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MI, USA
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Posted: 6/14/2005 5:25:01 PM EDT
[Last Edit: metroplex]
I have an AR15 that was built up:
Bushmaster 24" NM H-Bar, 4150 chrome-moly steel with stock A2 front sight/gas block (no-ban) RRA A4 upper receiver RRA lower parts kit Ameetec Arms lower Wolff Action Spring Wolff Extractor Spring MacFarland 1-piece gas ring Using Wolf 55gr JHP (green lacquer coated case, no neck sealant) will result in 99% FTF after the first shot. Using Winchester 45gr JHP varmint rounds will result in a 50/50 FTF. I had one actually get jammed so badly the bullet was coming out of the case. Using XM193 (Ammoman) or M855 (Sportsman's Guide) results in proper function. However, the M855 was working great 99% of the time. There were about 2-4 FTFs where the bolt did not go back far enough to feed another round. The Mags are SA80 / T-65 steel mags with Magpul followers. They had some problems working with the 45gr varmint rounds but possibly because the cartridges are "shorter" than the M855. The M855 cartridges were barely touching the edge of my mags while the varminter rounds were smaller and could move around. Forest was patient and addressed a few of the problems: 1). Possible gas hole isn't drilled correctly or aligned with the gas block hole correctly. 2). MacFarland gas ring is causing problems 3). Gas key screws are loose or broke off Some additional information: I've used Wolf w/ the stock 3-piece gas rings and ran into the same problem. The gas key screws are staked by RRA and I checked the torque so they're not loose. The gas key is tight. The bolt moves around in the bolt carrier like it normally should even with the MacFarland gas ring installed. Any ideas? |
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Posted: 6/14/2005 5:35:24 PM EDT
[#1]
describe the failure to feed?
bolt over base? stubbed round? three point bind? |
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MI, USA
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Posted: 6/14/2005 5:44:11 PM EDT
[#2]
The round will be halfway loaded into the chamber and looks like it overshot the feed ramp, and the bolt slams into the case. It will form a long "streak" and stop by making a huge "gouge" into the case. Another FTF is when you fire the first round (Wolf for example) and the bolt doesn't come back far enough to load the next cartridge or latch the BHO when it's the last round. It got to the point where I had to shoot Wolf in single loads only (1 Wolf rd per mag) otherwise I'd run into frequent jams. |
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Posted: 6/14/2005 7:04:11 PM EDT
[#3]
does the bolt lock back when you fire the last round out of the magazine?
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MI, USA
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Posted: 6/14/2005 7:06:44 PM EDT
[#4]
99% of the time with the M855 (5.56N) 100% of the time with XM193 (5.56N) 0% of the time with Wolf 55 gr JHP (223 Remington) 50% of the time with Winchester 45 gr JHP varmint (223 Remington) |
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Posted: 6/15/2005 12:41:43 AM EDT
[#5]
it's short stroking then, that's what is causing the failure to feed
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MI, USA
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Posted: 6/15/2005 5:04:51 AM EDT
[Last Edit: metroplex]
[#6]
I looked at the FAQ but couldn't find solutions to short stroking.
Forest said it's probably the gas hole not being drilled properly. What size should it be drilled? It's a 24" barrel with a rifle length gas tube. Since my gas key bolts are staked, what happens if I remove them and re-torque them? Do I need to re-stake? |
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Posted: 6/15/2005 5:23:42 AM EDT
[#7]
before you drill anything you need to check the entire system, a gas port that is too large is as bad a one that is too small and is harder to fix.
make sure that the gas tube is installed correctly and that the roll pin is present. check the rear of the gas tube to make sure it is not worn down and compare its outside diameter to that of the carrier key ID. next, try a different carrier, one from a known good rifle, use the same bolt. perform the short stroke check if none of that works pull the FSB off the barrel and inspect the gas port in the barrel and in the FSB. make sure all holes are complete and free of burrs. make sure that the hole in the gas tube lines up with the gas port in the FSB, make sure that the gas port in the FSB lines up with the gas port in the barrel. mic the gas port diameter |
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MI, USA
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Posted: 6/15/2005 8:42:53 AM EDT
[#8]
I read through minuteman's ordeal and it looks like it might be the Wolff XP action spring causing the problem. I also have a Wolff XP extractor spring and the Crane O-ring.
