Power Factor Question

I've searched a few forums, but I haven't had much luck finding an answer.

I'm shooting minor so the minimum PF is 125. How much of a buffer do most of you use to ensure you don't fall below. I finally got around to choreographing the load I'm currently using and it had a PF of 131.75 but with an SD of 28. I had one light round in the batch that dropped to 983 fps. If I add a tenth of a grain I get a PF of 134.125 (this time with an SD of 8 ). Is the 131 PF too close to the minimum?

IIRC..... When chronoed at a match, if just one round make PF, you are good to go.

I personally would NOT try to get very close to 125. Where you are at around 135 gives you the "safety factor" when temp and humidity change................

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Everyone has their own way of doing this. Will's method certainly makes sense. My way is to aim for 7 points over. I also noticed that you said that you have a standard deviation of 28. That seems like too much for me. I heard on tv that the major ammo vendors shoot for less than 10%. If you are using mixed brass, you should be able to get 15% on a really good day. This matters since you only get 7 rounds at the absolute max to get over your PF.

My two cents

That was the highest SD of 12 10 round strings. All the other loads were an SD between 8 and 12.

Looking back through my log I really think the first string was just anomaly. Even at that based off what ya'll are telling me it looks like my second string would be the load to go with.

String 1

4.1gr Titegroup 125gr FMJ
HI: 1077
LO: 983
AV: 1054
ES: 94
SD: 29
PF: 132

String 2
4.2gr
HI: 1088
LO: 1063
AV: 1073
ES: 25
SD: 8
PF: 134

String 3
4.3gr
HI: 1116
LO: 1063
AV: 1090
ES: 35
SD: 10
PF: 136

String 4
4.4gr
HI: 1124
LO: 1094
AV: 1108
ES: 30
SD: 10
PF: 138

I run 130 to 132 in Production.

When I shot major I was always 5 to 7 points over as well.

I like string 2! The boys shoot a 132 PF load with a SD of about 10.

I concur with the above. Official chronograph procedure can be found on pages 71-73 here: http://www.uspsa.org/rules/2010HandgunRulesProof3web.pdf

I say that I generally shoot for about 5-7 PF over, but truthfully I have never chronographed lower than 171 at a major match and have been as high as 177 in matches over the last 10 years in 12 or 13 different states. I haven't kept up with the average, but I would be willing to be it would be in the 173-174 range just based on memory. Differences in chronographs and varying temperature, altitude, and barimetric pressure all likely played a part. Better to be a little high than a little low though. It takes upwards of 10 PF for me to really be able to feel a difference anyway. 2 or 3 PF is nothing.

7 PF over is generally safe IMO.

Then again I shoot factory and my white box chrono's at 143 in my G34. :p

spanky wrote:7 PF over is generally safe IMO.

Then again I shoot factory and my white box chrono's at 143 in my G34. :p

Nice cushion. My range above only included .40's I reloaded for major. The Mississippi Classic in October 2000 was my first major match and my 3rd match ever. I shot factory 230 FMJ .45 and chronoed at something like 196 PF... We had a couple of competitors last year at the Classic in the 190's, too.

We shot with a guy at Space City who chrono'd at 199.

Could be, but I doubt it. I haven't seen one of those at any matches in the last decade, although I know a few guys that used to shoot them.

I'd bet good ole .45 ACP. That's only a 230 grain at about 865 fps, which is fairly common for factory hardball in a "fast" barrel. I've seen it go over 200 PF in the right gun on the right day.

It was a .40.

Wow. We were both off. Was it factory or a reload? What bullet weight?

I have a somewhat humorous and semi-related story: At a Nationals several years ago, I think it was 2005, we heard a rumor that Taran Butler (a perennial top 16 finisher at the Nats) had made some serious power factor at the chrono and it was largely due to carelessness and a bit of luck. Apparently, Taran hadn't been careful and had mixed up some 180 grain .40 ammo with some 200 grain .40 stuff. When he pulled 8 bullets for the chronoman, he got a mixture of the two. As luck would have it, they pulled a bullet and it weighed 200 grains, which apparently caught him off guard because he thought he had brought 180's to the match. The ones shot for velocity, however, were apparently 180's so the power factor was way on up there. (I don't remember the number, but a 200 grain bullet at typical 180 grain velocity should be in the 190 PF ballpark). He's a lucky dude though. I know my luck, and if it would have been me the bullet pulled would have been a 180 and the ones shot for velocity 200's leading to a not so impressive (and minor PF) result...

The right thing to do (IMHO) is to declare that you have shot two different loads at the match and have both chrono'd. I have brought two loads to both the 2010 Gator and the 2011 Alabama State match. The chrono guys were a little confused as to what to do, but shot both batches.

Yeah, that's a good question and I agree both should be tested. On page 72 of the link I included above, the rulebook says:

If a competitor’s match ammunition is retested, or if any authorized replacement ammunition is used, and different power factors are recorded when tested according to these rules, the lower power factor must be applied to all courses of fire, including those already completed by the competitor.

I don't know if TB got special treatment because of who he was or if they actually chronographed both loads finally and the story or rumor went around about what first occurred. I think part of the problem was what do you do when all of the ammunition is mixed up in a bag or box and you can't tell from the nose of the bullet which is which? Just keep shooting rounds until you can see a definite set of two velocities?

chbrow10 and I shot with a guy at the Gator shooting 45ACP who chrono'd I believe 212. Shooting Israeli factory hardball. He won SS divison.