Thursday, November 6, 2008

Bullets and Paper and Elevation and Polymer Tips


This post is really for my benefit and records since this will be easier to find than any paper I might accidentally throw away.
I finally finished sighting in my rifle today. David E. Petzal once said something to the effect that practicing shooting in big calibers is useful only if you figure out what you're doing wrong, or if you become monumentally better. He makes a very good point. Big calibers are finicky; if a barrel's too light, your shots will begin to scatter when the barrel gets warm; if the rifle's too light you can expect your accuracy to decrease as much as the stock market. And even if you handload your own ammunition, practicing with a big caliber is EXPENSIVE. The point he was making is to practice with a .22 to develop good shooting skills which cross over fairly readily with a big caliber.

Thankfully I used a mattress this time to sight in my rifle which was more stable than sitting. And I figured out a huge problem I was having while sighting my rifle in. The area where I was putting my target to sight in at 25 and 50 yards was flat. Virtually flat, maybe 3 to 6 inches difference in height, but flat enough that it wouldn't change the trajectory of a bullet. But because I couldn't maintain a line of sight on this flat part out to 100 yards, I had to dogleg the target down to an area where I could actually see it. And it wasn't until the saw my 4th grouping which made me gaze at my rifle with all the affection of an ingrown toenail that I realized the target's true altitude and my position's true altitude did not equal each other. The target was probably 8 feet below my position.

The point of sighting in a rifle is to position the correct amount of arc for the bullet's trajectory so that it will hit a target at a desired distance while at an equal height to the rifle. This is done by aiming the rifle at a slight upward angle so that the bullet has a small velocity in the vertical direction, which is accomplished by making the reticles on a scope aiming slightly lower than the rifle barrel. My problem was that I was aiming down towards the earth. By a LOT. A foot give or take would not make an appreciable difference in aiming, but this was enough to make my bullets go whizzing over the target or smack the top portion of the box I was using as a backstop. When shooting downhill, if you were to fire at at a target, your bullet's point of impact would change because it's no longer in an arc trajectory, but it would go the way all things go if you throw them flat or down: at 9.8m/s/s.

You can see this in the picture I drew in GIMP. Conversely the same is true for shooting uphill: you still aim low, because you're giving the bullet a higher vertical velocity, so it travels farther up than the point of impact that your scope would show. I still think this would be a great trick question to have on a physics exam.

Anyway, the altitude was enough for me to realize why I was sometimes trouble sighting in at 100 yards while I was getting accurate shots at 25 and even 50 yards. So I moved the targets to an area I thought was about even with my shooting position. And it worked! It was extremely windy today, but I was able to squeeze off some shots in between gusts. The wind did throw my bullets to the left and right, but the two groups I had were within an inch of the bullseye. And the groups themselves were about 1 minute of arc or better. That's not even telling what I could have done with a clean, cold barrel and an actual benchrest instead of a makeshift bedroll. The ammo I used was Federal Fusion with a flat tipped bullet, and the accuracy just wasn't there. Bullets would string, get thrown, and occasionally shoot a 2.73" ring, but nothing impressive considering how darn expensive the ammo was.
I was disappointed. Plus I had an atomic wedgie that was giving me a stranglehold from all the squatting and kneeling I was doing. But atomic wedgies aside, I used the Remington Premier Accutip and shot my first MOA group for the first time in 4 years. I was extremely pleased. For the second time in my life I felt like I knew exactly what I was doing and felt confident about myself. I also couldn't deny the resemblance of the ammo to Hornady's SST 130 grain. And neither could most of the hunters on the internet. The word is that this ammunition is actually made by Hornady for Remington. Looking at my grouping, I can believe it. The groups I made with Hornday are very similar to Remington ammo.

Apart from sighting in, I learned the importance of having the rifle butt firmly on my shoulder, or else the rifle would immediately begin to shift, throwing the bullet off. Learning to call shots was also very important and helped me feel better at shooting. I also got enough sense to know if there's a distinct breeze or gust, that it's best to wait until wind dies down before taking a shot. Ammunition is important. My rifle sent low end ammunition into 6 inch groups at 100 yards (from a prone position, unfortunately), but drove the high end stuff into tight groups which I was proud of. For future reference, further on down my hunting experiences, I'll need to determine which brand of polymer tip/spitzer ammo my rifle prefers, but for now I'll continue feeding it Hornady SST and Remington Accutip in 130 grain.
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