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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Extreme spread / Standard Deviation
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<blockquote data-quote="Steve Shelp" data-source="post: 21861" data-attributes="member: 22"><p>Milanuk,</p><p> I agree with Darryl above in the 20fps or less 100%. That's what the competition guys strive for. But also don't get caught up in the actual SD and ES numbers. 5, 10, or even 20 shots strings aren't enough of a sampling size to get good true numbers. I'm not a statistion so I can't say how many it would take either. So then the question is what numbers do you pay attention too? Your min/max spread. Shoot 10 shots and take the highest and lowest and find the difference. Keep good records and patterns wil start to emerge. This is what most shooters refer to when talking about ES. But it's not true ES in the statisical world of numbers. Just thought I would throw that out there for you to think about. My PACT chrono along with the other chrono out there automatically calculate ES, SD, and a host of other numbers but I don't pay attention to them. Just give me actual velocity numbers and go from there. Maybe Warren can keep me honest with the above statement??</p><p></p><p>Also you say your 200yd groups open up to 1.5" for 5 shots when your 100yd accuracy is .4" on the average. To save you some wear and tear on your rifle, I think your barking up the wrong tree by trying to minimize your min/max velocities with sorting cases and such right now, and here's why. Later on, yes you will want to sort cases, change primers, etc ,etc, but not right now.</p><p> If it was velocity change alone then you would need a velocity drop of approx. 270fps to make a bullet drop 1.1" (1.5"-.4"=1.1") more than another at 200yds. Your seeing 100fps spread and that is only worth .3" of drop at 200yds. So your seeing something else besides velocity variation to get a minimum change of 1.1" @ 200yds. <em>FYI: I based my above numbers on a Nosler 50gr BT at 3600fps and adjusted the velocity down from there in my ballistics program.</em> Also you mentioned you did this on different days so you don't think weather conitions played much of a factor. Don't underestimate the power of changing conditions at any range. Obviosuly I wasn't at your range when you shot so I can't say they did or didn't play into the equation. Just remember even if you can't feel it or see it the air is moving around out there and it is a factor.</p><p></p><p>What I think your seeing is the barrel harmonics causing the up/down in your groups. I've been down this road with rifles before and you need to adjust your load up or down until you start shooting round and smaller groups at whatever distance your shooting. Then start playing with cases, primers, and such to really fine tune it.</p><p></p><p>This harmonics thing is hard to explain typing here, but I've been there done that with my 338 long range gun. I've got one particular powder that gave me the less than 10-12fps extreme spread velocity mentioned above, but I could adjust that load (up and down) and shoot almost perfectly horizontal or vertical strings for groups and tuning in between wouldn't produce round groups in that barrel. Bottom line is that powder, bullet, barrel, etc, etc, etc combo didn't agree with each other. And all of the fine tuning I wanted to try wasn't going to tune that out. Those "stringing" groups were at 100yds and measured in the .3" for 5 and 10 shots, but at 1000yd in competition..... it was embarrassing. 16 and 18" groups going up and down but only 5-6" wide. Classic sign of harmonics/load tuning issue. In this particular case I ran into pressure but I could tune out the stringing. So I switched powders.</p><p></p><p>Play with your powder and loads first to get smaller and round groups. then fine tune.</p><p></p><p>Good luck with your Swift!</p><p>Steve</p></blockquote><p></p>
[QUOTE="Steve Shelp, post: 21861, member: 22"] Milanuk, I agree with Darryl above in the 20fps or less 100%. That's what the competition guys strive for. But also don't get caught up in the actual SD and ES numbers. 5, 10, or even 20 shots strings aren't enough of a sampling size to get good true numbers. I'm not a statistion so I can't say how many it would take either. So then the question is what numbers do you pay attention too? Your min/max spread. Shoot 10 shots and take the highest and lowest and find the difference. Keep good records and patterns wil start to emerge. This is what most shooters refer to when talking about ES. But it's not true ES in the statisical world of numbers. Just thought I would throw that out there for you to think about. My PACT chrono along with the other chrono out there automatically calculate ES, SD, and a host of other numbers but I don't pay attention to them. Just give me actual velocity numbers and go from there. Maybe Warren can keep me honest with the above statement?? Also you say your 200yd groups open up to 1.5" for 5 shots when your 100yd accuracy is .4" on the average. To save you some wear and tear on your rifle, I think your barking up the wrong tree by trying to minimize your min/max velocities with sorting cases and such right now, and here's why. Later on, yes you will want to sort cases, change primers, etc ,etc, but not right now. If it was velocity change alone then you would need a velocity drop of approx. 270fps to make a bullet drop 1.1" (1.5"-.4"=1.1") more than another at 200yds. Your seeing 100fps spread and that is only worth .3" of drop at 200yds. So your seeing something else besides velocity variation to get a minimum change of 1.1" @ 200yds. [I]FYI: I based my above numbers on a Nosler 50gr BT at 3600fps and adjusted the velocity down from there in my ballistics program.[/I] Also you mentioned you did this on different days so you don't think weather conitions played much of a factor. Don't underestimate the power of changing conditions at any range. Obviosuly I wasn't at your range when you shot so I can't say they did or didn't play into the equation. Just remember even if you can't feel it or see it the air is moving around out there and it is a factor. What I think your seeing is the barrel harmonics causing the up/down in your groups. I've been down this road with rifles before and you need to adjust your load up or down until you start shooting round and smaller groups at whatever distance your shooting. Then start playing with cases, primers, and such to really fine tune it. This harmonics thing is hard to explain typing here, but I've been there done that with my 338 long range gun. I've got one particular powder that gave me the less than 10-12fps extreme spread velocity mentioned above, but I could adjust that load (up and down) and shoot almost perfectly horizontal or vertical strings for groups and tuning in between wouldn't produce round groups in that barrel. Bottom line is that powder, bullet, barrel, etc, etc, etc combo didn't agree with each other. And all of the fine tuning I wanted to try wasn't going to tune that out. Those "stringing" groups were at 100yds and measured in the .3" for 5 and 10 shots, but at 1000yd in competition..... it was embarrassing. 16 and 18" groups going up and down but only 5-6" wide. Classic sign of harmonics/load tuning issue. In this particular case I ran into pressure but I could tune out the stringing. So I switched powders. Play with your powder and loads first to get smaller and round groups. then fine tune. Good luck with your Swift! Steve [/QUOTE]
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