How to figure out barrel pressure in 6.8 spc

[groverdunerider]

I'm tiring to figure out a load for 6.8spc using 150 grain bullet and h322 as the powder. Iv loading 5 rounds with 20 grains of h322. I have a chronograph on the way. Is there a way to figure out if I'm within safe pressures without just looking for signs of high pressure in the brass?

[NorCalFocus]

Pressure signs in brass are the best thing to look at. If your chamber is slightly tighter than others (with 6.8 SPC having a few different chamber specs, even more issues) it will reach max pressure sooner. Just because its published, doesn't mean that its safe in all guns.

I pulled Hodgens info and looked in my Lyman book neither listed info for a 150 grain bullet. So I'm guessing thats why your just guessing 20 grains, you can't find load data? First thing I'd do is figure out how far into the case that bullet will stick. Thats going to tell you how much room you have in the case. Second see how far 20 grains fills up a case. Does the bullet compress it?

I'd start as low as you can. (enough powder to power the bullet) and load one round at increasing charges in 1/2 grain increments. IE 19.0, 19.5, 20.0, 20.5...etc. Then you shoot each round inspecting the case after each firing. If you get slight pressure signs on one round, go up one more round and see if the signs get worse. Then you know the max charge, and you can back down from there to start your ladder or OCW testing.

[JackEllis]

load one round at increasing charges in 1/2 grain increments

I'm using Hornady 150 grain GMX bullets in a .30-06 and I was a bit suspicious of the manufacturer's published data so I did exactly as NorCalFocus suggested. Good thing because there were pressure signs well below the max load accompanied by higher than book muzzle velocities.

The load books use barrels that probably aren't like your so you have to be a tad skeptical of the data IMHO. Work up and be safe, or take shortcuts and run the risk of being sorry.

[groverdunerider]

Thank you very much first off.I am kinda new to reloading iv got about 2000 rounds of 223 iv done but never any 6.8 spc . Iv especially never worked up a load without data. Your guy's input is great.

[rsrocket1]

Quickload can give you an estimate guess (but my experiences have been very good). $153

20g H322, 150g Hornady SST 27402 bullet length 1.305" COL 2.283", bullet seat depth of 0.712 gives a peak pressure of 38,367 psi and out of a 24" muzzle, a MV of 2037 fps. A pretty tame load.

Pressure Trace II will give you a real measurement but it's at least $700 before you have all the stuff necessary to do the measurements and it helps to be a test engineer to get worthwhile measurements. You glue a strain gauge onto the barrel of your rifle, attach probes to the gauge, shoot factory loads to get a baseline measurement, then shoot your test rounds and use the reference measurements as a reference point.

With the Quickload calculation estimates, you can chrony your loads and if they are close to the calculated MV's you are in the right ballpark for load development. Powders can vary from lot to lot and with temperature so it's best to stay on the low side to be safe but your load ought to be pretty safe.