[mokin]

I've been developing a load for the .40 S&W using Hornady 155 grain XTPs and HS-6. I started with 7.2 grains as recommended as in the Hornady manual, then moved up to 8.0 grains. Neither showed any signs of high pressure and were pleasent to shoot. I moved up to 8.4 grains, and, as I was appreaching the recommended maximum load, I shot these over the chronograph. According to Hornady, the velocity should be around 1100 fps. The 12 rounds I clocked were moving at 1193.3 fps (avg). High was 1234, low was 1126, standard deviation was 32.07 fps. I was using Hornady data to base the load on. Cartridge length was 1.123 +/- .0015". Overall, the load was again pleasent to shoot and fairly accurate with no signs of over pressure. I'd like to make some more but as I know the velocity exceeds what is safe I am reluctant. I was shooting a Glock 29 with a Storm Lake drop in barrel chambered for .40 S&W.

Thoughts, ideas? Anybody else run into this?

[rcmodel]

HS-6 is Hodgdon powder.
They say 8.5 grains is MAX with the bullet you are using.
1,137 @ 33,200 PSI in a 4" barrel.
I'd believe them, regardless of the velocity.

Your Storm Lake barrel might just be a "fast" barrel.
Some barrels are and some barrels aren't.

Anyway, .40 Glocks are not guns I care to test the pressure limits in.

rc

[Steve C]

Don't assume velocity is a direct indicator of pressure. There are lots of things that increase velocity besides pressure and a load may show higher velocity in a particular gun without having higher pressure than the same load in a different gun even if its the same make and model.

[mokin]

Thanks,

I'm sort of leaning toward the "fast" barrel reasoning. I also chronographed a "pet" load I developed for another pistol using 180 grain Berry's Copper Plated bullets moving around 950 fps at around 1030 with the Storm Lake barrel. The load I'm developing doesn't exceed the published limits and as it is close I plan on stopping where I am. I don't like to test the pressure limits in any of my guns, Glock or otherwise. That being said, if I am using an aftermarket barrel in my Glock, does that mean it is still a Glock?

[1SOW]

Pressure is a component of how much gas is generated and the size of the gas container. Pressure drives the bullet.

When they test for speed and pressure, the test fixture might look like this one provided by "RFWobbly". The data provided is what a test fixture measured.
https://lh6.googleusercontent.com/-Wim0F4owMoM/UIdSG_8XX-I/AAAAAAAABfQ/5_nsQb_yxEk/s600/TYPICAL%2520LOAD%2520DATA%2520TEST%2520GUN.jpg
JMO:
If your bbl is a larger or smaller diameter, bbl has a slightly different twist rate, your case is softer or harder, or maybe even if your recoil spring is lighter or heavier, the pressures pushing the bullet will be different with the exact same bullet and powder. The containment/leakage of the gas behind (and in front of) the bullet changes, so the speed changes.
A hotter or colder primer will also have some affect on how fast the powder burns.

[jjjitters]

Test them at the hottest outside temp you will shoot in. Thats where they will have as high a pressure as any other time. When I run a hot load I test then, so I know it will not surprize me down the road when I decide to go shooting on a 90F day.