The three inch rule

[longcruise]

One of the questions that many muzzle loader hunters often ask is; "where should I sight my round ball to maintain a reasonable point blank range (PBR) for big game hunting out to 100 yards"? Usually other variables are included with the question such as; caliber, charge, powder, lube, etc., etc.?

The answer regardless of variables is simple; Sight to hit dead on at 100 yards and your maximum midrange trajectory will be right around three inches. That answer will pretty much remain unchanged for the majority of rifles and in calibers from .36 caliber up to .75 caliber. They pretty much shoot with the same trajectory given the typical velocities these calibers are shot at. Another option would be to sight for a point of impact (POI) 1.5 inches below point of aim (POA) at 100 yards and, theoretically, your rifle will never shoot outside a three inch circle at any point between the muzzle and 100 yards. You and your rifle together will shoot outside that circle, but how far out is for each shooter to determine by shooting under various conditions.

I don't advocate the use of a .36 cal or even .40 cal for big game hunting, but I included those two just to illustrate the universal application of the three inch rule.

The chart illustrating the three inch rule was generated using William Frenchu's Ballistic program version 4.13 and applying the British Round Ball Table of 1929.
The ballistic coefficient (BC) for each ball was derived using Frenchu's formula specifically tailored to the British Round Ball Table.

The front sight height setting was .70 inch above the centerline of bore. Sight height varies with different rifles, but those variations don't effect the chart results significantly.

The velocities applied to each caliber are based on my own experience with .36, .45, .50, .54 and .58 caliber rifles and the experience of other shooters with the remaining calibers.

The chart won't format here so here is a link to the page in my website.

Link

 

[Osprey]

Whew, when I saw the thread title I was scared this was something the girls at the bars had started talking about. :rotf:

 

[roundball]

This is interesting...I had noticed over the years that after I'd zero a PRB hunting load at 50yds, I'd try them at 100yds just to get an idea of drop and they were all basically about the same 2-3" below the bull, whether a .50cal, a .54, .58, etc...chaulked it up as a nice coincidence that my hold over would basically be the same for all those calibers but never thought about it in scientific terms...cool.

 

[hawkeye1755]

Very interesting.Thanks a lot. :bow:
:hatsoff:

 

[No Grease]

Thank you for the information. :thumbsup:

 

[davy]

I was thinkin they has met up with my old gurliefriend! :shocked2: :redface: :grin:

Davy

 

[shmrck1]

I was thinkin they has met up with my old gurliefriends!:shocked2::redface:

Davy,
:hmm::shocked2:
snake-eyes :surrender:

 

[longcruise]

Whoa! Shoulda titled this "shooters with 3 inch rulers"

:rotf:

 

[Slamfire]

Sounds like a fine idea, but I don't want to be tempted to shoot beyond 100 yards, given the velocity loss of a .490" round ball, so I zero at 85, and expect a 2.25" drop at 100 yards, and to also be 2.25" high at 50. I can't tell within that range where my ball will land, under field conditions, anyway.

 

[Jac Spring]

Good post. The only thing that I would take issue with is your statement obout hunting with .36 or .40 caliber rifles. Taken in context to round balls, yes, I agree that these are small game calibers.

However, with fast twist rifles using heavier conicals, even a .36 caliber rifle becomes a good deer hunting tool. The .40 even more so.

Just a comment.

 

[longcruise]

However, with fast twist rifles using heavier conicals, even a .36 caliber rifle becomes a good deer hunting tool. The .40 even more so.

I agree 100% with that. Also, quite a few guys talk about many successes with prb in the .36 and .40 too, but mostly it seems to be on whitetails and mostly in the south where the deer don't seem to be as big as in the north or west. For me it's out of the question because I'm nearly always hunting elk and deer at the same time so it's a .54 round ball for all of my hunts.

so I zero at 85, and expect a 2.25" drop at 100 yards, and to also be 2.25" high at 50. I can't tell within that range where my ball will land, under field conditions, anyway.

If you look at my chart for the .50 cal, you will see that you are pretty much doing exactly as my post suggests. Only diff is you are zeroing at 85 yards instead of 100. Your trajectory figures vary from my chart too, but the chart is based on a front sight being exactly .70 inch above bore centerline.

No paper chart such as mine provides a solution to field shooting on it's own merits. Each shooter needs to take their rifle to the range and test for themselves as you have done.

What I was going for with that post and the chart is to get a concept across that might help some shooters, especially new ones to ml, grasp a useful concept which of course must be tried to each shooters satisfaction.

And, your observation that you can't tell under field conditions where the ball will land is exactly the kind of observation that needs to be applied to the sterile math figures that I posted.

Thanks for adding that perspective.

 

[roundball]

"...quite a few guys talk about many successes with prb in the .36 and .40 too, but mostly it seems to be on[url] whitetails...in[/url] the south where the deer don't seem to be as big as in the north or west..."

Just for some balance, readers may conclude from that statement that .36 and .40cals are commonly used for deer hunting in the south and that's not the case at all...that's not to say there isn't one or two scattered around across the many states comprising the southern states, but I've been at this for quite a few years and don't know of any personally.

Also, its worth noting that the idea of deer in the south being 'not as big' has been repeated and grown so much it gets a lot of too-casual overuse...while in the big picture the average weight among any of the various geographically dispersed strains of whitetails does vary, the difference is not at all enough to result in geographically different choices of caliber for deer hunting..ie: deer in the south do not magically make a .36 or .40cal ball a sound choice for deer hunting.

If anything at all in the south could be pointed to as a reason that I might get away with a small caliber like a .45cal, it would be the thick dense woods I hunt in which makes deer sightings in the 25-35yard range normal...nothing to do with their size.

These two were taken with a .50cal ball at 25 yards each...as close as they were they probably could have easily been killed with a smaller caliber heart shot, but as a rule, people don't go deer hunting with .36 and .40cal round balls.

 

[Vaino]

How many states allow deer hunting w/ a.36 or.40 even w/ conicals? Wisconsin doesn't....Fred

 

[longcruise]

Also, its worth noting that the idea of deer in the south being 'not as big' has been repeated and grown so much it gets a lot of too-casual overuse...

I plead guilty!

It;s probably based on those south florida deer that I saw. About the size of a german shepard!.

Your "just for balance" post reflects my own view on these calibers for deer. I would not hesitate to use a .40 with a heavy conical for deer, but not a round ball.

How many states allow deer hunting w/ a.36 or.40 even w/ conicals? Wisconsin doesn't....Fred

Actually, my state (colorado) allows a .40 for deer, bear and antelope as long as the projectile weighs at least 170 grains. In many years of hunting CO, I've never met a hunter in the field or out of the field who hunts big game here with anything less than a .50 cal.