Case Volume

***crnama*** · 07-13-2011, 06:46

I have been loading with 180grn XTP bullets for most of my loads, but I am wanting to change to something cheaper. I now have some Hornady FMJ/FP and some Berry's plated FMJ. These new bullets are shorter than the XTPs. So, would I want to keep the COAL the same at 1.260" that I used for the XTPs or do I shorten the COAL so the internal case volume is the same?

ModGlock17 · 07-13-2011, 07:21

Glad you asked. I have the same question as well.

Kegs · 07-13-2011, 08:07

Safety fellas. Keep it at 1.26" COAL and work back up your load. Each bullet is unique - don't let the mass alone fool ya. There will probably be a lot more similar results with the same mass of bullet, but there is always a need to work back up slowly to develop a decent round.

Test first, production load after.

_The_Shadow · 07-13-2011, 08:32

While the bullet occupies less space (pressure maybe slightly less) you are still trying to push the same mass with slightly less frictional surface area thru the bore. Will you notice much difference that all depends on the powder of choice...

Well no mention of powder of choice was made here. The faster the powder the least amount of change will be observed but the slower powders will show a little more change. Therefore how much change will be related to the powders burn rate.

The Chronograph will probably show the difference in velocity. Only measurements will provide the difference as an average.

Some manuals (Speer#14) list the use of the bullets specific to weight for the powder charge weight. Like their GDHP and the FMJ's using the same powder charge...Why they have given a charge weight that works with both.

21Carrier · 07-13-2011, 13:34

Nope, I wouldn't shorten it. You likely COULD shorten them and stay at the same max pressure, but could and likely do not make me feel all warm and fuzzy. If you WANT to shorten them for some reason, or increase the powder charge, you should do so as part of a new work-up.

***crnama*** · 07-13-2011, 16:47

I had planned to load to 1.260" then work up a new load from there. Thanks for the input guys. This reloading sure is addicting.

Taterhead · 07-14-2011, 09:40

For plated bullets, you want to seat them out to 1.26" to disturb the plating as little as possible. Also give a generous bell on the case mouth.

ALSO! The load data for the XTP must be backed off by 10% when running plated bullets. They generally have higher pressures than jacketed bullets.

Lastly, you won't be able to drive them as fast as XTPs since they become unstable beyond about 1100 depending on the powder.