Truing velocity issues

[danatkins]

So went to my parents place the other day for some range time while I'm on call and figured I'd double check my dope. My chronograph was acting goofy last time I tried using it so I just sat a target out at 359 yards. Longest I can get without moving a bunch of old equipment. Shot this 5 shot group and this is what my strelok was telling me to set velocity to. Originally dialed 1.9 I was using fgmm 175 data since my load is close to that. My load is 41.5 of imr4064 under a 175smk. This seems weird that I would need that high velocity for truing.

 

[Dthomas3523]

Based on the vertical spread in that group, I’d say shooter error.

Either that or the range is wrong.

 

[danatkins]

Ranged with rangefinder more than once. What would I have done wrong to cause that error

 

[Dthomas3523]

Ranged with rangefinder more than once. What would I have done wrong to cause that error

Recoil management on shooter side.

Bad mirage could also do it

 

[danatkins]

There was barely any mirage and the rifle was going up and right when I shot just a bit. I need a better rear bag. Running a armageddon xwing it's a little short

 

[Deleted member 113831]

175 SMK has a G1 of .505 and that load moves out at 2630fps from my 24" barrel.

If you previously zero'd in strong sun and shot in overcast, then it could easily be that much higher.

Either way, 1.4mils is a 300 yard come up not a 360 yard come up. Something is screwy with the system, not the app.

 

[danatkins]

System meaning the rifle?

 

[Deleted member 113831]

System meaning the rifle?

I should have used a better term.

I suspect you had a zero shift due to lighting conditions, or something to do with the shooter, rifle or scope.

Your initial presumption of 1.9mils is spot on for that round at that distance.

 

[danatkins]

Thays what it gave before I trued it and was hitting .5 mils high so I went into the truing on strelok and subtracted .5 from 1.9 and it gave me that velocity. I just can't imagine it being that fast it's only a 308

 

[Deleted member 113831]

Thays what it gave before I trued it and was hitting .5 mils high so I went into the truing on strelok and subtracted .5 from 1.9 and it gave me that velocity. I just can't imagine it being that fast it's only a 308

The laws of physics are notoriously rigid, so the actual ballistics won't change much...especially at 359 yards. It's just not far enough to see that much change. You could go from sea level to 10K ft and not see that much change at that distance.

The app (Strelok) is also spot on, because it gave you an entirely reasonable come up. So your inputs must be good as well.

However, the shift was obviously real. So all that leaves... is either the shooter/rifle system, or light.

Shoot it again, but shoot it at 100 yards before you dope it to check for zero shift.

 

[danatkins]

Okay so how would light change my zero I'm a bit confused about that 1

 

[Dthomas3523]

Okay so how would light change my zero I'm a bit confused about that 1

If you zero’d in say high mirage and now not shooting in mirage. That could do it.

And light refraction in general. Here’s a good video to illustrate. It’s a very often overlooked/unknown issue.

 

[iceng]

As the above post said. Check your zero conditions vs current conditions. Your zero MUST be true to do this.

Also did you accidentally range in meters and set in yards ? That can also change distance a bit, so confirm that too.