What Limits 9mm Form Factor

the charge. if you want to create it really thin you have to design it with that in mind from the start, like the PPS.

Several things come into play.

Overall eight is one; you need a fairly specific amount of weight if you are using blowback; the parts needed to use a Browning style action add weight, too (and you need room for the parts in the frame, too.

Ammunition count is a factor, too. You may have a hard time selling a 5 shot 9x19; also, you probably are not going to get the barrel and slide much skinnier that 18-19mm, and that pretty much no invites some level of double-stacking the magazine. Now, suddenly you are closer to 22-25mm wide. Which just added weight to the thing.

These things are a juggle, and all juggling involves some level of compromise. And,"we" as a buying group can be fickle about compromises.

Rohrbaugh R9 was extremely close to the same size as the LCP, but weighed a couple oz more.

380's are usually a blow back design which works well with the less powerful .380 and smaller cartridges.

For a 9mm (9 x 19 parabelum) you really need some kind of breach lock because the mass of the slide would have to be so great for a 9mm blowback the gun would become rather ungainly... aka. the Hi Point 916 9mm blow back pistol.

To answer your question why can't you have a 9mm LCP? - the recoil spring would have to be so strong to handle the 9mm cartridge with that light of a slide you probably would not be able to rack the slide. That much spring weight and that little slide mass probably would not be very reliable.

I carry a Diamond back DB9 which is the smallest 9mm I know of... or atleast the smallest I can afford.

MikeInOr

For a 9mm (9 x 21 parabelum) you really need some kind of breach lock because the mass of the slide would have to be so great for a 9mm blowback the gun would become rather ungainly... aka. the Hi Point 916 9mm blow back pistol.

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My first semi-auto was an Astra Model 600 in 9x19mm. and it was a straight blowback pistol. And even though it was a decent design (though racking the slide with that recoil spring required considerable effort on my part), and fairly well built, it still didn't keep that gun from beating up the web of my shooting hand after running 50 rounds through it! I believe I would have been better off not shooting the gun and just whacking my hand with a hammer to achieve the same effect!

To this day I think I still wince in pain (subconsciously that is), every time I see one those Astras!

Believe or not, it's the operating pressure and power of the 9x19mm (9mm Luger, 9mm Parabellum) cartridge that precludes it from being chambered in something as small as an LCP. While it isn't physically much larger than the .380 ACP cartridge, it operates at an exponentially higher level on the power scale.

A 9mm needs to be a locked-breech gun. Sure, there are blowback guns like the Hi-Point and a few others. Those are all large, heavy, ungainly guns with very stiff recoil springs. They just can't be scaled down to a pocket gun.

Speaking from experience with a Kel-Tec PF-9, you'd be quite surprised at how much recoil a mini-9mm pistol can generate. We're kind of conditioned to believe the the 9 "mini-meter" is a weak sister in the service pistol realm, but reality is the rest of the world has considered it an effective combat round since about 1902. That Kel-Tec was downright unpleasant to shoot in my hands, very fussy about how it was gripped and kind of hard to hold on to. Going any smaller would only cause more issues.

And that's another point: as you scale down the operating system, you start to limit its window of reliably function. Take something like a full-size Beretta 92, or a Glock 17. Those are very forgiving with a rather wide range of ammunition. When you start reducing slide mass, you're increasing the slide speed, and now suddenly you're having to run very stiff magazine springs to keep up with the slide, or rounds stop being presented fast enough to feed. You can probably get it to work with a couple of types of ammunition, but change that and you can change the recoil and cycling dynamics to fall outside of that operating window. Remember the Kimber CDP 9mm? They came with a warning to only use standard pressure 124gr and 147gr ammo, and it might have even been a couple of specific brands and loads recommended. (It's been a while since I looked at them and I can't recall the specifics.)

To be 100% honest, the smallest 9x19mm pistols that seem to be regarded as fairly reliable at the Walther PPS and the Glock G43. Some of the larger Kahrs are OK, but I know I've read plenty of reports of reliability issues with the smallest models, particularly the polymer framed ones.

