Zeroing any firearm is the process of understanding the relationship of Point Of Aim (where the shooter aims the firearm) [POA] to Point Of Impact (where the round actually strikes the target) [POI].
For Soldiers to achieve a high level of accuracy and precision, it is critical they zero their [sighting system] to their weapon correctly. The Soldier must first achieve a consistent grouping of a series of shots, then align the mean point of impact of that grouping to the appropriate point of aim.
–Appendix E – Zeroing, Department of the Army Training Circular 3-22.9 – Rifle and Carbine, May 2016
This is the process most shooters are familiar with regarding zero. However, zeroing a fixed sighted handgun is different than zeroing a rifle.
Bottom Line up front: With rifles, we zero the sights to the ammunition. With fixed sighted handguns, we zero (adjust) the ammunition to the sights.
Even the most rudimentary sighting systems for rifles have some means of adjusting the POA to the POI. Consequently, those who learned to shoot using a rifle are somewhat familiar with the concept of adjusting the sights to coincide with the POI of a particular type of ammunition. Different types of ammunition will frequently shoot to different POI so any given zero can only be considered workable for the type of ammunition with which the zero was originally verified. If a different type of ammunition is used, the zero must be verified again by a testing process to see if it is still valid.
Handguns, unlike rifles, frequently have limited or no capability to adjust the Point Of Aim. A few handguns have fully adjustable sights, meaning the sights can be adjusted by the shooter both in the vertical axis (up and down) and the horizontal axis (right and left). However, such sights are relatively rare on defensive handguns.
More often, an autoloading pistol will have a rear sight that can be adjusted by drifting (pounding it with a hammer and punch) in the horizontal axis and no adjustment at all in the vertical axis. These are typically referred to as ‘Fixed Sights.’ Sometimes, front or rear sights are available in different heights. By substituting a sight of a different height, the vertical POA can be adjusted. This is a process usually beyond the capabilities of a casual gunowner, however.
Revolvers for defensive purposes typically have sights that have no adjustment capability whatsoever. These are also referred to as Fixed Sights and that meaning is quite literal. The front sight is integral to the barrel and the rear sight is a notch cut into the top strap of the revolver’s frame.
Short of using a file to reduce the height of the front sight or to increase the width of the rear notch in one direction, there is no way for the shooter to change the Point Of Aim of a fixed sighted revolver. In days gone by, a trained armorer could use a ‘babbit bar’ (a bar made of lead) to strike the frame and actually bend it slightly, there by changing the horizontal Point Of Impact to coincide with the Point Of Aim. This method can only be used for steel frame guns, however. In extreme cases, the muzzle of the revolver can be recrowned (cut with a machine tool), which will often change the Point Of Impact of the revolver. Using a babbit bar or recrowning are solutions that require specific tools or skills beyond those possessed by even advanced firearms hobbyists.
In the case of today’s most commonly found defensive revolver, what this means is that many commonly recommended types of ammunition will NOT shoot to the Point Of Aim and there is very little the shooter can do about it. Fixed sighted revolvers in .38 Special caliber will typically shoot to Point Of Aim with 158 grain ammunition. Higher pressure or lighter bullet weight ammunition will often shoot to a different Point Of Impact than the Point Of Aim.
To zero a revolver with fixed sights then, the way we zero it is to change the ammunition to align with the Point Of Aim since the sights cannot easily be adjusted. It is possible to carefully file the front sight lower, which will raise the Point Of Impact in relation to the Point Of Aim. Most owners are reluctant to do this, and it must be considered a permanent modification to the gun. If the gun shoots significantly off on the horizontal axis, it will require attention from an experienced revolver gunsmith or return to the factory for adjustment.
Another aspect of ammunition and zeroing is the shooter’s ability to actually hit the target with any particular type of ammunition. The phrase in the Army Circular, “The Soldier must first achieve a consistent grouping of a series of shots” is a key consideration in ammunition selection. Common sense tells us that, regardless of any perceived superiority of terminal ballistics, if the shooter can’t hit the target, then the terminal ballistics of the round are irrelevant and meaningless. Consequently, when the question of what ammunition is best for defensive purposes comes up, my counsel is:
Whatever shoots to the sights and you can shoot a meaningful performance standard with.
Having ammunition that shoots to the sights is an integral component of being able to shoot a meaningful performance standard. It is not uncommon for lighter bullet ammunition to shoot lower than heavier bullets.
For example, this revolver was shot with four different types of ammunition at 10 yards.