From his problem, it appeared over-action might be the culprit since when he used a heavy buffer to slow the action, it functioned properly. On my rifle, I noticed that when the rifle is fairly clean, the Wolf ammo may either cycle properly or the carrier will catch the BHO catch instead of the bolt lugs. All cases are extracted properly although when in heated rapid fire, the cases will come out at the 1-5 o clock positions inconsistently. After 400 rounds, the rifle would not cycle properly after firing each Wolf cartridge. I was basically using a bolt-action rifle having to manually feed the second round OR trying to fix a jam. I'd like to think Bushmaster set up the barrel, gas port, and FSB properly. I am using their gas tube with their gas tube pin. The "mushroom" is worn out all around on the gas tube. |
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OR, USA
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Posted: 6/22/2005 12:54:09 AM EDT
[#9]
?Buffer spring problem?
Rick |
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Posted: 6/22/2005 2:22:56 AM EDT
[Last Edit: Tweak]
[#10]
you need to replace the gas tube then, you're losing a lot of gas right there. solve the short stroke first as it will exacerbate any other malfs. |
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MI, USA
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Posted: 6/22/2005 5:05:00 AM EDT
[#11]
How do I prevent the mushroom from wearing out?
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Posted: 6/22/2005 5:08:41 AM EDT
[#12]
don't shoot your rifle.
you can make it last longer by insuring that the gas tube is properly alined with the carrier key |
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MI, USA
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Posted: 6/22/2005 6:43:09 AM EDT
[#13]
From what I can see, the gas tube mushroom is worn evenly all around. That suggests it is aligned with the gas key, right? The only other thing I can think of is the RRA gas key is too small, causing it to wear out the gas tube mushroom... But I've only shot a total of less than 1000 rounds through this rifle (more or less).
FWIW, when I was firing the Wolf ammo, I heard the "SPROING" sound of the action spring followed by a very quick "bump". The empty case ejects but the next round does not get fed into the rifle. When firing XM193 or M855PD, I hear the SPROING and the "BUMP" comes quite later (bolt slapping home with a new round chambered). I do see some gas residue blown forward of the gas tube/gas key seal. In other words, there's some residue on the gas tube between the delta ring and the upper receiver and under the top handguard near the upper receiver. I checked the carrier and did not see any signs of a lot of gas seeping out of the key. Next I looked into the gas port sizing you suggested. Without a reference for what I should be looking for (port size) I did find a chart on the MD AR-15 site: 20" w/ 0.625" diameter barrel: 0.086"-0.093" 20" w/ 0.75" diameter barrel: 0.093"-0.096" 24" w/ 0.825" diameter barrel: 0.089" The distance from the gas port to the muzzle for the 24" is greater than the 20", and my 24" barrel is a Bushmaster H-Bar. Should I be checking to see if it's 0.086"-0.093", 0.093"-0.096", or just 0.089"? From the "DIY" article about installing FF handguards, it doesn't seem too hard to remove the FSB and to replace it properly. I'm just hoping it does not go back on canted. |
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Posted: 6/22/2005 5:51:22 PM EDT
[#14]
gas port is the same size on 20" and 24". you need to mic the end of the gas tube and compare it to the ID of the key. if the FSB is pinned on pulling it off and reinstalling it won't change the alignment. on the BFI barrels you can pull the FSB and look at the spot of Parkerizing left on the barrel by the internal gas port in the FSB, the spot should be centered on the gas port in the barrel. While you have the FSB off check that the holes in it line up with the holes in the gas tube.
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MI, USA
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Posted: 6/23/2005 7:42:33 AM EDT
[#15]
So what gas port size am I looking for?
0.093"-0.096" or 0.089"-0.093"? How tight should the gas key ID be compared to the OD of the mushroom? |
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Posted: 6/23/2005 8:06:33 AM EDT
[#16]
where are you located, I can get ANY ar to run, I am in monroe, come on down and we will get her going
Tim |
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MI, USA
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Posted: 6/23/2005 4:59:08 PM EDT
[#17]
I'm going to try and test out my AR-15 with some changes first:
standard action spring instead of Wolff XP action spring standard extractor spring instead of Wolff XP extractor spring no Crane O-Ring standard 3 gas rings instead of MacFarland 1 piece gas ring I checked the gas tube mushroom and it's gone but I can feel a slight bump where it used to be. I do not have any measuring tools that can go that deep into the gas key to get an accurate ID, but AFAI can tell, the gas key and gas tube seal is rather snug in order for the mushroom to have worn down. Do you have or know where to find pics of "normal" mushroom wear vs "abnormal" mushroom wear? |
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Posted: 6/24/2005 2:49:39 AM EDT
[#18]
what is the OD of the tube?
