Home Forums Hunting & Shooting Ask The Gunwriters Acceptable accuracy , out to 400 yards

my hunting rifle barrel is still dirty from 3 or 4 years ago maybe longer ? in the past it shot just under an inch 3 shot group at 100yards and i was happy with that always .this year i loaded Hammer bullets for this rifle with the dirty barrel and now it shoots 1/2 inch 3 shot groups i did 2 of these 3 shot groups both were 1/2 inch / 100 yards i said good enough took rifle deer hunting took 1 shot at 125 yards was a bang flop on the shoulder of the buck where i aimed at buck was standing when i smack him. barrel still dirty will check it next fall before deer season again.i will be using Hammer bullets again too with the barrel still dirty.

Regarding 3 shot groups and what if anything they can predict:

Since anyone can look at a 10 shot group and pick out 3 shots that look great or bad, and since any of those 3 shot choices are just random in the 10 shot cluster I got to wondering just how many possible combinations there could be.

Here's the math I came up with. If it was just numbers instead of bullets it would be simple; 10 digits from 0-9 would be 10 x 10 x 10 = 1000. That meshes rather well with what we know about counting. With bullets its a little different, we don't want to use the same bullet hole twice so the math is 10 x 9 x 8 = 720 possibilities. Seems high doesn't?

Well the number is right, if the order of hitting is important. Lets suppose we don't care too much about order and concede that group ABC is the same as CBA or BAC. That reduces things a bit, since there are 6 ways three things can be arranged. 3 X 2 X 1= 6. That brings the total number of combinations down to 120. 720/6 = 120.

Of those 120 possible combinations there are 8 combinations of 3 that would exactly reflect the 10 shot group. You don't need math for that; if you have the 2 most widely spaced bullet holes in your selection the third doesn't change anything.

So 120 possibilities, 8 right answers, and 112 wrong ones. You could calculate the odds fairly easily; 120/8 = 15. So the odds of a single 3 shot group matching the 10 is 1 in 15. How about multiple 3 shot groups? Well, if you shot 2 3s and a 4 you would have 10 shots invested. Your best group would mean exactly zero for predicting the 10 shot result. The average wouldn't mean much more since that is just a number saying that half will be higher and half lower than the average number. Your worst group might have a chance. A 3 to 15 chance if you wanted to calculate it.

Or just shoot the 10 shot, or the 2 3s and a 4 and stack the targets. Your chances of prediction are one heck of a lot better than 1 in 5. It might be close to 1-1.

For load development, I like to settle on .75-1.0” at 100 yards then tune the zero to a 200 or 250 yard zero depending on the cartridge ballistics and scope reticle. I’m not a turret twister and generally keep my shots at game under 350 yards. I don’t like to miss, although I missed a coyote last month because I guesstimated the range hurriedly and was off by more than I care to admit. He went into hyperdrive when that LRX landed between his feets.

We do tend to sweat the small stuff way too much. Consider group size, for example. If our rifle shoots an eight inch group at 400 yards (about two MOA) that does not mean we’ll miss our aiming point by eight inches, but by a maximum of four inches. The probability is that the hit will be a bit closer than that.

What matters as much or more than group size is a rifle’s zero and it’s ability to hold it, as well as practice in field conditions that include wind doping and the knowledge to make appropriate corrections.

As a certified Loony, I like most here will obsess over getting tiny groups, fussing endlessly with loads, rifles mounts and scopes. But when it boils down, I am OK with a 1.5 MOA rifle and scope combination that puts the bullet in the same place boringly year after year.

When I say “OK”, I’m not really happy but know I won’t miss that 400 yard deer or elk. The Loony in me still wants sub-MOA, despite the knowledge that it just doesn’t matter.

As far as wind, it's effects multiply as you get further out. At 400, wind effect is approx 2X what it was at 200 in MOA. In inches, that's about 4X greater.

300 to 600 is a similar story, wind is approx 2X in MOA. In inches, it's over 4X.

And even a very slight wind gust of 5 mph (or 5 mph difference in wind speed from one shot to another) can turn a 0.75" group into a 1.1" or 1.2" group at 100 yds.

The difference between the groups the OP is currently getting and what several of us suggested as a goal for targeting deer at 400 yds is the same difference as 5 mph crosswind at 100 yds.

I think it's an exponential dependence, but I'd have to go through it to confirm.

Quadratic functions deal with squares, and are are parabolic in shape. One value varies as the square of another. I think this is the mathematical way to describe wind drift over distance.

I have a 243 that averages about an inch at 100 yds, that i have shot 3 shot groups of 3" @ 500 yds. from prone field position. The best way to find out about 400 yd accuracy is to hang a target at 400 yds

It takes a 400 yard shooter to make an accurate 400 yard shot......there are very few that can do it in the field. Always a lot of chest pumping shooting from the bench. Just my gray haired experience. As far as accuracy from the bench, I want my rifle to be as accurate as it can be......I am good with 1" and no fliers.

I shoot for (pun intended) 1 moa…. from bench! memtb

I'm a wee bit familiar with quadratics.

I recognize that. Yet you posted that wind drift would be greater than quadratic. How to you figure that?

I double-posted...like a champion.

I looked at a scenario using a ballistics calculator and the numbers didn't quite fit a pure quadratic growth.

^^^^^^^^^^
Truth

Well there is sitting and prone also.

Actually a 10 shot group will tell you more about your rifles accuracy potential.Can show if your rifle is bedded properly and a host of other things.Is it important to shot 10 shot groups for hunting.You are correct,no.

Yes, that is very true.
While Newtonian drag force increases quadratically with velocity, the trajectory of a projectile experiencing Newtonian drag is very difficult to solve analytically without some assumptions and approximations. An assumption that allows for an analytical solution is that the projectile is fired at a negligible polar angle (nearly horizontally), which is the case that we are interested in. Wind drift increases linearly in lag time, which increases linearly in flight time,

wind drift = B * wind speed * cos(theta) * lag time
= B * wind speed * cos(theta) * (flight time - vacuum time)

where B is some coefficient that depends on the units you use for the various parameters, theta is the azimuthal angle of the wind vector (full value at theta=0), and vacuum time is the time of flight if the bullet were in a vacuum.

Flight time is a function of the bullet's horizontal position, described by t(x)=[(exp(x*C*p*A/2m) - 1) * 2m] / (v_0*C*p*A), where x is the horizontal position, C is the drag coefficient, p is the air density, A is the cross-sectional area of the bullet, m is the mass of the bullet, and v_0 is the muzzle velocity.

If you insert the flight time, t, for a given distance, x, into the wind drift equation, you will see that wind drift varies exponentially with distance.

True but it doesn't matter, again as related purely to the rifle/load's precision, whether they are all fired as one group, or fired as three separate 3-shot groups plus 1 additional shot.