TANFARM Posted November 5, 2015 Share Posted November 5, 2015 I hope this is the correct venue for my question. I'm loading 9 mm 147grn. Xtreme HP over N320. I finally purchased my chronograph to actually figure out the corrolation between making Minor power factor and my various loads. My question is .....my deviation on the multiple strings I tested were running between 7-30. My last batches were showing a deviation of 7-13. Can someone explain this situation to me ????.....my last several loads made Minor with a little to spare. Sorry if this is a dumb question ......but what accounts for such a sever spread, what are acceptable ranges, and how can I correct this......Thanks in advance!!!!! Link to comment Share on other sites More sharing options...
kneelingatlas Posted November 5, 2015 Share Posted November 5, 2015 That's not an unheard of spread. A number of factors could be at play: are you using mixed brass? How many charges to you drop before making a test batch? Bullet shape inconsistency causes variances in seating depths causing higher pressures; fast powder and heavy bullets are espescially susceptible to this. Link to comment Share on other sites More sharing options...
Youngeyes Posted November 5, 2015 Share Posted November 5, 2015 What chrono? There are a number of posts on the Forums on correct usage of a chrono. http://www.brianenos.com/forums/index.php?showforum=145Search for standard deviation. You might be shooting through different areas between the wires. If you shoot high or low you will get different velocities. It may be inconsistencies in your loading. Try some good factory loads and see what you get. Your numbers are not that bad anyway. How many loads were in a string? I would sort your brass by headstamp, weigh out some bullets and weigh each charge for consistency. Try that string. Shoot at least 20 rds. This will rule out loading errors. Make sure you shoot each rd through the same area between the guide wires on the chrono. Link to comment Share on other sites More sharing options...
superdude Posted November 5, 2015 Share Posted November 5, 2015 Those number sound fine. With some powders you can get 100 fps (or more) variation in a 10-shot string. Link to comment Share on other sites More sharing options...
rowdyb Posted November 5, 2015 Share Posted November 5, 2015 Any standard deviation under 20 I am happy with for 9mm minor loads. Link to comment Share on other sites More sharing options...
Hi-Power Jack Posted November 5, 2015 Share Posted November 5, 2015 I've had low std dev for five shots - but NEVER had a low std dev for 20 shots. That's why I always fire 20 rounds over the chrono. Link to comment Share on other sites More sharing options...
amokscience Posted November 5, 2015 Share Posted November 5, 2015 Normal spread. Link to comment Share on other sites More sharing options...
IDescribe Posted November 6, 2015 Share Posted November 6, 2015 It's in part that bullet. Depending on the position of the sun and cloud cover, Light glinting off the nose of jacketed and plated bullets can throw off the chrono' sensors a bit, so they often don't chrono as consistently as lead or coated bullets. The shinier the plating or jacket, the worse the effect. XTreme HP are super shiny. But there is something else with them. I was running ladders with them once, and the sun broke from the clouds, and the chrono started having fits. I was getting swings of a couple hundred feet per second from one round to the next. I THINK the issue is the hollow point cavity, which in XTreme HP is not round, but hexagonal, so you have six shiny facets spinning at however many thousands of RPMs, and if you get sunlight coming in from the right angle, you (or at least I) get wild chrono results with those bullets. For the record, I was testing a couple of different weights of XTreme HP that day, and once the issue started, it continued with all weights of the XTreme HP. For the record, I sort by headstamp, do most of my load development with Starline brass, and I'm accustomed to standard deviations under 10 with 9mm. 7 and 8 are common. 6 makes me happy. Try taking a black Sharpie and coloring in the hollowpoints plus color a bit of the nose around the hollowpoint. If that helps, you'll know the issue is the bullet. Link to comment Share on other sites More sharing options...
Red Ryder Posted November 7, 2015 Share Posted November 7, 2015 A decent SD is in the single digits. I always shoot 20 shot strings. N320 has given me the lowest SD. As low as 2, with Montana Gold 124 CMJ, same brass, same OAL, Case pro 100 brass, Federal small pistol primers. I average an SD of 7. Doesn't mean much in this game anyway. Link to comment Share on other sites More sharing options...
jtaylor996 Posted November 8, 2015 Share Posted November 8, 2015 Any standard deviation under 20 I am happy with for 9mm minor loads. I think you must be thinking of extreme spread of 20. A SD of 20 would suck balls. Link to comment Share on other sites More sharing options...
RDA Posted November 8, 2015 Share Posted November 8, 2015 Any standard deviation under 20 I am happy with for 9mm minor loads. I think you must be thinking of extreme spread of 20. A SD of 20 would suck balls. 20 isnt' that bad, normal would be 1X-20 in my opinion. Under 10 is very good/consistent. SD really doesn't mean a lot in my opinion unless you have a minimum power factor and you want to flirt with it but I I think that isn't very wise. I agree with Red Ryder, my lowest SDs have been with N320 Link to comment Share on other sites More sharing options...
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