Gp90

[theBuilder]

So, i have an excellent condition schmidt-rubin sporter that i have really been wanting to breathe some life into. I loaded up afew rounds for it and just wanted some more experienced opinions..

7.5x55 ppu brass resized, but not trimmed to 53.5 because it chambered just fine in the rifle after resizing (average case length was 55.5mm)
CCI bench rest large rifle primers
165g speer btsp .308 bullet
38 grains of IMR 4064 (it was the lowest charge for 30-40 krag in my manual for that powder)
OAL is 3.05"

My main concern is the amount of empty space in the case, 38g of imr 4064 doesnt take up a lot of room in the 7.5x55 casing, and i dont want there to be any spikes in pressure with this old schmidt rubin action. I unfortunately didnt think of this until after i loaded up 10 rounds. Any opinions? Thannks

 

[VinnyQC]

It sounds like you're affraid that too much free room in the case will create a pressure spike. Am I correct? I don't see why that would be the case.

The case capacity of the 7.5x55 is 12% higher than the krag (4.22cm3 vs 3.75cm3), so it'll be a lower pressure for the same amount of powder, or possibly in some cases partial detonation (which will definitely be lower pressure, but brings its own set of problems). A pressure spike is created by burning too much powder too quickly, and although the speed at which the powder will burn might be slightly influenced by the position of the powder in the case, it shouldn't create a pressure spike unless the load wasn't safe to begin with. Either your load is safe for your gun or it isn't.

If you want to approximate the pressure in your chamber, you can use the 30-40 krag pressure with the load you choose, and divide by 1.12 (that's 7.5x55 case capacity divided by krag case capacity). It'll give you a ballpark number.

 

[Hitzy]

I load my K31 fairly light, I like to use 308Win data and work up. With faster powders SEE isn't really a concern.
I usually use 45gr varget with 150gr fmj, good accuracy and just a bit over 2600fps.
Your loads will be fine, but likely dirty as pressure won't be very high...necks will be black after firing, maybe whole case.

 

[theBuilder]

Alright, sounds good guys, thanks.