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I'm looking to improve the consistency of my velocities. I rented a chronograph at the range the other day and noticed quite a variation in velocities. 3 shot group examples: .308 Win cases Sierra 150 SBT CCI #34 primer 41.5 IMR 4895 Fps: 2649 2673 2613 second group: 2651 2646 2682 .308 Win cases Sierra 150 SBT WLR primer 41.5 IMR 4895 fps: 2596 2620 2580 second group: 2604 2637 2617 I weighed each powder charge on a Lee balance scale. Uniformed the primer pockets but didn't chamfer the flash hole (just got the tool after the fact). All cases were sized the same but not weighed. Looking for any improvement tips. Thanks. | ||
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In my opinion a 3 shot test is not much to go by. For me 10 or better yet 20 gives you a good base. Extreme spread is one thing but I feel standard diviation is better. SEE CORRECT DEFINITION BELOW. Less than 20 is good 10 is very good. Key issue is how do they group? "Post corrected" As usual just my $.02 Paul K | |||
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I used the Lee factory crimp die set to just past a half turn in the press. | |||
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Actually Standard deviation is defined as the square root of the variance. Where variance is the average squared deviaton of each number from its mean. Take each variation from the average and square them and average those results. Then take the square root of that and it will give you the SD. In the first 6 shots above, the variance is 483 fps (which is the sum of the squared variations from the mean) this gives a SD of almost 22 fps. IMHO Small SD's really only affect group sizes significantly in hunting rifles when shooting at long ranges (>600 yards) more importantly how do the loads group? If you are concerned with reducing the Standard Deviations then my recommendation are to reduce as many variables as possible, case weight, case length, bullet bearing length, primer pocket depth, flash hole variances, primer differences (switch to BR primers) barrel temperature, bedding, shooting technique (shoot free-recoil) trigger consistency,etc. Frank "I don't know what there is about buffalo that frightens me so.....He looks like he hates you personally. He looks like you owe him money." - Robert Ruark, Horn of the Hunter, 1953 NRA Life, SAF Life, CRPA Life, DRSS lite | |||
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Cases trimmed too? | |||
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Thanks for correcting me.  My brain wasn't working this morning and I just let my Chorny give me tha answer anyway. I normally worry about group size. In my hunting rifle I will double check the group at 3-400 yds. That is the max I will normally shoot anyway. As usual just my $.02 Paul K | |||
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 Your velocity spreads are a lot better than I get. Decided long ago, when I got my first chronograph, I would never go on the quest you are on. Thought it might become a never ending goal rather than a means to some other achievement. Besides that, if I did, I'd have to admitt that I was screwing up somewhere on my reloading process.NAW!! rogerOld age is a high price to pay for maturity!!! Some never pay and some pay and never reap the reward. Wisdom comes with age! Sometimes age comes alone.. | |||
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 I've gotten over being a "Spelling Nazi" but I still have issues. Frank "I don't know what there is about buffalo that frightens me so.....He looks like he hates you personally. He looks like you owe him money." - Robert Ruark, Horn of the Hunter, 1953 NRA Life, SAF Life, CRPA Life, DRSS lite | |||
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 I really have trouble when I don't have spell check. Was really having a moment this morning. Like I said my Chrony calculates it or for my other data EXCEL does it.Unless Excel fails me too I get 24 for the first 6 and 20 for the second. As usual just my $.02 Paul K | |||
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Case trimmed, FL resize, and checked against a case guage. | |||
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I'm not sure but I thought I read an article in one of the national stab and blast magazines comparing variations in velocity to group size and came up with some intersting data. I think the final conclusion was that velocity flucuations were not all that detrimental to group size and that if the group size was acceptable for the application, no sweat. Can't remember the name of the magazine!!!! | |||
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In co-oberation; In testing DP 85 we ran into someting interesting. We chronographed 7 loads that were identical except for the powder charge, which varied in 1/2gr increments. From slowest to fastest the velocity varied 300 fps. The 7 shots formed a close to .5" group at 100 yds.I guess I don't know everything I understand?????  rogerOld age is a high price to pay for maturity!!! Some never pay and some pay and never reap the reward. Wisdom comes with age! Sometimes age comes alone.. | |||
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That agrees with my experience. I don't think that you could measure a difference in group sizes at 100 yards with SDs of 25 fps. But I know people who shoot at 1,000 yards all the time who can see group variations with SDs of 10 fps. The only people I see worrying about SD are benchrest shooters where a .001" is a big group difference, the F class shooters and 1,000 yard benchrest competitors. Frank "I don't know what there is about buffalo that frightens me so.....He looks like he hates you personally. He looks like you owe him money." - Robert Ruark, Horn of the Hunter, 1953 NRA Life, SAF Life, CRPA Life, DRSS lite | |||
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Frank "I don't know what there is about buffalo that frightens me so.....He looks like he hates you personally. He looks like you owe him money." - Robert Ruark, Horn of the Hunter, 1953 NRA Life, SAF Life, CRPA Life, DRSS lite | |||
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In my Sako AII 24 inch varmint rifle, with a medium contour varmint barrel the 70gr Nosler Ballistic Tip Varmint and 42.7grs Varget gave me a 5 shot group at 125 yards of 0.354. Velocity of that load taken at 5m from muzzle (range rules mean that I have to shoot through a tyre tunnel), so couldn't place chronograph close to muzzle are as follows: shot 1: 3463fps Shot 2: 3463fps Shot 3: 3454fps Shot 4: 3445fps Shot 5: 3445fps. I use Lapua .243 brass exclusively with Federal 210 primers. By the way, the Sako has never been bedded, it is an honest Sako factory rifle . Only thing that has been done to it is the trigger lightened. Regards, Michael. She was only the Fish Mongers daughter. But she lay on the slab and said 'fillet' | |||
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What kind of chronograph did you rent? I would also suspect the cheaper Lee scale could be causing as much as 0.2gr diff. in your "weighed" charges. Did you leave lube inside the case neck when you seated your bullets? Has all the brass been fired the same number of times? How long did you leave a round in the chamber before firing? All kinds of things can affect SD. While I like small SD, it's more about how well the rounds group. I've hsd single digit SD loads give mediocre groups & rounds w/ SD in the high 20s go sub 1/2moa. LIFE IS NOT A SPECTATOR'S SPORT! | |||
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If we're talking about a hunting rifle, your velocity variations (I won't say SD as someone may give me a long definition that I don't want) is not bad IMO. Your velocity will usually change from shot to shot if for no other reason because of fouling accumulating in the bore. Just as your pressure climbs from a clean bore to one that is fouled. I think a Chrony is a valuable asset to reloading but too often we try to put too much bench rest technology into a sporting rifle application. What you need the Chrony to tell you is how fast are my bullets going?? So I can make a viable drop chart (altho the only really accurate drop chart is one you make by shooting at distance) and choose a proper bullet. I can also tell you when you're working upward toward max. Even the stool shooters, with their super anal cartridge prep, can't achieve a 0 sd. So I wouldn't angst about it too much if your bullets are clustering nicely. | |||
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I'm not sure what brand of chrony I rented, it looked to be in real good shape. No lube in the case necks. And the brass is all the same lot with the same amounts of firings. I'm glad to hear your input. This was just the type of infomation I was hoping to hear. This is for an M1A rifle, so I'm kind of worried about pressures. I'm gathering that with the Winchester brass I can increase the load slightly to compensate for more case volume than LC brass? | |||
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