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PA, USA
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Posted: 3/6/2024 2:15:35 PM EDT
I did some digging and couldn't find much (here or elsewhere) on a specific issue I'm having with my 300 Blackout. Here's the SBR setup:
- 10.3" Daniel Defense upper (M300S) - DD bolt/carrier - H3 buffer, standard carbine spring; cycles and locks back supers/subs unsuppressed - Diligent Defense Enticer S suppressor I'm getting sporadic bolt over brass malfunctions specifically with 110gr. Vmax across multiple manufacturers (e.g. Ammo Inc., AAC). These malfunctions occur with both 5.56 and 300 blackout magazines (GI, Pmag, Lancer) and have persisted with H, H2, and H3 buffers. I have no malfunctions with a clean/lubed rifle, they only start happening after 60-70 rounds through the pipe when the rifle begins to foul up. It only affects the 110gr. Vmax, and no other ammunition (e.g. 200/220 subs, 150 FMJ) either clean or fouled. Is this likely an issue with the feed ramps, where fouling makes a potential problem worse? Is 110gr Vmax just ultra sensitive to fouling? My next step is to try a sprinco blue spring to rule out overgassing (even with an H3 it cycles subs and locks back unsuppressed) but it would seem a few mags through the rifle would make it cycle slower rather than faster. In all range sessions so far, the rifle cycles them just fine for a few magazines, but the sporadic hiccups afterwards don't give me a warm and fuzzy feeling using it for home defense at this point. Any help would be appreciated |
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Posted: 3/6/2024 3:12:22 PM EDT
[#1]
When it is getting dirty and the malfunctions start, will the bolt hold open on empty?
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PA, USA
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Posted: 3/6/2024 3:16:54 PM EDT
[#2]
Quote HistoryOriginally Posted By VeritatisUnus: When it is getting dirty and the malfunctions start, will the bolt hold open on empty? Yes, zero problems with bolt hold open with any mag or ammo, clean or dirty |
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SC, USA
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Posted: 3/6/2024 4:11:01 PM EDT
[Last Edit: hcrum87hc]
[#3]
It sounds like something to do with the geometry of the V-Max bullet doesn't jive with your rifle for some reason. Do you have to run the V-Max? Have you tried the Barnes black tips? They're a longer bullet and may be more agreeable in your case.
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WV, USA
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Posted: 3/6/2024 4:23:17 PM EDT
[#4]
I am wondering if they are too short for your rifle. I run them, from a bunch if different manufscturers, in a Remington bolt action and a frankengun
Zero issues. Another issue could be that your rifle is cycling too fast |
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Posted: 3/6/2024 4:30:38 PM EDT
[#5]
I would try another BCG just for troubleshooting purposes.
That ends up swapping out a lot of the important parts of the gas system and allows you to rule that out completely. |
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Posted: 3/6/2024 4:38:21 PM EDT
[#6]
And to clarify the malfunction, is it a live round above the bolt or a fired case?
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PA, USA
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Posted: 3/6/2024 4:38:35 PM EDT
[#7]
Quote HistoryOriginally Posted By badguybuster: I am wondering if they are too short for your rifle. I run them, from a bunch if different manufscturers, in a Remington bolt action and a frankengun Zero issues. Another issue could be that your rifle is cycling too fast Same, I'm sitting on a mountain of it from a bolt action SBR and another upper, no problems with either. They hand cycle just fine, and work fine on a clean rifle until 2 or 3 mags... this should rule out geometry or OAL issues.. Something with the fouling and/or heat of the rifle is either increasing bolt speed, or decreasing the speed the rounds are pushed upwards in the magazine. I'll be trying the springco blue with various buffers next, and also changing suppressors to a Sandman K (much lower back pressure than the Enticer S) I'm stumped on this one. Top quality upper otherwise |
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PA, USA
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Posted: 3/6/2024 4:40:32 PM EDT
[Last Edit: Horrible_Aim]
[#8]
Quote HistoryOriginally Posted By VeritatisUnus: And to clarify the malfunction, is it a live round above the bolt or a fired case? Live round below the bolt, like this pic (not my rifle.. google search). Mine pushes closer to the chamber and at a steeper angle. Fired cases eject without issue. 
