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

[fabio]

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 I'm 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?

 

[davewilson]

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.

 

[Varmint Hunter]

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.

 

[davewilson]

i assumed he meant he had 10-15 rounds down the barrel since he cleaned it last.not sure though.

 

[duckinalaska]

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.
Brandon

 

[grit]

How quickly do you fire your groups? Do you allow the barrel a chance to cool between shots?

 

[fabio]

Thank you for your replies.

That's 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.

I'm 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…

I'm 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 he's 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.

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

 

[fabio]

some pics for fun... [image]http://www.huntingpictures.net/photo/006694[/image]
http://www.huntingpictures.net/photoview...694[/img][/url]

 

[fabio]

[/image]

 

[fabio]

[image]http://http://www.huntingpictures.net/photo/004968[/image]

 

[BillLarson]

Bedding.....

 

[fabio]

The rifle is a Blaser R93 Offroad: with a particular design where the entire receiver is "bed moulded" into the stock and the barrel into the receiver with no direct contact with the stock.
The stock's forehand section is quite flexible and when shooting with the bipod attached it is very easy to cant the rifle a little just by twisting it instead of adjusting the length of the bipod's legs.
Of course I'm careful not to do that while shooting although I think it shouldn't affect accuracy because of the rifle's specific design…
May be the solution lies in switching barrel but a new Blaser barrel costs between 650€ to 1000€ depending on the contour and I can get an entire new Sendero rifle for that amount…so I'm hesitating what to do.
[image]http://www.huntingpictures.net/photo/004976[/image]

 

[ATH]

You're shooting way too fast to expect a tight group. I was out shooting a couple weeks ago in 85F weather, and the first couple groups were miserable compared to the rifle's norm....1.5" or so. I was taking a minute and a half between shots. I started taking 5 minutes between shots, and groups shrunk to .4-.6 inches (300WM).

 

[fabio]

A repeatable 2 shot group within 2cm (centre to centre) hitting 4-5 cm consistently above point of aim at 100m is enough LR accuracy for my purposes as far as that very first shot is always hitting exactly where it is supposed to.
I used to achieve that with this rifle up to about 60 shots ago.
So far the barrel has fired a little less than 220 rounds and never more than 3 shots without letting it cool down completely after. It shouldn't have lost its accuracy yet…

I'll try shooting your way next range session to se if groups shrink.

By the way can I ask you if you know witch one among these is the right code to copy and paste in to post my picture right?

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