Shorter Case=Dangerous Pressures?

[Action_Can_Do]

Hello everyone. While reading a thread in this forum I was reminded that most of the Hornady brass used in conjunction with their new FTX bullets is notably shorter than the SAAMI length. I then recalled loading some ammo for my 460 S&W that was a near max load. The brass was originally factory ammo loaded with the FTX bullet. At the time I didn't even take the shorter brass length into consideration. I just measured it now and the brass is 1.78 on average while the minimum trim length is 1.79. Not much of a difference, I know, but I figure the brass was probably slightly shorter than that before it's last firing. How much extra pressure is this creating? Is it taking it into dangerous areas?

 

[918v]

Brass length has nothing to do with pressure. Overall length affects pressure.

 

[Oyeboten]

Ummmmmmm...I think it is loading density - or how much room the Powder has - for the powder and projectile in question, which then occasion final pressure.

If a shorter Case causes a lower seating depth for a given given Bullet over a given charge usually intended for a longer Case, then one will have created a condition of increasing the loading density, and, one will probably create higher pressures ( in some ratio depending on the powder).

Heavier walled Cases can do this also, by having less volume for Powder and Air to be under the Bullet...even if it is only slight.

 

[Doug b]

What was your work up to a near max load?

 

[918v]

Ummmmmmm...I think it is loading density - or how much room the Powder has - for the powder and projectile in question, which then occasion final pressure.

If a shorter Case causes a lower seating depth for a given given Bullet over a given charge usually intended for a longer Case, then one will have created a condition of increasing the loading density, and, one will probably create higher pressures ( in some ratio depending on the powder).

Heavier walled Cases can do this also, by having less volume for Powder and Air to be under the Bullet...even if it is only slight.

Case length has nothing to do with seating depth or load density. The overall length determines case volume and load density.

 

[Oyeboten]

Lol...


They all work together...anyway.

Granted, OAL is a more exact deteminer but only when respecting the actual-particular Bullet.

Not everyone has OAL figures for every Bullet option they may be considering to Load.


If one wants to have the Crimp occur where the Bullet itself anticipates it, then Case length can be a factor for ultimate loading density acheived, or, depending on the Powder Charge, anyway.

But, far as I grasp this, the final arbiter of pressure, will be the loading density allowed the specific Powder in question, for the actual Bullet weight and kind and the depth to which it is seated.


So yes, small variations in Case length as such would be incidental so long as internal volume for Powder and Air are accounted for or remain the same...

Is what I was driving at.

 

[918v]

If you seat a 1" bullet in a 3" case to an OAL of 3.5", then the internal volume of the case and load density will remain the same if the case is shortened to 2.75" but the OAL remains the same 3.5".

 

[Oyeboten]

Yes...

 

[CraigC]

Since this discussion pertains to a revolver round to be fired in a revolver OAL is moot if there is only one crimping groove. Revolver rounds need a heavy crimp to keep the bullet in place and slow burning powders like H110 need the resistance for a proper burn. Since all loads woud presumably be crimped in the same place, regardless of case length, then case length IS a factor affecting pressure. Whether or not it's enough to make a difference is another matter.

I don't know about you guys but I sure as hell would rather buy longer cases or reduce my loads by a grain or two than have to turn another cannelure in all my bullets. I do this for my jacketed .38-40 loads but only because I HAVE to.

 

[rcmodel]

Brass length has nothing to do with pressure. Overall length affects pressure.

But in this case, he is asking about a revolver cartridge.

We must assume he is crimping it in the crimp cannelure on the bullet.
So the OAL will be shorter, and internal volume will be less with his shorter cases.
And that would raise pressure.

But unless he is loading a full tilt bogey max load, probably not enough to cause over-pressure.

rc

 

[918v]

He is questioning Hornady's decision to use a shorter case. The position of the cannelure on the projectile dictates case length here. Maybe Hornady had to move the cannelure closer to the base due to the longer bullet nose. You can't put a cannelure at the ogjive. If the cannelure is at location X in relation to the bullet base, and Hornady wants to maintain a certain OAL to fit in a cylinder, then Hornady needs to use a case short enough to crimp at location X. if that means the case needs to be .010" shorter than normal then so be it. It has nothing to do with pressure, though.

 

[rcmodel]

We know why they did it. The spitzer FTX is longer then normal pistol bullets, so length had to be reduced to work in lever-actions and some revolver cylinders.

But if you load some other bullet besides an FTX in the short case and crimp it, it may very well reduce the case capacity due to the location of the cannulure on the different bullet.

rc

 

[918v]

Like I said before, OAL dictates pressure here. If the case is .010" shorter than the others, and the cannelure is wide enough, the OP can maintain the original OAL and not raise pressures, and still get a good crimp. If he decides to reduce the OAL by .010", then he will raise pressures. Still, a .010" OAL reduction on a large caliber round is within tolerance and means nothing for the most part.

 

[Action_Can_Do]

For those who asked, I was using Hornady 240 gr. XTP-MAG with Winchester large rifle primers and 44.6 gr. of Enforcer.

 

[Action_Can_Do]

So I take it the pressure increase isn't enough to matter, even with near max loads?

 

[lwknight]

If you are a recipe loader , there is a lot of tolerance built in to the recipe.
A 10/1000 difference will be infintecimally affecting to the load in a big case like that.