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What could be causing my first shot hitting target off group?

 
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  #1  
Old 06-25-2006, 06:08 AM
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What could be causing my first shot hitting target off group?


A new tendency is affecting my 3 shots groups:
the first shot (fired from a cold barrel) hits the target about 3.5 up to 4 cm low to the right and the following next two shots make a nice 1.5cm cluster.
It has always happened the other way round:
1st and 2nd shots get very close (into less than 1.9 cm) and the third one opens the group up to 2.4 cm. as the barrels warms up.
These are the potentially responsible factors that I have already eliminated:

-The barrel is free floating (no contact with forehand section or shooting rest)
- The barrel is dry, no oil or solvents and has settled from previous cleaning with 10 to 15 fired shots.
-No scope parallelax aiming problem because Im using a rubber eye piece.

This new weird manners occurred with Winchester 7mmRM factory 160gr Accubonds and with my last new reloads using Brenneke 150gr TOG's bullets.

Has any experienced LR reloader an idea of what could be the cause? Is there any typical sensitive reloading aspect directly related to such problem?
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Old 06-25-2006, 09:29 AM
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Re: What could be causing my first shot hitting target off group?

might be the difference in temperature as to how long it takes the barrel to warm up.it seems by your past experiences that a warm barrel changes your POI.was your previous testing done in a colder time of the year? might be a summer to winter type of thing.
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Old 06-25-2006, 01:17 PM
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Re: What could be causing my first shot hitting target off group?

Were those groups shot from a clean barrel or from a fouled barrel? My 1st or 2nd shot from a clean barrel, even with no oil in the bore, will often shoot a bit differently (and slower) than subsequent bullets.

Many rifles need a fouling shot or 2 after a bore cleaning before the rifle settles into shooting to the expected point of impact again.

Just a thought.
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Old 06-25-2006, 05:04 PM
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Re: What could be causing my first shot hitting target off group?

i assumed he meant he had 10-15 rounds down the barrel since he cleaned it last.not sure though.
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Old 06-25-2006, 06:46 PM
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Re: What could be causing my first shot hitting target off group?

I'll agree with varmit hunter 100%. If you clean your barrel, then it will change your POI. I have noticed on my rifle it can be pretty dramatic. Everytime you clean your barrel you need to shoot a couple of fouler shots.
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Old 06-26-2006, 12:03 AM
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Re: What could be causing my first shot hitting target off group?

How quickly do you fire your groups? Do you allow the barrel a chance to cool between shots?
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Old 06-26-2006, 05:12 AM
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Re: What could be causing my first shot hitting target off group?

Thank you for your replies.

Thats right: Ambient temperature is a variable element I did not consider and all my previous ammo testing have been conducted at a much lower temperature (around 8-10C compared to actual 23C)

The groups were fired from a cold barrel with 10-15 previous fired shots after last cleaning.

The first two shots are fired with a 15-20 seconds interval and the third one 40-60 seconds after the second One.

Im always trying to recreate typical hunting conditions where the first shot is the one that counts and where the second shot might be a follow up shot at a running fox and the third one at the same (young) fox (or at another one) after he stops a while trying to figure out where the threat is coming from

Im going back at the shooting range this afternoon for some more ammo testing including those that are usually grouping the typical fine way.
Any way my 7mmRM sporter barrel is quite fussy about the ammo he likes:
The few he likes hes grouping outstanding well (3 shots into 1.6cm at100m) whether he deceives completely with about all the others he does not printing lousy 5-6cm groups. That is sadly the case with the fine accuracy renowned factory Federal 140gr ballistic tips.
He loves heavier bullets with cylindrical long rifling contacting surface such as the RWS tig.

Im thinking about changing barrel for a 300WM or the 300RUM but Im wondering if the latter with a sporter contoured barrel will not be kicking too much compared to 7RM
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