CaspianSeaMonster wrote: Thu Dec 06, 2012 11:39 pm
Thanks. I'm always really hesitant to run that whole explanation; I've done it a million times before, and it gets tedious after a while. I've also been called all number of bad names for "defending" the early AR-15 and I've gotten quite tired of it. And also yes, of course, having my credibility challenged on the basis of gender.
M16 smear threads are like mousetrap bait for me though; I'm impressed I made it a whole four days without chiming in on this one!
wlewisiii: If anyone made a reproduction FAL in .280 Brit... oooh man...
I'll take two, and a set of dies.
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Since you guys seems interested enough and it is related to my last post, I'll add this little nugget of information. Like I said near the end of my writeup, the carbine variant AR-15s are a much worse story than the rifles.
Dwell time - that is, how long the gas impulse lasts, dictated by the distance between the gas port and the muzzle - is one of those things that plays into balancing an autoloading system. If the gas dwell time isn't long enough, you have to crank up the pressure and/or reduce spring power/bolt weight to get it to cycle, and now you're giving the bolt a sharp kick instead of a (relatively) slow push.
Colt's early attempts at building a carbine variant of the AR-15 all involved clipping the barrel off just in front of the gas block; in fact the very first one, the Colt Model 605, was nothing more than a Model 604 (USAF M16) with the barrel clipped at 15", no other changes. Most of the carbine prototypes had shortened gas systems (same length as the modern M4,) 10.5" barrels - literally almost having the flash hider screwed up against the front of the gas block - and shortened buffer tubes and buffers (same as on the modern carbines.) The carbine buffer was identical in design to the dead-blow rifle buffer but, being shorter, it was also lighter. Because the dwell time was so short, they
couldn't go to a heavier buffer or it would short-stroke. Most of them actually had larger-than-standard gas ports to kick up the pressure, and gas port pressure was already a lot higher than on the rifle because the port was so much closer to the chamber; they had no choice but to run the bolt fast, and got all the same reliability problems that came along with that.
Eventually they bumped the barrel from 10.5" (XM177E1) to 11.5" (XM177E2), and added a small suppressor-like reflex muffler (GAU-5A) before finally giving up and just using a 14.5" barrel (Model 653 "M16A1 Carbine" and onward to the present M4 family.) This sorted out the dwell time problem, but you're still running higher gas port pressure than on the 20" rifle
and still running a lighter recoil buffer. The carbines have always demonstrated the same over-gassing reliability problems that the original M16s showed. They implemented a whole bunch of band-aid fixes on the M4; cutting the feed ramps lower, making the magazines more reliable to keep up with excessive bolt speed,* using more powerful extractor springs with rubber buffers to fight centrifugal force - all of these being good improvements, but not addressing the root problem until they had the bright idea of replacing some or all of the steel anti-bounce weights in the buffer with heavier tungsten-carbide weights. That's where the H/H2/H3 buffers are from; having one, two, or all three steel weights replaced with WC. I think the heavy carbine buffers came out in the 1990's and the gov't finally started implementing them on the M4 and M4A1 some time during the Iraq war; after four decades of dicking around with the problem, the stupid things
finally run reliably.
*Not to suggest that the magazines didn't work well to begin with, but the general rule used to be that a magazine that would run perfectly in an M16A2 would work okay in an M4, while a mag that would work okay in the M16A2 wouldn't run at all in an M4. Colt fine-tuned the magazines to death with new follower designs and more powerful springs.
--Katemonster