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Posted: 3/7/2022 10:57:30 AM EDT
I've got this barrel:
Barrel Gas block lined up, verified with compressed air. It runs fine with supers. I've already got a lightweight skeletonized BCG, and I'm using the Maxim CQB brace with the supplied 3.3oz buffer Maxim Sub ammo was 200gr Magtech. There is not enough gas to cycle even with an Obsidian 9 installed. I have a Sandman L I will try next, but has anyone tried removing weight from their buffer with a similar configuration? 
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Posted: 3/7/2022 11:18:44 AM EDT
[#1]
How new is your pistol?
I have the same brace, but it utilizes a jp scs (h1 weight) system. Once assembled and lubed, it was single shot with 220gr subs. Opened the gas up a tad, rem oil'd the snot out of, then a healthy amount of lube. Finally, racked the charging handle for nearly a minute. Runs like a Swiss watch now. Eta: vox S can on the end |
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Posted: 3/7/2022 11:25:55 AM EDT
[#2]
An adjustable gas block might also be worth liking into as well.
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Posted: 3/7/2022 11:33:29 AM EDT
[#3]
Quote HistoryQuoted: An adjustable gas block might also be worth liking into as well. |
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Posted: 3/7/2022 11:35:08 AM EDT
[#4]
Quote HistoryQuoted: How new is your pistol? I have the same brace, but it utilizes a jp scs (h1 weight) system. Once assembled and lubed, it was single shot with 220gr subs. Opened the gas up a tad, rem oil'd the snot out of, then a healthy amount of lube. Finally, racked the charging handle for nearly a minute. Runs like a Swiss watch now. Eta: vox S can on the end When you say you opened up the gas, are you referring to an adjustable block or did you ream the gas port in the barrel? Thanks! |
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Posted: 3/7/2022 11:35:58 AM EDT
[#5]
No shit it's not going to run.
You're running a barrel length that is already on the short end of factory reliability and trying to pair it with light for caliber subs that are only 1000 FPS out of a SIXTEEN inch barrel. You need more gas. Or a heavier sub (which, leads to more gas). I'm not even a little surprised. Change to 220gr subs, or subs that are designed for short barrels. Or reload and use a gassy powder. Or try a carbine buffer because that's 10% lighter but you're going to have earlier unlock which is going to cause an already dirty setup to run dirtier. |
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Posted: 3/7/2022 11:41:31 AM EDT
[#6]
Quote HistoryQuoted: No shit it's not going to run. You're running a barrel length that is already on the short end of factory reliability and trying to pair it with light for caliber subs that are only 1000 FPS out of a SIXTEEN inch barrel. You need more gas. Or a heavier sub (which, leads to more gas). I'm not even a little surprised. Change to 220gr subs, or subs that are designed for short barrels. Or reload and use a gassy powder. Or try a carbine buffer because that's 10% lighter but you're going to have earlier unlock which is going to cause an already dirty setup to run dirtier. I can't use a carbine buffer, it's longer than what will fit in the buffer tube I'm using, that's why I posted a link and photo of my gun. I've got friends with 5.5 inch and 4.75 inch barrels that run subs no problems. Not sure which ammo they are using to get these good results but I'll ask. |
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Posted: 3/7/2022 11:44:35 AM EDT
[#7]
I'm using a Q barrel with 1:5 twist and their proprietary gas block (comes a package deal).
What twist rate is your barrel? Eta: reading is hard for me apparently. I opened the gas block via a set screw by 3/4 of a turn. I'm aware you're wide open on your gas setting  Any idea how big your port is? |
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Posted: 3/7/2022 11:47:34 AM EDT
[#8]
Quote HistoryQuoted: I'm using a Q barrel with 1:5 twist and their proprietary gas block (comes a package deal). What twist rate is your barrel? |
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Posted: 3/7/2022 11:53:25 AM EDT
[#9]
Quote HistoryQuoted: 1/7 - does the faster twist make a difference with the dwell time? Additional questions in my previous post |
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Posted: 3/7/2022 12:12:59 PM EDT
[#10]
Quote HistoryQuoted: Uh thanks I guess. I posted here for advice because I'm new to 300blk and was unaware that the gas ports are on the edge of functioning and so sensitive to bullet weights. I can't use a carbine buffer, it's longer than what will fit in the buffer tube I'm using, that's why I posted a link and photo of my gun. I've got friends with 5.5 inch and 4.75 inch barrels that run subs no problems. Not sure which ammo they are using to get these good results but I'll ask. The issue is you are running the least reliable of everything. Dwell time on a 6" pistol gas barrel is almost non-existent. Shorter barrels run micro gas and actually have more dwell time. There is also the fact you are running subs that out of your barrel are probably only generating maybe 800 FPS. Maybe less. A 200gr at 800 FPS isn't generating a ton of gas. If you were to reload you'd have to add powder to get your velocity back up to 1000-1050, thus generating the gas you need. Increasing projectile weight has the same effect. You need more powder to sling a heavier bullet, thus generating more gas. Considering Magtech is cheap ammo I'm sure they are running a very fast powder that uses a very low charge to get maximum profits, but unfortunately that means very very little gas. Buy a box of cheap Remington and even that slight step up I bet you'd at least function. But ideally on a barrel that short that doesn't have micro gas you would be better served handloading. |
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Posted: 3/7/2022 12:46:27 PM EDT
[#11]
Quote HistoryQuoted: It has an adjustable gas block and is wide open. I need more gas, not less. 
