Blow-back in 9mm

[str...@my-deja.com]

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.

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[Robert Rubenstein]

On 7 May 2000 22:42:57 -0400, str...@my-deja.com wrote:

#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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[Roger]

str...@my-deja.com wrote:

# 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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[kontiki]

Carbines (and sub-guns) are larger than pistols and therefore can get
away with using larger and heavier bolts and return springs. The practical
size and weight of a pistol limits the size of it's bolt and return string.

[Dave Williams]

Blowback could work in about any caliber as it is a matter of having a heavy
enough bolt and/or stiff recoil spring to hold the bold closed. The
practical reason for not having many straight blowback pistols in the higher
calibers is that they would be too heavy or have a stiff recoil spring which
would make operating the slide manually for loading difficult. For
carbines, you can have the necessary heavy bolt as they are larger and
therefore heavier anyway.

Dave

<str...@my-deja.com> wrote in message news:8f59jh$chq$1...@xring.cs.umd.edu...
> ...

[David Steuber]

str...@my-deja.com writes:

' 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.

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All bits are significant. Some bits are more significant than others.
-- Charles Babbage Orwell

[Ron Seiden]

Because in a carbine (or other firearm larger than a pistol) you have a
heavier slide which soaks up the impulse from the blowback without the
need for a too-heavy recoil spring. The chunk of metal used in blowback
guns like the Thompson submachine gun (.45acp) or the Uzi (9mm, .45acp)
is heavier than most entire pistols.

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 ?
#

[Strider]

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

[fl...@alaska.net]

Someone wrote:

# 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

[Clark Magnuson]

You can make any gun a blow-back, the problem with bigger guns is the
bolt gets massive and the spring gets stiff.

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

[Rtr302]

I had an Israeli made, Sardius SD9 a few years ago that was a small (drop it in
my shirt pocket) 9mm Parabellum semi auto. It was simple blowback, DAO. The
trigger cocked a striker (and pushed the slide back a bit as it did!), then
released it to fire the weapon. It produced light primer strikes that too
often failed to fire it, so I got rid of it, but it was a nice, little,
parkerized chunk of pistol. I still find it hard to believe it was simple
blowback, but it was. How could such a small pistol be both simple blowback
and 9mm Parabellum without blowing up?

Chas