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How do you lower S.D.?

 
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  #1  
Old 02-02-2008, 12:29 PM
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How do you lower S.D.?

What is the biggest culprit of a large spread in S.D.?I am trying to lower mine on a 300 win mag load(180gr. SMK)I have tried IMR7828 and H4350,WLMR primers and CCI primers,various seating depths.The best I have gotten was about 60.I am shooting a Browning A bolt,maybe that is the problem?
My groups are any where from 1 1/2''-2 1/2'' @ 100yds.I am sure I can tighten these groups up if I could get more consistant velocities,I am not sure where to start.
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Old 02-02-2008, 06:00 PM
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If you want to reduce Standard Deviation you need consistancy. You might want to look at the rifle, if it is bedded and freefloated. I'm not sure if there is any one answer to your question. How do you prep your brass? Are you weighing each load of powder? Are your components stored properly? I don't load for the 300 win so I don't have any pet loads. I load for the 06 and 300 WSM and I really like H4350 for powder.
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Old 02-02-2008, 06:30 PM
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I load as consistantly as I can,I use an RCBS charge master to dispense my powder,I trim all cases to the same size,and full length size all my cases.Maybe it is my gun,I didn't realise the gun could cause inconsistant velosities,I thought it was all in the load.I have a new savage coming next week,maybe if I run some of the same loads through it,that will answer my question.
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Old 02-02-2008, 07:47 PM
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Chrono?

What Chrono are you using and was the light conditions changing while shooting. Mine will read different if the sun goes behind a cloud.

Also, is there a load that is in the 90-95% densit (powder volume in Case). I have had better SD with full loads of powder. More uniform burn.

I might be wrong, but the gun is going to have little to do with velocity spreads...BUt the group will suffer if not bedded correctly.

One other thing i have read is using non magnum primers..I have not tried it in my 7 rem mag, but it was suggested to tighten groups up.

Willys
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Old 02-02-2008, 08:04 PM
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I've never owned or shot an A-Bolt, but I've heard they have thin barrels. Maybe if you give the barrel more time to cool between shots your groups will tighten up a little. I wouldn't worry too much about standard deviations. The load with the tightest velocity range won't necessarily be the one that shoots best in your rifle.
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Old 02-02-2008, 09:23 PM
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double check the scale

I would just for kicks check the zero on the scale and double check the powder weights. Some powders don't go through the chargemaster all that great, although I think 4350 would be fine. With the other variables youve eliminated by prep work its the only thing that would mess with sd.

Unless your popping off rounds at a great deal of speed I don't think a thin barrel would make any difference in sd. The only way I think it could feasable would be if you rattled off some really rapid shots and heated up the barrel to the point that it heated the round and the powder to the point that its burn ration changed. I doubt that is a real big factor, although I could be wrong.
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Old 02-02-2008, 09:33 PM
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Quote:
Originally Posted by Natty Bumpo View Post
I've never owned or shot an A-Bolt, but I've heard they have thin barrels. Maybe if you give the barrel more time to cool between shots your groups will tighten up a little. I wouldn't worry too much about standard deviations. The load with the tightest velocity range won't necessarily be the one that shoots best in your rifle.

I agree with the first part of your post but couldn't disagree more with the last part. If long range shooting is the goal, one must pay attention to the standard deviation of the load to avoid big vertical dispersions in group at distance. In fact, if using some of the longer range bullets that have long lengths, they may not shoot super tight groups at close range but if the standard deviations are low, they can shoot amazingly good groups at longer range.

Btw, standard deviations would have very, very little to do with the mechanics of the rifle. Standard deviations deal with combustion and pressure among other internal ballistic properties. To get low Sd's, the brass must be uniform, have equal neck tension, and have deburred flashholes. Then the powder must be consistently charged, the primers seated same, and the bullets must be seated uniformly to maintain equal distance from the riflings. And even after all that had been done, the standard deviations can still be large if the wrong amount and/or the wrong powder was chosen. To fix it, go up in charge .5 grains until it improves. If it never improves, then switch to a different powder and try again. This should yield some load that has good sd's.
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