jimbullet Posted June 7, 2014 Share Posted June 7, 2014 (edited) I am wanting to know is there an acceptable fluctuation on the velocities of a pistol cartridge? I am using a Dillon SDB and have in my loads checked the powder charge in every 50 - 70 rounds and they appear to be spot on. OAL I have used for 40S&W is 1.158 however every often when I check with a caliper, it shows up at 1.162, 1.158, 1.160, 1.165. Not sure why its not as consistent as I thought it would be. I checked the seating stem and its fairly tight so its not likely moving on me as after loading 200 rounds recently, I made a dummy round without primer/ powder and checked OAL and it was spot on at 1.158. However randomly checking the loaded ammo, I got the variations. I have been carefully never to short stroke the press as well so I am beginning to think that this might be normal. testing the ammo on the range. The velocities I am getting averages at 958 fps. Unfortunately I was unable to write down each shot but from memory the spreads were a high of 990 fps and a low of 948 fps. Weather was cloudy, overcast temperatures hovering 13-15 deg, feeling like 9 deg. I could remember seeing some muzzle flash on my rounds, shooting at 8am. would appreciate thoughts, your experience. Edited June 7, 2014 by jimbullet Link to comment Share on other sites More sharing options...
SWprotected Posted June 7, 2014 Share Posted June 7, 2014 (edited) I usually see similar fluctuations and found it to be due to mixed brass. If I only use one headstamp it stays pretty Much the same. Edited June 7, 2014 by SWprotected Link to comment Share on other sites More sharing options...
jimbullet Posted June 7, 2014 Author Share Posted June 7, 2014 I did not realise brass has a significant impact on velocities. Yes I do use mixed brass but arent brass just the same in volume/ space? Um, will clean or dirty brass have any significant impact too? Link to comment Share on other sites More sharing options...
jmbaccolyte Posted June 7, 2014 Share Posted June 7, 2014 Some brands of brass are thicker than others and so have less internal volume. But I can't shoot well enough to make it worth worrying about. Link to comment Share on other sites More sharing options...
bowenbuilt Posted June 7, 2014 Share Posted June 7, 2014 Stackable tolerances are present even if you are using the same brass all made the same day and with bullets hand picked for weight, diameter and length. It is nearly impossible to make each shot a mirror image of the one before no matter how much you measure and weigh. Throw in mixed brass and just forget it, it ain't happening. The differences in wall thickness, case tension, primer depth, flash hole size, bullet ogive imperfections and the ever indifferent powder charge drop and all of a sudden 50 FPS starts to look pretty damned good. Some of us can't get it down to 50 FPS if everything is exactly the same. If you are getting that with mixed brass bully for you! Link to comment Share on other sites More sharing options...
jimbullet Posted June 7, 2014 Author Share Posted June 7, 2014 Glad to know that nothing to worry about. I was just making sure I get well within major pf. I had the horrible thought that what if every round went 948fps as I might be doing something wrong and might get stuffed on a match chrono. Thanks guys. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
RPatton Posted June 11, 2014 Share Posted June 11, 2014 Load it heavy enough to be sure at the chrono. How would you like to drive 800 miles to a match and go minor. It's not like you have to make a 180 PF these days. Link to comment Share on other sites More sharing options...
bowenbuilt Posted June 11, 2014 Share Posted June 11, 2014 ^^^^^What he said.... Link to comment Share on other sites More sharing options...
jimbullet Posted June 14, 2014 Author Share Posted June 14, 2014 (edited) I've increased the powder charge by another 1/10th of a grain and it is giving me a pf of 175. Should be safe enough I think? One of my friends is loading with a PF of 179. I wonder if I should aim for that to cover all weather/ altitude changes... Out of curiousity, running a 180 gr projectile at a PF180 would mean that it would consistently be at 1,000 fps and there will be some fluctuation perhaps going higher a tad. Is a 1,000 fps ok for 40's? I hear that pressures could be a risk on 40's Edited June 14, 2014 by jimbullet Link to comment Share on other sites More sharing options...
Rob01 Posted June 14, 2014 Share Posted June 14, 2014 Always good to have some room to play with different chronos. At home my load is a 178pf but chronoed at my last match at 175pf. I like having some room to play and not worry about becoming minor. Could I drop it down a little? Sure but it shoots good where it's at so it will stay there for now. I really wouldn't go below around 170-172pf myself. 1000fps is ok with the .40 and a 180 with right powder. My Hornady Steel Match factory ammo is in the 1040-1060fps area. Link to comment Share on other sites More sharing options...
jcc7x7 Posted June 15, 2014 Share Posted June 15, 2014 I like 175 as a mean for Major and 135 for Minor. with that said my 40 loads avg 173 and 45 about 178 at match chrono's minor (only one major chrono match) was 135 Link to comment Share on other sites More sharing options...
Justsomeguy Posted June 16, 2014 Share Posted June 16, 2014 If it was really only less than 15deg outside temperature in June where you live I feel sorry for you! Plus, at those temperatures a lot of powders will shoot poorly. Some are "reverse temperature sensitive" and indeed may be MORE powerful at those temperatures, but most will be weaker. Soooo... be careful about loading up to a fairly high power factor at low temps and then later in the year shooting the same load on a 90 degree day... things could go wrong! It would be good to test those loads at various temperatures as things get milder and see just what they are doing so you have a clue as to how to proceed. But, like Bowenbuilt said, some variance in ES (extreme spread) and SD (standard deviation) is to be expected with ANY round factory or handload. While it is nice to see very small ES and SD figures, especially SD figures in the single digits, they are not always necessary to produce accurate rounds. Building in a little cushion to around 170PF or maybe a bit more is always best when you have to count on a power factor for a match, but don't go overboard. You just penalize yourself if you're shooting 180PF loads when others are shooting 167-170PF on a given day. Therefore, it is nice to know the possible effects of weather variations as well as perhaps altitude variations if you shoot under different conditions than you loaded the rounds at. So keep your chrono handy and try some "favorite" loads out on various days with different temperatures and look for opportunities to test at different altitudes too if you can do it. Such data will stand you in good stead for matches that will come up. Link to comment Share on other sites More sharing options...
jimbullet Posted June 21, 2014 Author Share Posted June 21, 2014 Thanks, well it's winter in our part of the world. Cheers. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
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