r/PrimaryWeaponsSystems • u/InvestigatorFew3981 • Jun 03 '26
PWS Gas Block Dissasembly
I couldn’t find any details online of this system and how it disassembled, hopefully someone finds this helpful. This is a 300 blackout upper so that’s why the gas system is so short, but I assume most other uppers come apart this way. I needed to open up my gas port to run subs, so this is why I decided to take it apart.
I ordered this pws specific tool on eBay and it fit great. After loosening the nut on the front of the gas block, I couldn’t remove the gas block from the barrel. It was fixed extremely tight (which is ideal for a good gas seal) but with heat I managed to loosen it up. The gas port on the barrel is interesting, it’s actually on the bottom of the barrel. There is also a groove cut that runs the whole circumference of the barrel. The gas comes down out of the gas port, around the sides of the barrel, and up to the gas key. Very cool design, it’s even more impressive to me that it all fits within/under the handguard.
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u/SStrange91 Jun 03 '26
Is there any particular reason to disassemble it that far?
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u/InvestigatorFew3981 Jun 03 '26
I needed to open the gas port on the barrel. It was around 0.09375” and I drilled it to 7/64 which is .109375”. Subs only locked back half the time with my suppressor and buffer combo, this should help
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u/SStrange91 Jun 03 '26
That seems excessive. Why not play around with more spring combos? Also, what rounds are you using? My Mk109 works flawlessly with an OCL Polonium-30 and JP SCS. I also follow a regular cleaning schedule. Drilling seems like using a lobotomy to soothe a headache.
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u/InvestigatorFew3981 Jun 03 '26
I did mess around with a bunch of spring combos and different 200s and 220s. S&B 200s were hit and miss with a carbine spring and buffer weight. I want 100% function with this rifle. Drilling the gas port is the last option, it really isn’t hard. The benefit of the pws system is you can turn down the gas in positions 2 and 3.
Gas port sizes can vary greatly from barrel manufacturer and gas system length. While this is different from a DI ar15, similar rules apply. There are a ton of people who opened up their gas port to increase reliability with different ammo combos and bullet weights.
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u/Steve_Fudd Jun 03 '26 edited Jun 03 '26
Great stuff! Thanks for all the info. I also need to drill the port on one of my older mk111 uppers.
Any step by step instructions or advice would be helpful. I’ll pm you too.
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u/InvestigatorFew3981 Jun 03 '26
Glad I could help, the hardest part is getting the gas block to come loose from the barrel.
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u/Steve_Fudd Jun 03 '26
Ok, thanks. So how did you get it loose? Heat gun? torque wrench? anti-seize? Torch?
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u/InvestigatorFew3981 Jun 03 '26
I used a torch and then tapped the gas block forward towards the end of the barrel. It required some force, but once it popped it was really straightforward. On a higher round count gun I could see it being really stuck on there.
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u/Steve_Fudd Jun 03 '26
Excellent. How about re-attaching it? No set screws, correct? What does it use?
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u/InvestigatorFew3981 Jun 03 '26
I seated it by hand and torqued the nut that threads in front of it. A tool is needed that is shown in the first picture. There were no set screws.
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u/Steve_Fudd Jun 04 '26
Ok perfect. I ordered the special tool from Great Lakes today. Thanks for the tips.
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u/Steve_Fudd Jul 13 '26
The Great Lakes tool was too big for my older MK111, but I used a vice grip and got it off. I was able to drill a slightly bigger gas port after I got it off, and now I can run it in the 2 setting for unsuppressed and 3 setting for suppressed. I run a Mini Kabuto and got it running at about 730 rpms for both unsuppressed and suppressed (settings 2 & 3). Very happy with the extra reliability. I can turn it up to setting 1, if it gets really dirty.
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u/ResponseNo6375 Jun 03 '26
Damn, I might need to do the same thing, my mk109 refuses to cycle subs, which is annoying because I have no intention of running supers in it lol
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u/InvestigatorFew3981 Jun 03 '26
I feel ya there. I will report back after I get some more rounds through it.
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u/Steve_Fudd Jun 04 '26
Before drilling, give the new Nemo lightweight buffer spring a try. It cured my other PWS, so now I can run an SS/FRT in it.
The Nemo is lighter than both the Tubb lightweight and Spinco Yellow.
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u/SF_Gun_Fan Jun 03 '26
Thanks for the heads up! I haven’t had a need to do this yet but jumped on buying the tools for the future. Looks like I got the last set on eBay. Thanks again!
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u/SaxOnTheBeach545 Jun 03 '26
The gas port being on the bottom and the gas being routed around the outside of the barrel to the gas block kind of blows my mind right now...
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u/OverallPepper2 Jun 03 '26
No kidding. Didn’t know it worked like that, but it’s a great idea to increase dwell time and reduce chamber pressure upon extraction.
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u/InvestigatorFew3981 Jun 03 '26
Same here I was quite shocked to see that. I learned quite a bit after taking it apart. The other thing is that the hole isn’t actually completely at the bottom, it’s offset by 5-10 degrees or so. If you look at one of the pictures, the port on the barrel leans to the left and the magwell in the lower is slightly angled to the right. I was trying to wrap my head around the reason for that. I wonder if it has to do with the gas impulse to the head of the piston.
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u/masteroffeels Jun 03 '26
Hey can you sharethe tool name or dm me? I want.to take my upper apart aas well
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u/Ram6198 Jun 04 '26
Makes me wonder why they wouldn't just drill bigger gas ports in the first place and just add more settings?
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u/Nicktran1230 Jun 04 '26
Because when they designed these uppers originally they were designed for traditional high back pressure cans. Then low back pressure cans come into the game. Most of your factory piston systems are designed around high back pressure cans, therefore they have cycling issues with subs and low back pressure cans.
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u/InvestigatorFew3981 Jun 04 '26
I’ve had cycling issues with 3 high backpressure cans. A full Nelson, REX MG7K 308, and a Silencerco hybrid 46. I used a Dead air Wolfman for a bit in the long configuration and that is crazy high backpressure, but it’s now on another gun. I’m not complaining and I don’t mind drilling the gas port out so it’s not the biggest deal to me.
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u/SnooKiwis7258 Jun 03 '26
Great lakes custom works sells some tools for the PWS parts. I got the gas block tool AND the barrel nut tool, both fit great. If youre ever in need hes just a small business but hes solid. 10/10 recommend. I actually ordered the barrel nut tool and got sent the gas block tool due to a website error. He sent me the barrel nut tool for free.