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standard deviation & groups

 
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  #1  
Old 02-08-2003, 09:27 AM
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Join Date: Oct 2002
Location: virginia
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standard deviation & groups

What is the minimum extreme spread and maximum standard deviation that you guys look for in a keeper load?

I have a load that shoots 2 inch groups at 500 yards, but has a high SD, 17 to be exact. This load would be great if it wasnt 55gr Nosler BTs at 4300fps. They dont have the stomp past 400 yards and they are going to ruin my throat.

Ive been doin all I can to get my 107 MKs to shoot good, the SDs are a lot lower, 7-10, and groups are in the 3.5-4.0 inch range at 500.

The BTs are easy to hit hogs with, but they dont kill very good past 350 yards, usually requiring several shots. Ive managed to hit a few hogs with the MKs past 350 yards and they act more like a bomb going off.

The rifle is a 6mm remington ackley, 700s action, mcmillan a-4 stock, shilen 2 ounce trigger, shilen 1.25" straght cylinder 28 inch select match 1-8" barrel, Mark 4 rings and bases, and a 8.5-25*50mm Leupold scope.

Any suggestions would be greatly appreciated.
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Old 02-08-2003, 10:51 AM
MAX MAX is offline
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Join Date: Sep 2001
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Re: standard deviation & groups

I'm not expert is this arena but IMO your SD's are just fine. Any time you wander into single digits w/ spreads and SD, AND the gun shoots well you have done about as well as can be expected. Sometimes I see loads with stellar numbers that do NOT shoot [img]images/icons/frown.gif[/img] ...very perplexing and frustrating. Others may disagree but I think the twist in your rifle favors the heavier bullets in caliber. None of the lightweights have a lot of snap left beyond 300 yds or so, and though they may shoot on paper, their performance on larger game than prairie dogs is suspect. LONG range shooting is primarily the domain of high BC and heavy bullets for caliber(yes, they're related). That would be my .02 worth.
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Old 02-08-2003, 09:08 PM
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Join Date: Oct 2002
Location: Paragould, AR
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Re: standard deviation & groups

Max: you wrote:
""LONG range shooting is primarily the domain of high BC and heavy bullets for caliber(yes, they're related). That would be my .02 worth.""

So, if a fella wanted to take a 300-400 yd shot with a .338 Win Mag on elk-sized game (I realize the .338 is not the ideal long-range rig!), you would advise going with a "heavy for calliber" bullet such as 225 or a 230 grain Failsafe or a 250 grain Nosler or sierra GAMEKING? Rather than a 200 grain or 210 grain? Right?
Or is 200 grain heavy enough that you really don't have to worry about using a heavy for calliber bullet at that range?
My gun just happens to like the 200 grain and does not do well with the 250 grain.
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Jon C. Bischof
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Old 02-09-2003, 11:20 PM
 
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Re: standard deviation & groups



[ 07-11-2003: Message edited by: S1 ]
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  #5  
Old 02-10-2003, 11:51 AM
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Posts: 1,459
Re: standard deviation & groups

The proof is on the paper. With that level of accuracy, I wouldn't bother with SD, etc. You are pretty much at the mechanical accuracy of the bullet.

When working up a load for my rifles, I use my Chrono to make sure that I am not exceeding pressure limits. I let the group size determine the rest.

It is rare that an accurate LR load does not have small SD and vel. spreads.

Jerry
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  #6  
Old 02-11-2003, 04:21 PM
MAX MAX is offline
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Join Date: Sep 2001
Posts: 263
Re: standard deviation & groups

JCB,

I'm not sure it would make a huge difference at that range in any case but my inclination for the .338 is the 250 gr weight, JMO. The cartridge has enough snap at 400 yds and more to utilize any of those bullets. Which one shoots in you gun would be the deciding issue in my mind. In the final analysis it is necessary to A) hit the beast B) with a bullet that provides proper terminal performance. A bullet that detonates at high velocities will quite likely perform nicely at longer distances. The Nosler Ballistic Tip is one example.

There are others here that have more experience than I, but that's my opinion anyway.
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  #7  
Old 02-12-2003, 07:05 AM
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Location: Fredericksburg VA
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Re: standard deviation & groups

Keeper load for what? Hunting or BR?

LR hunting loads are normally geared towards higher MV and less concern with SD and ES.

LR BR loads are normally built around the lower SD and ES (less than 10) which is normally your best grouping load. If you have a low ES and SD and it will not group, then it is normally a bullet consistency problem. LR BR shooters fight vertical more than horizontal in groups normally (no or low wind conditions). Custom VLDs are normally seated well into lands, often as far as .030-.040 on some guns while Sierras tend to shoot better just kissing or no more than .010 as general rule. Poor neck turning and inconsistent neck tension is always a concern and cause for many match cases to be shown the "sighter pile".

You have varying schools of thought as how to best sort that problem and bullets out. Not sure there is one that is absolute best. More like what do you like and makes you feel more confident in what you are doing.

Some use the Juenke machine ($750)which is supposed to show bullet inconsistency in jackets and cores. Some guys swear this is great and others swear it is not. I know quite a few top 1K BR shooters use it, but do not really know if it does what it claims, but they say "it cannot hurt"

Some sort by length of bearing surface using a tool ($275 by Bill Shehane) or just two Stony Point comparator tools ($40)screwed to your caliper. I use this and I seem to get very good results. Has really cut down on "fliers" and made groups more consistent. 338 shooters at Hawks ridge in NC have been real successful shooting bullets sorted this way.

S1 seems to like the Harold Vaughn designed machine built using compressed air and an oscilliscope to find the CG of each bullet and sort by that. Never knew anyone who used this machine so cannot speak on how well or how much it costs for a machinist to make.

I know that Sierra bullets are made on multiple machines and dies and dumped into the same box so that leads to inconsistency in their bullets. Sierra does not weight jackets and sort like that, they simply turn on the machines and while running occasionally weigh a bullet and either cut or lengthen the lead core to try and maintain consistency. Right now JLK bullets are the most consistent in weight, length of bearing surface and on a Juenke according to guys who use the Juenke and by what I have measured. Berger had some real problems last year on the 30 cal jackets and guys say they got a lot of bad bullets.

Take your pick of any of the above methods and sort bullets and see what you get, if you think it is a bullet problem. Shoot LR groups and see what the load and chrono say. Find out by testing.

Good luck

BH
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