On Dope

Sorry.  I couldn’t resist.  Let’s get down to the actual business of the post.

Now that my main rifle has a scope that is easy to adjust, and also allows for informed holdovers, I am suddenly inspired to commit my trajectory information to memory.  Here’s how I’ve been going about doing that.

I zeroed my rifle and chrono’d the loads.  I entered the data, along with the current trend in my local atmospheric type stuff, into the Berger Bullets Black Box of Ballistics (sorry, couldn’t resist again).  I used that instead of my little iPhone appbecause I like being able to print the results out on paper.

The output of the program can be configured in whatever range increments you want out to whatever maximum range you desire.  I figured I should learn it out to 1200, just to be overly thorough (conventional wisdom says the .308 Winchester is an 800 yard gun).  I was most concerned with ranges out to 600 right off the bat, since these are more likely for me to encounter.  I printed off 2 sheets, one out to 1200 in 100 yard increments to get the “coarse” numbers, and one in 50 yard increments out to 600 yards to get more detail, but still fit it on one page.

To facilitate my memorization I made a quick reference card to tape to my pocket notebook.

025
The wind and lead info above goes with another rifle.  I’ll fix that part later.

To get my memory going I would look at an object in the distance, make a range estimation, then try to recall my elevation correction to the tenth mil.  At first just getting the even hundreds seemed like too much to remember.  After about 2 days I had it down to 1200.  I added the 50’s and had them all the way to 900.  If the above cheat sheet had been a little longer I could have gotten all the way out to 1200.

After I had my 50 yard increments down to where I could recall them every time, I started testing myself on my ability to guess on anything in between.  If you imagine every segment as a trajectory in and of itself, and you know the elevation correction above and below, it doesn’t take long to get the hang of making a pretty good guess.  I would say that 60% of the time my guess was right on with my data, and the other 40% of the time I was within 0.1 mils.  The only thing is that it took too long to do even under completely relaxed circumstances.  If I had been under stress it probably would not have worked for me.

The trajectory inside of 50 yards is pretty interesting and varies quite a bit for minor changes in distance.  Luckily, unless you’re making a surgical shot this doesn’t matter much.  I’m going to tackle that segment of my trajectory after I get my 50 yard increments out to 1200 down.  So far, as far as within 50 yards is concerned, I can remember that at 10 yards my comeup is 4 mils, at 15 it’s 2.3, and at 25 it’s 1.0.  I’ll get it down to 5 yard increments eventually.

One thing to keep in mind about memorizing trajectory is that the numbers aren’t written in stone.  They will change as conditions change.  Changing the load would be a rather huge change, so let’s just not go there yet.  My goal is to learn this load well enough, and in sufficiently varied conditions, that I will be able to adapt to all but the most demanding of shots.

I mentioned above about recalling the numbers or making a guess in between known increments under stress not being feasible at this point.  I have to get them more hard wired, which I think will also allow me to have it down well enough to understand changes that environmental conditions will cause.  I would like to learn them backward, i.e. be given a correction and relate it to the distance or distances to which it corresponds for my rifle.  I think that, and a lot more time and practice, could make it happen.

I’ll be sure to keep y’all updated with how it’s working out.

8 thoughts on “On Dope

  1. Once upon a time I spent many fascinating, fun-filled hours perusing the back of my Sierra Manual (I do that when I need a break from my exciting social life).

    One thing I noticed is that for wind drift, there was a consistent and fairly predictable progression of increased wind drift in inches over the first few hundred yards. From 100 to 200 yards the drift increases by a factor of roughly four, then from 200 to 300 it increases by a factor of two and a quarter to two and a third, and from 300 to 400 by a factor of around 1.8 to 1.9 or so. The precise amount varies with different bullets, but the rough ratios remain close. I used to have it committed to memory for quick-and-dirty work (no longer!).

    • Federal Gold Medal Match .308 Winchester with the 168 grain Sierra Matchking, so I guess it’s not really *my* load. If my Chrony was telling me the truth, it’s flying at around 1590 fps at or near the muzzle of my 20″. My sight height over bore is ~1.87″.

    • It looks like I probably meant to type a “2” instead of a “1” in the thousands place. I was probably eating donut holes or an ice cream sandwich and my finger just took up two keys instead of one, and I was in a sugar induced stupor and didn’t notice. But you did. Good spot.

    • We shouldn’t overlook the point of the post in this case by getting too detailed. After all, there is a picture of Mr. T with a clever play on words (OK, maybe not clever, but at least juvenile) AND I included a photo of my notebook. Who cares about muzzle velocity details when you have pictures like that?

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