General discussion question

First topic message reminder :

I recently acquired some really nice bullseye firearms. I purchased these because they all had iron sights and all had been previously accurized.

My question to you guys is this..... What is the best way to "sight" a new to me firearm in ?

I am nearsighted and wear corrective lenses, should I start with a white sheet and a black cross in the middle from a sandbag or from my own right hand in shooting stance.

At what distance will be optimal ? 50 foot because we are indoors this time of year, or 25 yard as an average of both indoor and out ? My range supports 75 foot depth.

The first test run to be sure each gun was solid I found myself elevating the point of contact and shifting the windage to the right. 

Thanks in advance.

Ed Hall wrote:

Magload wrote:If you cant the gun some when shooting it will change the POI both in elevation and windage.  Think of the dot being the center of the circle and the bore the outer edge.   Sighted in 100% vertical puts the bore at 6 o'clock on the circle.  A little cant to the left moves the bore right and up.  The higher the dot above the bore the more the movement.  Levels are often put on rifle scopes and some scopes have build in indicators.   I have levels on my Matchdots that I shoot benchrest pistol with trying for one hole groups indoors.  Don

What you descibe is at the gun and is counter-intuitive, since canting to the left actually moves the bullet hit on target left and down due to the sight line and bullet drop differences.  I have an article detailing this at:

Pistol Shooting: The Art (Part 12)

Ed that was a good read and I have read your article before.  Will say the numbers did hurt my head trying to follow them but was never that good with math.  I don't follow the bullet moving to the left as the pivot point is around the dot as you are going to but it on the center of the target.  That moves the bore to the right.  With a 90 degree cant to the left the bore would be at 3 o'clock on the target and yes the shot elevation would change.  Don

The part to make your head hurt is that to have the bullet hit the point your dot is indicating when you are zeroed with 0 degrees of cant the bore is actually aimed above the dot by an amount equal to bullet drop.  As you cant counterclockwise (left), while at the gun, the bore may be physically located low right to the sight, but where it is pointing is now to the left and a little lower from the point above the dot.  As the cant is continued through a circle, there are other circles created:

- We will assume the drop is equal to the radius of the black for this illustration.
- We will rotate the gun about the dot (line of sight) with the dot remaining on the center of the black.
- The bore is located directly under the dot at 0  degrees cant.
- Since the bullet drop is equal to the radius of the black and the gun is zeroed to produce a center shot at zero cant, the bore is pointed at the 12 o'clock position at the top of the black.
- As the gun is rotated counterclockwise about the dot, where the bore is aimed is rotated counterclockwise about the center of the black.
- Due to the bullet drop being equal to the radius of the black, the bullet hits describe a circle with an equal radius to the black, but offset vertically by the radius of the black (bullet drop) to display as a circle with the top center coincident with the center of the black.

Ed I over looked the fact that the line of the bullet travel is not parallel with the line of sight.  I knew this but trying to picture what was happening with just the gun I over looked it.   Thanks for setting me straight.  I work hard at getting every thing level when mounting a dot on my guns and trying to maintain a vertical hold.  I watch a shooter at a club match that shot very well with a cant you just need to sigh in with the cant and keep it consistent.  Question and I am giving up trying to do the math.  So does windage change with distance 25 to 50yds?  Don

How much wind?

If your gun is zeroed with a cant and there is no change to the cant, there should be no lateral shift between the distances.  If the cant is great enough and the scope is level at true vertical, there may be a need to adjust the windage control.

If you shoot with a cant why don't you mount the scope so that it is true level when the gun is canted. I would think this would make it easy to adjust up/down and left/right.

pistol champ wrote:If you shoot with a cant why don't you mount the scope so that it is true level when the gun is canted. I would think this would make it easy to adjust up/down and left/right.

Are you asking me this?  If so I do not shoot with a cant I do my best to make sure everything is level.  I was only questioning the effects on POI if a gun set up vertical was canted.  Shooters have mentioned that when they start to tire they my start to cant a little.   Don

If you look at the 22LR subsonic bullet drop in the link posted several posts prior, the bullet drop from the muzzle is 3.95 inches.  Rounding to 4 this means that the bore is pointing at the top of the 8 ring on a 50 yard target assuming center hold.  So if you cant 10 degrees that puts the bore is now pointing on the 8 ring .7 inches towards the cant and the bullets will fall about .1 inches low.  If you were zeroed perfectly with a pistol and shooter capable of 10X knots, Then your 10X knot would be in the printed “X” on the lower leg on the side of the cant.  In other words a typical bullseye shooter might drop a few Xs or at most a point or two shooting a cant.  Bullseye shooters have more to worry about than a small cant.

cdrt wrote:A std velocity .22 bullet is traveling (arcing) "up" to the 25 yard line, it peaks and then is going "down" to the 50 yard line, so the point of impact is the same.

I haven't gotten past this concept - it should depend on the height of the gun, compared to the height of the target. The bullet wouldn't be traveling (arcing) "up" to the 25 yard line, if the shooter's hand was higher than the center of the target, in which case wouldn't it be falling lower to the 25 yard target, and still lower to the 50 yard target?

Gravity is still working over the horizontal distance that the bullet travels perpendicular to the point of gravity.  The projectile will still describe an arc relative to the line of sight that is larger or smaller depending on that horizontal distance (going to 0 arc at straight up or straight down) relative to the gravity source.    

A physics book or learning to shoot in mountains will both teach this. Gravity is always working on the projectile. 

CR

CR