Accuracy Testing
The gunsmith needs a working knowledge of accuracy testing to be competent in rifle work. After all it doesn’t matter whether it is a target, tactical, hunting or plinking model, if it is a rifle or pistol it has to be accurate to be interesting. While the intrinsic accuracy of the firearm is usually the focus, this is always intertwined with ballistics to achieve the end result of a hit on target. The standard definition of a rifle is a firearm that fires a single projectile through a rifled bore to the place the sights are aligned. Sounds easy enough, unless something goes wrong. Chances are if you are interested enough to read this you already know that a lot of things go wrong every shot. Your job is to find a way to eliminate these errors or at least mitigate their effects to get a grouping of shots close enough together to satisfy the shooter.
Ever wonder exactly what you learned when you shot that group of three with all holes touching? Did you learn just as much on the next group with two in one hole and the third a sickening two inches away. Maybe you did without realizing it. A lot of shooters fire thousands of rounds without stopping to think about what the groups display. The rifle is telling you a story and you need to know how to listen.
The rifle is telling you what size the cone of fire is for the ammunition. It is a term you are probably not familiar with but every rifle has a cone of fire or area where the bullets will impact. This undetermined area is defined by firing several shots with as little deviation as possible. Now you don’t have to be a math whiz to know that if you have an unknown area and select three random points inside that area it will never be an accurate representation of that area but this is the norm when it comes to rifle testing. Does this mean you need to fire 100 round groups? No, don’t go off the deep end. First lets look at what we are trying to do.
With any range testing scenario we want to duplicate what the rifle will be doing when it is working or doing the job it was built to do. A deer rifle for a still hunter lives around the concept of one shot fired from a cold ( sometimes very cold!) barrel. The data you get from three shots might not be an accurate picture of what this gun will do the next three times this gun is fired in a hunting scenario. For the average weight barrel in a highpower rifle the temperature change is probably 40-50 degrees between shots. Combine this with the understanding that three random points are no better than a 36% representation of the group. For this rifle we need to define the group with more shots but all fired from a cold barrel. Preferably fired in the same ambient temperature as the hunt. While this might not be possible just be aware of what is best. Rifles and ammo can behave differently with a big temperature change.
So you go to the range and take a long time between shots, fire several rounds, and have good data, but what if the rifle will be used with a hot barrel? My match rifle has to shoot ten shot rapid fire strings. So doesn’t matter about cold barrel zero. Wrong! To get the most out of the rifle you need to know where that first shot is going. Careful testing and record keeping will tell you if your rifle will need adjustment after the first few shots. My best 600 yard rifle required me to come down a full minute after firing the second sighter. This is a big move to make when the first 2 are in the x ring but keeping a data book proved it. Careful record keeping and tracking will pay off.
For most of us accuracy testing will be shooting off the bench. If you think this doesn’t require skill you are misinformed. If you have never had any instructions in bench technique you need to understand you are shooting a tuning fork.