lilabner
"The first shot out of a clean barrel often doesn't hit where later shots do. How do you handle that when you sight in? Do you set your scope for the first shot or for the group you get with later shots fired through a fouled barrel?"
Here is a response to a simular set of questions I answered.
"This year before deer and elk season I "confirmed" the zero of the three rifles I was going to use, a 6.5x55 and two 30-06s. I have grown into the habit of doing this every year. I shoot the rifles from a prone supported position over my backpack which is what I will use in the field for that precision long-range shot. A separate target for each rifle is used at 200 yards. From a cold, clean barrel I fire 5 rounds with each zeroed rifle. If I pull a shot and it goes to call I disregard that shot. However, I do not disregard a shot called good that does not go into the group. That's it for that day, one target and 5 shots. I take the targets home, mark the bullet holes and clean the rifles. A few days later I take the same target to the range and run the same test again. The sight or scope is not adjusted for any shifts in impact. I do this for five separate five shot groups fired on separate days at the same target. I believe this gives me a realistic idea of what the rifle and I are capable of in the field.
I have shot numerous 5 shot groups of around MOA with all three rifles and can honestly say they are MOA rifles. However, using the above test I find that zero of any given group will shift as much as 1/2 MOA in any direction on any day. There are many reasons for this but slight changes in my shooting position day to day are the basic reason. All three rifles produced a common 25 shot group at 200 yards of right at 3 inches. What this tells me is my rifles and I are good for 1 1/2 MOA in the field under the best of conditions. For sporter big game rifles this is excellent in my opinion.
Glad you appreciated the method I use to confirm a rifle zero. I donÂ’t take credit for it, as it is a mere refinement of methods IÂ’ve seen or read about. One thing I didnÂ’t get into is what I do if the composite 25 shot group is not centered over the point of aim and you may find my technique interesting and useful also. Using this technique not only provides a confirmed zero but the process itself provides practice from the most stable position you will use in the field if necessary to make a long precision shot. It also gives you confidence in your own ability to make the shot or to make the decision not to shoot.
As I said earlier the most common influence on a point of impact change is the slight variations to your position each time you assume it. A well-practiced HP shooter can assume a very consistent position each time but even a practiced hunter will have difficulty doing that under the pressure of field conditions. We must also be cognizant of wind when shooting at 200 yards but I always try to shoot when wind is not a factor or wait to shoot until the wind drops. I also wait at least a full minute between shots to not heat up the barrel. Someone has mentioned “why 5 shots”. Well the answer is simply because that’s what the magazines of the rifles I was using hold. If a rifle holds more than that I still use 5 as it gives reliable data. If the rifle holds 3 or 4 in the magazine I use that number. For single shot rifles I use 3 shot groups. We must use a number of shots that will provide sufficient data to achieve the required results, i.e. obtain a consistent know zero. The one other factor that can change POI to a small but certain degree is the thickness of the cross hair or how much of the aiming point it covers up. Most reticles in hunting scopes set at 7 thru 10X will cover quite a bit of the aiming point at 200 yards. Thus we will have a small deviation between the center of the crosshair (actual point of aim) and the actual desired point of impact. With the thicker crosshairs this can be as much as ½ MOA itself.
Another problem is a rifle that will not put the first shot out of a cold clean barrel into the group at the desired zero range.. If I have a rifle that does this I will first change the load, and if that does not correct the problem; I will then sell the rifle. Over the years I have not had to sell very many rifles due to this problem.
As an example of how I refine this procedure for a precise zero lets use the five 5 shot groups we discussed previously. As discussed can be up to a ½ MOA POI shift from the desired POI/POA due to differences in position. With a variable scope of 9 or 10X I use a 1 inch black paster as a diamond target and use the bottom tip of the diamond as the POA. I draw a 1 inch radius circle around the POA which makes for a MOA area of deviation. Also knowing there will be some small shift in POI due to my aligning the crosshairs differently on that POA for that group, how much am I willing to accept for the center of the group to be from the actual desired POI (zero)? In my case I don’t want the center of any group to deviate more than ¼ MOA from the desired POI. At 200 yards this means I want the center of the group to be with in 1/2 inch of the POA I usually center a quarter (25-cent piece) over the bottom diamond point (POA and desired POI) and trace around it with a pencil.
How do we determine the center of the group? There are several ways but the one I use is; take each 5 shot group separately. Find a the bullet hole that has two shots to the right of it and two shots two the left of it and draw a vertical line through it at least as tall as the group. Now find the bullet hole with two shots above it and two shots below it and draw a horizontal line through it at least as wide as the group. These bullet holes with the line through them may or may not be the same bullet hole. Where the line intersects is the center of the group and is sufficient for our purpose.
I find the center of each 5 shot group. If the rifle is properly zeroed the center of each 5 shot group will fall with in the larger circle of deviation from the POA. I then find the center of the whole 25 shot group. Finding a bullet hole with 12 shots above and 12 below and then the bullet hole with 12 shots to the right and 12 to the left, draw the lines and where the lines intersect is the center of the whole 25 shot group. If this center is within the smaller circle of deviation and is less than what one “click” or graduation that the scope adjustment would move it I consider the rifle is zeroed. However, if the center of the 25 shot group is outside the smaller circle or is inside but yet more than one “click” or graduation of scope adjustment away from the POA I will make that adjustment and re-run the test.
When successfully completed we now have a good known zero for our rifle/load that we are confident of in the most stable field position we will encounter when hunting. None the less, we still must practice from other field positions so we know our capabilities and can readily assume those positions in the field. When instructing hunters, soldiers or police on the viability of practicing or training and that they must use all the equipment they would have in the field I use the analogy of dancing. You may be the best “two-stepper” on the dance floor. You whirl and twirl your partners with little thought and with seemingly flawless precision. All the girls are thinking and talking among themselves; “Gee that guy can dance. Sure wish he would ask me”. Some of the bolder girls will ask you. You can do no wrong. However, then comes a waltz and the most beautiful thing you have ever seen walks up and says, “Oh please, waltz me around the floor”. Your heart throbs and there is an instant adrenaline rush. The smile in her eyes seems to also say; “Maybe you can waltz me through life, forever”. Now, my friend, if you have not learned to waltz or have not practiced the waltz then I’m afraid it’s going to be pretty sad out there on the dance floor.
And so it is with the shooting part of hunting. If all you shoot or practice is from the bench or prone then come the time you are asked to “dance” from the sitting, kneeling or standing position you are not going to do so well. I have seen far too many who are very accomplished shooters from the bench or prone who can’t hit the proverbial “bull in the butt with a hand full of buckshot” from other positions. When confronted with a shot in the field at some ‘ole buck it becomes obvious they are not practiced at taking the most stable position available and begin to fumble around. The heart starts throbbing and they get an adrenaline rush (most often referred to as “buck fever”) and unless they are practiced at what to do they perform very badly. They usually just start blazing away. I have seen many a very good bench shooter fire away wildly at a deer at 200 yards or farther from the off hand standing position.
With a known zero and practice at the positions you most likely will encounter when hunting (I was referring to using sporters and hunting) you will have the training and confidence to over come the “buck fever” and make a good shot. And yes, I too still get the heartthrob and an adrenaline rush when I see a big ‘ole buck, whether hunting or not but when hunting I know the dance."
Larry Gibson
