Taking advantage of a longer barrel for pistol rounds

[Forgetful]

I couldn't find a subforum for this, so here goes. I'm going to be testing some round-nose castings in my Just Right Carbine 40S&W. The FN rounds jam up. There is some sort of relationship between chamber pressures and how hard it cycles, because there is also a jam on ejection sometimes. My plan is to use Round Nose and wildcat a cartridge that works better for this carbine.

I want to use a slower powder to make better use of the longer barrel, so that the projectile doesn't accelerate to max velocity in the first 6 inches, but uses the chamber pressure better to achieve max velocity at 18 inches instead. (barrel length is 18.6")

I want to use K&M's primer pocket correction tool to cut the primer pocket on the 40S&W brass to fit Large Rifle Primers to make better use of the slower powders. For now I want to presume the hammer and firing pin are strong enough to reliably det these primers.

There is an issue with unsupported headspace in older 40S&W brass where the feed ramp is cut so deep that the brass used to explode (pre-2004 or so) but it's also trying to get a 180gr round to 1000fps in 6 inches....

I want to get that 180gr round to 1500fps in 18 inches. Am I asking too much? Seems plausible to me! This could be a big step for pistol carbines, making them slightly less useless if they can start acting like rifles.

[seaboltm]

I think you can get close to that. I also think a small pistol primer is more than adequate to ignite the relatively small amount of powder in a 40 S&W case. Interested in seeing the powders you use and the results.

[Forgetful]

The case will only hold around 7 grains of powder. I thought having a stronger primer would allow for the slower charge to get going better and to provide more energy to the cartridge. Slower powder should be lower pressures, which should leave a little room for increasing the pressure with a stronger primer.

I'll start the loads with Herco since it is slower than Blue Dot. I'll work my way down to rifle powders. I thought of this last night, thought it was a great idea. Not so sure if I'm compromising the brass by cutting out the large primer pocket.

[Thompsoncustom]

I've done something like this. Pushed 130gr 9mm bullets to 1700fps in my 16in carbine. I don't think ur asking to much just make sure u have a good solid chamber if your gonna start cracking up the max pressure.

[Harter66]

Real life .
I had a 38/357 carbine, it delivered 400 fps higher velocities with both and with both Unique and Red Dot over a 6" Security 6.

A 16" 45 Colts delivers over 1400 from a 900 fps deferance load from the companion RBH of 7.5 inches.

I don't think you will have any trouble with nominal pistol loads reaching the higher velocity you are looking for. There's no need to wildcat a 40 (note need vs want) to get a go fast hit like a truck round Winchester loaded the 1 of the last -40 (I wanted to say 44-40 but ....) with a 200gr slug to 1400 fps from 2nd Gen SAAs and while I'm not versed in the 10mm it is a thumper from a closed breech as well. You can of course cut a x39 case off any length you want or not at all to get it to go faster. As long as there is a higher pressure than that needed to move the boolit it will excererate , 18" may be beyond the diminishing returns lines because of case volume and powder speeds .
I agree with the adequacy of the Small pistol primers you could try a magnum or small rifle primer if you need more spark or pressure control.

[Outpost75]

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. USGI TW55 hardball was fired as control. Test loads here were all assembled in Federal NT cases with Federal 200 small rifle primer.

CONTROL REF: TW55 Ball M1911 957 fps, 31 Sd, 78 ES
(858, 28 Sd, 72 ES in 4-5/8" Ruger Blackhawk)
HM2-453-200FN Cowboy, 5.5 grains old Hercules Bullseye 1054 fps, 4 Sd, 15 ES
(951 fps, 11 Sd, 33 ES in 4-5/8" Ruger BH)
H&G68 200-gr. SWC, 16 grs. old Herc. #2400 1433 fps, 11Sd, 34 ES
Accurate 45-245D, Auto Rim flatnose bullet, 16 grs. old Herc. #2400 1375 fps, 15Sd, 40 ES.