I had one of those Kel-Tec PF9's for a while, too. I got a used one for super cheap and figured I could just get my money back if I didn't like it. The recoil wasn't too terrible for me (my hands are used to getting beat up), but the trigger was. I also had a Ruger LC9 and a Taurus... I think it was called a "slim". The Taurus was shaped wrong for my hand and the original LC9 trigger was pretty bad. Finally I got a good deal on a used G43, and my search for a small 9mm pistol that I liked ended there.

Sorry if that was a bit OT...

What I was eventually hoping to get around to was that I don't think I could control a 9mm pistol much smaller and lighter than the ones I mentioned above. I have big hands, and I don't think I could get enough fingers on an LCP-sized 9mm to keep it from twisting badly in my hands when I shot it. Maybe someone with very small and very strong hands could do it, but I couldn't.

If someone could invent a loading system that didn’t utilize a reciprocating slide that would probably open the door to a smaller design. With current designs the slide mass/recoil spring weight balance is probably the limiting factor.

Elkins45 said:

If someone could invent a loading system that didn’t utilize a reciprocating slide that would probably open the door to a smaller design. With current designs the slide mass/recoil spring weight balance is probably the limiting factor.

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Sounds like a revolver would fit the bill.......

kidneyboy said:

Sounds like a revolver would fit the bill.......

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Where do you put the magazine?

Yup, been covered by a couple folks well. But, not quite all at once as I read it.

No problem:

• Barrel length. 9mm works just fine from 3" and shorter barrels, and new powders, etc. mean they are getting optimized cartridges for shorter ones yet!
• Materials. In the past, we've had issues esp with metallurgy of the operating parts, but today, you can make a tiny gun of practically any weight you want. If you are willing to pay for it.
• Accuracy. We have figured out how to cut rifling and make tiny sights, or add on lasers etc when that's implausible. You can actually hit targets just fine.
• Ergonomics. A challenge, but only in design. We know a lot about HF/E to make something like this work for human hands. Reliably, accurately, safely.
• Manufacturing. Again driven by costs, you can do this all repeatedly to any level of precision you want. And, you don't even have to hire out skilled workers or build a factory. You can outsource pretty much all of it. Give me say $4 million in working capital and a $10 million LOC and I can do this for you

Big problems:

• Reliability. Momentum is your friend for all mechanical systems. Gas turbines (e.g. jet engines) are crazy reliable despite operating at insane temperatures, basically because they "just spin around." No starting and stopping, very little change in rotational speed. And they go... forever. What breaks on them? Accessories like oil pumps which don't simply spin around.
  • So, we're going back and forth, over very short distances instead. Forget damaging the system, it simply has no momentum in the movement. We're using ALL spring return force to load, for example. Nothing else is available to overcome dirt or odd-shapes, and the speed varies across the movement path a lot. This is a bad way to design a system. It gets unreliable in ways very hard to mitigate or trace down.
• Longevity. Not of the big mechanical parts, but the small ones. Springs and buffers especially. But also things like pins and small parts (e.g. extractors) subject to a lot of tension. Springs are a special problem. A well designed spring system will last practically forever. When you get this small, things cannot be "well designed." The springs are far past their happy place for most of their operating cycle, so wear fast. End users do not change springs so the gun will get a reputation for unreliability. Seen systems like this that needed spring changes every 800 rounds. That'a a day of shooting.
  • You could alleviate this almost entirely with some electronic monitoring and suggestions of replacement cycles based on just on shot count, but temperatures, etc. Yes, cheaply and within the size needed.
  • There is nothing else remotely this complex, at this cost, I would even consider designing without sensorizing and a HUM system.
  • But electronics in guns!?! Monitoring your shooting?!? Politics override a lot of what would be best practices, so that's out of the question.
• Controllability. Small size means all the tricks to soak up recoil or even perceived recoil are set aside. Cannot run out the slide, use mass, use flex of the frame, use slower delay mechanisms, etc. It is gonna recoil like a fixed breech gun. The cycle issues means the slide is gonna snap forward pretty violently also, so it will feel even worse than that!

