Reticule Cross Hair Placement on Game at Various Distance for Clean Kills
Pre-Season range work will pay off in your confidence of knowing where the shot will land. Do you know hunters that pull ole reliable out the week before hunting season and shoot at the proverbial pie plate at 100 yards? That’s a large window for shooter error not to mention any impact shift if you change the scopes magnification.
Fall/Winter brings on cooler weather and prompts hunters to drag out the guns from last hunting season. Some are cleaned, others, well not so clean. This month I want to discuss optics that drift the point of impact when you change the variable magnification of the scope.
Conventional optics use an erector tube that houses the reticule while spring tension moves the tube when applying or decreasing pressure via the scope turrents. Yes, optics point of impact will shift during magnification change. This is more evident with second focal plain optics than first focal plain scopes. One easy method to help lesson the effects of less erector tube spring tension flyers is to always increase magnification before the shot. If you lower magnification for any reason, turn to a lower setting than you want and just bump the setting up to your desired power. What this trick will do is put positive spring pressure on the erector tube to help stabilize the zero. Ever see guys smack the scope after adjusting clicks? Yes, they are trying to stabilize the spring tension. Today we will look at a totally different type of optic, the digital electronic version. ATN Smart Optics makes a day/night scope. It’s a X-Sight II HD. I told you about them in a previous post and with the help of some fine tuned 300 BlackOut rounds we will test point of impact drift during a range session.
300 BlackOut loaded with converted Lake City 5.56 brass, necks turned to a even .012″ and a stiff charge of IMR 4227 ignited with a CCI 400 primer. The bullets are Sierra #2124 135 grain varminters made just for the BlackOut velocities and they are darn fine shootin’ bullets. At 100 yards, this load will group sub-moa consistently.
Cold temperatures and changes in humidity will play havoc on those finely tuned hand-loads not to mention factory loads too. A good grouping load will shift point of impact in colder weather and when you are zeroed in on that one split second shot at winter freezer meat, then what just happened? A miss? It happens ballistics are math and high humidity is science and equals thinner air (less drag), colder temperature lowers velocity (and chamber pressure), so what to do to keep a good all weather zero?
Point Blank Zero
Point Blank Zero is what I use for hunting loads and it all focuses on what game you are hunting. Varmints need a smaller kill zone while deer will need about an 8″ kill zone. Yardage must be determined with a maximum effective range of the selected cartridge as the bullet drops under the line of sight. Think of an oscilloscope screen with the flat line as “line of sight” and the sign wave curve as bullet high/low trajectory. Now with the deer example, an 8″ kill zone would allow 4″ above the line of sight and 4″ below the line of sight for a total minimum/maximum elevation window of 8″. Some information needs to be known to do the ballistic calculation for point blank zero and that will be typically: Bullet weight/diameter, Drag function, Ballistic coefficient, Elevation, Temperature, Humidity, Velocity and Max Distance. These are just a sample and the specific ballistic calculator program that will specify needed info. I’ll list my 22-284 Winchester varmint hunting load as an example.
22-284 Winchester
75 grain A-Max
Velocity 3488 fps
Zeroed at 230 yards; Maximum trajectory height 1.58″ at midrange of 137 yards; -1.58″ at point blank range of 268 yards
This window allows no aiming correction from a dead on zero hold, out to 268 yards with this load. That’s a 3.16″ kill zone out to 268 yards, no hold over needed.
The fact that you have bullet impact anywhere in the point blank range will allow for some weather condition deviation on impact. We are not looking for pin point benchrest groups just kill zone area impacts. As an example, during a 2017 hunting season a Michigan White Tail deer presented an opportunity for filming the 10 point buck that was in my kill zone zero with the 300 BlackOut. The impact of the bullet was a solid hit thru the shoulder plate and then fragments exited thru the neck. I was well within my point blank zero so no consideration to sight correction was needed. A clean kill and dead in his tracks.
ATN offers an interesting option to shooting with conventional optics with the X-Sight II HD 3-14 scope. You can utilize a program called “Smart Shooting Solution” to make distance corrections in the menu. A ballistic calculator is turned on and a range is selected. The operating system makes the reticule correction and you just hold center and shoot. Now this is not a point and shoot quick adjustment to make, however, if you have time to push a few buttons and set up the shot it’s very accurate. I was shooting 300 BlackOut subsonic loads at 50 yards and decided to push them out to 100 yards. To check out the program, subsonic velocities are in the 1000 fps range and this load will drop 3.75″ at 100 yards. The day I shot the test was cold, 20 degrees with 95% humidity so the air was thin, less drag. You guessed it, bullets hitting high would be the assumption. I input the corrected weather conditions and applied the ballistic calculator function for 100 yards. This was the results.
Going a bit further I moved out to 200 yards on another day. Again adjusting the ATN X-sight for the huge elevation drop of the Rainier Wedge 180 grain sub-sonic loads.
To sum this all up it doesn’t matter if you choose to use a digital optic or a conventional optic. Current weather conditions will need to be considered for correct shot placement in the kill zone. With a Point Blank Zero you will be able to hold dead on without consideration of environmental conditions (wind is an exception). Time spent at the bench tuning the zero while twisting turrents always pays off when the pressure is on to make that quick shot while hunting.
Until next time, get some bullets in the air to tune your Point Blank Zero!
Right On Dead On All The Time
knowyourzero 