case streaching / shrinking

[Bob Maerdian]

I recently purchased some new Starline 40-65 brass to use in two 40-65 rifles, a model '85 and a model '86 Winchester rifles. When the cases arrived I measured the case length and found that they came out running around 2.08". I loaded 30 cases with light loads and was surprised to find that the cases shrank to around 2.05-2.07 inches, shooting a 400 gr. boolit over 23.3 gr. of AA2495.

Would I want to shoot the 400 gr boolit over a load of around 34-35 gr AA2495 to get the cases to "grow" to 2.100"

I would appreciate some suggestions.

Thank you.

Bob

[uscra112]

If your rifles have proper headspace, altering the load won't do anything at all. But not to worry, it's not a critical dimension in a straight case. Just load so all the cartridges are the same overall length, or if you're crimping using the seating die, trim all the cases back to a common length so that you'll get a consistent crimp.

The fact that they shortened might be an indication that your rifle has an oversize chamber, or that the cases came from Starline sized way small. "Blowing-out" an undersize case to fit the chamber will shorten it, but usually not that much in my experience, even with bottleneck cases.

Measure a few diameters on a fired case, then full-length size it and see how much it gets squeezed down. If it's a lot, (say .015"), the case may even lengthen a bit from the sizing. Compare to a case you haven't fired yet, too. You can never have too much data.

Don't do more than neck-size if your chamber is big. The working back and forth of the brass will only make it fail sooner.

If your rifle has excessive headspace, firing heavy loads can make the case lengthen, but it's not a good thing. All the stretching takes place close to the head, and that thins the brass and leads to failure.

[44man]

Don't worry about brass length as long as it is all the same.
Brass does shorten for certain low pressure cases because it expands to fit the chamber.

[243winxb]

FL sizing will make them longer, but i am sure you know this already. :mrgreen:

[popper]

30-50 thous below max COL - don't worry about it. FL will make them grow depending on the expander type. No way a M type will lengthen.

[montana_charlie]

The new case shortened when it was blown out to fill the chamber. How much of that happens depends on make of rifle, usually, but it's a common occurrence.
Full length resizing will recover most of that length, but the same thing will occur next time it's fired. In each instance, the case gets shortened before the bullet starts to move.

If you have a chamber of the modern style, it has a 45 degree angle at the front where the 'throat' transitions down from chamber diameter to groove diameter.
If you shoot a soft lead bullet with black powder, the bullet will bump up immediately to fill all of the chamber and throat.
If there is a space between the end of the case mouth and the beginning of that 45 degree transition the bullet will take on the diameter of the chamber in that 'void'. As it moves forward, some of that 'fat' lead will be scraped off by the 45 degree step.

If the bullet happens to be paper patched, the paper will be shaved by the step, leaving 'paper rings' in the chamber instead of leading.

A grease grooved bullet can be fired in 'short cases' without leading the chamber and throat if it can be seated so that there is an exposed grease groove filled with lube right at the case mouth.

But, the real cure (when using black powder) for throat leading and paper rings is brass that matches chamber depth.

You can buy cases that are too long and trim them back, or you can use a stretcher to lengthen them. In any case, final length should be set with the case in the 'as fired' condition ... and never full length resized again.

If you use smokeless powder, you can just shoot short cases. Bullet bump up doesn't occur as early, and the bullet will probably be past the 'void' before it gets 'fat'.

CM

[popper]

Moving the shoulder back & forth by FL & shooting will NOT mean the case gets longer. Pulling a sizing button through or the 'pull' of a boolit may.

[montana_charlie]

Moving the shoulder back & forth by FL & shooting
The discussion is centered on .40/65 straight cases ... no shoulders.

CM

[popper]

My bad, I looked it up and wiki seemed to say it was necked. It's rimmed so I still done see what diff 0.30 makes.