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Posted: 3/6/2024 6:00:18 PM EDT
[#9]
Quote HistoryOriginally Posted By Horrible_Aim: Live round below the bolt, like this pic (not my rifle.. google search). Mine pushes closer to the chamber and at a steeper angle. Fired cases eject without issue. https://i.imgur.com/aWzftas.png Quote HistoryOriginally Posted By Horrible_Aim: Originally Posted By VeritatisUnus: And to clarify the malfunction, is it a live round above the bolt or a fired case? Live round below the bolt, like this pic (not my rifle.. google search). Mine pushes closer to the chamber and at a steeper angle. Fired cases eject without issue. https://i.imgur.com/aWzftas.png Overgassed/bolt is outrunning the mag spring makes sense, except that I have no idea why that wouldn't happen for the first couple mags. Unless the lube you use decreases resistance when hot, but that would seem to be an unlikely culprit. |
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Posted: 3/6/2024 7:07:42 PM EDT
[#10]
A couple 3 magazines, gun gets hot.
I'm thinking maybe something expanded and your getting a gas leak. Possible that you're getting less gas for recoil. Eventually, it's enough to kick out the previous bullet but not clear the next round and overides. |
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PA, USA
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Posted: 3/7/2024 1:45:54 PM EDT
[#11]
Did some more testing today.
- Malfunction happens unsuppressed, just takes longer - Sandman K and some form 1 cans made no difference - I tried with a Geissele Super 42 and H2/H3 buffer to slow bolt speed. Made no difference Gorilla 110 Varmageddons worked great, as dirty as this thing is now, as well as 150 FMJ , 125 FMJ, and various subs. There's something with the geometry of the round AND fouling that the rifle does not like. Genuinely stumped. Unfortunately I'm sitting on 1400 rounds of Vmax, might just put it up for sale |
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Posted: 3/7/2024 3:10:19 PM EDT
[#12]
Seriously... try another BCG.
Even DD is human and makes mistakes sometimes. |
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PA, USA
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Posted: 3/8/2024 1:03:14 PM EDT
[#13]
Quote HistoryOriginally Posted By gogetumnow: Seriously... try another BCG. Even DD is human and makes mistakes sometimes. This fixed it. I had a spare brand new DD BCG from an upper I just got and it worked great. Put 200 rounds through it within 15 minutes (testing heat and fouling) with zero malfunctions. Thanks all! |
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Posted: 3/8/2024 10:15:08 PM EDT
[#14]
If B/C swapped solved the problem, the problem with old B/C is carrier key is leaking at of carrier, and its the heat to the bolts that is casing them to grow, and making the leak worse.
So new key bolts, lap the bottom of key into carrier top, sealant between the two (red loctite will work fine), new key bolts torqued to 27ftlbs, and re-peen the key metal into the side spines of the bolt heads. And yes, there is a new high torque spec for the key bolts, but that is due to the new spec for the bolt being higher as well. So without knowing the spec of the new bolts your getting, use the old spec so you don't chancing stretching the bolts of torque to cause the problems again, and all will be right with the world. |
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Posted: 3/10/2024 4:55:15 PM EDT
[Last Edit: Cascade-Dude]
[#15]
Originally Posted By Horrible_Aim: I did some digging and couldn't find much (here or elsewhere) on a specific issue I'm having with my 300 Blackout. Here's the SBR setup: - 10.3" Daniel Defense upper (M300S) - DD bolt/carrier - H3 buffer, standard carbine spring; cycles and locks back supers/subs unsuppressed - Diligent Defense Enticer S suppressor I'm getting sporadic bolt over brass malfunctions specifically with 110gr. Vmax across multiple manufacturers (e.g. Ammo Inc., AAC). These malfunctions occur with both 5.56 and 300 blackout magazines (GI, Pmag, Lancer) and have persisted with H, H2, and H3 buffers. I have no malfunctions with a clean/lubed rifle, they only start happening