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Posted: 3/7/2022 12:47:36 PM EDT
[#12]
Quote HistoryQuoted: Additional questions in my previous post |
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Posted: 3/7/2022 1:08:36 PM EDT
[#13]
Quote HistoryNot 100% sure I'd resort to this but may be an option. If I recall correctly BA already has fairly large gas ports. I want to say they are 0.097 but I may be wrong there. I'd not really want to go above 0.100. You also have to be careful with these larger gas port sizes as they can start to cut into the lands, and introduces another potential issue of shaving jackets and/or coatings. Learned that one first hand a decade ago when I was first getting into 300 BLK. |
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Posted: 3/7/2022 4:15:21 PM EDT
[#14]
Quote HistoryI'd rather lighten the buffer and or switch up ammo if that will alleviate the problem. |
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Posted: 3/7/2022 9:10:41 PM EDT
[#15]
Quote HistoryQuoted: As this point I don't think that's even possible unless I cut the gas block off. It's press fit and wouldn't budge with a torch and hand tools. Thanks for the suggestion. I'd rather lighten the buffer and or switch up ammo if that will alleviate the problem. If you can't increase the gas, reduce the mass. Lighter buffer, lightweight carrier. There is more than one way to get there. I don't know enough about suppressors to offer advice, but I do know that some create more back pressure than others. Sometime shit just needs a few rounds on it to start running right, been there. |
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Posted: 3/8/2022 5:16:05 AM EDT
[#16]
As was said above. A six inch barrel is a little small for reliable operations. 8 inch in the 300BLK is about as low as you want to go without doing all the tricks you are having to do to get it to function. Good luck and I hope that the lower buffer weight works out. Just make sure to check it on the supers after the subs because now you may have a problem with them.
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Posted: 3/9/2022 12:45:57 AM EDT
[#17]
I've got a V7 6.5" barrel that runs like a spotted ass ape.
OP, I'd try different ammo first. Least invasive option. If you have the ability to handload, that will serve you well. How much does your BCG weigh? |
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Posted: 3/9/2022 9:17:41 PM EDT
[#18]
Quote HistoryQuoted: As was said above. A six inch barrel is a little small for reliable operations. 8 inch in the 300BLK is about as low as you want to go without doing all the tricks you are having to do to get it to function. Good luck and I hope that the lower buffer weight works out. Just make sure to check it on the supers after the subs because now you may have a problem with them. |
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Posted: 3/9/2022 9:20:13 PM EDT
[#19]
Quote HistoryQuoted: I've got a V7 6.5" barrel that runs like a spotted ass ape. OP, I'd try different ammo first. Least invasive option. If you have the ability to handload, that will serve you well. How much does your BCG weigh? I've got some Remington 220gr subs on the way to try. Hopefully the Sandman L will help some too. BCG is 8oz BCG |
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Posted: 3/9/2022 9:39:57 PM EDT
[#20]
The DDM4PDW is 7" but it comes with a lighter spring for subs.
Can't find it at Maxim, but Daniel Defense will sell you both standard and light springs for $20. Might give Maxim an email or try DD. https://danieldefense.com/maxim-defense-pdw-buffer-spring-kit.html I'd try that before drilling the port or taking apart the buffer. It might be worth making sure the buffer is standard weight and wasn't accidentally mismarked in the covid gun run as well. My DD will run 200grain supers on the heavy spring with H1 buffer with a Sandman K no issue at all. |
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Posted: 3/9/2022 9:57:40 PM EDT
[#21]
Quote HistoryQuoted: My DD will run 200grain supers on the heavy spring with H1 buffer with a Sandman K no issue at all. A 6" and a 7" are wildly different. your BCG is seeing nearly twice (1.8x to be exact) the amount of gas as OP's. Dwell time is 180% as long in a 7" compared to a 6". |
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Posted: 3/9/2022 10:08:18 PM EDT
[#22]
Quote HistoryQuoted: A 6" and a 7" are wildly different. your BCG is seeing nearly twice (1.8x to be exact) the amount of gas as OP's. Dwell time is 180% as long in a 7" compared to a 6". Thank you for your help. However the point is try a lighter spring, and confirm the buffer weight before taking more extreme measures, not to analyze the difference in dwell time between a 6&7" barrel. |
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Posted: 3/9/2022 10:16:59 PM EDT
[#23]
My 8.5 inch 300blk wouldn't work with those Magtech subs either. It's also new and not broken in.
