Power factor margin of error

[ttolliver]

I sort, but only avoid military brass. I tend to use S&B last because of the tighter primer pockets, but I use all commercial brands.

No wait, I just remembered AMERC. Toss that as it tends to have off center primer pocket holes.

[GunBandit]

I'm using Titegroup under a 230 gr LRN. It was the only pistol powder the local shop had and I wanted to try some loads. I have read that isn't too temp sensitive. However I know some are, like the H414 I use in my .243 Win. I used the load tables in Hornady's 9th edition and from Hodgdon's site. I'm pretty confident in my loads making PF and I agree with TTOliver that the loader should be aware of his loads and keep a keen eye on the process as you are pulling the lever on the ram and the powder measure. I'm doing these on a single stage so I am paying particularly close attention.

[snertley]

I load W231, it tends to be reveares temp sensitive.

[AJE]

I was testing for temp sensitivity today.

I set one magazine outside (5 degrees) and one next to the fire place... the powder was WST, which is supposed to be reverse temp sensitive.

Well... it is. My chrono wasn't working all that well but the cold loads were about 100fps faster than needed for minor power factor, while the loads that sat by the fireplace (in all honesty they were probably too hot for a real world test, as they were hot to the touch) failed to cycle the slide on my Glock 34.

I need to get a little more scientific on the test (or travel to matches with my magazines on ice).

[basman]

For minor I like to have 135 PF over my chrono, that usually puts me at 131-138 at match chrono's.

I don't know about you, but when the buzzer goes off, I can't tell the difference between 130 and 135 PF!

[9146gt]

CED says accuracy of their chronos is + -10%

Tom

[G-ManBart]

I was testing for temp sensitivity today.

I set one magazine outside (5 degrees) and one next to the fire place... the powder was WST, which is supposed to be reverse temp sensitive.

Well... it is. My chrono wasn't working all that well but the cold loads were about 100fps faster than needed for minor power factor, while the loads that sat by the fireplace (in all honesty they were probably too hot for a real world test, as they were hot to the touch) failed to cycle the slide on my Glock 34.

I need to get a little more scientific on the test (or travel to matches with my magazines on ice).

Your results are actually pretty accurate. A buddy of mine just did controlled temperature testing of WST in 9mm, and found something like 95fps difference going from ammo cooled to 30*F (for several hours) and ammo heated to something like 120*F. He's planning to go back and reduce the high temp to something more realistic, like 100*F, since he doesn't plan to shoot matches anywhere that it will be 120*F+.

[ttolliver]

CED says accuracy of their chronos is + -10%

Tom

Hmmm... Now that needs some looking into.

I just read everything they had on the M2 on their website. The only reference to accuracy I found was in response to a question about using longer spacing arms than the standard 2 foot

"The CED M2 Chronograph is designed with advanced digital firmware and processing speed that eliminates the need for longer rails. At 2 ft. spacing of the sensors, it provides 99.8 - 99.95% accuracy"

But it would be interesting to hear their thoughts on any other sources of variations, such as lighting conditions.

[Rwm983]

Can someone help me calculate power factor properly? If the bullet weight is 124.85 grains is that number, including the decimals used in the calculation.? Same for velocity, are decimals calculated if the chrono displays them ?

Also are the muzzle to chrono distances the same at all the matches in ipsc and uspsa?

[AJE]

I was testing for temp sensitivity today.

I set one magazine outside (5 degrees) and one next to the fire place... the powder was WST, which is supposed to be reverse temp sensitive.

Well... it is. My chrono wasn't working all that well but the cold loads were about 100fps faster than needed for minor power factor, while the loads that sat by the fireplace (in all honesty they were probably too hot for a real world test, as they were hot to the touch) failed to cycle the slide on my Glock 34.

I need to get a little more scientific on the test (or travel to matches with my magazines on ice).

Your results are actually pretty accurate. A buddy of mine just did controlled temperature testing of WST in 9mm, and found something like 95fps difference going from ammo cooled to 30*F (for several hours) and ammo heated to something like 120*F. He's planning to go back and reduce the high temp to something more realistic, like 100*F, since he doesn't plan to shoot matches anywhere that it will be 120*F+.

I was trying to rig up a way to get the "hot" testing done with a kitchen thermometer for that reason. 120* isn't probably far out of what should be tested for me.... hot day, range bag and mags end up sitting in the sun... just a thought. I think mine were a lot hotter than that, though. I'd might like to jump divisions eventually, and I still carry a .40 sometimes, so a few extra fps shouldn't make that much of a difference anyway.

I just loaded up some rounds with a slightly increased powder charge to try out as well.

I'm going to try a few of them today just to feel the recoil difference.

Edited February 9, 2014 by AJE

[Sarge]

Can someone help me calculate power factor properly? If the bullet weight is 124.85 grains is that number, including the decimals used in the calculation.? Same for velocity, are decimals calculated if the chrono displays them ?

Also are the muzzle to chrono distances the same at all the matches in ipsc and uspsa?

All decimals are used in calculating. It's just that when all calculations are done 124.99 is still just 124. Nothing is rounded.

[9146gt]

CED says accuracy of their chronos is + -10%

Tom

Hmmm... Now that needs some looking into.

I just read everything they had on the M2 on their website. The only reference to accuracy I found was in response to a question about using longer spacing arms than the standard 2 foot

"The CED M2 Chronograph is designed with advanced digital firmware and processing speed that eliminates the need for longer rails. At 2 ft. spacing of the sensors, it provides 99.8 - 99.95% accuracy"

But it would be interesting to hear their thoughts on any other sources of variations, such as lighting conditions.

The 10% number came from CED when they had mine in to check inconsistent readings with both sky screens and Infrared screens. Many times there would be a 100 fps difference between the screens. I was told they were in spec when they were checked...with an air rifle. As they have no other way to check them.

Tom

[Sarge]

I pretty much heard from the horses mouth that they can be off by 10%. Hence the reason to run two of them together at a major match. Take a look at the chrono readings on your gun next time you are at a major. One shot, chrono 1 will read higher than chrono 2. The next shot it may be exactly the opposite. This is why I like staying well away from minimum PF's.

[9146gt]

I pretty much heard from the horses mouth that they can be off by 10%. Hence the reason to run two of them together at a major match. Take a look at the chrono readings on your gun next time you are at a major. One shot, chrono 1 will read higher than chrono 2. The next shot it may be exactly the opposite. This is why I like staying well away from minimum PF's.

Maybe USPSA needs certified chrono's and scales at major matches. Oh and boxes.

Tom

[ttolliver]

Sorry if I can't get past the 10%, but wow...that's huge!

I guess it's not that unreasonable to envision compounding every possible means of introducing error into a perfect storm.