after 60-70 rounds through the pipe when the rifle begins to foul up. It only affects the 110gr. Vmax, and no other ammunition (e.g. 200/220 subs, 150 FMJ) either clean or fouled. Is this likely an issue with the feed ramps, where fouling makes a potential problem worse? Is 110gr Vmax just ultra sensitive to fouling? My next step is to try a sprinco blue spring to rule out overgassing (even with an H3 it cycles subs and locks back unsuppressed) but it would seem a few mags through the rifle would make it cycle slower rather than faster. In all range sessions so far, the rifle cycles them just fine for a few magazines, but the sporadic hiccups afterwards don't give me a warm and fuzzy feeling using it for home defense at this point. Any help would be appreciated I am having the same exact problem with AAC 110 grain V-Max in my .300 BO AR Pistol. Aero Precision lower, 10.5" AR Stoner upper (I know, I know but it's all I could get three days before our state's ban went into effect), PMAGS. Also has a BCM buffer tube and spring. It malfunctions exactly like your photo but after more rounds, maybe 80 to 100. Unsuppressed. |
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Posted: 3/10/2024 4:59:06 PM EDT
[#16]
Quote HistoryOriginally Posted By Horrible_Aim: This fixed it. I had a spare brand new DD BCG from an upper I just got and it worked great. Put 200 rounds through it within 15 minutes (testing heat and fouling) with zero malfunctions. Thanks all! I'm going to my spares locker to try a different BCG. |
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Posted: 3/10/2024 5:00:27 PM EDT
[#17]
Quote HistoryOriginally Posted By Dano523: If B/C swapped solved the problem, the problem with old B/C is carrier key is leaking at of carrier, and its the heat to the bolts that is casing them to grow, and making the leak worse. So new key bolts, lap the bottom of key into carrier top, sealant between the two (red loctite will work fine), new key bolts torqued to 27ftlbs, and re-peen the key metal into the side spines of the bolt heads. And yes, there is a new high torque spec for the key bolts, but that is due to the new spec for the bolt being higher as well. So without knowing the spec of the new bolts your getting, use the old spec so you don't chancing stretching the bolts of torque to cause the problems again, and all will be right with the world. If my problem is the same, and if I take my BCG to a competent AR gun smith with your instructions, is that something they should be able to do for me? Thanks! |
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PA, USA
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Posted: 3/10/2024 10:49:45 PM EDT
[#18]
Quote HistoryOriginally Posted By Cascade-Dude: I'm going to my spares locker to try a different BCG. Let me know how it works. I want to do a few more test runs but so far so good. I asked DD about a replacement BCG.. not worth the money or effort to rebuild it myself |
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UT, USA
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Posted: 3/10/2024 11:13:01 PM EDT
[Last Edit: RWA007]
[#19]
I have a 300blk SBR that I set up years ago for kind of a dedicated hd setup. AAC 9" (factory upper), with an Omega suppressor that I leave on it when I'm not using it on other guns. For HD setup, I tested lots of ammo, and read lots of ammo reviews and decided that the 110 Barnes black tip ammo was the best setup for 300blk for HD. I handload and was able to find the bullets, powders, primers, etc. and handloaded a bunch of it, along with buying FACTORY ammo to use in my dedicated HD mags. I'd go out and practice with it and was burning thru my 110gr Barnes Blacktip ammo and it was $$$$$. So I found some bulk 110gr VMAX ammo in 300blk, figuring I could at least PRACTICE with that stuff. Turns out I found out that those bullets do NOT feed reliably in either one of my 300blk AR15's. (I also have a factory Daniel Defense/Ambush 16" 300blk). And furthermore, it's the same misfeed situation that you described above. I was very frustrated at first, but everything else that I've tried feeds flawlessly (likely 15 or more different brands/bullet profiles/weights/manufactures,etc.)
