Horizontal Cmore Mount Offset and POI

[FTP_Shooting_Sports]

Hi guys,

I am able to find ballistics calculators that can tell me how much the vertical offset of the scope affects POI at various distances, but how do I  determine how much the horizontal offset of the amount affect windage at various distances?  Any help would be appreciated.

Edited November 20, 2016 by flgcwpg

[drewbeck]

The ballistic calc should be able to do windage as well.  It will assume full value wind i.e., 100% cross wind, so you'd need to derate the wind value according to the angle it's hitting you.  Full head wind is 0 impact, full crosswind is 100%

 

saying a cmore mount leads me to believe you're concerned about windage with a pistol... if that's true don't be, it's wasted brain effort closer than 100 yards, if the wind if blowing hard enough to move a bullet at uspsa ranges, you're gonna be hard pressed to hold the pistol still enough to hit the target as it is

[drewbeck]

The ballistic calc should be able to do windage as well.  It will assume full value wind i.e., 100% cross wind, so you'd need to derate the wind value according to the angle it's hitting you.  Full head wind is 0 impact, full crosswind is 100%

 

saying a cmore mount leads me to believe you're concerned about windage with a pistol... if that's true don't be, it's wasted brain effort closer than 100 yards, if the wind if blowing hard enough to move a bullet at uspsa ranges, you're gonna be hard pressed to hold the pistol still enough to hit the target as it is

[zzt]

flg, if your calculator does not compensate for vertical drop, use it for horizontal offset.  Just set the height above bore to the horizontal offset dimension and compute.  If that won't work, try this.

I'm guessing you set your zero for around 17 yards, so we'll use that as an example.  If the height of your C-More is 2" above the bore and you are zeroed at 17, the bullet will be 2" high at 34 yards, not counting for bullet drop.  The same applies to horizontal offset.  Say you have a lot, 3/8" to the left.  Well, then you will also be off by 3/8" at 34 yards, but to the right.  You'll have trouble splitting playing cards anywhere but at 17, but it's close enough for USPSA and steel. 

[FTP_Shooting_Sports]

Thanks everyone. That helps a LOT!

[theWacoKid]

Your horizontal offset with offset mounts is only a small fraction of an inch.  Unless you zero it at 2 yards you should never notice the drift just from the horizontal offset.

If the dot offset is 1/4" left (and it's actually less than that) and you zero windage at 20 yards then your poi error is 1/4" right at the muzzle, 0" at 20 yards, and then would be 1/4" left at 40 yards.  Not worth fretting over for standard pistol game accuracy.

Edited November 21, 2016 by theWacoKid

[drewbeck]

You referring to a ballistic calc made me think you were concerned with actual wind in the "windage" reference.

 

if your just worried about the poi vs poa shifting due to the slight lateral offset, don't even think about trying to figure it out with math.  Just zero your gun at the distance you want and then test every 5 yards from 5-50 so you know what your load does at those ranges in case you ever need it.

 

i was surprised to find out that I was zero at 15 and 100yards

[zzt]

I think Waco meant to say you would be 1/4" left at muzzle, 0 at 20 and 1/4" right at 40.

[theWacoKid]

1 hour ago, zzt said:

I think Waco meant to say you would be 1/4" left at muzzle, 0 at 20 and 1/4" right at 40.

No.  If the dot is offset to the left like normal than POI at the muzzle is right of the dot.  It crosses at 20 yards so POI is dead on.  After crossing at 20 yards, POI will be further left than the line of sight and increasing with distance.

If you zero at 100 yards, POI will be to the right 1/4" at the muzzle and slowly approach zero at 100 yards.  But POI will be slightly right all the way between 0 and 100 yards.

Edited November 21, 2016 by theWacoKid