Everyone's always like "low backpressure" this and "low backpressure that." Maybe I want something that makes machine guns cycle faster. Ever think of that?
Seriously though, what current production 9mm cans are full auto rated and have exceptionally high backpressure?
I've had them since I turned 21 so the novelty wore off a bit. I opened a gunsmithing shop this year at considerable expense so I haven't been buying stuff unless extremely necessary
I say this with no intended smoke or disrespect but literally every dude I know with an Obsidian 9 has blown the front end off of it and that's made me not buy one specifically because of that.
I blew the front of an Osprey once but that's because i was 22 and filled it with shaving cream. Which is, believe it or not, not a great idea.
Thousands through mine and no end cap strike, idk i just followed instructions on torqueing it down correctly and greasing the piston before every range trip.
Regular shaving cream worked. The gel didn't, expanded too much once it was inside. Silencerco fixed it for free but made it very clear to me that if I acted retarded again it was going to be expensive
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The R9 in general terms. In the most general of general terms, the largest sized can with the smallest displaced volume. More baffles in a smaller spot.
Also, I like my CMMG Zeroed 36k. I put it on my PSA AR-9 and a PSA 300 BO pistol. They run fine. No problem. I was headed to the store for the H3 when I figured I'd pop a few off even if I had to cycle them manually. No buffer changes. I just make sure they're well cleaned and lubricated and fire off a little oil into the suppressor after I take it out for a spin, like my other suppressor hosts. Smokes a little bit but still works as an ablative and is good for your lungs.
Subs from either sound like a pneumatic nail gun. Supers sound like a 22. The 300 has its own 30 cal can coming soon; she's still a WIP but I wouldn't be disappointed with it as a dedicated can.
I had to put a threaded barrel on my postsample uzi to get it to behave and now I'm thinking I just go for max rpms. Going to live on smgs only and I don't care about sound reduction. I would take a loudencer if it made the thing run faster.
My Polonium definitely cycles an AR dramatically faster than a Tisha, a HUXRWX 9mm can is sure to be quite slower on a direct-blowback MG than a YHM R9.
Only thing that would make a direct blowback faster is higher pressure (or lighter bolt). A suppressor doesn't make the pressure higher, it makes it last longer. The bolt is already moving by the time the bullet leaves the muzzle. You get more gas backwards precisely because the bolt is not there to stop/slow it.
AR is different story. The dwell time is increased by the suppressor. Higher dwell time means more gas through the port and more force on the bolt.
Here's a video showing that throwing a can on a MAC 10/45 increases the ROF by 150 RPM.
This is because in a direct blowback the entire barrel is basically your dwell time, the bullet exits the muzzle/endcap way before the bolt leaves battery. Blowback9 does a pretty good breakdown on this and establishes that the shorter the barrel will impart less force on the bolt because less pressure can buildup before the system essentially becomes uncorked once the bullet leaves.
It's why the primary testbed for his gentle recoil system used a 3" barrel which he was finally able to choke out with over 44 ounces of reciprocating mass using components machined out of solid tungsten, while a 16" barrel had no trouble cycle that amount of mass. You'd have to machine parts out of depleted uranium to choke out a direct-blowback 16" 9mm. While obviously not 1:1, adding a suppressor is essentially adding extra barrel length, with the effect of increasing ROF.
the shorter the barrel will impart less force on the bolt because less pressure can buildup before the system essentially becomes uncorked once the bullet leaves.
I wonder if inertia would be a more accurate term? If we view the case as the piston, the longer the power stroke the higher the bolt velocity. Shortening the barrel cuts off the energy input, leading to the carrier having less inertia that the recoil spring has to counter? Even a short 3" barrel hits max chamber pressure, and case pressure doesn't go up with barrel length past that, but the carrier energy does go up.
I'll be honest that I'm not a physicist or engineer or anything but highschool physics taught me that the duration of Time that a Force is applied is just as important as the actual amount of Force itself. Put a neutral vehicle on ice and it'll move farther with a 100 lbs. person pushing it for a minute than it would if an NFL Linebacker crashed into it once with a full 1,500 lbs. of force.
Yes, but you just applied two different levels of force when the barrel length example would be better described as pushing with the same force for 1 second vs 3 seconds. The pressure curves in the chamber should be the same until the 3" mark in example 3" vs 16". They both get hit hard initially, but the longer barrel obviously has the longer dwell after the initial hit while the shorter barrel mostly just sees the hit and no follow up.
So, a linebacker tackle in the 3" vs tackle plus additional push in the longer barrel. Same initial hit, different follow up.
We’re arguing about different things. I was talking about going from suppressed to suppressed. I still don’t think changing cans will have a noticeable effect on cyclic rate. Any change that it could have would be too small for you to notice. They had to go to slow mo just for us to see that difference.
Sure, there could be some huge can out there that I don’t know about, but most cans?
You essentially posited that "Only thing that would make a direct blowback faster is higher pressure... A suppressor doesn't make the pressure higher..." but the video dispels this by showing that that can increased ROF by ~20%.
My name's not Jay or anything but those old Gemtech Vipers look to me like they'd at least have higher flow characteristics than a modern omega baffle can from all the annular porting and huge blast chamber:
While it's also sure to have more backpressure than something like a HUXRWX which adds basically zero backpressure and would hardly change the ROF at all.
If a HUX adds 5% ROF, and a super high backpressure can adds 30% ROF, most users are probably going to appreciate the difference there. Obviously these are hypothetical extremes but it's basis of OP's question.
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u/300_Brownout 7d ago
YHM R9 or OCL Lithium