Over max 9mm for carbine use?

[Lloyd Smale]

for one your going to probably have problems with extraction and secondly a 100fps more does very little to the killing power of any load. If plus p 9mm isn't enough its time to step up to a 40 or 45.

 

[HJ857]

Justin, Walkalong and Mach IV, thanks for posting AR specific info.

Casting a buffer out of pure lead wouid be easy enough, but the unsupported case is likely the problem that stops the experiment in it's tracks.

 

[MachIVshooter]

Casting a buffer out of pure lead wouid be easy enough,

Lead, no matter the alloy, is insufficiently hard. You'd want to use a tungsten alloy (far heavier than lead anyway; 1,204 lbs/cu ft vs. 708 lbs/cu ft)

 

[justin22885]

yeah, take a steel buffer, drill a hole straight through it front to back, and then with a shop press, press a tungsten rod into it if you want to increase its mass

 

[dogmush]

Well there is the obvious solution:

A 9mm case head is only .016" bigger then a 5.56 case head. Take a 5.56 bolt, turn the breechface a little wider so a 9mm case will fit in there. Then chamber a standard barrel to 9mm, install and headspace a barrel extension and assemble your DI locked breech 9mm AR carbine. Then you can start trying to load a 9mm case hot enough to generate enough gas to cycle the weapon, which I suspect might be a challenge, but it probably won't blow up on you.

(I'm only half kidding.)

 

[ny32182]

For load data, you might try a competition forum like brianenos. USPSA Open shooters have to make major power factor with a 9mm caliber cartridge. Most choose something like 38 supercomp, but some use regular 9x19. It just depends on that guy's brass logistics from what I can see...

Anyhow, the "9 major" guys are pushing, usually, a 124gr bullet at over 1400 fps from a 9x19 cartridge. I think they only load each case two or three times at those pressure levels. They are probably also loading a lot longer than most standard 9mm rounds.

I'm not one of those guys, so I only know what they tell me, but I believe there are only one or two powders they use... I know HS-6 is one, and I forget the other.

Barrels are in the 5" range and they are shooting from recoil operated 2011's most of the time.

In a blowback design this might be a bad idea.

 

[eldon519]

In a blowback design it would be a bad idea.

 

[lysanderxiii]

That is totaly incorrect. The reason so many have recommended changing the 11 pound factory spring in the camp carbine is because the bolt speed is too high and cracked stocks have been a problem with this model. The recommended weight is a 21 pound Wolfe recoil spring. So yes, springs can and do make a difference.

Sorry, but you are wrong.

The thrust pushing the bolt back on a typical 9mm is in the neighborhood of 3500 to 4000 pounds.

The spring force is around 5 to 8 pounds, increasing the the spring stiffness to 20 pounds would make about 0.5% difference in the blow-back force.

The bolt mass is what makes the difference in safety.

The stiffer spring only makes a difference in how fast the bolt hits the back of the receiver, it has very, very little to do with how fast the case comes out of the chamber.

 

[RecoilRob]

I tried loading 9mm carbine ammo a long time ago, and found the case volume too small to hold any worthwhile amounts of slow enough powder to take advatage of the longer barrel to any degree.

The 9x21 or 9x23 would be much better in this regard, and I'd imagine some interesting possibilities could be had in a carbine with a load made for it...but that throws the standard 9mm magazines in the trash. If you're going to the trouble to build a carbine for 9x23....why not 10mm? Or 45 Super? Anything with more case volume is going to be a step in the right direction.

I just use a 154 lead BTRN Lyman at 1000fps out of my carbine and it works great. No worries about super-sonic dropping back through the Mach inaccuracies and those boat-tails really fly nicely.

 

[ColoradoShooter77]

I can gain 300 fps with my Hi-Point 40 cal carbine, over a pistol. The 40 cal responds well to the longer barrel and a slow powder like Longshot.

 

[ThomasT]

The spring force is around 5 to 8 pounds, increasing the the spring stiffness to 20 pounds would make about 0.5% difference in the blow-back force.

The bolt mass is what makes the difference in safety.

The stiffer spring only makes a difference in how fast the bolt hits the back of the receiver, it has very, very little to do with how fast the case comes out of the chamber.

The factory spring is 11 pounds not 5. And the heavier spring increases the dwell time allowing the pressure to drop somewhat. I never addressed case speed on ejection. I believe someone else did.

The whole idea of a super 9mm is silly anyway. There are much better rounds in the same caliber without trying to overload a small pistol case. And the information I gave came from the gunwriter J.B. Wood. If you disagree take it up with him.

 

[MachIVshooter]

The factory spring is 11 pounds not 5. And the heavier spring increases the dwell time allowing the pressure to drop somewhat.

Not by any appreciable amount, and what additional delay is present has more to do with the spring being heavier in terms of mass than heavier in terms of required compression force. An extra ounce in the bolt will do far more to keep it closed on firing than doubling your spring weight.

 

[justin22885]

The factory spring is 11 pounds not 5. And the heavier spring increases the dwell time allowing the pressure to drop somewhat. I never addressed case speed on ejection. I believe someone else did.

The whole idea of a super 9mm is silly anyway. There are much better rounds in the same caliber without trying to overload a small pistol case. And the information I gave came from the gunwriter J.B. Wood. If you disagree take it up with him.

uuh, dwell time is the length of time in which a gas system in a gas operated rifle is under pressure, non applicable to blowbacks.. what prevents the bolt from moving rearward before pressures drop to safe levels is the mass of the bolt, and only the mass of the bolt

as ive pointed out earlier the heavier springs just aid in slowing that bolt down before it hits the back of the action too hard, its not going to allow you to run at pressures any higher than the limitations with the lighter spring

adding more pressure or running a lighter bolt increases bolt velocity and also cyclic rate when in full auto mode, but theres a threshold here as to just how fast that bolt can actually open before you start ripping off case heads.. no amount of spring is going to change that.. trust me, physics and experience in both designing and using blowback weapons are on my side

 

[ThomasT]

You can believe what you want. I really don't care one way or the other. I think any over pressure round is an irresponsible idea. Need more power? Get a bigger gun. More powder is not the answer.

Besides the OP was about the pressure for AR barrels and how much they would take.

You guys have fun with it, I'm done.