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MI, USA
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Posted: 6/24/2005 3:45:17 PM EDT
[Last Edit: metroplex]
[#19]
Tweak:
The OD of the gas tube is 0.171" The OD of the gas tube where the mushroom used to be is 0.176" The ID of the gas key is 0.182" What does my fortune say? New gas key, new gas tube, or everything's ok and to check the gas port sizing and FSB alignment? FYI the gas tube came off with my bare hands. In fact I simply twisted it a bit with my index finger and thumb, then gently yanked it out. I've pulled out splinters w/ more effort than this. ~700+ rd through this Bushmaster gas tube. I also stuck a piece of 2000 grit sandpaper wrapped around a 30 cal nylon bore brush and ran it in the chamber with a cordless drill. 2000 grit sandpaper isn't abrasive enough to remove a lot of metal but it will smooth out any quasi-fine surface. Am I right in assuming that ALL AR-15s should be capable of firing Wolf 55/62 gr cartridges w/o any problems? |
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MI, USA
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Posted: 6/24/2005 9:50:51 PM EDT
[#20]
ttt for the night crew zzzzzzzzzzzzzzzz
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Posted: 6/25/2005 4:16:40 AM EDT
[#21]
I don't think it's your gas tube.
Definately not worn.
Ehhhh, technically yes. But you can really change the chamber dimensions on a chromed barrel so if it's tight, it's going to stay that way. How do your carrier key screws check? |
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MI, USA
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Posted: 6/25/2005 6:26:41 AM EDT
[#22]
Hi Tweak
I removed the gas key screws before, checked the alignment, and applied High Strength red threadlocker (the stuff I use on my ring gear bolts) and torqued the screws to 40 in-lb. I noticed that RRA did not properly stake one of the bolts but the key did not "feel" loose in the beginning. |
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Posted: 6/25/2005 6:36:11 AM EDT
[#23]
have you pulled the FSB? tried a different carrier?
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MI, USA
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Posted: 6/25/2005 6:43:51 AM EDT
[#24]
This is my only carrier and I haven't pulled the FSB.
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Posted: 6/25/2005 7:00:19 AM EDT
[#25]
would be the likely place to start checking.
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MI, USA
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Posted: 6/25/2005 9:01:54 AM EDT
[#26]
Tweak
I noticed the gas residue pattern on the gas tube was odd. Rather than having a pattern similar to the ID of the hole in the gas tube, the splash pattern was much larger than the hole on the tube. I saw pics of the gas tube in your FAQ where the residue pattern looked like it fit the gas tube hole. Does this make any sense? |
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ZWE
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Posted: 6/25/2005 9:53:02 AM EDT
[#27]
Gas patteren/burn on the barrel should be the size of the block passage hole (read nice round pattern around the barrel gas port, and not off to one side, nor larger than the block gas passage hole).
If you have a spatter effect pattern on the barrel that is larger than the gas block hole, then the FSB is not sealing correctly and leaking out threw the block/barrel. As for the gas tube hole and the FSB gas passage hole, check to mark sure that they are aligned. If needed, open the gas tube hole (at the block) to align with the FSB passage hole. |
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MI, USA
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Posted: 6/25/2005 11:54:03 AM EDT
[#28]
The pattern on the gas tube indicates the FSB hole is much larger than the gas tube hole (I'm not talking about the gas port). There is no splash pattern on the barrel itself.
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ZWE
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Posted: 6/25/2005 12:37:09 PM EDT
[Last Edit: Dano523]
[#29]
Use a drill bit threw the bottom of the FSB (the same hole used to drill the passage hole when it was built, which may be tapped for a set screw) and open up the gas tube hole so it is the same size as the FSB passage hole. Often on after market gas blocks, the two do not mate correctly, and the gas tube side opening for the FSB needs to be enlarged to align.
Note: Go slowly or you will punch threw the top of the gas tube, or eat into threads for the set screw. |
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OK, USA
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Posted: 7/1/2005 11:31:16 PM EDT
[#30]
I had/have the same problem, wolf xp action spring. My solution is to use only XM193 and M855PD ammo. If I need to use a weaker load I know all I have to do is replace my buffer spring with a mil spec. I did clip 3 coils off the wolf spring (contrary to the advice of Tweak and others.) I'm 100% with NATO loads. I would definetly change buffer spring before to spec before any thing else. If anyone can alert me to a problem I may have caused by clipping my XP buffer spring I would much appreciate it.