Cases extracted and ejected easily with no excessive pressure signs, no barrel leading. Bullets cast of wheelweights lubed with Lee Liquid Alox. The .45 ACP loads fired in the carbine all grouped about about 1-1/2" at 25 yards and in proportion roughly 6” for 10-shot groups fired at 100 yards, which is typical performance for an iron sighted, 5 lb. carbine firing handgun ammunition.
120354

[MarkP]

Hornady 10 mm's have large pockets, you could trim these to 40 S&W lengths if you want the larger primer pocket. Primer pockets have a tight diameter tolerance, I would not think you could hold tolerance with a hand held cutter.
Large primers should not be req'd for the small case volume.

[Forgetful]

x39? That's interesting. Tell me more! They seem close. I can cut an x39 down and full-length size the case to 40? What about the steel cases? That would rock, and solve the unsupported headspace problem.

I knew the carbines naturally provide more velocity to pistol rounds, but not so much on 180gr in the JRC. It's been said that the carbine steps up the round, so a 9mm hits like a 40, a 40 hits like a 10mm, etc. You do get more speed in the lighter rounds, but not so much on the 180gr. I'm thinking it gives another 50fps above the 1000 or so. It shoots so quiet, like the pressure is almost nothing by the time the round leaves the muzzle. But then it's also so slow, we were all laughing this one time at the range, everybody on the line stopped shooting and there's this pause while we wait for my round to hit the steel gong at 100 yards. It was just a natural pause, ... Bang! delay delay delay delay DING. Round of laughter. Rainbow the whole way. So yeah I'd love to flatten that trajectory and keep the mass the same.

Also there's a chance the action is cycling before the round leaves the bore, bleeding all the pressure. It's a timing issue when it comes to direct blowback. All input is welcome, I appreciate all contributing thoughts on the matter.


Hornady 10 mm's have large pockets, you could trim these to 40 S&W lengths if you want the larger primer pocket. Primer pockets have a tight diameter tolerance, I would not think you could hold tolerance with a hand held cutter.
Large primers should not be req'd for the small case volume.

It's not exactly hand-held. You could, but I use a drill press so it's perfectly square. This K&M tool will cut the pocket to the perfect dimensions.. I also have the flash hole uniformer, which I would also use to open up the flash hole for these large primers. I love the idea about trimming down 10mm's. x39 would be better if they weren't generally berdan primed.

https://www.kmshooting.com/catalog/primer-pocket-correction-tools/large-rifle-primer-pocket-correction-tool.html
https://www.kmshooting.com/images/products/med_104923224.jpg

[Thompsoncustom]

If ur gun is a straight blow back design then really slow powders aren't going to work.

With my 9mm experiment (also a straight blow back) I could not get more than 1700fps no matter how much power pistol I jammed into a case. I believe 7.5 grains was the max before it made no difference everything above that was still only 1700. Super compressed 9+ grains with magnum primers also didn't give me any more velocity past that point.

What sucks is that u need the powder that's 100% burned right before the slide starts bleeding pressure but who knows what powder that will be.

[Harter66]

x39? That's interesting. Tell me more! They seem close. I can cut an x39 down and full-length size the case to 40? What about the steel cases? That would rock, and solve the unsupported headspace problem.

The biggest issue is case capacity loss and the "neck" would have to be turned or reamed. With that you could manipulate the timing slightly with neck tolerance. I would think that the steel cases would slip more but that delves into physics and friction coefficients. I think that Herco or Blue Dot would be and upper reach of slow powder for your goals. The 18"bbl may slow it up rather speed it up. The best way to know for sure is w a factory base line or other known lot and go from there.
You may be able to modify your springing in a blowback action also .

[Garyshome]

Use a Magnum primer.

[dondiego]

Get a .44 mag carbine.

[Forgetful]

This gives me a good starting position. I could buy the 45ACP conversion kit -- perhaps the buffer from that would help my improved 40 loads. Honestly I'd rather spend that money on a 45-70 or something.

