this post was submitted on 30 Nov 2023

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Silent With No Suppressor - The 7.62x42 SP4 (1970s) (lemmy.world)

submitted 11 months ago* (last edited 11 months ago) by FireTower to c/forgottenweapons

18 comments fedilink hide all child comments

This design allows a gun to be much quieter without a suppressor. It's fairly simple in its concept. When it's fired the blast (and noise) is on the rear side of the red piston. Next the piston is propelled towards the case mouth, pushing the projectile (gray cylinder) out of the casing, through the barrel, and into to the target. The piston remains in the casing, crumpling and forming an air tight seal.

~~This Soviet concept to my knowledge doesn't have a NATO equivalent~~ there is something similar if you search up Quiet Special Purpose Revolver. Despite the fact it's reportedly only 110 db loud, roughly as loud as a silenced 22lr.

Three firearms models have been chambered in it the NRS-2 knife, OTs-38 revolver, and PPS pistol. (Shown in order)

Here is it being fired out of the NRS-2 knife gun:

https://youtu.be/vW3ZBLlPz_c?si=UCoCEwzaqVANMcY_ [00:11]

It's simply a really clever approach to a design requirement, but of course there's at least three reasons it's not more popular.

One, the piston system must increase the cost to produce each round.

Two, The ATF treats these as silencers legally. This means each shot come with a $200 tax for anyone in the world's largest civilian firearms market.

And three, how often does a government or individual need to fire a silenced shot but can't bring along a suppressor? Is this a solution looking for a problem?

Also heres some more stuff about the NRS-2:

top 18 comments

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[–] chemical_cutthroat 57 points 11 months ago (4 children)

So, you fire the projectile with the knife facing towards you?

[–] [email protected] 26 points 11 months ago

In Mother Russia, gun have a knife.

[–] FireTower 22 points 11 months ago* (last edited 11 months ago) (1 children)

It does come with a sheath he could have on. But yeah, hopefully 7.62x42 SP4 doesn't have much recoil. Otherwise our friend here might earn himself an eye patch.

[–] GONADS125 3 points 11 months ago

Could easily see someone losing a fingertip firing it.

[–] cmbabul 6 points 11 months ago

A prototype of the RX9 knife missle!

[–] Idreamofcheesy 4 points 11 months ago

Ahahaha right? It looks so dopey!

[–] [email protected] 18 points 11 months ago (1 children)

This one was very interesting

[–] FireTower 11 points 11 months ago

I absolutely agree. It's real outside the box thinking.

[–] GONADS125 12 points 11 months ago (1 children)

I have known about the knife for years, but not that it shot this type of projectile. Had no clue this type of munition existed. Really interesting but seemingly impractical.

[–] FireTower 5 points 11 months ago* (last edited 11 months ago)

I'm glad to hear you learned something. This is one thing Ian hasn't covered so I hoped it'd be new to some people.

[–] [email protected] 11 points 11 months ago (3 children)

This is probably a stupid question but what if you used these rounds and and a silencer together?

[–] CaptainS7ark 4 points 11 months ago

I was gonna ask the same exact thing.

[–] FireTower 4 points 11 months ago

It should be quieter. But I'm skeptical as to how much, I don't think it'd be too crazy quiet. Any audio engineers in the chat?

[–] [email protected] 4 points 11 months ago (1 children)

Depends on a bunch of things like the volume of the suppressor, the gun it is mounted on etc. Theoretically it should be quieter as any escaping expanding gas is bled off, including the air around the projectile in front of the piston as it gets superheated and compressed etc. I doubt it would be noticeably quieter to the human ear as I'm guessing the rounds are already subsonic out of all the guns that use them, but I could be wrong.

There are a couple potential side effects though. It is possible the silencer decreases the ballistic performance significantly. I'm going to guess these rounds are barely lethal in their stock configuration so even a 10-20% drop in velocity could be a big hindrance to their effectiveness. Also suppressors tend to increase back pressure so it seems possible that could mess with the function of these rounds. Would it delay the piston coming forward, or possibly blow the primers out the back of the rounds? Hard to say without testing but it is a possibility.

[–] FireTower 2 points 11 months ago* (last edited 11 months ago)

~~Most models of suppressors will raise muzzle velocity just like adding barrel length does. Unless you have rubber wipes in there.~~ Edit: I realized that because the gases are all trapped in the cartridge it won't continue to extert force through the length of the barrel or suppressor.

I found one source https://dockeryarmory.com/7-62x42mm-sp-4/ claiming they are 153 grain bullets moving at 621 fps at the muzzle. So they are subsonic.

It also claims 133ft/lbs at the muzzle and the low end of lethal is supposedly ~58ft/lbs.

[–] Junkers_Klunker 8 points 11 months ago

That is friggin cool.

[–] [email protected] 2 points 11 months ago (1 children)

This is pretty cool, but what kind of muzzle velocity or impact energy would these rounds have?

Part of the reason for longer barrels is to let the powder burn and fully push the round. A subsonic round would probably give similar performance on a traditional cartridge.

If you're concerned with noise, a suppressed .22 is quieter than a pebble thrown in the woods.

[–] FireTower 1 points 11 months ago

I found one source https://dockeryarmory.com/7-62x42mm-sp-4/ claiming they are 153 grain bullets moving at 621 fps at the muzzle. So they are subsonic.

It also claims 133ft/lbs at the muzzle and the low end of lethal is supposedly ~58ft/lbs. Sub sonic 22lr is ~90ft/lbs.

One other cool thing about this though is that it doesn't need the length of a barrel (beyond what it needs to stabilize) because it isn't gaining anymore velocity after the piston hits the bullet.