How to Determine Ballistic Charts for a Rifle
Well, it’s been a while since I’ve done a info topic thread, so here’s a new one. Over the years, I’ve been asked about using a tactical scope and how to use one. I’ve seen multiple threads both here and the hide forum asking this question also. So, I figured I would do a write up about what someone new to long distance shooting should do to get their new fancy fangled long distance shooting rifle/scope up and running. This isn’t going to cover how to mount the scope or what equipment is better, etc. This is about what one needs to do to figure out their ballistics and use a tactical scope for long distance shooting. Tactical scopes, for the parameters of this discussion, are scopes that have either variable or fixed magnification at a high enough level to shoot accurately to 300+ yards, has a range determining reticle of some design, and has the ability to accurately move the reticle with adjustable knobs (turrets).
So, you have this rifle set up for shooting long distance, and you put the tactical scope on it and now you want to set up ballistics for the rifle. First, zero the rifle with some factory ammo to 100 yds. If you know of a reliable factory load, use it. If the rifle is a 308, the Federal GMM or Black Hills Match are both excellent choices for this. A super cheap and probably the most accurate ammo I’ve found for this initial step is Remington PSP ammo in the green and yellow box. It’s very cheap and seems to just shoot MOA out of just about any rifle. It can save you a few bucks in this initial step. Once zeroed, if you are using factory, buy a couple of boxes of the various match grade ammos and shoot groups at 100 yds with them to determine which one your rifle shoots best. You are looking for tight groups on this stage. Don’t bother making adjustments to each type of ammo, just shoot as precise a group as possible with each type. Expect good results with each type, but you can typically see that the rifle will favor one type over another. Groups should be 1 MOA or smaller, .5 MOA is more typical even out of a stock Rem PSS or Savage 10. If they are not, you have issues and need to troubleshoot the problem before moving on.
If you are reloading for the rifle, this is when you should reload a test set of ammo and fire them to determine your accuracy node and pressure levels. ACCURACY and PRECISION are more important than velocity, period. One of the mistakes I see some people make here is they place more importance on faster velocities than the accuracy of the load. It’s a mistake. Every gun want to push the respective bullet at a certain velocity with accuracy. That velocity may not be near the higher end of the pressure spectrum for the caliber. So, they continually try different powders for faster loads with the same accuracy. I’m all for testing different loads in a gun, but in order to get faster velocities, you will have to change bullet weight and design and probably powders too. It’s a lot of work, and can get expensive to find the ultimate load. If you get a load shooting .5 MOA or even smaller, STOP there. You have struck gold and screw the couple of hundred fps of velocity. If you are concerned about going subsonic at a certain distance, this is a question of caliber selection, not a reload issue. You can't shoot 1600 yds with a 308 Win. Choose a bigger caliber. If factory ammo, I recommend buying as much of the accurate ammo as possible, and if you can get cases of it, get all of the same lot. If/when you change lots, check the zero of the new lot. They may change. Same goes for reloads but based on the amount of times the case has been reloaded. New brass in comparison to the first, second, third etc reload can shift the impact point. I have seen much less shift in reloads from lot to lot in comparison than factory. I have also seen much less loss of accuracy in reloads in comparison to factory. With that said the newer match factory loads are just about as good as reloads any more.
So, now you have found your load for the rifle and are on paper. Zero the scope at 100 yds with the load. Here is the biggest and most common mistake I’ve seen in long distance shooting. You have to shoot your rifle with the load and collect actual data. If you don’t shoot the rifle and the ammo at the distances you want data for, you won’t ever figure out your ballistics. Ballistic calculators are great to get you in the general area at the distances desired, but they won’t ever get you true data. Initially, calculators are theoretical data. The data can be refined after actual data is collected and it becomes even more accurate, but at this point, you are in the data collection phase. Chronograph your chosen load immediately. This is crucial data for longer distance shooting. Record everything. I use a 90 cent small spiral notebook and jot down notes about the load, shooting conditions, range, dialed adjustments, etc every time I shoot my longer distance shooting rifles. Do this every time, you are collecting data, so collect it.
So, why all of the above info if we are talking about scopes? Well, without the previous info, knowing how to use your scope is irrelevant. You might as well be throwing rocks. You have to have the accuracy piece of this taken care of first. Then the rest falls in place.