[seaboltm]

I agree that with direct blow back you will reach limits quick. The slower powders will probably not develop enough pressure fast enough to cycle the action. And if you get the pressure where it needs to be in the timing department, it will probably start cycling the bolt before chamber pressure has fully dropped, which could actually be dangerous. I would be careful wildcatting a blow back design too much. Cycle rate is controlled by mass of the bolt and spring pressure. I suppose you try a super heavy spring, but that will make the slower powder problem even worse.

[Forgetful]

You may be able to modify your springing in a blowback action also .

Doing some research, I stumbled on this gem. Somehow I think it's the right direction. They didn't come out with a 10mm because they wanted to stick to a carbine buffer tube, but couldn't get a heavy enough buffer without using a rifle buffer tube and rifle buffer.. So while I'll never fit 11oz without a new tube, maybe an 8.5oz XH Carbine Buffer + Wolff XP Spring?



My JRC in 45ACP took a lot of patience. IT was a very early model. I live near where they are manufactured and had a lot of visits there. Very nice people who even offered to exchange out the carbine for whatever model I wanted. The 9mm and 40 S&W models worked fine. Being an engineer I could not stop without fixing the issue.


The problem with the 45 ACP model was timing, The carbine worked faster than the magazine could feed them after the first 7 rounds were fired. The normal lessening of spring tension in the magazine as round were fired meant that each round loads a wee bit slower than the last one. Several different buffer weights were used. They finally put an extension tube in place that made it as long as a rifle tube. Then they put a heavier buffer in place. They still had a carbine length spring in place though. This was better, but I still had a few stoppages with the bolt riding up over the cartridge. This was always started when feeding round 8 out of a 10 round magazine. Looked like a short stroke but it was not. The Glock mags just could not keep up. Not a problem with the magazines as they work fine in Glock products. The issue was slowing down the carbine.


To finally solve my issue I installed a rifle length buffer tube spring and an AR15R-XH - 11 ounce rifle buffer from Heavy Buffer. Once I did this I shoot over 500 rounds of various types in 45ACP without any problems. Then NY passed it's "SAFE" act and the carbine now resides out of state. The JRC buffer will not work with a rifle length spring as it is too short and the spring bottoms out. This would lead to premature spring failure.


Then of course, this:


Q: Can I shoot Plus-P (+P) ammunition in my JR Carbine? It should not be a problem for you to use Plus-P ammo in your JR Carbine. We initially prohibited Plus-P ammunition because the JR Carbine is a direct blowback weapon with a non-locking bolt. The added power of Plus-P ammunition caused a significant increase in gas discharge through the ejection port without giving any ballistic advantage over conventionally charged cartridges. We were concerned that the higher power ammunition could cause the bolt to move rearward too soon in the firing sequence, before the chamber pressure had dropped sufficiently, thereby prematurely exposing the case wall and causing potentially dangerous case failures. We have subsequently modified our bolt design and significantly increased the weight of our proprietary buttstock buffer. As a result the bolt stays in battery for a longer period, directing more of the combustion gases into the barrel and out of the muzzle. Plus-P ammunition may or may not provide a significant increase in performance at this point, but it should not cause any problems.

[petroid]

Longshot is the slowest powder I have heard used and used myself in the 40s&w. 8gr behind a 180gr bullet is the max and as much as you can fit. It is a hot load in a pistol I've wondered how it would work in a carbine but I don't have one to try it. I find 6.5gr gives good accuracy and reasonable recoil with good case expansion and seal. Lower charges don't develop the pressure to seal the brass and cases are quite sooty. As long as you work up a load watching for excess gas venting I think it would be a top performer

[243winxb]

Good Luck. http://www.photobucket.com/kabooom

[Forgetful]

Good Luck. http://www.photobucket.com/kabooom

I'd rather have advice to avoid kabooms, than luck. Experienced handloaders have repeated again and again that you can substitute a larger primer if you back off the charge and work it up. Slower powders make this safer.

Or am I wrong?

[petroid]

http://www.thehighroad.org/archive/index.php/t-757408.html

[petroid]

http://thefiringline.com/forums/showthread.php?t=432390

[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.