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AR15 gunsmith near Plymouth/South Bend
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Upper is a RRA upper with a DD 300 blackout 16" CHF 1:8 twist barrel. SEEN HERE Carbine gas system. UBR stock and the buffer tube they provide(A5 I believe). The bolt will cycle 2-3 rounds perfectly fine without issue and then what is shown below happens. The BCG gets stuck in the buffer tube and jams the next round into the feed ramps. To clear this malfunction I have to separate my upper and lower. This is unacceptable to me in a defensive situation obviously. I have tried to lube the BCG extra wet and that only made it worse. I haven't tried different buffer weights or anything like that yet. I am running a standard weight buffer(as in the one that comes with the PSA parts kit). I don't know what the gas hole diameter is. I don't have any of the tools necessary to work on my upper to check that. I don't know what else to try. I literally have this AR EXACTLY how I want it and am very frustrated that it doesn't run how it should.
It's not an A5 (Vltor) tube, it is a shorter "entry" type tube, uses regular carbine buffers and springs.
Does the bcg travel freely when you "rack" it with the charging handle? (no ammo or mag)
Does the bolt lock back if you load ONE round and fire it?
What mags are you using?
Does the bcg travel freely when you "rack" it with the charging handle? (no ammo or mag)
Does the bolt lock back if you load ONE round and fire it?
What mags are you using?
not a huge problem.
1st, you don't have to pull the gun apart to clear that. put the charging handle to use. "mortar" it if you have to, but it shouldn't take too much force to pull the bolt off the jammed cartridge.
That's a common bolt-over malfunction. The bolt isn't traveling rearward enough to get behind the round, it's trying to feed it by sliding along the top.
Common sources of the problem are weak ammo (have you tried various types of ammo?), bad mags or mag springs, or under-gassed (barrel gas port too small, etc).
Does the bolt lock back by itself on an empty mag?
Sometimes if it's brand new, a little break-in will solve it if the carrier travels a little rough in the upper...
UBR stock is a carbine size buffer, not A5 afaik, so you could try a lighter buffer.... but first, if you haven't tried various types of ammo, I'd run some other brands and loads to see if that helps...
are you using good mags? .300blk is a lot of weight for the mags designed for 5.56 to lift. Does it do it if the mag is more full, or more if the mag is more empty?
I always start w/ the ammo w/ these types of issues...
Who built the upper since you don't have the tools? Someone you trust to get it right and make sure everything is aligned right in the gas system?
-rvb
1st, you don't have to pull the gun apart to clear that. put the charging handle to use. "mortar" it if you have to, but it shouldn't take too much force to pull the bolt off the jammed cartridge.
That's a common bolt-over malfunction. The bolt isn't traveling rearward enough to get behind the round, it's trying to feed it by sliding along the top.
Common sources of the problem are weak ammo (have you tried various types of ammo?), bad mags or mag springs, or under-gassed (barrel gas port too small, etc).
Does the bolt lock back by itself on an empty mag?
Sometimes if it's brand new, a little break-in will solve it if the carrier travels a little rough in the upper...
UBR stock is a carbine size buffer, not A5 afaik, so you could try a lighter buffer.... but first, if you haven't tried various types of ammo, I'd run some other brands and loads to see if that helps...
are you using good mags? .300blk is a lot of weight for the mags designed for 5.56 to lift. Does it do it if the mag is more full, or more if the mag is more empty?
I always start w/ the ammo w/ these types of issues...
Who built the upper since you don't have the tools? Someone you trust to get it right and make sure everything is aligned right in the gas system?
-rvb
It was put together by Belcher's gunsmithing in South Bend. When the bolt jams the next round, the charging handle flops around freely and doesn't catch on the bolt. It happens when the mag is full and when I only load a few rounds. All mags are pretty new and shouldn't be warn out. Ammo being used is 220 gr. Remington UMC...should I try 208 gr?
You might try good GI or Magpul 30 rounder. the MP 20's don't have the best reputations (I don't know about the lancer 20s).... however, if it's not locking back if you just load/fire one, that's probably not the problem..
the charging handle WILL catch on the carrier, just pull it back. It "flops around" since the bgc is stuck and not putting forward pressure on it. Pull it back till it 'catches' on the carrier, then yank it back.
Remington umc is known to be weak stuff in the .223 and some guns that otherwise run fine will choke on it... I don't know about .300blk, but you might try a different manufacturer.
If you look at the face of the buffer, can you see what weight it is (should say something like H1, H2, H3... or nothing at all). If it's really heavy, and the gas port is on the small size (and/or the ammo is relatively weak), you might be able to fix it w/ a lighter buffer...
couldn't you get the place the built it to look at it?
... but first, I'd at least try some other ammo....
-rvb
the charging handle WILL catch on the carrier, just pull it back. It "flops around" since the bgc is stuck and not putting forward pressure on it. Pull it back till it 'catches' on the carrier, then yank it back.
Remington umc is known to be weak stuff in the .223 and some guns that otherwise run fine will choke on it... I don't know about .300blk, but you might try a different manufacturer.
If you look at the face of the buffer, can you see what weight it is (should say something like H1, H2, H3... or nothing at all). If it's really heavy, and the gas port is on the small size (and/or the ammo is relatively weak), you might be able to fix it w/ a lighter buffer...
couldn't you get the place the built it to look at it?
... but first, I'd at least try some other ammo....
