Taking advantage of a longer barrel for pistol rounds

[dkf]

I don't see the point in using LP primers when SP magnum primers are available, though IMO you don't need either. Maybe uniform the flash holes if they are small. Usually the slowest powder for .40 that is used is AA#9, but it is very bulky and stout load will be a compressed charge. Really a carbine is better suited to the .357sig vs the .40 IMO if you want to get velocity out of it. Less volume in the 9mm diameter bore vs the .40. Similar principal why once you get around a 16" barrel with .45acp the velocity levels out or starts dropping off. If you want higher velocities in .40 you are better off IMO to use a lighter bullet (like 135gr) as a long 180gr bullet takes up a lot of precious powder space.

[Geppetto]

One thing to remember with blow back guns is that the weight of the bolt is the only factor that really matters. The spring just closes the bolt. Increasing spring force doesn't affect the pressure it takes to get the bolt moving. The inertia and mass of the carrier define that.

[Harter66]

I would disagree. The springing has much to do with load management. I am not acquainted enough to give numbers,but an ISP?? shooter doing their own gun tuning probably can. Realizing that a tuned 1911 race gun has nothing in common with the typical pistol calibre carbine. For a larger example take a look at and older A5 Browning. Spring spacing and curves make all the difference in feeding or not with different loads from 1 Oz trap loads to 1 3/8 game loads.

[Forgetful]

I don't see the point in using LP primers when SP magnum primers are available, though IMO you don't need either. Maybe uniform the flash holes if they are small. Usually the slowest powder for .40 that is used is AA#9, but it is very bulky and stout load will be a compressed charge. Really a carbine is better suited to the .357sig vs the .40 IMO if you want to get velocity out of it. Less volume in the 9mm diameter bore vs the .40. Similar principal why once you get around a 16" barrel with .45acp the velocity levels out or starts dropping off. If you want higher velocities in .40 you are better off IMO to use a lighter bullet (like 135gr) as a long 180gr bullet takes up a lot of precious powder space.

-I like the idea of a harder cup and the initial bullet dislodging caused by the det force, for lower pressures.
-Flash holes are only ever uniformed when small.. Can't uniform a larger hole than your tool can make.
-Herco is a little faster, and I don't think I'll make it to compressed charges with this heavier primer. Going to see how slow I can go, might make it down to 4227.
-I want the larger volume for the higher BC and velocity. Using the longer barrel should make the Charge/Velocity relationship more efficient.

One thing to remember with blow back guns is that the weight of the bolt is the only factor that really matters. The spring just closes the bolt. Increasing spring force doesn't affect the pressure it takes to get the bolt moving. The inertia and mass of the carrier define that.

- That's bang on.

I would disagree. The springing has much to do with load management. I am not acquainted enough to give numbers,but an ISP?? shooter doing their own gun tuning probably can. Realizing that a tuned 1911 race gun has nothing in common with the typical pistol calibre carbine. For a larger example take a look at and older A5 Browning. Spring spacing and curves make all the difference in feeding or not with different loads from 1 Oz trap loads to 1 3/8 game loads.

-The spring affects the velocity of a moving object since it has no static force to stop something from moving. It's all dynamic force.
-The gun can't be tuned quite like a 1911, so I'm tuning the ammo for the gun.
-The Auto-5 uses different friction ring settings for different loads..

[Pinsnscrews]

I have been warned to not use 4227 in my 10mm due to possible detonation rather than burn due to the small charge. I have load data for 2400 in 10mm for a TC Contender.

[243winxb]

Longshot powder on Hodgdon"s website shows the highest velocity for both 40 S&W & 10 mm using a 180 gr. Then you have Alliant's Blue Dot. Check the burn rate chart https://www.hodgdon.com/burn-rate.html Both powders should come close to highest possible* fps out of the carbine barrel using lead and listed maximum powder charges.

[seaboltm]

One thing to remember with blow back guns is that the weight of the bolt is the only factor that really matters. The spring just closes the bolt. Increasing spring force doesn't affect the pressure it takes to get the bolt moving. The inertia and mass of the carrier define that.

