Russian Nagant Gas Seal
I did a previous question about 32-20 brass for the Nagant revolver. Got a couple of replies about the gas seal. I have no clue what is being refered to. Hate sounding that stupid, but I would feel even more stupid not asking. I always thought the gas seal was when the brass swelled, sealing the chamber. Enlighten me. Thanks for your time.
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The gas seal everyone was talking about refers to the way the cylinder of the revolver moves forward when you fire the gun.The 7.62 Nagant bullet has a crimp over the bullet itself and when the cylinder moves forward it creates the gas seal,giving it a boost in velocity.You're right about the brass swelling but only when the bullet leaves the case.If you have any 7.62 Nagant ammo look at the case.hope that helps. 0 -
Not just a velocity boost, but it makes it possible to put a working silencer on it... I think it is the only revolver design that can do that...
quote:Originally posted by the_punisher_
The gas seal everyone was talking about refers to the way the cylinder of the revolver moves forward when you fire the gun.The 7.62 Nagant bullet has a crimp over the bullet itself and when the cylinder moves forward it creates the gas seal,giving it a boost in velocity.You're right about the brass swelling but only when the bullet leaves the case.If you have any 7.62 Nagant ammo look at the case.hope that helps.0 -
If you google up some pictures of authentic old factory Nagant 7.62X38R, you'll notice the bullet is completely buried in the case. Now, if you cock the revolver with rounds (or empty cases)in it, you'll see the cylinder gets pushed forward.
What happened was the case mouths of real Nagant ammo stuck out ever so slightly past the end of the cylinder. When you cocked the hammer, it would push the case mouth into the end of the barrel so no gas got out from the barrel-cylinder gap. Any revolver seals the back of the cylinder by having the case expand into the chamber walls when the pressure is high, but the Nagant also seals the barrel-cylinder gap.
The cylinder is pushed forward by the rims of the cartridges so it has to be loaded.
The starline/grafs cases are a little too short to seal, plus their rims are so thin that the cylinder doesn't get pushed forward much and there's a huge gap. 32-20 brass usually has such a thick rim that the barrel cylinder gap is almost eliminated, but that's not the same as using Russian ammo. Also, you need to use an easy-to-ignite powder because the chambers were designed for a case which goes all the way to the end of the cylinder-there's nothing around the bullet after it leaves the neck.
It supposedly only added about 50fps. It would have been simpler to use a slightly thicker cylinder and a smidgeon more gunpowder to make up for the gap. However, I believe the system may have been invented to keep blackpowder fouling from blowing around into places you couldn't get it out of easily.0 -
Reading the above caused me to check facts with my like-new Russian 1895 dated 1931 and original Russian ammo, I have a few rounds. First the ammo case sticks thru the end of the cylinder about 1.8mm. The cylinder does not depend on head thickness for its shift forward, which is about 2.0mm. The shift is part of the mechanical action constructed into the gun and occurs loaded or not. When the cylinder is forward in the cocked, firing position, there is a gap of about 1mm to the barrel, which the proper ammo case bridges over. Dimensions approx, measured with a scale rather than a micrometer.
Shooting ammo that doesn't close the gap, with the 1mm space, is several times the usual max gap for a conventional revolver.0 -
As rhmc posted - there is a plunger located in the recoil shield that pushes the cylinder forward when the hammer/action is cocked. The cylinder rides on a hollow "pin" and is spring mounted so that when the plunger returns to the rest position after the action is unlocked the cylinder springs back to the normal position. The crimped end of the cartridge casing extends into a relieved area in the forcing cone when the cylinder is in the forward/cocked position. 0 -
No, it's pushed forward MORE if there's a case in the gun. 0 -
quote:Originally posted by rhmc24
Reading the above caused me to check facts with my like-new Russian 1895 dated 1931 and original Russian ammo, I have a few rounds. First the ammo case sticks thru the end of the cylinder about 1.8mm. The cylinder does not depend on head thickness for its shift forward, which is about 2.0mm. The shift is part of the mechanical action constructed into the gun and occurs loaded or not. When the cylinder is forward in the cocked, firing position, there is a gap of about 1mm to the barrel, which the proper ammo case bridges over. Dimensions approx, measured with a scale rather than a micrometer.
Shooting ammo that doesn't close the gap, with the 1mm space, is several times the usual max gap for a conventional revolver.
edit When checking out mine, the shift forward seems the same with/without cartridge in cylinder. Precision measurement would prove one way or the other. Comment: It doesn't seem like designer would depend on cartridge head thickness to determine cylinder position, considering rotational drag, etc.0 -
So, if I'm reading this correctly, the casing will prodtrude a few .000's out the front of the cylinder during the moment the bullet transitions from the cylinder to the barrel? Am I understanding this correctly?
If so, the cylinder must manually retract very early on during the rotational cycle in order for the empty brass to clear the forcing cone as the empty chamber is moving away from the barrel.
It has to be a mechanical camming device in the gun itself that forces the cylinder forward, regardless of whether you have six, one, or zero rounds in the cylinder. Am I off the mark on this? Thanks, Joe0 -
Givette - pretty much on target. Case stick out about 1/16" and into what is the forcing cone of the usual revolver. The cylinder is moved back and forth to enter and seal off the gas loss and back so the cylinder can rotate. I'm looking for a drawing I can refer to. 0 -
The hand (the cylinder rotating device) pushes the cylinder forward some, even if there's no case. The rim has to be thicker than the amount the hand pushes it forward, in order to see a difference in how far the cylinder moves.
Load an empty case and cock the hammer. Then push the cylinder forward by hand while looking through the frame at where the case rim is pushed by the breechblock. You'll see a slight gap open up unless you have 32-20 brass and there's no clearance.
I have observed a difference in barrel-cylinder gap when going from grafs/starline nagant brass to 32-20 which has a thicker rim. It caused one of my nagants to actually interfere-the cylinder hit the back of the barrel.0
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