I see that you fixed your issue that you were having with them....I tried different bolts, buffers, etc. and could never get them to work. I basically just decided not to use those Vmax's in my 300blks. |
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PA, USA
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Posted: 3/12/2024 2:24:12 PM EDT
[Last Edit: Horrible_Aim]
[#20]
Quote HistoryOriginally Posted By RWA007: I have a 300blk SBR that I set up years ago for kind of a dedicated hd setup. AAC 9" (factory upper), with an Omega suppressor that I leave on it when I'm not using it on other guns. For HD setup, I tested lots of ammo, and read lots of ammo reviews and decided that the 110 Barnes black tip ammo was the best setup for 300blk for HD. I handload and was able to find the bullets, powders, primers, etc. and handloaded a bunch of it, along with buying FACTORY ammo to use in my dedicated HD mags. I'd go out and practice with it and was burning thru my 110gr Barnes Blacktip ammo and it was $$$$$. So I found some bulk 110gr VMAX ammo in 300blk, figuring I could at least PRACTICE with that stuff. Turns out I found out that those bullets do NOT feed reliably in either one of my 300blk AR15's. (I also have a factory Daniel Defense/Ambush 16" 300blk). And furthermore, it's the same misfeed situation that you described above. I was very frustrated at first, but everything else that I've tried feeds flawlessly (likely 15 or more different brands/bullet profiles/weights/manufactures,etc.) I see that you fixed your issue that you were having with them....I tried different bolts, buffers, etc. and could never get them to work. I basically just decided not to use those Vmax's in my 300blks. I don't know what it is about the Vmax's geometry that makes it so sensitive. 110gr Varmageddons are another good option with similar performance, excellent reliability. Just don't buy the Nosler factory ammo.. OAL way too short. I put another ~200 rounds downrange this morning, up to around 400 now without a malfunction or cleaning. Ridiculously expensive process but I can say I trust the rifle at this point. Varmageddons will remain my HD round but at least the stockpile of Vmaxs will work now! Btw, it cycles subs unsuppressed with a Sprinco blue and H3.. gas port must be gigantic |
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Posted: 3/13/2024 2:50:41 PM EDT
[#21]
Quote HistoryOriginally Posted By Horrible_Aim: I don't know what it is about the Vmax's geometry that makes it so sensitive. 110gr Varmageddons are another good option with similar performance, excellent reliability. Just don't buy the Nosler factory ammo.. OAL way too short. I put another ~200 rounds downrange this morning, up to around 400 now without a malfunction or cleaning. Ridiculously expensive process but I can say I trust the rifle at this point. Varmageddons will remain my HD round but at least the stockpile of Vmaxs will work now! Btw, it cycles subs unsuppressed with a Sprinco blue and H3.. gas port must be gigantic Since you invested so much in this, I'm going to follow your lead so we'll have another data point. I swapped out the un-marked BCG that came with the the AR-Stoner (Midway) upper and replaced it with an Aero Precision BCG. The difference in quality was noticeable. I took it apart and lubed it wet, then put it in. I have 300 rounds but I won't shoot all of it if the problem persists. If it's running fine, I'll use it all. This is my HD round. If the BCG swap fixes it, I'll throw away everything in the original BCG and install one of the Bravo Company bolts and upgrade kits from the spares locker, then put it in the spares locker (after testing, of course). I hope my results are as good as yours. 
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Posted: 3/14/2024 1:01:50 AM EDT
[#22]
I had to abort mission to rescue my daughter from a broken automobile. Reset for tomorrow.
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PA, USA
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Posted: 3/14/2024 12:37:35 PM EDT
[#23]
Quote HistoryOriginally Posted By Cascade-Dude: I had to abort mission to rescue my daughter from a broken automobile. Reset for tomorrow. All good, thanks for doing some testing! My malfunctions also happened with Ammo Inc. 110 Vmax, which has a near identical OAL but not loaded as hot as the AAC |
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Posted: 3/14/2024 5:22:46 PM EDT
[#24]
No joy. I fired less than a hundred rounds and had four failures to feed. Clearly, I need to find a dfferent load for my home defense purposes. I have several hundreds rounds of Winchester 170 grain XP that will stand in for now. I have yet to have a F to F with them but I haven't rapid fired them either. I'll do that too, maybe tomorrow. The good news is I have a bunch of 300 blackout brass I can reload with whatever I want.
