Luger Chambers VS Modern Chambers

[mrerick]

It's basic internal ballistics. Look up "freebore' and "throat". This is how the initial pressure peak is managed in a modern handgun or rifle chamber. For a reference, see George Nonte's classic book on "Pistolsmithing".

Consider this analogy... Driving a nail into wood is similar to pushing a bullet up the leade of a barrel into the rifling. When you drive a nail, do you put the mass of the hammer against the nail head and push, or do you swing the hammer's mass across a distance of air and strike the nail into the wood? You can still drive the nail without using the momentum and mass of the hammer, but it takes considerably more pressure building against the hammer before the nail will start to overcome the friction and start to move.

Without adequate freebore, the bullet won't have the momentum to easily engage the leade and start down the rifling. Pressure will continue building in the chamber until the movement finally provides more volume to expand in.

This can be measured in an instrumented chamber.

If a cartridge OAL is too long, the initial pressure peak will be higher and sometimes dangerous.

BTW, Luger was experimenting with the chamber of his design from the beginning. There is a step in his 9mm Chamber as well as an oblation ring to help with the seal and release of the case.

[Doubs]

Originally Posted by mrerick

BTW, Luger was experimenting with the chamber of his design from the beginning. There is a step in his 9mm Chamber as well as an oblation ring to help with the seal and release of the case.

Interestingly I have a Grand Power Stibog 9mm which is classified as a pistol by the BATFE. (It has a "brace" and not a shoulder stock) It's made in Slovakia and the action is a blow back design. The barrel is 8 inches and the magazines are either 20 or 30 rounds. Date of production is 2019. Accurate and reliable, it's the most fun gun to shoot that I own. (Picture below)

I use the same load in the Stribog as I do in my shooter Lugers. What's interesting is that the fired cases show that the chamber has a step in it. There is a clearly delineated line around the case where the step is smaller in diameter than the rest of the chamber.

Did the Grand Power engineers duplicate the original Luger chamber? The step indicates that it's possible.

WRT the bullet touching the leade or lands, in most cases it's a bad idea because of pressures. Some benchrest shooters and other precision rifle shooters will sometimes find their best accuracy with the bullet touching or even a few thousands into the lands. Their powder is adjusted to prevent high pressures. For those of us who shoot Lugers or other handguns chambered for .30 Luger or 9mm, the bullet should be a few thousands off of the lands. That was the reason I pointed out the differences in chambers between my vintage Lugers and newer production handguns.

[Chichaco98]

Walther PPS M2 also uses a stepped chamber.

[DonVoigt]

Originally Posted by mrerick

It's basic internal ballistics. Look up "freebore' and "throat". This is how the initial pressure peak is managed in a modern handgun or rifle chamber. For a reference, see George Nonte's classic book on "Pistolsmithing".

Consider this analogy... Driving a nail into wood is similar to pushing a bullet up the leade of a barrel into the rifling. When you drive a nail, do you put the mass of the hammer against the nail head and push, or do you swing the hammer's mass across a distance of air and strike the nail into the wood? You can still drive the nail without using the momentum and mass of the hammer, but it takes considerably more pressure building against the hammer before the nail will start to overcome the friction and start to move.

Without adequate freebore, the bullet won't have the momentum to easily engage the leade and start down the rifling. Pressure will continue building in the chamber until the movement finally provides more volume to expand in.

This can be measured in an instrumented chamber.

If a cartridge OAL is too long, the initial pressure peak will be higher and sometimes dangerous.

BTW, Luger was experimenting with the chamber of his design from the beginning. There is a step in his 9mm Chamber as well as an oblation ring to help with the seal and release of the case.

Sorry Marc,
I"m not buying the "jump" business- unless you can point us to an authoritative source- comparing a bullet to a nail is .
JMHO.

Benchrest shooters for years have set their bullets "out" to engage the rifling slightly just so the bullet won't "jump" and upset/deform and negatively effect accuracy.

What is "dangerous" is a cartridge that is so long that the neck is constricted by the rifling and thus wedges the bullet in the case neck.

[Doubs]

Originally Posted by DonVoigt

I"m not buying the "jump" business- unless you can point us to an authoritative source- comparing a bullet to a nail is . JMHO.

Seating a bullet to touch or enter the lands will raise pressure significantly higher than a bullet that is allowed to travel - jump, if you will - a short distance before contacting the lands.

OTOH, seating a bullet deeper into a case will reduce internal volume and also cause an increase in pressure.

Here is a link to an article written for Berger Bullets, one of the makers who cater to precision shooter. Read the article but pay attention to the text under figure 2 and the summary a little farther down.

https://bergerbullets.com/wp-content...13/03/COAL.pdf

[Sieger]

Originally Posted by Doubs

https://bergerbullets.com/wp-content...13/03/COAL.pdf

Doubs,

An excellent article, though mostly a review for me.

Thank you kindly for attaching it.


Respectfully.

Sieger