16ga.com ~ View topic - 2 3/4 data in 2 1/2 hulls- pressure increases

Joined: 16 Jul 2015 Posts: 2126 Location: Hudson,Wy

I may be developing some new loads for 2 1/2"hulls using 800-X and Longshot if I can't find any that have already been tested.

That stated, I have a lot of low pressure data for 2 3/4" hulls that can be used as a starting point. I have no desire to roll crimp and most other folks don't either, so if I am going to spend a bunch of money on testing, it will be fold crimped ammo since this data will be shared with the reloading community.

Reducing internal capacity by going to a shorter hull, with the same data/ components does raise pressure. I have been under the impression that the average increase is 500 psi, although it varies.

Does anybody have experience/ data/ research, etc. that shows this correlation in a quantitative manner? If so, please share. Load testing is pretty expensive and I want to get my calculations close before I build any test loads so I don't have to do numerous repeat testings.

Joined: 04 Mar 2019 Posts: 1842 Location: Central ND

Wyo, Kinda like roll crimps vs fold crimps....sometimes the pressure does not change and sometimes it changes by 1,000 PSI. The 500 PSI figure is a good guess, but that is why every load is supposed to be tested, as you just never know how much.

The reason for the increase is because you are compressing the wad, while crimping, to the point where there is nothing to collapse upon ignition thereby decreasing the volume of the combustion chamber made by the hull walls, basewad and the obturaing cup of the wad.

As an aside to this response, the length of the hull has nothing to do with the slight (even 1,000 PSI is slight) chamber pressure increase.

Member Joined: 16 Dec 2007 Posts: 592 Location: Minnesota

An option would be to contact hodgdon and see if they will provide guidance.

Joined: 18 Apr 2018 Posts: 28 Location: Alaska

About cramming a 2.75 recipe into a 2.50 hull. Bad idea. The pressure will change and the crimp may be unstable.

There is data for 2.50 Chedite hulls on the Hodgedon web sight but component availability may be limited.

Not knowing what reloading press you are using I don't know what is available to crimp short shells.

You may want to look into old data for card and filler loads. They rarely came with pressure data so testing would still be in order.

Joined: 16 Jul 2015 Posts: 2126 Location: Hudson,Wy

The problem with old data is that so much of it used powders that are no longer available. The reason for asking this question was to establish a correlation so I could calculate a good starting point for loads to be sent to a ballistics lab. The gun I need the data for, well it's being sent back to the seller so I'm putting this on hold depending on what I end up replacing it with.

Joined: 01 Mar 2017 Posts: 52

The reason for the increase is because you are compressing the wad, while crimping, to the point where there is nothing to collapse upon ignition thereby increasing the volume of the combustion chamber made by the hull walls, basewad and the obturaing cup of the wad.

As an aside to this response, the length of the hull has nothing to do with the slight (even 1,000 PSI is slight) chamber pressure increase.[/quote]

Can you explain please, how the volume of the combustion chamber will be increased, when the load components are compressed to fit into a short hull?

Joined: 04 Mar 2019 Posts: 1842 Location: Central ND

Misspoke, I meant decrease, Thanks for catching that.

Joined: 21 May 2010 Posts: 603 Location: Victoria BC Canada

I see no reason that similar loads can't be run-up for both cartridge lengths. The big difference is that a shorter wad column has to be employed.

If the load fits without heavy pressure then it is likely no problem. I have regularly loaded 2 3/4 - 1oz recipes into roll crimped 2 1/2 with ease and without issue.

I would have reservations about doing so with heavier that required heavy pressure to make it fit.

Observing how much space wads have in moving up and down in a hull leads me to believe. There is plenty of room in a 2 1/2 inch hull.