Point of impact issues

[robescc]

Hello gents. Yesterday I shot my Knight MK85 in .54 cal for the first time. It’s a Rocky Mountain elk foundation model made in 1993 and yesterday was the first time it was fired. I put William’s globe sights on it.
I got it zeroed at 50 yards and was shooting 1” groups with 100 grains of FF Triple Seven and 348 gr Power Belts. The issue started when I went to 100 yards. I was consistently shooting 20 to 24” low. This makes absolutely no sense to me as I should have only been a couple of inches low. I also tried 120 grains of powder and didn’t move the point of impact much. I then switched to some 250 grain saboted bullets and the point if impact was no different.
What in the world could be the issue?

[robescc]

No advice at all?

[Blacktail Sniper]

Maybe the twist rate in the barrel is not good for that projectile? 

[birddogdad]

the math makes no sense.. that is where you should be at about 300 yds not 100.   

are you certain that the poa is not off? i know its a stretch idk if everything you toss is there (2' low) ...

[Bob33]

That doesn't sound logical at all. Can you shoot at distances between 50 and 100 yards to see what happens?

[2MANY]

Loose Sight

[robescc]

That doesn't sound logical at all. Can you shoot at distances between 50 and 100 yards to see what happens?

I'd have to go to a pit somewhere.

[robescc]

Loose Sight

I used loctite on all the screws. I can go back to 50 yards and I'm in the bullseye. It's not loose sights, I ruled that out.

[callturner]

So, you got it on paper now. Adjust your sights to hit at 100. You can see where you're hitting at 50 afterwards.

[Bob33]

The only explanation from a ballistics perspective is that you have very slow velocities in the neighborhood of 700 ft/second. If you have access to a chronograph you could verify that.

[HntnFsh]

Are you fudging on your sight picture so you can see the bullseye?

If so that could account for part of the problem.

[buckfvr]

Twist rate not compatible with projectiles?    Is that rifle designed for round ball which would have a much slower twist and not be suitable for modern muzzleloader projectiles.....Just a thought.

[buckfvr]

Maybe the twist rate in the barrel is not good for that projectile?

 

[ghosthunter]

If you need to barrow a chronograph,I have one and am close by.

[bkaech]

Another thought is bad powder making low velocities, but that would likely make everything inconsistent so not likely. Are you measuring your powder wrong? A problem with your powder measuring might mean you are only loading 50grains???  I'm just spit balling here....