If larger calibers require a locked breech, how come there are blow-back
operated carbines in 9mm and even .45 like the Ruger and Marlin ?
TIA.
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#If larger calibers require a locked breech, how come there are blow-back
#operated carbines in 9mm and even .45 like the Ruger and Marlin ?
The Ruger PC9 in 9mm has a massive bolt/slide unit and a heavy spring to balance
out the force of recoil. This unit itself weighs more than some locked-breech
9mm handguns. Also, the design and weight of a carbine makes it easier to work
the action by hand, than it would be if the same force were required in a
handgun.
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# I've read many times that the largest caliber suitable for a blow-back
# mechanism handgun is .380 (or Makarov). Larger calibers require a locked
# breech (yes, I know there are exceptions such as weird Astras).
#
# If larger calibers require a locked breech, how come there are blow-back
# operated carbines in 9mm and even .45 like the Ruger and Marlin ?
#
# TIA.
#
Tanfoglio/Witness of Italy now comes with a 9 mm blowback
the headportion of the cartridge ( 9mm FAR) is extremely long
see pics at: http://www.handgun.no/nr1-2k/2000FAR-Tanfoglio.htm
(sorry: text in norwegian only)
this gives a delayed function on extraction, so the pressure inside the
barrel
is like zero when the brass is ejected
no locking.lugs on barrel/slide, straight blow back
time will show if it works
D v C
Roger
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Dave
<str...@my-deja.com> wrote in message news:8f59jh$chq$1...@xring.cs.umd.edu...
> ...
' If larger calibers require a locked breech, how come there are blow-back
' operated carbines in 9mm and even .45 like the Ruger and Marlin ?
The only reason for the locked breach is to allow the chamber pressure
to drop before the brass starts to eject. Once the bullet clears the
barrel, the pressure drops very quickly and it is safe to eject the
brass case.
In a straight blow-back design, the bolt and recoil spring are heavier
so as to reduce the motion before the bullet clears the barrel.
The Heckler & Koch P7 uses a retarded blow-back design. There is a
gas port just ahead of the chamber that bleeds off gas into a cylinder
under the barrel. A piston attached to the front of the slide enters
this cylinder. As the pressure drops to safe levels, the slide is
able to move back against this cylinder pressure and recoil spring
pressure.
--
David Steuber | Hi! My name is David Steuber, and I am
NRA Member | a hoploholic.
All bits are significant. Some bits are more significant than others.
-- Charles Babbage Orwell
However, there are ways around the problem, such as the gas retarded
blowback in pistols like the HK P7, where some gas is bled off and used
to hold the action shut until the pressure drops, thereby avoiding the
problem with light slide and recoil spring vs. heavier recoiling
cartridge.
#
# I've read many times that the largest caliber suitable for a blow-back
# mechanism handgun is .380 (or Makarov). Larger calibers require a locked
# breech (yes, I know there are exceptions such as weird Astras).
#
# If larger calibers require a locked breech, how come there are blow-back
# operated carbines in 9mm and even .45 like the Ruger and Marlin ?
#
Much larger parts and springs to absorb the inertia. Pistols, due
to size limitations, just can't have springs & slides that bulky.
They must use some mechanism to spread out the recoil cycle.
Strider
# If larger calibers require a locked breech, how come there are blow-back
# operated carbines in 9mm and even .45 like the Ruger and Marlin ?
Even .50 BMGs can be made in blowback design, if the breechblock and
spring are heavy enough. The Marlin carbine has a heavy block which
retards action cycling, but it would be too heavy in a handgun. The
Ruger is a hybrid, but the same ideas apply. Ditto the Tec-9 handguns
and their clones - heavy, not too accurate, but blowbacks all.
Jay T
If you increase the bullet momentum, the bolt mass and/or recoil spring
force requirements go up.
If you increase the recoil spring force, the bolt weight requirement
will go down.
What follows is a .223 blowback bolt and spring requirement calculation
I did for rec.guns.
i= inch, f= foot, s= second, fp= foot pound, A= area, p= pound, E=
energy, G= gravitational acceleration, M= mass, V= velocity, F= force,
D= diameter
assume: Peak chamber pressure = 50kp/i/i
assume: average chamber pressure = 25kp/i/i
assume: Peak bullet velocity = 2500 f/s
assume: Barrel length = 16i = 1.33f
assume: brass case inside diameter = .35 i
calculate force from chamber = PA = [25kp/i][.35i/4][.35i/4][3.14]= 600
p
calculate time of chamber force = 2 1.33f/[2500f/s]=.001 s
assume: action 2.5 i long = .208 f
assume: spring force = 20 p
calculate spring energy =fd=20 .208 =4.17 fp
calculate distance chamber pushes bolt = E/F =4.17fp/600 p = .0069 f
This means the bolt will be accelerating back for .001 seconds until it
has gone .0069 feet back and then it will be slowed down by the recoil
spring for 2.42 inches where it just runs out of speed as it reaches the
back of the action.
calculate bolt peak velocity = 2D/t = 2 .0069 f/.001s = 6.9 f/s
calculate mass of bolt = 2 E/VV = 2 4.17fp/ 6.9 f/s / 6.9 f/s = .175
pss/f
calculate weight of bolt = GM= [32.2 f/s/s] [.175pss/f] = 5.6 pounds
Clark
Chas