Negative Ghost Rider. The total force matters, which will involve the mass of the bolt, the force of the spring, and friction. For a gendankenexperiment, imagine placing a 450 pound per inch car coil spring behind the bolt. Upon firing I promise you the bolt won't move. The spring matters. A lot. Also, mass is how we measure inertia, so "mass and inertia" is somewhat redundant.

[Forgetful]

Negative Ghost Rider. The total force matters, which will involve the mass of the bolt, the force of the spring, and friction. For a gendankenexperiment, imagine placing a 450 pound per inch car coil spring behind the bolt. Upon firing I promise you the bolt won't move. The spring matters. A lot. Also, mass is how we measure inertia, so "mass and inertia" is somewhat redundant.

Have to wonder how much that spring would weigh, or just the front half that would be handling the kinetics. I think the bolt would move, if the spring had no extra mass to provide a static force, but it would rapidly decelerate within the first quarter inch and slam back closed. That's the problem with springs. Can you imagine a strong enough spring to keep your front door closed, with a pre-loaded tension, if a 300lb man was bashing against it from the other side? If it's X sized and he can bash it open a foot, and you double the size, it might only be a few inches or half a foot, but it will still open. This is called shock-loading, and is based on the inertia of the spring coils.

[badbob454]

[QUOTE=Outpost75;2984184]I have experimented with case capacity charges of #2400 loads in a converted H&R single-shot in .45 ACP with 20” barrel. DO NOT try these loads in an M1911 pistol, but only in the New Model Blackhawk convertible or a suitably strong rifle which supports the case well. In shotgun actions it is necessary to bush the firing pin for these loads to prevent punctured primers. ......
i dont understand what is bush the firing pin

[GhostHawk]

In H&R rifles the hole for the firing pin can be larger than the pin. This could allow pressure to blow out the primer.

Bushing the firing pin is basicly putting a spacer around the firing pin where it comes out of the action. Keeping it more airtight, prevents the gas from seeking a week spot back into the frame.

In my Handi rifle however the hole is sized perfectly and there is no way you would get a bushing in there that lets the firing pin come out.

The main point is you don't just JUMP into those big max loads. You start with starting loads and work up slowly. Examining each fired round closely for pressure signs, primer deformation, etc. Stop as soon as you see something and back down your load a bit.

[seaboltm]

Have to wonder how much that spring would weigh, or just the front half that would be handling the kinetics. I think the bolt would move, if the spring had no extra mass to provide a static force, but it would rapidly decelerate within the first quarter inch and slam back closed. That's the problem with springs. Can you imagine a strong enough spring to keep your front door closed, with a pre-loaded tension, if a 300lb man was bashing against it from the other side? If it's X sized and he can bash it open a foot, and you double the size, it might only be a few inches or half a foot, but it will still open. This is called shock-loading, and is based on the inertia of the spring coils.

you are describing the effects of F delta T = M delta V, which is the impulse-momentum theorem. If the spring is static (the spring can only compress, not completely slide), the only things that matter for a spring are the spring constant and the amount of compression. For a simpler experiment on the blowback, take a real strong 9mm spring and put it in a 380 blowback. It won't cycle. The spring will keep the bolt shut. Or, just put a 380 cartridge in a 9mm and fire away. It won't cycle: not enough force generated by the little 380 to cycle the slide. Yes, the slide may begin to move, but that's it. I have tried that one many times just for grins.

[Forgetful]

Yes, the slide may begin to move, but that's it. I have tried that one many times just for grins.

Precisely. It bounces.

[Geppetto]

Here's some discussion to what I was referring to. Springing is important for cycling, but not for containing increased pressure. http://www.orions-hammer.com/blowback/

[seaboltm]

Here's some discussion to what I was referring to. Springing is important for cycling, but not for containing increased pressure. http://www.orions-hammer.com/blowback/

Good reference.