Overpressure 380?


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shadow9
October 17, 2011, 11:49 PM
This is a dangerous proposition, and very "n00b", but I figured I'd ask - what if one were to intentionally overpressure a .380 case?


In the nature of the Browning design, overpressure rounds go kaboom...
However, with a straight blowback design, the moment the powder ignites and begins propelling the bullet forward, it simultaneously starts propelling the slide back. This means that much of the pressure built in a .380 round is absorbed with recoiling the slide, and the rest is usually filtered out of the ejection port with the spent case and out the barrel with the bullet, if I have the process right...
Or, is a .380 a weak case, and would the case blow like a normal action?

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Vec
October 18, 2011, 12:04 AM
Not having researched it... but I have a guess.

In a blowback design I would be more worried about the pressure the normal, thin part of the brass would have to withstand. I'd be highly concerned about a case rupture. Brass isn't really that strong...

The slide doesn't "absorb" the energy inside the case, just the recoil. With more energy it might push the slide back faster exposing the weaker parts of the brass earlier when there is still high pressure in the chamber/bore.

In a normal locked-breech design the chamber supports the case while there's high pressure. In some designs there might be less support around the case web (e.g. Glocks), but it's not disastrous for the most part. I'd much rather have thick steel trying to contain the pressure than 0.01" brass.

Like I said though... speculation. :-)

Shadow 7D
October 18, 2011, 12:26 AM
So, let's throw the car at 8o miles an hour at the 60 mile per an hour guardrail instead of just hitting it at 60mph...

Depends on the gun, also depends how much you enjoy the possibility of the slide being removed from you face.

to put it politely, exceeding the maximum is never suggested, and on some guns the may be able to handle it.

Now think of the POS Zinc guns, how many times of you hammering it with over pressurized rounds will it take to break the pin holding the slide on?? Do you really want to find out?

shadow9
October 18, 2011, 02:42 AM
The slide doesn't "absorb" the energy inside the case, just the recoil. With more energy it might push the slide back faster exposing the weaker parts of the brass earlier when there is still high pressure in the chamber/bore.

Exactly the point I was looking for to disprove my mad scientist theory.

Shadow (A pleasure to meet :P), the gun in question is a blowback with the slide recoiling against the full frame of the pistol, not being held in place via a slide-pin like many other designs. Nonetheless, not something I'd like to try...

Thank you for the input!

ants
October 18, 2011, 04:57 AM
A little too much pressure splits the case at the mouth.
Way too much pressure splits the case just above the web.
WAAAYYYY too much pressure splits the eyelids just above the eyeball,
and peels the cornea from the eye while burning all the hair clean off the eyebrows.

Now, explain again why you wanted to know?
Trying to figure a way to make that pocket pistol as powerful as a 9mm?
Not a useful task for us mortals. You make a wise choice not to try.
Ballistics labs use 223 Remington rifle cases cut down to .680 inches.
Inside ream the mouth to 0.353". Use 0.956" oal.
Powder type and charge are not published,
they use universal receiver to work up the load.
And they get near 9mm performance, almost.
But it pretty much tears up the hand holding a small grip on a pocket pistol.
It isn't really worth it, is it?

1911Tuner
October 18, 2011, 05:24 AM
In the nature of the Browning design, overpressure rounds go kaboom.

And you got this notion where?

However, with a straight blowback design, the moment the powder ignites and begins propelling the bullet forward, it simultaneously starts propelling the slide back.

And the same thing happens with the locked breech/short recoil operated design, as per Newton's 3rd Law of Action and Reaction.

The only real difference between the locked breech and the straight blowback is in the way that breech opening is delayed. The blowback uses slide mass...inertia...and action spring tension. The barrel and slide aren't mechanically connected. Barrel is fixed to the frame and the slide will move independently of the barrel.

In the locked breech design, the slide starts to move at the same instant the bullet starts. The slide grabs the barrel by the lugs and pulls it backward with it for a short distance...keeping the breechblock...the slide...from separating from the barrel...until the bullet has exited and pressure has dropped. In this one, the slide's inertial mass and the barrel's frictional resistance imposed on the bullet effect the delay.