-rvb
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Does it shoot supersonics without the malfunction? My 300 Noveske 10" upper would act like yours if I shot subsonics without the suppressor. I changed buffers, and a lighter one helped some, but didn't cure the issue. The good news is that after I'd fired a mix of several hundred rounds of both sub and supersonic ammo the upper "loosened up" and the problem went away. It now reliably fires Remington 220gr subs without a can.
And are you sure it's a carbine length gas system? My understanding is that most 300BLK use pistol gas, even on longer barrels?
And are you sure it's a carbine length gas system? My understanding is that most 300BLK use pistol gas, even on longer barrels?
According to the link he gave to Daniel Defense, yes it is a carbine length gas system.
https://danieldefense.com/cold-hamm...arrels/16-300-blk-s2w-carbine-chf-barrel.html
I certainly appears that it's under gassed with subsonic ammo.
1. It may "break in" after more rounds are put through it, but that's not guaranteed and ammo isn't cheap. I guess I was lucky with my 10" pistol; it always fired subs with a can (which is the only way I want to fire subs), and over time it "loosened up" enough to to fire them without the can.
2. The gas block may not be aligned with the gas port in the barrel. Since you lack tools I won't go into how to fix this issue. Sometimes gas will escape from under the gas block and leave carbon streaks on the top of the barrel if it's misaligned or loose, but that's not always the case and I'm not sure if subsonic 300 BLK with a carbine gas system will have enough pressure to leave much of a sign.
3. The gas port is too small. Given that it's a DD barrel I would think that this would be pretty unlikely but it's possible.
4. As RVB described and I experienced with my 300BLK, 20 round PMAGS can exacerbate bolt over malf's in a 300 BLK. I have (4) 20 round PMAGS and before my gun loosened they were much more likely to be in the gun than a 30 rounder when a bolt over malf occurred.
From the FAQ at http://www.300blktalk.com/forum/viewtopic.php?f=128&t=73274
Q: Is an adjustable gas block required to shoot subsonic unsuppressed, subsonic suppressed, full power unsuppressed, and full power suppressed?
A: It depends on the brand. An AAC will shoot all four configurations wihout any adjustment needed when using Remington or similar ammunition. No doubt several top makers will have products which will do this, but not all will.
Q: Should I look for an AR upper with carbine or pistol gas?
A: First, there is no barrel length which works with mid-length or rifle gas. The choices are carbine or pistol. For barrels under 16 inches, pistol is needed - the bore is larger than 5.56mm so the gas pressure drops off faster. For barrels 16 inches or longer, carbine or pistol gas will work.
Q: Well then - for a 16 inch barrel, why would someone chose one type of gas vs the other?
A: If you are the type of person who prefers mid-length gas on a 5.56mm because it has less gas port erosion and less stress on the bolt and extractor, then choose carbine gas. If you want to experiment with extra fast-burning powders and are willing to either not shoot full power ammo or have an adjustable gas block - then use pistol. Remington subsonic ammo generates enough gas pressure to be compatible with carbine gas in a 16 inch barrel.
1. It may "break in" after more rounds are put through it, but that's not guaranteed and ammo isn't cheap. I guess I was lucky with my 10" pistol; it always fired subs with a can (which is the only way I want to fire subs), and over time it "loosened up" enough to to fire them without the can.
2. The gas block may not be aligned with the gas port in the barrel. Since you lack tools I won't go into how to fix this issue. Sometimes gas will escape from under the gas block and leave carbon streaks on the top of the barrel if it's misaligned or loose, but that's not always the case and I'm not sure if subsonic 300 BLK with a carbine gas system will have enough pressure to leave much of a sign.
3. The gas port is too small. Given that it's a DD barrel I would think that this would be pretty unlikely but it's possible.
4. As RVB described and I experienced with my 300BLK, 20 round PMAGS can exacerbate bolt over malf's in a 300 BLK. I have (4) 20 round PMAGS and before my gun loosened they were much more likely to be in the gun than a 30 rounder when a bolt over malf occurred.
From the FAQ at http://www.300blktalk.com/forum/viewtopic.php?f=128&t=73274
Q: Is an adjustable gas block required to shoot subsonic unsuppressed, subsonic suppressed, full power unsuppressed, and full power suppressed?
A: It depends on the brand. An AAC will shoot all four configurations wihout any adjustment needed when using Remington or similar ammunition. No doubt several top makers will have products which will do this, but not all will.
Q: Should I look for an AR upper with carbine or pistol gas?
A: First, there is no barrel length which works with mid-length or rifle gas. The choices are carbine or pistol. For barrels under 16 inches, pistol is needed - the bore is larger than 5.56mm so the gas pressure drops off faster. For barrels 16 inches or longer, carbine or pistol gas will work.
Q: Well then - for a 16 inch barrel, why would someone chose one type of gas vs the other?
A: If you are the type of person who prefers mid-length gas on a 5.56mm because it has less gas port erosion and less stress on the bolt and extractor, then choose carbine gas. If you want to experiment with extra fast-burning powders and are willing to either not shoot full power ammo or have an adjustable gas block - then use pistol. Remington subsonic ammo generates enough gas pressure to be compatible with carbine gas in a 16 inch barrel.
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Tried a 3 oz buffer weight and it's still a single shot AR currently. I have some 208 gr. Amax on its way. Cycled supers just fine still like usual. I didn't see any leakage around the gas block. At least I'm narrowing down the possibilities.
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