Maximum Safe Radial Expansion for Brass Cased Rifle Cartridges

[jmoore]

Continuation of discussion fron L-E forum:

Link below.

Headspace question. - Military Surplus Collectors Forums

The OP did not actually have an headspace problem.

Information

Warning: This is a relatively older thread This discussion is older than 360 days. Some information contained in it may no longer be current.

[jmoore]

Mr. Horton, the Book exerpt limits itself purely to hoop stresses, which, although pertinent, are mostly associated w/ axial case failure (lengthwise case splits), that don't directly address my concern.

I'm thinking of the area that also fails first in cases of excess headspace, the case body/web transition area. Although the annular failure may appear at the outset similar, the outward deformation mechanics seem to be a bitmore involved.

Variables that come to mind immediately are:

case wall thickness
wall taper
internal radius at the transition area
ability of the forward body to be drawn rearward due to low friction
bending versus stretching of the case wall at the bulged area

Out of time- some days I can let the machine run a bit, but no opportunity today- its hands on! ("High speed rotation" turbine components- of which you might be familiar)

[Edward Horton]

Mr. jmoore

The only "radial" that concerns me are my tires, and as long as they give me good traction and long life I don't care "how fat" they get when I pump them full of air.

The same applies to the brass cartridges I reload, if they fall apart when you reload them, then it's time to look for cartridge cases with deeper tread and a higher speed rating.

For you geeks who want to "see" radial and axial excess case expansion the red and yellow areas below are the parts of your tire that are going to have blowouts.

[ireload2]

You can have a case head failure in a rifle with minimum headspace if the chamber to case clearance is too great. This is due to excess radial stretching.

[jmoore]

The illustration above is still more in reference to the localized stresses due to the unsupported back end moving straight to the rear.

I'm think of the situation of NO rearward movement, purely outward.

As a practical experiment I'm thinking of adapting a .303 British case to a 7.62x54R chamber by shortening the case and pushing the shoulder back until it can be snuggly inserted into a 1891 barreled action I've got as a spare parts donor.

The base diameter difference is about 0.030" - That ought to show results!

Don't think I've 7.62x54r dies, though. Will check when I'm not at work- which is almost never for the last month!

[Edward Horton]

"I'm thinking of the situation of NO rearward movement, purely outward."

Mr. jmoore

Your talking about the big bang theory and the expansion of the universe, how are you going to fit all that in a .303 case traveling at the speed of light in a Russian rocket? Or are you going to grease the case and create a warp drive with twice the thrust?

[jmoore]

Both!


See how far it goes.
1. oiled, w/EH-ring to center cartridge
2. dry, w/EH-ring
3. oiled, made as far off center as possible
4. dry, off center

[ireload2]

The illustration above is still more in reference to the localized stresses due to the unsupported back end moving straight to the rear.

I'm think of the situation of NO rearward movement, purely outward.

As a practical experiment I'm thinking of adapting a .303 British case to a 7.62x54R chamber by shortening the case and pushing the shoulder back until it can be snuggly inserted into a 1891 barreled action I've got as a spare parts donor.

The base diameter difference is about 0.030" - That ought to show results!

Don't think I've 7.62x54r dies, though. Will check when I'm not at work- which is almost never for the last month!

A combination similar to this can exist with several rifle ammo combinations.
One set up is the .270 or .280 fired in a 7MM Magnum chamber.
These routinely blow the magazine out of BARs when the case head opens up due to the larger chamber diameter.

[ireload2]

Another way to test this is to polish a rifle chamber larger in small increment os say .003 and reinstall. Test fire disassemble and repeat the polishing and test firing until it fails.

[Edward Horton]

Or you can oil or grease the cartridge case and trash the whole rifle.



If you really feel brave you can stick the cartridge case in a missing knot hole in your back yard fence and hit the primer with a nail and hammer. This should give you maximum radial expansion and also help apply a "red wood" stain to the wood.