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Knowing When I've made the Velocity (power factor) goal?

Discussion in 'Handloading and Reloading' started by DesmoDucRob, Dec 14, 2009.

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  1. DesmoDucRob

    DesmoDucRob Member

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    W231 Is my go-to powder for a few reasons. I like it; I shoot primarily 9mm in USPSA production division, and use 124 grain cast round nose from Missouri Bullet Co. There is little smoke, and no leading to speak of with either my LWD barrel or my factory polygonally rifled barrel.
    I notice that many folks who use W231 and 125 grain cast bullets claim that you will make power factor at 4.1 grains of powder. In my glock 17, I need somewhere around 4.4 or 4.5 grains of W231 to get the velocity over 1000 fps every time.

    So my question is: do you folks who are meeting a power factor goal only stop when your chrono confirms that every single round is over the “threshold velocity”, or do you take an average. I’d hate to have eight out of ten rounds make power factor and then roll the dice when I get to the chrono stage at a major match. It may also be worth mentioning that as I incrementally increase my powder charge towards the 4.5 grain mark, I notice less standard deviation in velocity, so not only are my bullets moving faster, but they’re also more consistent.
    Thanks-
     
  2. Rugg_Ed

    Rugg_Ed Member

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    I gave myself a 2% margin over average to make sure I met the power factor.
    Nothing worse than losing the works because of under minor power factor.
     
  3. EddieNFL

    EddieNFL member

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    For major PF I need an average of 850 FPS. I shoot for an average of no less than 880 FPS to add a little insurance. If the accuracy is what I want, I stop; if not, I'll fine tune.

    About 25 years ago I was shooting a state championship match in FL (or AL or GA, somewhere in the SE). I was chrono'ed early on the second day and it happened to be cooler than normal. I made PF with 2 FPS to spare. That's when I decided I need a little wider comfort zone.
     
  4. chbrow10

    chbrow10 Member

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    I agree with all of the above. I have a cheap chrono, so I give myself some margin to the tune of 8 PF points. So I make sure that the average of 10 shots is 132 PF for minor, 172 for Major.
     
  5. DesmoDucRob

    DesmoDucRob Member

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    It sounds like I should be focussed on an average. I started getting comfortable results around 4.1 grains, but it wasn't untill above 4.4 grains that every single round chronoed above 125 pf. I'll probably keep things around 4.5 grains for now, but WOW! those 4.1 grain charges feel like I'm shooting cotton balls :)
     
  6. twofifty

    twofifty Member

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    That's because they're called puff balls. ;)

    My load is set to yield a 132PF, a nice comfort margin. I don't mind that it hits the poppers a bit harder, esp. if my aim is off somewhat or when engaging the popper at an angle.
     
  7. DesmoDucRob

    DesmoDucRob Member

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    After a little research, I believe some of the folks claiming to meet power factor at the 4.1 grain mark are shooting a G34, as opposed to the 4"-barreled Glock 17 that I've got.
     
  8. 1SOW

    1SOW Member

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    I use 130+PF for minor. My CZ 4.73" bbl takes around 4.2 for jacketed rounds.
     
  9. chbrow10

    chbrow10 Member

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    Rob,

    Another thing to consider is standard deviation (of the sample). If you have a good standard deviation, your velocities are are centered tightly, and there is less chance that one of your sample will drop below the minimum and lower your average. I have heard that the factory ammo guys look for 10% or less standard deviation.

    You being one of those sciency guys, I'm sure you can figure when Excel function that is!!

    DVC,
    Chris
     
  10. DesmoDucRob

    DesmoDucRob Member

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    Yeah, but I try to keep work at work. ;) Seriously, though you're right on the money. The only reason I haven't reduced my load is for fear of a round randomly falling below power factor. Once I can reach that 10% SD mark you mentioned, I'll pretty much be able to dial in my power factor at ease. I'm going to evaluate a few variables independently (specifically case OAL) and see if I can streamline my velocity a bit. I'll keep you posted.
     
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