7mm stw 175 gr sierra Spin drift/coriolis efsect

[ajstew32]

Hello all,

I just found a load with the new stw and was shooting at longer range to see what the groups were like out far. The groups are a little more to the right of what I was expecting at 650 yards, so I thought I'd ask some more knowledgable people. If any of you are willing to help that would be great!

My round is a 175 gr sierra gameking going 3030 fps from a 26' 1 in 9" twist(RH twist).
Weather was pretty near dead calm if any it was coming from 20-30 degrees and I was facing about 185 degrees(just off south), humidity was around 80%. The latitude is right above 52 degrees.

 

[wbm]

Reaper Tips: Spin Drift and the Coriolis Effect | Loadout Room

 

[WildRose]

Hello all,

I just found a load with the new stw and was shooting at longer range to see what the groups were like out far. The groups are a little more to the right of what I was expecting at 650 yards, so I thought I'd ask some more knowledgable people. If any of you are willing to help that would be great!

My round is a 175 gr sierra gameking going 3030 fps from a 26' 1 in 9" twist(RH twist).
Weather was pretty near dead calm if any it was coming from 20-30 degrees and I was facing about 185 degrees(just off south), humidity was around 80%. The latitude is right above 52 degrees.

At that range neither spin drift or coriollis are having any significant effect, no more than 1/4 to 1/2 MOA with any bullet. They really don't become problematic till you get to about a thousand where it's more like 1moa or close to it. Are you using a ballistic calculator and dialing or just attempting to hold or not accounting for it at all?

Most likely it has to do with your scope not being perfectly plumb and square to your action or you aren't reading your wind correctly.

Get a piece of plywood and set it up at 200yds. Set your zero point target in the lower quarter and draw a perfectly plumb line straight up from it.

Get on the 200yds zero point and then dial it up 20 or 30 MOA and see if you are still hitting with the center of your grouping on the line.

Try it then dialing up whatever max you have without forcing it and repeat.

IF your groups are moving off of that line your scope is not true to plumb/square with your action.