simonrichter
New member
Is there a formula for calculating the spring force in a straight blowback handgun with a given cartridge impulse and slide weight?
Thx
Thx
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Cartridge impulse - slide weight - spring force
- Thread starter simonrichter
- Start date
ShootistPRS
New member
Kozak,
That is a great resource! Thanks.
That is a great resource! Thanks.
simonrichter
New member
I still don't get it - if the spring force was irrelevant for the blowback action, why would you have to change the spring e.g. when changing caliber in multi-caliber pistols?
It's not irrelevant.if the spring force was irrelevant
It's just not what holds the bolt in place alone.
It's purpose is to cushion the blow, and return the bolt to battery.
Most blowback pistols and rifles will work fine without any return spring at all, and some have been made that way, including a single shot rifle and a single shot pistol, both .22. At least one .32 ACP pistol has been made with no return spring. A few pistols made for use with suppressors have a padded bolt and no return spring so as to keep the bolt clatter to a minimum. Of course, the bolts have to be returned to battery by hand.
Jim
Jim
Is there such a critter as a multi caliber blowback?I still don't get it - if the spring force was irrelevant for the blowback action, why would you have to change the spring e.g. when changing caliber in multi-caliber pistols?
I'm not sure on this one....
carguychris
New member
The HK HK4 was offered as a 4-caliber kit with .22LR, .25 ACP, .32 ACP, and .380 ACP barrels. It was also offered in 2-caliber centerfire/rimfire combos, most commonly .22LR and .380 ACP. The pistol incorporated a mechanism to switch the firing pin position as needed for rimfire and centerfire, although I don't recall the design details.Hal said:Is there such a critter as a multi caliber blowback?
Additionally—although factory caliber-change kits may not have been offered—many blowback pistols offered in both .32 and .380 with barrels that aren't fixed to the frame can be switched between calibers easily. For example, the Beretta 81 and 84 can exchange calibers with a simple barrel and magazine swap; the recoil springs are actually the same!
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For example, the Beretta 81 and 84 can exchange calibers with a simple barrel and magazine swap; the recoil springs are actually the same!
I'm sure there are others, but add the Astra 4000 to the list. It also had a separate slide for .22lr. Neat little gun and a good example with a full kit (all components for .22, .32, and .380) used to fetch about 2 grand or so in good shape. Despite being neat, it suffers from the same quality issues that many other Spanish pistols faced in the middle of the last century.
Is there such a critter as a multi caliber blowback?
M3A1 "Greasegun". WWII .45acp blowback SMG, had a conversion kit (barrel, bolt assy, and mag) to convert it to 9mm Luger.
I forget which volume its in, but in one of the volumes of "The Machine Gun" (col Chinn) there are formulas for calculating bolt mass & spring tension needed for blowback operation of various cartridges.