- 158 grain +P Lead Semi-Wadcutter
- 158 grain standard pressure Full Metal Jacket
- 130 grain standard pressure Full Metal Jacket
- 110 grain +P Jacketed Hollow Point
The difference in Point Of Impact is noticeable. If the only performance standard being used is to hit a Q target at 4 yards, this difference probably makes no difference. However, if we use a more challenging performance standard, then the difference begins to be more important. The bare minimum performance standard to graduate from the NRA Basics Of Pistol Shooting course is to place 5 shots in a 4 inch circle at 10 feet with no time limit. This must be done 4 times, not necessarily consecutively, to graduate from the course. As can be seen in this photo, although all the shots are in the circles, they are all low. The ammunition used was 130 grain standard pressure Full Metal Jacket.
A more difficult performance standard that students in BOPS are encouraged to meet is to repeat the test at 20 feet. At this distance, ammunition that shoots low may require an adjusted Point Of Aim, as is shown in the below picture.
Distance will only increase the difference in ammunition’s Point Of Impact as compared to the Point Of Aim. Consequently, it’s wise to choose ammunition that impacts (zeroes) close to the Point Of Aim. After considering the zero, then consider the ability to shoot it reasonably well, and finally, the terminal ballistics of the ammunition.
There is probably not a simple answer to this question, but how does one know whether the sights are truly “off” and should be zeroed or if it’s an issue of improper trigger control/manipulation on the part of the user?
There are two possible methods.
1) Load the cylinder with three live rounds and two fired cases. The sequence should be 2 live, 1 fired, 1 live, 1 fired. Spin the cylinder and close it without looking at it. Assuming the shooter actually sees the sights, it will be obvious if a bad trigger press is made when the fired cases come up because the gun will take a nose dive. If a coach is available, it will be obvious to the coach whether the trigger presses are good or jerky, even if the shooter can’t tell.
2) Load with five rounds. Fire one shot, open the cylinder, spin it, and then close it without looking at it. Press the trigger until another shot fires. Repeat the process every time a live round fires. Continue until all five rounds have been fired. Again, if the shooter actually sees the sights, it will be obvious if a bad trigger press is made when the fired cases come up. I used this drill as part of my snub classes and still do it when practicing.
Great tips! Thanks.
[…] Understanding Zero for Handguns […]
I’ve found that the shift in in POA/POI is especially pronounced in the shorter barreled revolvers that have an XS std dot & big dot front sight. My S&W 386 Night Guard came w/ the XS std dot front sight combined with the C&S Extreme Duty fixed rear sight from factory and past 7m the shift of POA/POI with .38Spl+P+110gr and +P 125s are significant when compared to 158+P. The 110 +P+ is in excess of 5″ lower than 158+P and the 125+P is around 2.5″-3″ lower than 158+P. One must always take their anticipated duty/carry ammo for a test drive!!
In production fixed sight revolvers for government contract orders were commonly zeroed using the specified ammunition provided as government furnished material. While specs varied in accordance with contract specifics a .38 Special or .357 revolver would commonly be shot off sandbags at 20 yards, aiming at a 2-inch bull, or the aiming point being scaled to one inch per ten yards. A 3″ circle would be printed on the target which was tangent to the aiming point at 6:00. Five out of six rounds were usually required to strike within the 3″ circle. The correct front sight height would be determined by firing a ten-board sample of revolvers with the contract ammunition to obtain the correct elevation. WIndage adjustments would be made, if necessary by rotating the barrel in the frame using directed strikes with a babbit bar. With revolvers point of impact for elevation is determined more by bullet weight than velocity. Heavy bullets shoot high, lighter bullets shoot low. In ordinary civilian production it was common to use 148-grain wadcutter ammunition because zeroing with this provides a useful point of impact for most common ammunition and the wadcutter lead bullet provides a better functional test to detect “spitters” in which a new fit-up might over-rotate the cylinder (OK up to about 5 degrees to compensate for service wear).
To determine how much to adjust the fixed sights use the formula X=RE/D where X is the amount of correction needed, such as shortening the front sight to move the impact up, or installing a higher front sight to lower point of impact, or rotating the barrel tighter in the frame, moving the front sight left to move impact to the right, etc. R is the sight radius in inches. E is the error correction needed between point of aim and point of impact, and D is the target distance. ALL dimensions are in inches.
In extreme cases an old cop gun may have a bent frame from being used as an impact weapon, and/or the crane is bent out of alignment. A good gunsmith can fix these. There is absolutely no reason any a 2-inch .38 snubby cannot be zeroed precisely and shoot accurately. My S&W Model 36 former basket case reworked by Sandy Garrett of NoVa Gun Works now shoots ten-ring, 25-yard groups with wadcutters, and quality defense or service loads should do likewise in a mechanically correct gun.