Many shooters, especially long range shooters, tend to wrestle with the question of "what distance should I zero my rifle". The reason for this is they want to take full advantage of a cartridge flat trajectory to allow a dead on hold for as far out as possible.
For hunting, this allows humane shots to be taken at longer ranges, relatively speaking, without having to worry about distance estimation errors, and therefore hold over. The further out you can hold dead on, the less chance there is of making an error resulting in bad shot or a miss altogether.
I have seen recommendations all over the web for what distance this should be. These recommendations are sometimes made by experienced shooters and may or may not make sense when you look at the cartridge's trajectory tables. The fact is, data doesn't lie, so if you want to maximize your dead on hold distance, look at the trajectory table to see what makes sense for your rig and set up.
For the standard factory 17 HMR with a muzzle velocity of around 2500 fps and a 17 grain bullet, the maximum dead on hold can be achieved with a 25 yard zero. See the table below which compares bullet drop with different zero distances.
These tables, showing different zero distances, are not readily available for all calibers but you can usually find something close for the more popular flatter shooting cartridges. If not, you can easily create your own by using a ballistics calculator. Most bullet manufacturers offer these on their websites for free. For the table above, I used the Hornady calculator located here.
After entering all of the variables for my rifle, bullet, and set up, I just ran the calculations for the different zero distances listed above and combined the data into one table. Easily done in excel.
Dead on hold zero for hunting and targets
Which zero distance has the smallest deviation from the point of aim out to 300 yards? In this case, it's the 25 yard distance. This means, if your acceptable impact area is less than, say, 8 inches on your target, you can zero at 25 yards and hold dead on out to 275 yards .
If you choose 50 yards as a zero distance, your dead on hold will be 225 yards for the same 8 inch target discussed above. This proves that changing your zero distance can have a pretty big impact on how far you can hold dead on, especially on rimfire cartridges.
You also need to take into account the variability that you add through your human error, barrel, and ammo variability. When this is added to your drop, the zero hold difference becomes even shorter.
If you know you shoot a 3/4 inch group at 50 yards, that then becomes 1.5 inches at 100 and around 3 inches at 100 when applied linearly. That would reduce your dead on hold to 250 with a 25 yard zero on the 8 inch target above.
In a hunting situation, your only concern once you know your dead on hold distance is whether or not the bullet will perform acceptably at the maximum distance you have identified. This is another subject that we will go into in another article but the bottom line is the bullet should have enough energy at this distance, or be designed to expand enough to deliver a quick, humane kill. Hollow points or more frangible bullets typically give the best results at long range.
If your acceptable impact area is say 2 inches because your are hunting smaller varmints, you will need to shorten your maximum distance at which you can hold dead on and take the shot to around 100 yards or less.
Drawbacks to a 25 yard zero
There is only one drawback to having the 17 HMR we have been discussing zeroed at 25 yards. That is from 50 to 150 yards you will shoot slightly high. At 100 yards your will be slightly over 2 inches high. No problem with normal sized game but if you are shooting very tiny targets, you must keep this in mind and either compensate with hold "under" at these distances or dial in the zero setting for that range.
What if I dial each distance
Dialing each distance with the goal of placing the shot exactly where you aim is how I prefer to hunt or target shoot. I am always trying to make a very precise shot with every one I take.
This may not always be possible though when hunting or even in a timed competition. If you are on a prairie dog town with targets popping up and quickly back down again anywhere from 80 to 200 yards, dialing in may not be practical.
Or in a timed competition when the requirement is to move from long to short targets several times during a stage, screwing around with elevation adjustments could easily cost you targets or points by eating up your allowed time.
If you know the distance you will be shooting, then of course dial in that distance if you have the time, but it always pays to commit your drops to memory and have your rifle zeroed for a dead on hold should a shot have to be taken quickly.
Of course, the distance at which you zero your rifle is a all shooter's have to make for themselves. I found that it pays when hunting to keep my scope set at the 25 yard setting. If I have to take a fast shot, I am ready. If I have the luxury of time to change my setting, and those settings are very handy written somewhere on the rifle, or better yet committed to memory, all the better.
Happy rimfire shooting!