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Any thoughts,400 yards?

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  #1  
Unread 01-25-2009, 06:15 AM
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Any thoughts,400 yards?

I was shooting yesterday at 400 yards with my .308 PSS using 168 vlds,it was blowing between 12 and 17 mph at 12 o'clock and i was only managing 4" groups,normally it would do half of that or so. What i wondered was will a straight on headwind affect group size much?
I'm fairly new to this and just teaching myself and reading in places like this!
Any help or opinions would be appreciated. Thank you.
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  •   #2  
    Unread 01-25-2009, 09:22 AM
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    Re: Any thoughts,400 yards?

    Quote:
    Originally Posted by farmer7 View Post
    I was shooting yesterday at 400 yards with my .308 PSS using 168 vlds,it was blowing between 12 and 17 mph at 12 o'clock and i was only managing 4" groups,normally it would do half of that or so. What i wondered was will a straight on headwind affect group size much?
    I'm fairly new to this and just teaching myself and reading in places like this!
    Any help or opinions would be appreciated. Thank you.
    Yes it will effect group size because of wind speed changes and even though
    it appears to be comming strait at you the direction will change/swing a few
    degrees left or right.

    At 1000 yards I have seen the wind ( With Flags at every 100yrds )blowing in 3
    different directions and still feel the same at the firing line.

    This is the reason that a lot of people like BIG FAST BULLETS for long range,less
    flight time, more mass and better BC's.

    The lighter the bullet the more effect the wind will have on it.

    J E CUSTOM
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      #3  
    Unread 01-25-2009, 10:52 AM
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    Re: Any thoughts,400 yards?

    To understand what JE is trying to tell you, take a look at the water in a river the next time you are out there. Sure the water is going downriver; but, it is not straight in the channel as it will move from side to side of the river channel. Secondly, it will have many localized swirls and eddies where the water is from every direction including up and down. Wind blowing up a rifle range or powerline ROW is much the same and if it is gusting up to 17mph then for sure it has lots of swirls and eddies (called non-laminar flow).
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      #4  
    Unread 01-25-2009, 11:57 AM
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    Re: Any thoughts,400 yards?

    Is it possible the wind was affecting the steadiness of the rifle? When I shoot on windy days it's a challange for me to hold as steady as on calm days. Infact, I just can not hold extremely steady in anything more than a 5 mph crosswind that is pushing on my rifle. It bounces around, not much, but enough to affect accuracy. So I do not shoot for groups in those conditions. This is on a stout portable bench with sand bags.

    Also, with all due respect to JE, who is an experienced contributor on this site, weight actually has little *direct* affect on resistance to wind drift. The only two factors that affect wind resistance are BC and velocity. A .277 bullet weighing 150 gr, with a BC of .5 and an MV of 3000 fps will experience exactley the same wind drift as .338 bullet weighing 300 gr and a BC of .5 with MV of 3000 fps. They will both arrive down range at the same distance with the same velocity, trajectory and TOF.

    Having said that, weight is a factor in determining BC. Generally speaking, a heavier bullet in the same caliber of similar design will have a higher BC. But a smaller bullet with a greater BC than a larger bullet, traveling at the same velocity will buck wind better than the larger bullet.
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      #5  
    Unread 01-25-2009, 12:33 PM
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    Re: Any thoughts,400 yards?

    Quote:
    Originally Posted by MontanaRifleman View Post
    Is it possible the wind was affecting the steadiness of the rifle? When I shoot on windy days it's a challange for me to hold as steady as on calm days. Infact, I just can not hold extremely steady in anything more than a 5 mph crosswind that is pushing on my rifle. It bounces around, not much, but enough to affect accuracy. So I do not shoot for groups in those conditions. This is on a stout portable bench with sand bags.

    Also, with all due respect to JE, who is an experienced contributor on this site, weight actually has little *direct* affect on resistance to wind drift. The only two factors that affect wind resistance are BC and velocity. A .277 bullet weighing 150 gr, with a BC of .5 and an MV of 3000 fps will experience exactley the same wind drift as .338 bullet weighing 300 gr and a BC of .5 with MV of 3000 fps. They will both arrive down range at the same distance with the same velocity, trajectory and TOF.

    Having said that, weight is a factor in determining BC. Generally speaking, a heavier bullet in the same caliber of similar design will have a higher BC. But a smaller bullet with a greater BC than a larger bullet, traveling at the same velocity will buck wind better than the larger bullet.

    Exactly. The only benefit of more mass in a bullet is the energy delivered to the target. This is still subject to how the bullet reacts to the impact. So, shear mass does not necessarily mean better terminal performance. Bullet choice will make or break the performance of any caliber.

    Given all this info, your choice of bullet is probably avail in the larger calibers, where it will most likely out perform the smaller caliber.

    I would look for terminal performance, bc, and speed. In that order.

    Sorry that I strayed from shooting the target to hunting, couldn't help it.

    Steve
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      #6  
    Unread 01-26-2009, 06:02 AM
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    Re: Any thoughts,400 yards?

    Thanks for the replies guys, I didn't really think about wind shifts, just assumed a 12 o'clock wind all the way to the target. Its a a lot calmer today so i'll try again and see if i get on better.
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      #7  
    Unread 01-26-2009, 11:55 PM
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    Re: Any thoughts,400 yards?

    JE pretty much hit the nail on the head.

    I would say with the velocity of the wind you describe, 4" at 400 yards isnt bad results. Any time you can attain 1MOA at any range over 300 yards in real world conditions you are doing good. We all talk about our .25-.5 MOA rifles but that is what it takes to hit a 1-2 MOA target at long range. Just because our rifles are sub half minute rifles doesnt meen we are going to hit a half minute target. Hitting a half minute target or shooting a half minute group at distance isnt and has never been the point. Having a half minute rifle to shoot a 1-2 minute target or shoot a 1 minute group in bad conditions is the point. If youre in the 1 MOA zone in bad conditions you should be extatic, not curious.
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