Can't make sense of this.

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Yesterday I went to the range to sight in and old (yet very clean, and lightly used) CVA Magbolt 150 I inherited. At 50 yards all my shots were touching, yet at 100 the groups were around 12 inches. Even at 70 yards the groups were about 6”. Am I doing something wrong?

I’m really not too worried about it though since the land I hunt on has very dense cover (swamp outside of Savannah, GA) and the furthest I have ever even seen a deer is about 50 yards, and the furthest shot I have ever taken is about 35 yards. Is there anything I can do to improve this a bit or at least and explanation of what is going on?

 

[Patocazador]

How's your eyesight? If the target looks fuzzy at the 100 yard distance, that could be the problem. Also heat shimmer can enter into it.

How many shots make up your group? A 3 shot group can mislead you. 5 shots is better but you had better be swabbing out between shots to get a meaningful group.

 

[signsfollowing]

Details

The rifle is scoped and I was firing off a bipod on a bench. So my eyes aren't the problem. I was using 3 shot groups, but I fired multiple groups to confirm these results. I swab the rifle between each shot. I was using Hornady 300 gr. bullets in a sabot over 95 grains of pyrodex.

 

[TheRodDoc]

scope parallax not adjusted out properly ?

 

[BADUNAME30]

Try a cold clean Bbl at 100 yards and see if it does the same thing.
Also, check your stock screws to see if any are loose.
Does the Bbl float or is it suposed to make full contact with this gun ?
If it supposed to float.Try sliding a dollar bill between the stock and bbl.
Does the fore end touch one side of the Bbl and not the other ?
Or, any contact between the bottom of the stock channel and the Bbl ahead of the front stock screw ?
Any one of these can creat the scenareo you are experiencing.

 

[Oldnamvet]

I see your problem. You would think that the groups at 100 yds would just be twice the size at 50, right? Seems logical but if your bullet is losing stabilization as it slows down, it could start veering off the line. Maybe it starts losing right after 50 yds? Possible increasing your powder charge would increase the range before the hypothetical stabilization situation happened. Try groups at 70 yds with your normal load and with another 10 grains to see if the groups are tighter. If not, I'm fresh out of ideas.