There is more than one way to use a tactical scope. There are different types of reticles and adjustments on scopes too. I’m going to discuss using a couple of different types of scopes and reticles, but I’ll be the first to tell you. I’m not versed in all the different types and I don’t take the scope use to this in-depth, highly technical, entity. I keep is simple. I am using mil-dot reticles, second focal plane, and .25 MOA adjustments on my current scopes. These are the most common types of scopes out there, and they are less expensive too. The system works, but takes a little math to use as range finding. Learn these scopes. Everything else is easier in comparison, and learning these scopes is a solid foundation for anything else you may use.
The two basic ways you can use a tactical scope for aiming is by dialing in the adjustments for the yardage (we’ll discuss windage later) or using the mil-dots in the reticle for aiming, lets call this ‘hold-over’. I prefer dialing in my yardage, but I have used hold-over to figure out my ballistics. I consider 'hold-over adjustments the next level of learning a tactical scope. It's essentially using the reticle marks, mil-dots as a known aiming spot. For example, I know If I aim for mil-dots below the center crosshairs of the reticle, I'm really close to my 600 yd zero on my 308. This is not as accurate as dialing in the range adjustment, and is primarily a skill used for fast target acquistion. Learn to dial in the adjustments and set your ballistic charts up first. Then you can learn and practice hold-over.
The method I use to figure out my bullet drop is I set initially set up paper targets at 100 yd intervals, 200 to 600 yds. I do this on a day with little to no wind. Wind is the devil, and adding this to the mix will cause you to go home, curl up in the fetal position in a hot shower, and cry. Mark the targets with a decent size aiming point. I like about a 2” black circle or square on a white target. Then shoot 3 to 5 rounds at the first distance, 200 yds. MAKE NO SCOPE ADJUSTMENTS. Shoot the target with the 100 yard zero and all the target knobs set to zero. Then go to the target and with a tape measure, measure the drop to the center of the shot group. Now the math comes in; take this distance (3.6”) and figure out how the equivalent adjustments for the scope. .25” adjustment knobs at 200 yds will adjust .5” at 200 yds; .75” at 300 yds, 1.0” at 400 yds, 1.25” at 500 yds etc. For every 100 yds added to distance, you add .25” to the one click. .25 times the yardage after it’s divided by 100. So, to determine the value of one click on the turret at 880 yds I would multiply .25 by 8.8 and this equals the value of one click of adjustment. .25 * 8.8=2.2”. Now, lets figure out how many clicks of adjustment you need to make for the 200 yd target One click equals .5” at 200 yds so 3.6” divided by .5” equals 7.2 clicks; round to 7 clicks. My knobs are marked in 4 clicks for every one full MOA. So, I want 1 ¾ MOA of adjustment to the scope, 7 clicks. Make the adjustment and shoot for results. Adjust accordingly until you are hitting accurately at 200 yds and record everything. Now for 300 yds. Same thing, rezero the scope and shoot a group at 300 yds (12.00”). 12.00/.75=16 clicks. 16/4=4, so 4 0/4 MOA adjustment to scope. Record and repeat. Longer distances require you leave the scope adjusted to the previous yardage or you start dropping off the paper. In this case, simply consider your previous adjustment as the zero value. Then once you are hitting accurately, record the overall scope turret setting for that range's adjustment.
So, how do you do this with a milrad scope? Well, shoot the target, see how many milrad the bullet is below the bullseye, and adjust the turret that many milrad up. Shoot for effect. Ya, it’s that easy. Just make sure you have the scope adjusted to the right magnification for the milrad scale if it’s a second focal plane scope. If it’s a first focal plane scope, any magnification amount will work. You can do adjustments with a mil-dot scope reticle and MOA adjustments too, but it’s just easier to go measure it and do the math. It can be cheaper too.
Once you have the 100 yd increments figured out, you can now narrow down the ballistic drop for the intermittent yardages to the distances desired. I keep the info to 50 yds. Others prefer every 25 yds, and some go as far as every 10 yds. I have a quick reference chart taped to the inside of my rear scope cover. Not a lot of room in that so I just went every 50 on it out to 600 yds. It’s nice to keep a range card for the rifle and ammo with crazy amounts of accuracy. Having a larger card with adjustments at every 10 yds to the max range of the caliber is ultimately what you want.
Figuring out long distance ballistics takes a lot of time, ammo, and commitment. In the end, you can’t fake the data. There are ways to take short cuts and save a little time, but ultimately, only the no-shit actual data from SHOOTING will count. I’m sure there are other systems to reach the same end results, but this is what I’ve done and it seems to be the most accurate for my rifles.
I thought about adding info about windage and using the reticle for determining distances. Those are probably best in their own separate threads. There is enough technicality in all three of these for separate threads. I’ll get to the other two sooner or later…
