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Splain me this 50gr Z-Max or 52gr Spitzer 21/2 left of 69gr SMK


CocoBolo

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Went to check Zero today ahead of a match, and took my standard long range loaded 69gr SMK, hit 1.8" high at 50 for 300 yard Zero perfect, nice tite group. I've loaded what I could get 50gr Z-Max and 52 Gr Nozler Spitzers. So I throw the gun up take a 5 shot group with the ZombiesMax, not a bad group but 21/2 left. Next up the 52gr Spitzers again nice gorup but 2/12 left. I repeated a dead on group with the 69gr SMK, then a couple more with the light bullets the results repeatable.

Now I get the up and down variance with light bullets even a .5gr is a couple inches but I have never seen the walking left.

Rifle is 18" 1/8 twist. I shot these same loads in my 20" 1/9 twist rifle and they all 3 hit about the same spot but with an EO Tech the groups were nothing to brag about. So is it just the twist?

Is this normal or?

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The last 2 barrels I used did the same thing. I got used to my old guns that shot to same spot. The elevation would shift but no horizontal shift. Luckily I found out before the match. I am zeroed for the lighter stuff and dial in if I go to the heavier bullets. One note is that the 55 gr Nosler ballistic tips shot same as the 69 smk. I am planning on just running 55gr at the match this weekend. Hopefully the wind won't be so bad.

Mike

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Went to check Zero today ahead of a match, and took my standard long range loaded 69gr SMK, hit 1.8" high at 50 for 300 yard Zero perfect, nice tite group. I've loaded what I could get 50gr Z-Max and 52 Gr Nozler Spitzers. So I throw the gun up take a 5 shot group with the ZombiesMax, not a bad group but 21/2 left. Next up the 52gr Spitzers again nice gorup but 2/12 left. I repeated a dead on group with the 69gr SMK, then a couple more with the light bullets the results repeatable.

Now I get the up and down variance with light bullets even a .5gr is a couple inches but I have never seen the walking left.

Rifle is 18" 1/8 twist. I shot these same loads in my 20" 1/9 twist rifle and they all 3 hit about the same spot but with an EO Tech the groups were nothing to brag about. So is it just the twist?

Is this normal or?

can't explain it but my JP shoots to the left with light bullets. My Noveske does not. I don't care so much as they both track as they should once zeroed in from100 to 500.

pat

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The last 2 barrels I used did the same thing. I got used to my old guns that shot to same spot. The elevation would shift but no horizontal shift. Luckily I found out before the match. I am zeroed for the lighter stuff and dial in if I go to the heavier bullets. One note is that the 55 gr Nosler ballistic tips shot same as the 69 smk. I am planning on just running 55gr at the match this weekend. Hopefully the wind won't be so bad.

Mike

Sunday we gonna find out who can luk out and hit at 600 yards, I'm thinking that I'll just aim at pluto. The 9 mph wind won't be a good excuse for missing, with all the rain we have had no dust signature so you can't just walk it up. Glad I found out that the lights bullets turn left.

Edited by CocoBolo
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As I understand it, rifle barrels especially free floated barrels, viberate when fired. The most accurate and forgiving barrels viberate in a straight line up and down. But some viberate in a circular motion, thusly when bullets exit the muzzle at different velocities, they exit at a different spot in the circular pattern. So bullets loaded to different velocities shoot to different spots.

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As I understand it, rifle barrels especially free floated barrels, viberate when fired. The most accurate and forgiving barrels viberate in a straight line up and down. But some viberate in a circular motion, thusly when bullets exit the muzzle at different velocities, they exit at a different spot in the circular pattern. So bullets loaded to different velocities shoot to different spots.

That seems to make some sense, the 69gr SMK's are 2700 and change 55gr are 2800 and change, but the those 50gr are 3300+ fps, and it is free floated, the 20" rifle has a heavier barrel and less twist so maybe it don't vibrate as much.

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As I understand it, rifle barrels especially free floated barrels, viberate when fired. The most accurate and forgiving barrels viberate in a straight line up and down. But some viberate in a circular motion, thusly when bullets exit the muzzle at different velocities, they exit at a different spot in the circular pattern. So bullets loaded to different velocities shoot to different spots.

That could be but I have a slightly hard time believing it because my anschutz does the same thing when changing to different ammo. All match ammo so 1050 +/- 50fps. I just can't believe a 22lr can change the vibration on a free rifle to change the poi a half inch at 50ft. The barrel has a WAY larger cross sectional area then any AR barrel I have seen. I always wondered if it was how the bullet left the rifling.

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Browning put a "tuning" weight on some of their rifle barrels. Maximum accuracy is achieved when the bullet exits the muzzle at the top or bottom of its arc when the muzzle is stopped or nearly stopped. The weight was screwed in or out change the period of the barrel vibration.

I'm sure there are other factors that could effect poi. 22lr is especially sensitive to the amount and consistancy of priming compound (since the ratio of primer to powder is much bigger in a 22). A big part of being a match ammo is getting that consistancy. Personally, I'm just happy when I can hit a rabbit at 50 yards with my 22!

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Spin drift? Which direction of rifling and a 600ish fps change would more than likely be the culprit. My jp is zeroed at 200 with Berger 70 gr VLD's and hits about 1 1/2 inches high right with my 55 fmjbt load, 1:8 twist 2650-2975 70 gr to 55 gr. 100 yd 55's, 200+ 70's I just know where to point and its on, or if I'm really wanting to be on I can just give 2 clicks on my aimpoint and its good to go for the 55 gr load

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It's just harmonics. Different barrels react differently. If you get a barrel that will shoot different weight bullets to pretty much the same point of impact, consider yourself lucky!

I have a Lothar Walther barrel that will print 55 Hornady FMJ's and 77 Sierra Match Kings within 2 inches at 300 yards. Same group size too. A White Oak SPR, shoots the 77 SMK's about 9 inches lower than the Hornady 55's. Another barrel will shoot Hornady 53 match bullets 1 inch to the right of Sierra 52 Match Kings, with the same powder charge.

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