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MI, USA
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Posted: 7/21/2005 6:12:52 PM EDT
[#31]
UPDATE
I finally got the time and courage to remove the FSB to look at the gas port. As I suspected, the gas port is 0.093" just what is required. I put a #42 bit on a cordless drill and carefully went in just to double check and make sure there weren't any obstructions. Through the bore, there does not appear to be any burs. From outside the barrel, there were no burs. I slapped everything together again but have not had a chance to fire the rifle. So far I have done: * Polished chamber using 1000 grit and 2000 grit sandpaper wrapped on a 30 cal nylon brush * Changed action spring to standard (instead of Wolff XP). I am still using a Wolff XP extractor spring but w/o the rubber insert. * I also lapped the gas key and re-torqued the gas key screws and staked them. I also used a liberal amount of red threadlocker as the gas key sealant and threadlocker for the screws. * I went back to the original 3-piece gas ring instead of the MacFarland 1-piece. Tweak, any other ideas if this does not work? |
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MI, USA
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Posted: 7/21/2005 6:16:11 PM EDT
[Last Edit: metroplex]
[#32]
For those tuning in:
Bushmaster 24" H-Bar, A2 flash hider RRA upper RRA bolt carrier group (All RRA parts) |
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MI, USA
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Posted: 7/22/2005 11:14:28 AM EDT
[#33]
ttmft
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Posted: 7/22/2005 7:01:09 PM EDT
[#34]
Check the ID of the gas tube and the mismatch between the ID of the carrier key and the OD of the gas tube end. |
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MI, USA
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Posted: 7/22/2005 7:12:45 PM EDT
[#35]
Hmmm I thought I already posted results somewhere? It's a tight fit. |
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Posted: 7/22/2005 8:31:49 PM EDT
[#36]
you may have.
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MI, USA
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Posted: 7/22/2005 8:34:32 PM EDT
[#37]
 I think I checked everything: Action Spring Buffer Gas Rings Gas Key - to Carrier seal Gas Key alignment Gas Tube Mushroom OD Gas Key Port ID Barrel Gas Port ID (0.093"-0.094") FSB alignment I polished the chamber as best as I could and I never noticed any abnormal "rings" on the spent cases that would have indicated the cases fireformed into the grooves in the chamber. |
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Posted: 7/23/2005 5:12:05 AM EDT
[#38]
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MI, USA
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Posted: 7/23/2005 12:04:55 PM EDT
[#39]
ID of gas key: 0.181"
ID of gas tube: between 0.100" and 0.125" I didn't want to ruin the gas tube roll pin since i've already taken it off/re-installed it several times, so I used several drill bits that I had. It's slightly larger than 0.100" but definitely smaller than 0.125" |
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Posted: 7/23/2005 5:58:30 PM EDT
[#40]
key looks good, dim is 0.1805"+0.0008", tube ID should be closer to .125" than .100"
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MI, USA
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Posted: 7/23/2005 6:07:53 PM EDT
[#41]
I couldn't get my mic in there but there was some play with the 0.100" drill bit.
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MI, USA
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Posted: 7/26/2005 10:48:32 AM EDT
[#42]
What's the accepted spec for the gas tube ID?
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Posted: 7/27/2005 4:54:09 AM EDT
[#43]
the print doesn't give a hard number for the ID, just a reference dim of .125"
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MI, USA
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Posted: 7/27/2005 5:05:56 AM EDT
[#44]
Hmmm a 1/8" drill bit won't fit into the gas tube though and I mic'd the drill and verified it was 0.125"
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MI, USA
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Posted: 7/27/2005 7:22:56 AM EDT
[#45]
Shall I drill it out to 0.125" or just buy a new gas tube and hope the ID is 0.125"?
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MI, USA
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Posted: 7/27/2005 5:25:57 PM EDT
[#46]
Tweak
The gas tube at the port meausures 0.125" ID The gas tube at the gas key measures 0.120" ID |
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Posted: 7/28/2005 2:53:00 AM EDT
[#47]
Should be fine at .120", I know from experience that .110" and below doesn't work. This would be a good time to check the completeness of the gas tube hole at the plugged end. Make sure there are no burrs, the hole is complete, and that the hole is .125". You should be able to drop a 1/8" bit into the hole in the FSB and have the bit enter the gas tube easily with the gas tube roll pin installed.
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MI, USA
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Posted: 7/28/2005 5:12:08 AM EDT
[#48]
I drilled out the hole at the gas key end to 0.125" and noticed that the ID of that section was slightly smaller than that of the front hole, and it wasn't just part of the "tapered" mushroom. I noticed that the gas tube gets smaller towards the upper receiver: from an OD of 0.180" to 0.172".
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Posted: 7/28/2005 5:19:25 AM EDT
[#49]
there should be a step down in D behind the mushroom then back up before the rear most bend in the tube.
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MI, USA
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Posted: 7/28/2005 5:43:28 AM EDT
[Last Edit: metroplex]
[#50]
Yep, that's what I noticed too. 0.172" steps up to 0.180"
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