I'll post what happens with the Win XP here too. |
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Posted: 3/15/2024 9:11:59 PM EDT
[Last Edit: PvtJoeBauers]
[#25]
Quote HistoryOriginally Posted By Cascade-Dude: No joy. I fired less than a hundred rounds and had four failures to feed. Clearly, I need to find a dfferent load for my home defense purposes. I have several hundreds rounds of Winchester 170 grain XP that will stand in for now. I have yet to have a F to F with them but I haven't rapid fired them either. I'll do that too, maybe tomorrow. The good news is I have a bunch of 300 blackout brass I can reload with whatever I want. I'll post what happens with the Win XP here too. If you guys are interested SGAmmo had 150 XP for a pretty good price yesterday. https://www.sgammo.com/site_search?populate=X300BLKDS |
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Posted: 3/15/2024 9:21:26 PM EDT
[#26]
Same issues with an 8" AP and a 10.5" PSA with the FN barrel.
Pretty much just dont trust the Vmax any more. |
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Posted: 3/15/2024 9:28:49 PM EDT
[#27]
Quote HistoryOriginally Posted By PvtJoeBauers: If you guys are interested SGAmmo had 150 XP for a pretty good price yesterday. https://www.sgammo.com/site_search?populate=X300BLKDS Thanks for the heads up. I'm grabbing some. |
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OR, USA
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Posted: 3/21/2024 12:38:11 PM EDT
[#28]
The 110 Vmax is just too short to be totally reliable.
A round can move forward somewhere down in the middle of the magazine, then jamb or slow down the rounds moving up. Just give a loaded mag a few smacks on the front and you can see for yourself. It’s why the designed for 300 BLK bullets have a very long and skinny nose. |
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Posted: 3/21/2024 7:24:26 PM EDT
[#29]
I fired six mags (180 rounds) of the Winchester 170 grain XP into a Vital Guy target today, in about four minutes, at 25 yards. Everything functioned flawlessly. For now, it's my home defense round.
An expensive test but a vital one. But ... I now have about 600 empty .300 BO cases I can reload and find my ideal home defense bullet and load. And several hundred more rounds of factory v-max that's now expendable range ammo and more cases. When the guy at the range was checking my ammo, he looked into the top of one of my 300 mags and half-sang, "I love big bullets and I cannot lie." 
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Posted: 3/21/2024 7:56:33 PM EDT
[#30]
Quote HistoryOriginally Posted By -k-: The 110 Vmax is just too short to be totally reliable. A round can move forward somewhere down in the middle of the magazine, then jamb or slow down the rounds moving up. Just give a loaded mag a few smacks on the front and you can see for yourself. It’s why the designed for 300 BLK bullets have a very long and skinny nose. I agree 100% that the issue, at least in my case, is the short oal of the round. |
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Posted: 3/25/2024 3:03:49 PM EDT
[#31]
Quote HistoryOriginally Posted By Horrible_Aim: Yes, zero problems with bolt hold open with any mag or ammo, clean or dirty Bolt hold open by catch on bolt face, or just catch on bottom of carrier instead. Lighter bullet means less gas pressure to the gas system, B/C not coming back as hard, so problem is either gas leak in the system that is enough to cause the problems with the slightly reduced pressure, or just mags not recovering fast enough without the added harder buffer jolt to the rear of the extension receiver. As for 300, the bullet is too wide for the front inner ribs of a 223 mags, so need to either mod the inner ribs on the 223 mags to allow them to recover correctly, or just run the 300 blk out mags. As for gas leaks, they will get worse as the rifle heats up, so check the gas block to barrel, the gas tube to block, the carrier key to top of carrier, and even check to make sure that gas tube is correctly aligned to carrier key as well. As for sub sonic loads, verse super sonic loads, understand that on most rigs, can not be achieve with the same set up. So subsonic loads needs less buffer mass, and larger barrel port since ammo is producing less pressure, and when going to super sonic loads with that set up, need to decrease gas port pressure, and increase buffer mass to get bolt unlock slowed back down and in check. Note, if you are hand loading sub sonic loads, the burn rate of the powder you are using, does effect the amount of pressure at the barrel gas port. So for sub sonic loads, very heavy bullet, and use the slowest burning powder to just achieve the subsonic speeds as the bullet leaves the muzzle, which decreases the difference of gas port sizes need in the first place. |
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