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Strange point of impact-need advice please

 
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  #1  
Old 06-02-2008, 12:28 AM
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Location: Walla Walla, WA
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Strange point of impact-need advice please

I had a strange occurence recently while shooting at a bear and again today at the range while trying to figure out if my rifle was sighted in.
I am shooting a Winchester Model 70 Classic Stainless with a Rimrock sporter synthetic stock chambered in 300 Win Mag with a Broughton barrel that Greg Tannel installed last summer. Greg trued the action but I decided not to go to the extra expense of having him install the bolt bushings. Anyway the gun shoots the Barnes 180 TSX very well. I do most of my shooting at long range (250 to 500 yards) and have the Leupold 3.5-10x with Boone and Crockett reticle. I did the math before getting the scope and realized that it should work well with that bullet and a sane velocity. My load is using 72.5 grains of RL22 and I get an average of 3030 fps. During final load development I shot a group at 250 yards (the distance I want my main reticle zeroed at) that measured about 1.5"- I do not remember exactly. That group was perfectly zeroed. Then I fired a 3 shot group at 500 yards that measured under 2". Then I fired another 3 shot group at the same spot again at 500 yards and all 6 shots fired at 500 yards landed in just under 3" - I think it was 2.98". This group center was only about 1.5" high and 1.5" right of point of aim. Also since that final load development bench/paper shooting session I have often shot prone with my bipod and sling at 1 gallon jugs and hit them regulary. Not every time but probably about 70%. Obviously the misses are generally close enough that they would still hit a big game animal in the vitals. So enough of that.
I drew a spring bear tag for the Oregon Blue Mountains this year. I got a chance finally at a bear after many many days out looking for them. This bear was across the canyon late in the evening and we just did not see much chance of getting closer. It was 450 yards away and I was able to get prone with my bipod. Again I have the main crosswire zeroed at 250 yards so the next one down is zeroed with this load at 350 and the next one at 450 and the last shorter hash mark is zeroed at 500 with the top of the post very close at 550 yards. So I put the 450 yard mark on the bears chest and fired as it was broadside. The bear ran off but after a bit came back out. Not knowing for sure but assuming my first shot had connected (though the bear did not at this point appear hit) I fired again. This time the bear ran off and went into some brush then came out and kept trotting off. Again I assumed I had connected. I let out a kind of a screaming yell and that stopped the bear facing me at 530 yards. In my haste I used the 500 yard aim point and hit the bear essentially where I was aiming (within probably about 2"). I zeroed my rifle at 1100' elevation and the bear was at 4300'. My bullet should have hit about 7" low by using the 500 yard aim point with the bear at 530 yards. So this last week I was pondering what could be going on. We went out a few times in the ensuing week to try to get the last bear for our 3 member group. Finally I got a chance to go out shooting today.
So I fired two shots at 250 yards. One was above the other and they were less than an inch apart and were well centered vertically but were about 1.3" left as there was a breeze from the right. Then I fired 3 shots at 500 yards using my 500 yard aiming point. The group was fairly triangular with two shots higher than the other. The group measured 3.6" but group center was 6" high and 7" left (again the breeze was blowing a bit). I was surprised to see them so high after my earlier experience during load development and while shooting at milk jugs. I decided to try using my 450 yard aiming point while firing a couple shots at 500 yards. One of the bullets hit about 7" left and one inch low and the other hit about 3" left and 3" low. Then I fired 3 more shots at 250 yards at the same spot on the paper I had fired the initial two shots at 250. All five shots formed a 1.85" group and were perfectly centered vertically. My trajectory program indicates that there should be about 10" difference in drop between 450 and 500 yards. I just cannot figure out how now basically I can use my 450 yard aim point at 500 yards. If my velocity were 3300 instead of 3030 that would do it or if the BC of the bullet were now some how 0.7 instead of 0.45 that would do it but neither of those could possibly be. I wondered a bit today if mirage might have been an issue but I really do not think it was that as I have shot plenty on hotter days with more obvious mirage and have not witnessed such an occurence. And then there were those total misses on that bear at 450 yards. I guess my bullets must have gone just over its back. I am befuddled. Do you have any ideas? Thanks kindly, Brian Carlson.
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  #2  
Old 06-02-2008, 09:22 AM
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Join Date: Oct 2006
Location: Oregon City, OR
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Angle

Just a couple shots in the dark.
First...Were you shooting up or down hill at all? That with the elevation changes could amount to more than you think.
2nd...Are you sure you had the power set on the scope the same every time.
3rd..Did you change anything during reloading..New powder lot, new bullet lot, or Primers?

Willys
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Old 06-02-2008, 01:12 PM
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I don't know if you used a drop caculator on the internet or not, but if you did... You still need to shoot and create your own. Use the calculated one as a guide to keep you on paper. I've used the free calculators (still do) and came to terms with them not being 100% for your set up. I just go shoot confirm and document.
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Old 06-03-2008, 12:51 AM
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Join Date: Jan 2008
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Ill vote for the scopes power not being adjusted exactly the same from episode to episode.
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  #5  
Old 06-03-2008, 08:43 AM
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Join Date: Jul 2001
Location: Walla Walla, WA
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The angle was pretty much straight across the canyon- insignificant. I suppose it is possible that the power on the scope was not maxed out (which is where it needs to be for my reticle to work) but I seriously doubt it as I know it needs to be maxed out and it is easy to do so. Also these loads were all loaded up at the same time with the same powder etc. I will just have to do some more shooting and see if the trend continues. Bruin.
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  #6  
Old 06-03-2008, 03:13 PM
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PARRALAX... how good does your scope allow for parralax?

Oh yeah, welcome to long range shooting!
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  #7  
Old 06-03-2008, 07:32 PM
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Location: Walla Walla, WA
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Dave Wilson, thanks for that idea. My scope has no parallax adjustment. Hard to believe that I could totally miss the bear though just because of some parallax. Anyway I will do some more testing. Bruin
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