point of impact differences

B

borkon

Well-known member
yesterday i went out to shoot some rifles as it was dead calm. i have a savage 12 and a stevens 200, both in 22-250. i had them both shooting 1/2-5/8 inch groups at 100 yards off a bipod.set them both at 1.75 inches high at 100. i than set out a target at 297 yards and shot. the rounds out of the 12 printed a nice group, about 1.5 inches and about 3 inches low. thats what i expected. the stevens also shot about a 2 inch group but they were dead on the bullseye. 3 inches higher than the model 12. both were shooting the exact same round. 36 grains of rl 15,sierra 55 btsp. why the differnce in tragecory betwwen the 2
 
Do they both have same length barrel? As that will change velocity which would change trajectory down range out further than 100 yards
 
I think Dogman243 hit the right question on barrel length...It would have the most effect on the trajectory..considering that all other factors were identical..Scope parallax, etc..
 
yes, they both have the same bbl lenght.24 inches. as for twist, i'm not positive but i believe they are both 1-12
 
Could also be chamber size as that would affect pressure which would affect velocity. Can u chamber a fired round from one and then chamber it in the other, without sizing them?
 
Are the scopes mounted the same height above the bore? Could be that one barrel is just "faster". Does one foul quicker than the other?
 
It would take a big velocity difference to make that much difference. Are you sure you were not holding the Stevens in a way that you were putting extra pressure on the forend? I have a pre-accutrigger Savage and if I don't keep the sandbag or shooting sticks quite a ways back from the end of the forend, it will shoot a good 2" higher at 100 yards than it does with it rested farther back.

PS: I just went back and read your post again. I see you are shooting off of a bipod. I would bet that you are putting pressure on your barrel and even a very little bit will change point of impact a very noticeable amount at 300 yards.
 
yes, i shot 2- 5 shot groups outta each rifle. fired cases chamber in each gun with no force needed. both are mounted with 3x9 x40 redfields. low mounts on both.as for fouling, not sure. they both shoot their best with a fairly fouled bore. i seldom clean the bores. both are FULLY free floated and bedded. shot off a harris (short) bipod. no pressure at all on forend. good answers all
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Originally Posted By: borkon yes, i shot 2- 5 shot groups outta each rifle. fired cases chamber in each gun with no force needed. both are mounted with 3x9 x40 redfields. low mounts on both.as for fouling, not sure. they both shoot their best with a fairly fouled bore. i seldom clean the bores. both are FULLY free floated and bedded. shot off a harris (short) bipod. no pressure at all on forend. good answers all
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Are you shooting in the same "zoom" each time? i.e. 6x vs 9x? If so, there's the culprit. more than likely, the reticle and scope are first focal plane, and therefore, the size changes in an inverse relationship to the zoom you have it set on.

Not sure how that will help you, but I do know, whatever zoom I zero on, I check to make sure what the change in POI is for the different zoom's for the scope.
 
But are they shooting the same round at the same speed? Did you ever chrony them?

I have to admit, my first thought was POI change due to magnification change, such as what Brandon said.....
 
never crony'd them. all rounds were the same loads. it just does'nt make sence to me why they would be 3 inches differnce when sighted in to the same height at 100. ??
 
The simple answer is because they are two different guns. Ones exiting the
bullets on a down harmonic, the other up. Or as suggested two different
speeds, but that's a fairly close range to see that kind of spread with just
velocity variance. It would take close to 300 fps.
 
No 2 rifles or barrels are exactly alike.

Dial each one in separately, and who cares about the rest?

Kimber to tried to use a "universal jig" for bedding all of their rifles a few years back. Ask them how that turned out.....
 
you don't trust the ballistic programs.

They are there to get you in the ball park.

You want data to ensure you are on the mark. Go shoot THAT specific rifle.

At -20, at 20, at 40, at 60, at 80 and at 90 degrees.

Use a data logbook and go off that.

Computer is theoretical.

What you are seeing is the external ballistics and the effects it has on the bullet. From EVERYTHING that will effect it. Throat erosion, bore diameter, landing depth, headspace, temp, rate of fire, trigger, etc

And don't forget the other obvious factor. The nut behind the buttplate. Yeah, your head position will make a difference as well.

Just some of the things to start looking at.

Otherwise, just accept the fact that two guns shoot differently. Learn that difference.
 
After you go out and garner actual shooting data you adjust your entry
info to get the program to match known real world output. I start with
fps and if that doesn't make it match I tweak the bullets BC as well. If I have
100,300 and 500 yard real world drops and adjust the program to match
it will get me close at 800 yards. Then I can tweak it some more if needed.
 
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