An over pressure round will drive both bullet and slide to a higher velocity. In the blowback, you may reach a point that the breech opens before pressure has fallen to a safe level...but you'd have to really push it. The locked breech is much more forgiving. The slide moves rearward about 1/10th inch, and linkdown/cam down begins. At that point, the bullet is gone and pressure is gone with it. Whatever residual pressure is left is of no consequence. This linkdown/cam down is a timed event. It remains the same regardless of how fast or how slow the cycle occurs.

Walkalong
October 18, 2011, 07:39 AM
It would be dumb to overload the .380 for various reasons. Buy a 9MM.

SlamFire1
October 18, 2011, 04:33 PM
In the nature of the Browning design, overpressure rounds go kaboom...
However, with a straight blowback design, the moment the powder ignites and begins propelling the bullet forward, it simultaneously starts propelling the slide back. This means that much of the pressure built in a .380 round is absorbed with recoiling the slide, and the rest is usually filtered out of the ejection port with the spent case and out the barrel with the bullet, if I have the process right...
Or, is a .380 a weak case, and would the case blow like a normal action?

Nope. You will blow the case head just like this guy did with his 45 ACP in a M1911.

http://www.thehighroad.org/showthread.php?t=620649

Timing is extremely critical in all of these actions. All of these actions are timed such that the case is surrounded by the chamber when pressures are high enough to rupture the case walls. Call this your dwell period. The only thing holding the breech block shut in a simple blowback is inertia. There are more complicated blowbacks, roller bolts are delayed blowbacks, but the simple mechanisms used for 380 are basically a weight and a spring. The spring constant barely makes a difference in dwell.

You increase the breech pressure you will accelerate that breech block and the thin case walls will be exposed at pressures they cannot handle. This all occurrs in milliseconds.

Cases are simply gas seals, they are not structural elements, they are not expected to carry load.

Walkalong
October 18, 2011, 06:45 PM
Timing is extremely critical in all of these actions. All of these actions are timed such that the case is surrounded by the chamber when pressures are high enough to rupture the case walls. Call this your dwell period. The only thing holding the breech block shut in a simple blowback is inertia. There are more complicated blowbacks, roller bolts are delayed blowbacks, but the simple mechanisms used for 380 are basically a weight and a spring. The spring constant barely makes a difference in dwell. This.

MrWesson
October 18, 2011, 07:25 PM
Buy a hi-point .380, a vice and some string and find out :D.

shadow9
October 19, 2011, 12:23 AM
Thanks for the advice all, again, as stated in original post, was not 100% on understanding the functions/timing elements of locked vs. blowback designs. Wouldn't actually try, this was more of a "Why hasn't someone yet?" sort of thing.

Obviously it'd be easier to buy a 9mmP, but in that logic, you'd buy a small-block V8 in lieu of putting 36PSI into a 1.5L I4... ;)

Vec
October 19, 2011, 08:08 AM
I'm sure it's possible to design a .380 that will handle overpressure rounds all day long without it breaking.

If you look at race guns that are doing 9mm major, you have the same thing applied to the 9mm round. They're all working on a locked-breech design with the chamber and everything else that needs to deal with the added pressure beefed up to not fail. Firing those same rounds in my guns might cause a catastrophic failure.

What you'd wind up with is a .380 built like a 9mm (or even beefier since you might need higher pressures to achieve the same velocity). People playing with the gun games do all sorts of weird things to maximize their score and what they do isn't necessarily practical so I wouldn't use them as the best guide for making a small, high powered concealable weapon.

The engine analogy works quite well. People doing odd things to a car, many times for a competition, are trying to push the rules. The rules might say "Maximum 1.5L displacement" so you take a 1.5L engine and blow the hell out of it. Same thing with the guns: "Must make a minimum of 165 power factor" and rules about magazine size.

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