So trying new ammo is number 1 on the list. I think the brake and Sandman L will help too. Thanks everyone! |
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Posted: 3/9/2022 10:26:20 PM EDT
[#24]
Let us know how it works OP!
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Posted: 3/9/2022 10:38:01 PM EDT
[#25]
Super easy to remove weight from the maxim buffer
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Posted: 3/10/2022 1:02:23 AM EDT
[#26]
I see that the barrel you have is a 1:7 twist. So even when you get it to run, accuracy might not be great.
Is there any chance you can get one with a 1:5 twist? |
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Posted: 3/10/2022 1:38:18 AM EDT
[#27]
Quote HistoryQuoted: I see that the barrel you have is a 1:7 twist. So even when you get it to run, accuracy might not be great. Is there any chance you can get one with a 1:5 twist? I have other stuff to shoot for accuracy. |
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Posted: 3/10/2022 8:46:54 AM EDT
[#28]
Quote HistoryQuoted: I could but I'm not that worried about accuracy with subs. This is an enhanced subgun for me. Subs out to 25 yards and supers to 100 is fine. I have other stuff to shoot for accuracy. You will be fine. Stability and accuracy are fine for 200gr subs out of a seven twist. In fact it's fine up to 240gr or so. I probably wouldn't go higher than that. I've shot 245gr down to 800 FPS with zero stability issues. Plenty of stability calculators out there. Check one out. |
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Posted: 3/10/2022 9:40:48 AM EDT
[#29]
I have a SB Tactical PDW Brace (made by Maxim) and was having the same issues. I switched out the buffer and spring for ultra lights and now it will empty a mag but had no LRBHO.
Looking at the gas block is next. My subs were with 220 Gr Match Sig ammo. on the same 8.5" .300 BA barrel. |
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Posted: 3/10/2022 12:21:32 PM EDT
[#30]
Quote HistoryQuoted: I see that the barrel you have is a 1:7 twist. So even when you get it to run, accuracy might not be great. Is there any chance you can get one with a 1:5 twist? A 7 is plenty fast enough to stabilize a 200 even from that short of a barrel. |
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Posted: 3/14/2022 8:55:17 PM EDT
[#31]
Quote HistoryQuoted: Runs great with supers as is, low recoil impulse. I might just put a few hundred supers through it and try some different subs after that. Quote HistoryQuoted: Quoted: As was said above. A six inch barrel is a little small for reliable operations. 8 inch in the 300BLK is about as low as you want to go without doing all the tricks you are having to do to get it to function. Good luck and I hope that the lower buffer weight works out. Just make sure to check it on the supers after the subs because now you may have a problem with them. You are on the right path, I had to do that with my 7.5 300 blk even with a can. I have another build with the same 6" barrel as you and a short/light strike industries buffer with a standard BCG, it ran great out of the box with no can. (btw can someone recommend a photo hosting site? I'll add a picture of it elsewhere.) After a mag of supers, I tried subs, and it ran just fine unsupressed. My advice to you might be anathema, but here goes: first, make sure that your gas tube is centered in the upper and all the important parts are smooth and free of burs. Then tear the BCG down and make sure the gas rings are indexed and then cover them with a fairly heavy grease. I know a lot of smart people recommend against it, but I basically oil everything, especially during break in. This facilitates operation while you are breaking things in. I had to do this with my 7.5 300 blk when new, and it runs great now even when it gets disgustingly dirty. I still keep the gas rings on everything greased up. Hope this helps. |
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Posted: 3/14/2022 9:21:56 PM EDT
[#32]
I've run 4.75", 5.5" and 6.5" barrels with those magtech subs, I like them a lot.
If you swap a titanium bcg in, you're good. Or, cheaper, run a Tubb flatwire spring. Or as stated earlier, open up the gas port a tiny bit with a drill (which I noted you said would be difficult on yours) Heavier subs will help. More break in too, which is cheaper done with the charging handle than with supers. If you have to switch ammo, sell me that other stuff 
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Posted: 3/14/2022 10:02:59 PM EDT
[#33]
(btw can someone recommend a photo hosting site? I'll add a picture of it elsewhere.) I use imgur No complaints other than having to "find" my profile every once in a while. |
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Posted: 3/16/2022 3:53:38 PM EDT
[#34]
@azoutdoorsman
The gas port diameter of my barrel is .125 Not sure if that will help or not, but it is worth checking 
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Posted: 5/15/2022 2:38:15 PM EDT
[#35]
Problem solved. Bought a Maxim PDX with micro gas system and it runs everything no problem.
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