from other commands inside the US Army, the Army Ordnance establishment had initiated the Small Caliber High Velocity program, to investigate the possibilities of developing a lighter, more-controllable rifle capable of greater firepower than arms with bores of 0.30 inch. Much interest centered on projectiles of 0.22 inch diameter (5.56mm).
ArmaLite was interested; a team there “downsized” their AR-10 to fire experimental cartridges based on the 222 Remington (the real innovation here - made its appearance in 1950). Winchester designed their own SCHV candidate rifle, leaning heavily on the US M1 Carbine. Several other experimental rifles were developed, including a Garand-based specimen and an unusual rifle based on FN’s FAL - it looked like two FALs glued together.
Apparently, Army Ordnance was not satisfied with the 222 Remington’s remaining velocity at extended ranges. Remington designed two other rounds, which better satisfied the remaining-velocity requirement with a suitably-crafted 55gr boat tail bullet (these became the 222 Remington Magnum, and 223 Remington).
Army Ordnance selected the slightly-shorter round, which was adopted as 5.56mm Ball M193. Loaded with sporting bullets, it was introduced to the civilian market as 223 Remington, though all projectiles (222, 222 Mag, 223) were of 0.224 inch diameter.
Winchester dropped out when its rifle proved unable to meet the criteria for minimum group size.
ArmaLite’s candidate proved more promising. Small numbers were made and sent to advisory teams afield in Southeast Asia; results in action proved better than any prediction; more rifles were demanded, and series manufacture was investigated. At some point in this timeline, ArmaLite named its experimental rifle “AR-15”.
Barrel length may have been standardized at 20 inches, at about this time. Early results have been attributed to the slow twist rate, then 14 inches (standard for 222 Remington) or 12 inches, provided adequate stabilization in air, but performed less well in extremely cold air, and were observed to go unstable in denser materials (such as the human body).
ArmaLite was an engineering/development firm with no production facilities; they licensed production to Colt, and trademarked the designation. Colt began making rifles for USAF, which had expressed interest early on. At this point, US Army nixed the contract with the Air Force, citing its authority as DoD executive agent for small arms.
Poor grouping under all possible climate & weather conditions were cited as a factor in the Ordnance establishment’s opposition to the SCHV-preferred rifle; they were over-ruled by SecDef.
Early production thus went to ground forces, and the rifle was adopted as official standard, in modified form by order of SecDef.
Since then, military versions of the “AR-15” have been made in barrel lengths as short as 10.5 inches. Accuracy and group size seem moot, ever since the US Army officially adopted “shots per minute” as its doctrinal definition of firepower.
Why? How many bullets remain in flight for a minute?
RE: the article, what idiot announces he's going to compare the potential accuracy of different twist rates, then does all his testing with different barrels that all have the same rate of twist?
It's a shame the dinosaurs had to die so they could post this garbage.
It’s actually rather funny though. I shoot 80s from a 1/8 twist in hipower Comp. So, at 2750, the bullet is doing 247k rpm. But to get to 600 yds, it takes .87 seconds, so only60 rotations to go 18800 feet. Cool huh?
Oops, 1800 ft.
Quick formula: mv*720/twist
2750*720/8=247xxx. Time of flight in secis taken from ballistics program, so 247000/3600sec per hour*.87=59 and change.
Ian McCollum, is that you?
CC
That does not seem quite right. The bullet rotates once every 8 inches. With a 16 inch barrel it would rotate twice. in 18800 feet it would rotate 28,200 unless I need more coffee.
Oops squared! Wow, must have been a long day in the sun? Ok, I stand corrected- I mistakenly used seconds per hour (3600) instead of secs per minute (60), sooo, the correct answer will be 247500rpm/60 sec per min=4125 rev per sec *.87 sec (time of flight)=3588.75 revs.
Also, the rate of distance per rev does not remain constant- while the rate of spin remains almost constant (negligible deterioration) the velocity does degrade- from 2750 fps at the muzzle to around 1750 fps at 600 yards.
The equation is one of time and rotation, not rotation per unit distance once the bullet leaves the muzzle.
Time of flight is the key not the decaying distance per revolution.
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