ultrablue Posted September 24, 2011 Share Posted September 24, 2011 Today I went to the range and chronod some loads. I used 3.8 gr. of N320 with a Berry's 124gr rn bullet. I got an average of 993.68fps and an average pf of 123.2163 on a 10 shot string. My question; is there a mathematical equation to see if increasing the grains will produce a power factor number? I know I need to do the chrono again to verify the results. If I know mathematically I am close I won't have to load a bunch of unnecessary rounds. Or is anyone using these numbers for a minor pf in USPSA. I am using a 9mm xdm with a 4.5 inch barrel. Link to comment Share on other sites More sharing options...
DyNo! Posted September 24, 2011 Share Posted September 24, 2011 It would be logarithmic, not linear. Link to comment Share on other sites More sharing options...
Sarge Posted September 24, 2011 Share Posted September 24, 2011 Math, Schmath! Load a handful at 4.0, 4.1 and 4.2. You want to be a little over 130 PF anyway. I'm guessing you will solve the equation with 4.1-4.2. Link to comment Share on other sites More sharing options...
warpspeed Posted September 24, 2011 Share Posted September 24, 2011 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ What Kevin said. I'd suggest shooting them for group, off of sandbags & over the chronograph. Find the ones that make pf & are accurate. The 2 are not always the same. Link to comment Share on other sites More sharing options...
shred Posted September 24, 2011 Share Posted September 24, 2011 The curve on some powders (long ago the VV pamphlet had a little discussion of the topic) approximates linearity for a small range. However, even if you fall into that range, it's unlikely the formula will get you closer than +/- 0.1gr of where you want to be. Link to comment Share on other sites More sharing options...
gm iprod Posted September 24, 2011 Share Posted September 24, 2011 Kevin is pretty much spot on. So too is shred. I know for fact the following is true. In my gun, STI 6" 38Super, using 115gr Zero JHP, Federal Primers, Titegroup, OAL 1.225", only when between 4.0gr and 4.9gr each .1gr is about 30fps. Over teb years of testing it has varied between 24fps and 34fps for each incremental .1gr change. Go past that 4.9gr and the increase in velocity is much more than 30fps and once over 5.2gr the increase in velocity is much more again and sudden. So be careful by trying to extrapolate likely increases in velocity once you get to a certain point. Link to comment Share on other sites More sharing options...
michael b. Posted September 24, 2011 Share Posted September 24, 2011 Glad you ended up trying the N320. Did you like it? FYI, I've had great luck with 4.1, but your mileage may vary. Link to comment Share on other sites More sharing options...
ultrablue Posted September 24, 2011 Author Share Posted September 24, 2011 Glad you ended up trying the N320. Did you like it? FYI, I've had great luck with 4.1, but your mileage may vary. N320 seems to work well. I don't have enough expereince with it yet. I spoke with Powder Valley yesterday about the powder and it sounds like there is an importation problem with the product. They have gotten less than 10% of their ordered product. I will try the 4.1 charge. See you tomorrow? Link to comment Share on other sites More sharing options...
ultrablue Posted September 24, 2011 Author Share Posted September 24, 2011 Thanks folks for the replies. I think I am going to skip 4.0 and go to 4.1 and 4.2. Link to comment Share on other sites More sharing options...
Sarge Posted September 24, 2011 Share Posted September 24, 2011 Thanks folks for the replies. I think I am going to skip 4.0 and go to 4.1 and 4.2. Good call. You are low enough on the scale to be plenty safe running 4.1 to 4.3 even. Link to comment Share on other sites More sharing options...
shred Posted September 24, 2011 Share Posted September 24, 2011 OAL can be a pretty big factor with N320 too, so watch that. .01" difference can move you a PF point or two. Link to comment Share on other sites More sharing options...
villageidiot Posted September 30, 2011 Share Posted September 30, 2011 So I found this enlightening. It introduces the underlying physics and chemistry. Chapter 2 from Design of Guns and Ammunition by Donald E. Carlucci Carlucci-Theory and Design of Guns and Ammunition Ch 1.pdf Link to comment Share on other sites More sharing options...
rfwobbly Posted October 1, 2011 Share Posted October 1, 2011 Thanks folks for the replies. I think I am going to skip 4.0 and go to 4.1 and 4.2. Why would you do that? I don't understand why you would refuse to gather that information. How long does it take to load ten rounds at 4.0? You're already going to load ten each at 4.1 and 4.2gr. It doesn't matter that my gun or any other gun runs best at a certain load, your gun is unique unto itself. There are dozens of variables involved in working up a load; too many to through with a calculator. That's the whole point of shooting the extra loads. Sure, you'll discover "My gun runs great with 4.2gr", but you won't know why. Then, when the seasons change or other external events happen, you won't know which way to go. You'll have no supporting data. All I'm saying is that one data point does not make a graph. Link to comment Share on other sites More sharing options...
ChuckS Posted October 1, 2011 Share Posted October 1, 2011 So I found this enlightening. It introduces the underlying physics and chemistry. Chapter 2 from Design of Guns and Ammunition by Donald E. Carlucci Interesting stuff but it is copyrighted ( 2007 by Taylor & Francis Group, LLC.) It probably should not be posted here. Later, Chuck Link to comment Share on other sites More sharing options...
gm iprod Posted October 2, 2011 Share Posted October 2, 2011 I have to agree with wobbly. If you test everything from 3.9gr to 4.3gr you will know for certain what YOUR gun does under those conditions. If you get to 4.2gr and you are well over what you require then just shoot the 4.3grainers for extra info or giggles. N320 will go soft as the can gets older (over 3 or 4 years old that is). I do not like that about it. But I know what I have to do to get back to where I need to be if it does happen. Also don't be surprise of you have to do this testing every two or so years just to make sure the gun and load combo is at it's best. Link to comment Share on other sites More sharing options...
perlslacker Posted October 3, 2011 Share Posted October 3, 2011 The science geeks are flocking to this thread like flies on trash. The relationship between charge and velocity depends on the powder, the bullet weight, your barrel length, OAL, and phase of the moon. For the amount of work you would have to do in order to generate a large enough data sat to fit a curve that would allow you to accurately predict velocity, it's way easier to just work up the load. Based on the loading and chrono'ing I've done, the relationship of charge to powder is kinda-maybe-logarithmic. That tidbit of information and a buck will get you a cup of coffee. Link to comment Share on other sites More sharing options...
villageidiot Posted October 3, 2011 Share Posted October 3, 2011 So I found this enlightening. It introduces the underlying physics and chemistry. Chapter 2 from Design of Guns and Ammunition by Donald E. Carlucci Interesting stuff but it is copyrighted ( 2007 by Taylor & Francis Group, LLC.) It probably should not be posted here. Later, Chuck My understanding is that a chapter from a long book generally falls under fair use for educational purposes. Link to comment Share on other sites More sharing options...
villageidiot Posted October 3, 2011 Share Posted October 3, 2011 (edited) So I found this enlightening. It introduces the underlying physics and chemistry. Chapter 2 from Design of Guns and Ammunition by Donald E. Carlucci Interesting stuff but it is copyrighted ( 2007 by Taylor & Francis Group, LLC.) It probably should not be posted here. Later, Chuck My understanding is that a chapter from a long book generally falls under fair use for educational purposes. This is probably a better solution anyways. See chapter 2 Design of Guns and Ammunition Edited October 3, 2011 by villageidiot Link to comment Share on other sites More sharing options...
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