It’s just a short post this week. As you know, I’ve got a PRS Rimfire match in a couple of days and I’ve been getting my gear sorted out. One of the priorities I wanted to tackle was a simple way to have my rifle’s ballistic data with me. I’ve seen a lot of ways to cary DOPE cards (Data on Previous Engagements), and this is just a simple one I thought I could share with you.
I’ve noticed a lot of companies out there offer to sell these things for a few bucks. But the trouble I’ve always had with that is simply that it seems too limiting. Like a zero, a DOPE card is only correct for a specific rifle firing specific ammunition under specific weather conditions.
To me, it seemed like a bit of a waste to have someone else do these cards for me when I may very well change my ammunition or some other factor. So I figured I would do it myself.
I’ll be the first to tell you that the card I’m using for the match is only a “best guess.” I built it from gathering some information together and running it through JBM Ballistics. So what data do I need?
First, you must know the bullet you’re firing. In my case, that’s a Lapua Center-X 40gr 22LR cartridge. Lapua lists the ballistic coefficient (BC) as a .172 G1.
Second, you have to know your velocity. Never trust the velocity listed on the box. Using a Magnetospeed, I averaged a velocity of 1039.4 feet per second at the muzzle.
Third, you must know your zero distance. For this particular competition, I zeroed my rifle for 30 yards, in line with my theory on the ideal 22LR zero.
From there, simply plug in your numbers and define what data you want back. The trouble is that this is only a “best guess,” as it’s not actually based on any previous engagements. If I had time and a range up to the task, I would “true” the ballistic data by comparing what my card says to what actually happens and adjusting the numbers to match.
Is It Necessary?
I would wager that this isn’t strictly necessary for this match. While I set up three cards for going between 15 yards and 500 yards, we’ll see if I actually need to use them at all. One benefit of having my own template is that I can adjust the increment however I like. As you see above, because the little 22 starts dropping quick, I made the intervals more often as the distance got further.
Since PRS matches are rarely unknown distance, you typically have time before a stage to figure out your drops for each target using a live ballistic calculator. Most competitors then write than down on a piece of tape for the stage, then replace it with a new piece of tape for each stage thereafter.
I don’t know what to expect, so I might as well bring these cards along for the fun of it. I’ll have them stuffed in a commander’s arm board with plastic sleeves.
Since I already went through the effort of creating the things, I figured that I might as well share it with you. I’ve saved it as a Google Sheet, you can make a copy for yourself and edit away.
Get your DOPE Card
When printed, each grid is about 4.25″ by 2″, perfectly sized for my Tyr Tactical arm board. You could just as easily use it in a wrist coach or any other similar system. Cards also tuck nicely into a stock pack or shirt pocket.
I do suggest laminating them once you print them for durability sake. You may also choose to leave the distance data blank, laminate it, and then use a grease pencil.
Be sure to use the top row for specific data about the rifle, load, and important weather conditions.
That’s it! Good luck, have fun.