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Posted: 7/2/2009 4:54:42 PM EDT
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I have finally had a chance to test out a couple AR-15s Ive just recently built. Both of them are short stroking. Weapon number 1 - a Bushmaster 16" - The first bolt I tried in this gun was a bushmaster M16 BCG. It would short stroke for no apparent reason every shot. I switched over to my Denny's M16 BCG, same problem. We figured it might be the weight of the heavier M16 BCG causing the problems so swapped in a RRA semi auto BCG. It worked well for the first 200 round but again started short stroking after it dirtied up. Weapon Number 2 - Armalite 18" with full gas system - Tried this with the Denny's M16 BCG. It shot off about 40 rounds and then started short stroking every round. I cleaned it out with a bore brush and it shot maybe 5 more round before short stroking again. Basically I tried every combination of uppers and BCGs I had with me and experienced short stroking to varying degrees. I have checked the gas keys and they are all tight and lined up. The gas rings are also in good condition. I was using several different magpul magazines that are known to be good so that is not the problem. Here are my thoughts on the problem. 1. I was using Wolf 55 grain ammo and it is very dirty and underpowered. However I have never had a problem with this ammo before and I have been shooting it for years. I also switched over to some Lake City M855 and still had the same problem. Possibly a bad batch of ammo? 2. I am using hops #9 to lube my guns. I think I may have been using too much, running the guns "wet" because they are new and I didn't want to cause excessive wear. Would too much oil cause these guns to short stroke? Should I switch over to CLP instead of Hops? 3. The 2 full auto M16 BCG groups that I tried both short stroked much worse than the semi auto carriers. Is this because they are heavier? Also, do you have to use a special buffer and spring or is the standard carbine buffer and spring sufficient? 4. These 2 AR-15s are my first builds. I have always shot pre-built weapons before this. Let me know what you think. I have been shooting AR-15s for years and never had a problem like this. Even with dirty wolf ammo. |
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Out the gate,
Do not use Hoppes to clean or lube the gun. To clean and lube everything on the rifle except the bore, use BreakfreeCLP (read buy the 160oz spray can). To clean the bore, use something like Sweets since it will not leave a residue behind that will gum up if mixed with CLP. As for Wolf in either of the rifles, it's going to be your short comings until the barrels have broken in (self polished through live fire for around 1K of brass case rounds. Since you have used wolf in the rifles, they must be fully cleaned, so yes CLP down the bores/chambers, then the use of a chamber brush by hand to remove all the powderized Poly fouling that has adhere to the chambers (only solvents like Acetone will dissolve Poly fouling, and since it kills plastic, use the chamber brush and elbow grease). So, clean, clean, and clean some more. Then once you have everything clean enough to hand in to an armor without it being thrown back at you, lube the upper bearing area's of the rifles with CLP, and go break them in correctly with brass case ammo (yes the M855 will do nicely). Once you do get them to the 1K marks, them over lube the upper bearing area and try the wolf again (if you feel lucky, and remember that you will need to scrub out the Poly fouling when done shooting such). |
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Ok, I finally got around to working on the Bushmaster. I got some good ammo, Prvi M855 and some CLP. I cleaned the gun for hours, it was spotless, no sign of wolf ammo. I took it out to fire today: Shot better at first but would still short stroke every 10 rounds or so. The bolt would never lock back on an empty mag. It progressively got worse as the day went on... after about 100 rounds it would short stroke ever 2 or 3 rounds and started jamming too. I swapped the BCG with a known working gun's BCG. Same problem. I swapped the buffer/spring with a shorter and known working buffer/spring. Same problem. Any ideas? |
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When they started short stroking again, did you pull the B/C and relube the piss out the B/C's with CLP (heavy sprayed coat inside and out on the B/C). New rigs can have teething problem of being too tight in areas, and an added shot of CLP to relube them up often solves the beak in problem.
Also, on the Bushmaster B/C, confirm that the key allen bolts are tight (37 in lbs). |
| I know you just got done trying a new buffer spring, but I just got done building a new ar 15 with a carbine stock and had the same problem with mine and my dad's and it ended up being the buffer spring on a rifle length gas system. Although mine was short stroking from the beginning. Both Buffer springs appeared to be standard carbine, but for some reason when I replaced the spring mine ended up working just fine. |
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Give it a good chamber brush cleaning, shoot some of your brass cased ammo in it, and tell us if you see scratch marks in the casings. I am betting the bushy has a rough chamber.
If so, a 3/16th in brass rod with a slotted end on it and some 300 or so grit emory paper would work fine. so would an old cleaning rod. I do not have experience with armalites. Brett |
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Today I tried swapping the lower out with a known working one. Same problem so that rules out the lower. Again I tried a different bolt carrier group and the same problem... I went to town on the bore with a bore brush and some hoppes solvent spray. Did no good at all. I checked the brass for scratch marks and there is none. The inside of the bore looks smooth too so I don't think that is the problem. It must be something wrong with the gas tube... |
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Try a lighter spring/buffer.
May need to open the gas port a few thousandths. A gas tube is a gas tube, and unless something is majorly wrong, it's not the restriction in the system, the gas port is. Wolf MC is actually more powerful than PRVI m855 in my experience (in a 10.5" barrel at least). Before i had my pistol running right, Wolf would lock back, and PRVI m855 would not. I shoot all brass in my good guns, and usually wolf in the pistol / plinker. |
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Quoted:
Please, no sandpaper on the rod spun in the chamber!!! More chambers have been screwed up this way than corrected. If the chamber is beyond rough (reamer markings), then send the barrel back for a replacement. Yeah, i guess I should know mechanical aptitude of the poster before I throw that out there. 
Can't take out reamer marks for sure. Can take out roughness from less than perfect prep before and after chroming. Sorry Dano 
Brett |
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