Biggest problem:

• Marketing. It takes a lot of money to make an all new mechanical product (well, a good one at least) so you have to be sure you'll sell enough, at the price point.
  • Small things are "small" only. They loose a lot of the standard gun store / gun buyer feature list. They have small ammo loads, cannot fit other accessories like sights and stocks without messing up the overall package dimension, etc. Harder sell for the typical buyer.
  • Small mechanical things are small, so they should be less hard to make, so less money. Expensive small guns sell very poorly, or in tiny quantities which... raises the price more!
  • Perception. The accuracy/etc. stuff is still believed to be the same as the Saturday Night Special era. Small guns are cheap junk. Untrue but... good luck.

How much smaller than a Kahr PM9 or Sig P365 do you need?

I can pocket carry either with just about every style of pants/slacks that I own.

MikeInOr said:

380's are usually a blow back design which works well with the less powerful .380 and smaller cartridges. . .

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I saw this just in time to regurgitate one of my older rants:

I hear, "most small .380 ACP pistols are blowback operated," on a regular basis and I question it. It is almost into the category of "myths." As an example of .380 pistols, counting my 9mm Makarov, I have five [now six]. Of those, only the Makarov is blowback. I am not going to deny that there are blowback .380 pistols on the market. Of popular .380 pistols, both the Bersa and the High-Point are blowback. There, I am done, I have named all of the popular blowback .380 pistols. Yes, there is the PPK the Beretta Cougar family and a few extreme low-cost offerings. I think most can agree that those models are not hot sellers.

However, most modern .380 Pistols use some form of delayed blowback/locking breech mechanism. There is the entire Colt Government model family which includes, not surprisingly, the .380 Government model, the Mustang, Sig, Kimber, Springfield. Then there is the Glock 42, the Walther PK38, the Browning 1911-380 series, and Smith & Wesson Shield. There is the whole family of Kel-Tek derivatives. I can keep going, the point is, the, "most small .380 ACP pistols are blowback operated," is almost a myth.

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94045 said:

I suspect the real issue is the 21,500 psi .380 pressure vs 35,000 psi 9mm pressure. I could see where the LCP simply wouldn't be strong enough for a constant +63% Pressure.

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You have a slide velocity issue, too.

there are a few 9mm that are comparable in size.....

Rohrbaugh R9
Caliber: 9mm
Barrel: 2.9 in
Length: 5.2 in
Height: 4.0 in
Slide Width: .82 in
Width at thickest part of pistol: .95 in
Weight: 13.5 oz, magazine 1.6 oz
Capacity: 6+1 Rounds

The R9 is 13.5 ounces empty

The magazine is 1.6 ounces

Fully loaded with seven rounds of 115gr ammo, my pistol weighs 17.8 ounces.

I got these measurements from actually weighing it on a scale.

I.O Inc tried to make a 9mm semiauto slightly smaller than the Rohrbaugh R9, and they just couldn't do it.

They couldn't get it to cycle reliably at that size.

Hasaf said:

I saw this just in time to regurgitate one of my older rants:

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Really good point.

One I am very familiar with is the Star model S. BIG seller, to governments and all, across Europe. Big for aircrew weapon.

Impossibly small. Hard to believe it has a complete swinging link system in there!

Well... small across and tall. It's pretty long, and I suspect that's a reason it was popular. It is dead reliable with a wide variety of ammo, in wartime conditions. Hmmm... Bit of a hint there again isn't it

One other factor: Most semi-auto pistol designs depend upon the frame being a relatively motionless/stable base against which the slide can compress various springs. If the frame moves around too much, then the slide can't move relative to it enough to compress springs and fully cycle. This is basically what happens when a gun fails because of "limp wristing" - the frame is simply moving too much and too early for the slide to fully reach the end of its cycle and load all the springs.

What are the factors that keep a frame relatively stationary? There are 3 big ones: the shooter's grip, the inertia of the frame, and the softness of the recoil springs. Small sizes work against all of these things. It is certainly possible to design and build a small gun that is 100% reliable when fired from a vice, but which is too small for shooters to get a good purchase on, has the inertia of a ball point pen, and requires stout springs to return the slide to batter with basically no "running start" from a longer travel. You can make a small gun that works great right up until a human being is the one using it.