Why is some Handgun Ammo Straight Wall and most Rifle Ammo with Taper / Draft ?

[gunDriller]

I've been studying various ammo's and modelling them on the computer.

Also thinking about what is involved in machining parts for them.

The .38 Special, as an example, is spec'ed as a having a .379 diameter shell (straight wall, .379 top and bottom) and a

The bullet measures .355 and the case measures .3755.

From a machining point of view, the straight wall is easier to machine - if you're starting with standard parts, like a standard reamer without 'draft'/ taper.


On the rifle rounds, the 30 30 is spec'ed at .470 base diameter, .441 top-middle diameter (before the pronounced taper to the more straightwall section into which the bullet is swaged.)

I notice this consistently on rifle rounds.

Have you ever measured the chamber in one of your rifles to see if it is straight wall or has taper ?


I'm curious what you more experienced gun guys have noticed on the straight wall vs. taper aspect on both handgun and rifle bullets, and also what you see on the chambers.

Does a rifle bullet with taper always go into a chamber with taper ?

Does a straightwall (no taper) bullet like the 38 Special or .357 Magnum go into a chamber with straight wall - or taper ?

What design considerations affected whether a handgun bullet ended up being a straight wall (like the .38 Special) or with a taper (like some 9 mm) ?

http://en.wikipedia.org/wiki/.357_Magnum
http://en.wikipedia.org/wiki/9_mm

Is the taper associated with the use of bullets in automatic weapons, where it makes feeding easier ?


http://s403998394.onlinehome.us/first-buLLets-38-speciaL.jpg

Pic of the Winchester .38 Special I measured.

[horseshoe3]

I think it has to do with the higher pressures of a modern rifle making it harder to extract a straight wall case. Pistol cartridges have lower pressures so they don't have this problem. Then along comes the .357 magnum and throws a monkey wrench into that theory.

I do know that the purpose of a bottleneck case is to get more powder behind a smaller bullet and give it more velocity from the same length cartridge.

[Horn]

Does a straightwall (no taper) bullet like the 38 Special or .357 Magnum go into a chamber with straight wall - or taper ?

These are wheel gun calibers, if tapered they'd stay in the wheel afterwards.

[hoarder]

It's easier to manufacture revolver cylinders for straight wall cartridges.

[Heimdhal]

I could probably write a 10 page report on the actualities but heres a brief synopsis

Straight wall cylinders are easier to manufacture, but are also remnants of old manufac processes.

However, the biggest reason is for reliability and power factor. More powder can obviously be loaded into a larger case. Small diameter bullet + larger diameter case = much more powder behind that smaller bullet.

In more modern full auto's, the loser chamber clearences and tapered walls allow for greatly added reliability and function at higher rates of fire, while also bleeding off heat inside the chamber faster. When fired, the case itself expands to the chamber wall. Straight wall cases operating at much higher pressures than pistol rounds tend to stick more in tighter chambers.

This is actualy a large reason why the AR was(is) so prone to failure. THe fact that it was a round designed originaly for bolt actions, and thus had a very staight wall, combined with it dumping its spent gas and carbon right into the bolt face and chamber and tight clearences cause a lot of sticky cases.

In lower pressure rounds, or larger diameter rounds (like pistols and old black powder) dont need the taper like higher pressure rounds do.

This is the very, very very abridged version, omitting all physicas and engineering involved and the entire history of modern firearms, but thats a whole other thing.