Why aren't all ammo cartridges tapered?

[waldonbuddy]

Just a curiosity on my part that I want to know.

It would seem to me that the ammo used in all semi auto firing weapons should have a tapered casing since it take only minimal movement of the bolt for the whole cartridge to clear the chamber.

Unlike a straight cartridge, which has to move its entire length to clear.

So, why then are some cartridges tapered, and some not?

It seems to me that the use of tapered cartridges is one of the reasons the AK and some other weapons using the tapered round have such a reliability reputation.......

 

[atblis]

Some cartridges are intended for revolvers
Some cartridges are intented for bolt action rifles

Cartridges intended from the get go for semis that I can think of
5.56 is tapered
7.62x51 is tapered
9x19 is tapered

So what cartriges are you thinking of that are not tapered that you can say were intended from the get go for a semi?

45 ACP and 10mm/40 are the only ones I can think of.

EDIT: Looking at drawings for 45/10/40, it looks like they are supposed to have an ever so slight taper to them.

 

[merlinfire]

Basically, the history of firearms has been an evolution of calibers and technology, and a lot of ammunition types that may be less "ideal" by modern standards are still in use by nature of their ubiquity. Besides, if you still make factory loads for use in older guns, then people will sometimes still buy new guns in the same chambering, and then the process continues. 44/40 for instance - see Cowboy Action shooting.

 

[ChronoCube]

A different take on the question -- why are some cartridges tapered a lot more than others? E.g. why is .223 not tapered as much as 7.62x39? Age does not explain it -- .223 was developed relatively recently in firearm history.

 

[waldonbuddy]

I did not know the 5.56, or 7.62x51 was tapered........let me get my calipers. Yep, they are tapered.

I could never tell that by looking 5.56x45 vs a 7.62x39.

I guess my question then is why are some tapered more than others?

 

[Ed Ames]

Case taper is a trade-off, like everything else.

Some of it is obvious: If you have excessive taper in a revolver, for example, fired brass will push back and expand, and can wedge between the cylinder and frame to jam the gun.

One less obvious factor: many cartridge designs are adapted from other cartridges in order to simplify gun (by allowing standard bolt faces) and ammo (by allowing modification of existing brass or tooling) production. And, especially when the goal is to form existing brass to a new diameter, the result can be fairly arbitrary taper. Example: 9x19 has 0.011" or so of taper from base to rim because the case was adapted from an older round. .40S&W, OTOH, has .001" of taper IIRC.

 

[chuwee81]

well, if the taper is extreme on auto pistol, then the grip would be banana shaped ?? I think straight box magazine favors very little to no taper as far as ammo goes. just my .02, might be wrong.

 

[WardenWolf]

Taper also improves feeding, by allowing the mouth of the chamber to be wider than the forward part of the shell. This means the round can still insert at a slight angle and still feed reliably, which is a large portion of why the Tokarev pistol is so reliable. I honestly don't know why more pistol rounds aren't built like the 7.62x25 Tokarev round. It enables higher velocity and better reliability.

 

[waldonbuddy]

Lots of good answers.

Thanks for the replies.........

 

[natman]

Like most things, there is a trade off. Increased taper increases case head thrust as the case is wedged backwards. The 7.62x39 can get away with it because of it's relatively modest pressure (45,000 psi) and small case head.

 

[gondorian]

The .30 caliber carbine isn't tapered and it was designed as semi-auto round as far as I know.

 

[zxcvbob]

The .30 caliber carbine isn't tapered and it was designed as semi-auto round as far as I know.

Who told you that it wasn't tapered? (I have a .30 Carbine revolver, and that taper causes me all kinds of annoyances.)