Power Factor

[Putty]

Did some chronograph runs today. Noticed that the FPS increased dramatically from cold first shot through the subsequent firings. There was quite a bit of disparity between the rounds as well. Is this normal? I could easily be under the power factor if tested at a match with a cold gun, or quite a bit over with a "hot gun". 165 grn JHP's were used, which usually weigh [mean]=163grns. On the second string it seemed a bit more consistent. Oh, its 10 F degrees outside.

First run

1009.8 (pf 164.6)

1027

1020.2

1029.9

1054.2

1070.8 (pf 174.54)

Second Run (4 min wait between last run)

1025.3

1040.4

1032.7

1041.9

[AlamoShooter]

The second run sound normal to me. The first run I would say the air temp was under 35? deg. and the Barrel and amoe was cold?

The big question was what did the group look like? Do the test with everthing cold and see if the first and tenth shot hit within 1" of each other/?

Most of the Crono test will let you worm up the barrel and Amoe... they may even let you roll the bullets in your hand to worm them up

Edited February 20, 2006 by AlamoShooter

[Putty]

I did not shoot for groups, just banged it into a hillside. I rechecked the temp outside, it was 35F (low last night 10F). Shot a 3rd string on power factor only readings......all in the 170 area (167-172pf) with a 5 min delay between the string.

[revchuck]

Was the barrel clean for the first shot?

Also, an ES of 61 fps isn't that bad - factory loads often have wider ones. That would've given you an SD of about 20 - also not bad. Changing powder and/or primer might bring that down...or up.

As long as you keep your match ammo at least one SD above the minimum velocity needed to make the PF, you're probably good; two SDs above is much better.

[Putty]

Separate Run

Hi 1047.3

Lo 1010.9

SD 14.8

CV% 1.43

MAD 9.2

CV% 0.89

ES 36.4

Mean 1028.9

I have never cleaned my Shuemann barrel (he said not to) as I only shoot JHP's. I once swabbed with Balistol.

[al503]

I've found the same thing. The first couple of shots are noticeably lower in PF than the succeeding ones. During the rest of the session, PF is more consistent.

I do run a brush through my bbl and a patch of oil before testing.

[tightloop]

al503

why would you oil the bbl before you test fire over the chrony?

You aren't going to oil the bbl before you shoot a match or stage are you??

It should show you what is happening with the ammo under the conditions that you will shoot most shot under..