Strange point of impact-need advice please

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by rufous, Jun 2, 2008.

  1. rufous

    rufous Well-Known Member

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    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.
     
  2. Willys46

    Willys46 Well-Known Member

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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
     

  3. jmason

    jmason Well-Known Member

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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.
     
  4. Augustus

    Augustus Well-Known Member

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    Ill vote for the scopes power not being adjusted exactly the same from episode to episode.
     
  5. rufous

    rufous Well-Known Member

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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.
     
  6. davewilson

    davewilson Well-Known Member

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    PARRALAX... how good does your scope allow for parralax?

    Oh yeah, welcome to long range shooting!
     
  7. rufous

    rufous Well-Known Member

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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
     
  8. remingtonman_25_06

    remingtonman_25_06 Well-Known Member

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    Maybe you got bear fever!! LOL, all joking aside, the elevation, coupled with a field position could possibly have been the problem.

    I was in the same scenario last year when I missed 3 bears at relatively short distances,like 225, 350, and 450. The thing is, I was shooting pretty steep downhill on every one of them. I usually only got the 1 shot then they would run back in the brush and would not come out. I know I was over shooting them, but just couldn't compensate the right amount for it. It was a real bummer as 2 of them were pretty big bears...

    I figured that it was a combination of the elevation change, the downhill angle, and probly the last factor, ME! I sure get some adrenaline going when I see bears, hard to hold real steady sometimes.

    Anyways, I hope you or your other party members got a bear. Oregons getting to dang many! BTW, where was your tag for? I had mine for Weneha. It was a pain in the ass getting around up there. My favorite canyon is still snowed in, the one where I missed 3 last year.
     
  9. rufous

    rufous Well-Known Member

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    I did get that bear but on the third shot. My tag was for the West Blue Mountains units. We filled two out of the three tags. I had 74 bear sightings during the season and hiked about 100 miles. Bruin.
     
    Last edited: Jun 3, 2008
  10. davewilson

    davewilson Well-Known Member

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    Bruin, set your gun on sandbags or something that will hold it solid and aim it at something 4-500 yards away. now look through the scope without touching the gun and move your head around and see if the crosshairs move on the target. this is parralax. gotta go to bed now but tomorrow i'll tell ya how to eliminate that situation.
     
  11. rufous

    rufous Well-Known Member

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    Dave Wilson, I know what Parallax is but have not looked to see how many inches the reticle will move at 500 yards as I move my eye around in relation to the ocular lens. I know that consistent positioning is important to consistent grouping. It is certainly possible that my positioning while shooting at the bear was not like it normally is while shooting at the gravel pit but my shots at the range this last weekend were from the bench. Not sure why the bullets would have been hitting similarly high at the range from the bench as they were apparently on the bear. I look forward to your parallax tutorial as I am always wanting to learn. Bruin.