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Posted: 1/23/2009 9:11:25 PM EDT
| Looking for the pic of the Vietnamese soldier with a 652 rifle. He is standing out in the open in a field. |
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Seems the only pics I've seen like that are all E1's - my theory is that with the shorter 10" barrel some enterprising armorer found that they ran better with a rifle buffer - thus the A1 stock. IIRC, a rifle buffer is pretty close to the weight of an 'H' buffer - which they didn't have back then. Then the 11.5" barrels came out which gave the thing more dwell time, and the problem pretty much went away. We've come a long way in understanding how short carbines run - look at all the Mk18s and shorties being sued now - of course, the Navy has also been converting a number of Mk18s to 14.5" M4 barrel configurations - which I'd like to build a clone of someday.
ETA: I take that back - here's a pic of an E2 with fixed stock - one of my favorites, and another E1 in the second pic. 652's 653's and 654's weren't used in VN - I've never seen an 'in use' pic of a 651 or 652 (fixed stock carbines w/14.5" barrel) 
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As stated, before Colt realized that going shorter than 11.5 inches created problems with reliability, many armorers in Vietnam took the shorties with 10 inch barrels and put on the full length stock as that cured many of the problems with realiability. I have seen a lot of short barreled M16's that had reliability problems, and with the addition of the full length stock, the problems were cured. It was not so much the heavier buffer but also the longer buffer tube. The gas ports were opened up on the shorter M16's to make up in volume on the gas impulse for what they gave up for the amount of time of the impulse. This large increase in volume would sometimes force the bolt and carrier rearward with a great deal of energy so that they rebounded back in the opposite direction with such speed that the bolt closed, the carrier rebounded off of the barrel extension and started to unlock the bolt all before the hammer fell to pop the primer. This is referred to as bolt carrier bounce - not really bolt bounce as some call it as the carrier is what strikes the barrel extension and rebounds rearward taking the bolt with it. With a longer buffer tube and heavier buffer the energy that drives the bolt and carrier rearward can better be absorbed, so that there is not as much energy moving it back forward so there is not the excessive speed and do not get the bolt carrier bounce. Putting the full length stock could also be done with 11.5 inch barrels as some of them may be prone to bolt carrier bounce. So, putting the full length stock on any of the M16's may be done. It was decided on a case by case basis, so you may see the full length stock on rifles with 11.5 inch barrels also.
Charles Tatum |
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A little tidbit on bolt bounce, it's a bit off topic, but it might help somebody working on function problems with a shorty.
I built a "no gas " manually operated Ar for hunting ( no semis in PA ). Carrier is manually retracted, and the round is chambered by the buffer spring. I made a delrin buffer because I figured it didn't need the weight of a regular buffer. Often times it would fail to fire after a round was chambered until the FA was pushed and clicked the BC forward a tad. Seems that the BC was bouncing back after locking up and then unlocking. A buffer with the sliding weights cured the problem. I think the idea is that the sliders are pushed rearward by acceleration and slide forward on impact, hitting just as the BC is ready to rebound. |
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Quoted:
A little tidbit on bolt bounce, it's a bit off topic, but it might help somebody working on function problems with a shorty. I built a "no gas " manually operated Ar for hunting ( no semis in PA ). Carrier is manually retracted, and the round is chambered by the buffer spring. I made a delrin buffer because I figured it didn't need the weight of a regular buffer. Often times it would fail to fire after a round was chambered until the FA was pushed and clicked the BC forward a tad. Seems that the BC was bouncing back after locking up and then unlocking. A buffer with the sliding weights cured the problem. I think the idea is that the sliders are pushed rearward by acceleration and slide forward on impact, hitting just as the BC is ready to rebound. Did you use the standard charging handle? |
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Yeah I put in a regular spring first but with no change, I'm running the lighter one to make it easier to pull back.
I had the crosshairs dead on that fat old g'hog; I drop the hammer and ..click. CLICK??? WTF??? 
It took awhile for my slow brain to figure out what was happening. Don't you just love puzzles. |
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I would like to ad my experience with a 10" Colt barrel;
I had 45Bravo cut down a C MP CB marked 1 in 7 Colt 11.5" barrel to 10 inches, no mod to the gas port and I run a real NFA Colt modertaor and H3 carbine buffer with factory spring. It runs fast (950-1000 rpm) but so far no problems with reliability either cold or hot weather, this all on on my Colt M16A2 lower with 2 position tubed aluminum stock. Slickside upper with later 604 chrome BCG and I keep it nice and clean between firing. It has all Colt parts save the KNS pins. Yes, I know it is an A2 lower but I overlook this being a Machine Gun and all! 
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I suppose that the rest of us could overlook the A2 lower too since it is a machine gun. Far too few of the real thing available and way too expensive these days.
I made a 651 upper for my M16A1 lower though I've used my XM177E2 upper and other shorties on my A1 lower before I picked up a second M16. 
My current favorite carbine upper for my M16A1 lower is without a doubt the 605! 
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