How to determine proper powder charge with incomplete data?

[bullpen7979]

Greetings all,

How does one determine the proper powder charge for "in-between" load data? For example, Im using BE86, and I have the following load data for 9MM Luger.

http://www.alliantpowder.com/reloaders/powderlist.aspx?page=/reloaders/powderlist.aspx&type=1&powderid=38&cartridge=23

In this example, for a 125 grn LRN, the table calls for a 5.7 grn charge with a COAL of 1.12. My CZ P01 wont chamber cartridges of that length reliably. I need to be around 1.07-1.075 for this pistol. I also have an MP Shield, also in 9mm, and I wanted to come up with the load that shot best in it, and that the CZ would also chamber.

My question is this: How does one properly calculate powder charge for a shorter OAL than the table calls for?

I have been loading 4.7 grains, and the shield groups well (for me) with this load, with no signs that I can see of high pressure. Primers arent flattened, no blowback around the primer cup, no FTE's, etc.

This was merely an educated guess on my part. I see that the load for 147 gr at 1.08 is right about the same, so I felt fairly safe here, but I was wondering if there was a science to this. A ballistics program I might employ? I remember a program named Quickloads or something to that effect? Are there others you boolit masters use?

Also had another question regarding a choice of centerfire caliber, but I thought I'd post that seperately

Thanks and regards,
MP

[williamwaco]

I didn't see what powder you were using so as a general rule with the faster powders common in the 9mm, I would cut one half grain and work back up by tenths.

BTW: over the years I have settled on an OAL of 1.05 for my 9mm stuff.

.

[mdi]

Personally I'd go back to starting loads when I make any changes in bullet seating. I very rarely get near max. charges so my loads aren't "affected" (aren't pushed to dangerous pressures) by shorter OAL...

[reddog81]

Is the 5.7 grains a min or a max load? is 1.12 a min or a max COAL?

If 4.7 and 1.07 work for you i wouldn't worry about it too much. Many 9mm bullet and gun combos require an OAL around 1.06 to 1.08. Anything shorter than 1.06 and I would start to worry.

[leftiye]

First, I'd say that I always use established powders that are well known. And then I'd say powders that for the given caliber are top performers. I make premium loads and can't afford the time to make cockamamie cartridges. After that I'd say if data is available (and it would be unbelieveable if it were not) start safe and work up. Many who don't have a clue as to how to read pressure signs will try to tell you it can't be done. Ask them what we did before chronographs and pietzo electric pressure transducers existed for the average reloader.