Shooting a rifle upside down

Ry pointed out this thread to me on ARFCOM. Probably many people will want to stop at the picture and move on after that but the more interesting part to me is solving the sighting problem.

UpsideDownRifleShooting

Here is my thought process on the problem:

The drop is the same regardless of the gun orientation. Keep in mind that drop is independent of point of impact (POI) relative to point of aim (POA).

To solve this problem in general look up the drop for this range on the ballistics table for your ammo.

With the gun zeroed for this range the barrel is angled up such that it compensates for both the drop and the height of the sight (Sight Height or SH) above the bore.

Suppose the drop is 2 inches and the sight height is 1.5 inches. Hence the angle of the barrel is such that the bullet rises, relative to the muzzle, 3.5 inches between the muzzle and the target.

When you invert the gun you have the angle of the barrel giving 3.5 inches additional “drop” to the gravity induced drop for a total of 5.5 inches.

But you have the sight below the barrel which means you “get back” twice the sight height of the total. So the gun will be shooting -5.5 + (2 x 1.5) or 2.5” low.

Hence, the general solution for a gun zeroed at a given range when you turn it upside-down it will have a POI of:

POI = POA + SH – 2 x Drop

Or probably more useful is the POA relative to the POI:

POA = POI + (2 x Drop) – SH

7 thoughts on “Shooting a rifle upside down

  1. joe:

    what are the probabilities involved?
    — 66 year old man
    — bad right knee, e.g., no anterior collateral ligament
    — left knee not so hot anymore
    — blood pressure issues
    — shooting a high powered rifle, say a .308 winchester
    — not having been known for his “flexibility” even in his youth,
    and,
    — being just a bit arthritic
    of such a person ever being able to get into such a position in the first place, let alone choosing it in preference of other positions, in order to take a serious shot at something.

    i’d say the whole issue will never present itself to me. not in this lifetime, anyhow.

    but, an interesting post.

    john jay

    p.s. now, as a practical/practicable matter, i don’t think she is gonna hit much of anything at all, whatever the range. if you will look at hatcher’s notebook, you will find that about 1 and 1/2 degrees elevation of the bore line above horizontal is all that is/was required to send the standard service load in .30-06 about 1,000 yards. and, if you watch long distance shooters, you will find the bore not anywhere elevated as high to the horizontal/horizon as the barrel in this snap.

    i don’t know what she is aiming at, but, if that posture is a solution to a practicable problem, her target is a long long long long way off, a lot farther than she could hit with a high powered rifle, and a lot farther away than she could hit with a position rifle chambered in .22 long rifle equipped w/ “irons.” even very good ones.

    but, an interesting post.

    • I suspect the picture was taken before she was fully into position for the shot.

      I also suspect the “practical problem” she was solving was to make a shot difficult for someone else to duplicate in some sort of personal competition. Such as accepting a challenges of the nature of, “I’ll bet I can shoot better than you and you get to choose the shot.”

      • depends on range lees the 100 yards bullet is going to rise possibly 2.5 inches beyond 100 yards it drops about 1 inch per 100 yards with variation of bullet weight and velocity 180 grain fmj at 500 yards with velocity of 2800 fps will drop 4 inches that is from army sniper info

    • Yeah, but it’s well camouflaged.
      Not so much “woodland advantage” as “taking advant…” I mean “urban advantage.”

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