I have an article that John Wooters wrote years ago about PBR. If I remember the concept correctly you sighted in at a certain height and your point blank range was based on a chart he had. Your bullets line of flight was within 5 inchs of the line of sight out to the Maxinum point blank range. so you could hold dead on your target out to the MPBR.



I calculated this using a site I found.



Input Data

Muzzle Velocity: 2800.0 ft/sec

Bullet Weight: 225 grains

Ballistic Coefficient: 0.454

Drag Function: G1

Sight Height: 3.500 inches

Vital Zone Radius: 5.000 inches

Temperature: 23.3 �F

Barometric Pressure: 20.58 in Hg

Relative Humidity: 0.0 %

Altitude: 10000 feet

Air Density: 74 % of Sea Level





--------------------------------------------------------------------------------



Calculated Data

Maximum Point Blank Range: 368 yards

Maximum Point Blank Range Zero: 314 yards

Muzzle Energy: 3916.7 ft-lbs

Energy at Maximum Point Blank Range: 2580.5 ft-lbs



comments? tom



http://www.eskimo.com/~jbm/ballistics/pbrange/pbrange.html

I'd say your scope height is way off. 1.5 inches is more common.
10000 feet ? I think that's too high, but some places do have critters way up there.
Humidity 0% ? Even my dry deserts often have over 10%. I suggest using at least 30%.
If you want to stay inside a five inch circle, your zero range must be shorter than that. Don't forget the dispersion of your loads as the range increases. At 300 yds. even a very accurate rifle may shoot 3-4.5 inch groups. If your load is zeroed for 300 yds at the bottom of this 5 inch circle, half your hits will be outside it.
To stay in a five inches with the group center, you need to be either plus or minus 2.5 inches. In my experience with something like you are shooting, your zero would be more like 225 yds. E

E, I will let you tell the elk that they are up too high they don't listen to me lol. I have all ways sighted my rifles in 3 to 3 1/2 inchs high at a 100 yards.



Input Data

Muzzle Velocity: 2800.0 ft/sec

Bullet Weight: 225 grains

Ballistic Coefficient: 0.500

Drag Function: G1

Sight Height: 3.000 inches

Vital Zone Radius: 5.000 inches

Temperature: 19.0 �F

Barometric Pressure: 29.92 in Hg

Relative Humidity: 20.0 %

Altitude: 9500 feet

Air Density: 108 % of Sea Level





--------------------------------------------------------------------------------



Calculated Data

Maximum Point Blank Range: 352 yards

Maximum Point Blank Range Zero: 301 yards

Muzzle Energy: 3916.7 ft-lbs

Energy at Maximum Point Blank Range: 2290.2 ft-lbs



tom

I think what "E" was referring to was the sight height being the centerline of the scope in reference to the centerline of the barrel. Most set-ups I've seen are typically 1.5".

The Sight Height parameter is the height of the line of sight above the center of the bore. The program will calculate where the POI is at 100 yards for the specified Maximum Point Blank Range.

It still does not tell you where to sight in at a 100 yards. I sent an email to the guy to ask him about it. tom

My assumption is a .338" 225 Partition.



With a 1.5 sight(scope) height and 2800fps muzzle velocity:



100yds = +3.0"

200 = +2.5"

250 = O

300 = -4.1"

400 = -17.8"





Sorry to burst the bubble..................

Stick, yes your assumption is correct it is .338 225 NP. It would have been nice if he had included the 100 sight in height instead of the scope height. Your numbers make much more sense. thanks. tom

It gives you a down range zero. You can use that in the ballistics calculator to get the POI at 100 yards.

http://www.eskimo.com/~jbm/ballistics/traj_basic/traj_basic.html

It's all there.

Pumpgun I have the John Wooter's article and accompanying tables in front of me, It is from the 1989 Guns and ammo action series volume 7 number 5.Titled Deer Rifles. It gives the 338 win mag with a 225 grain bullet reaching a height of 3.3" at 100 yards, and it reaches it's highest point of 4" at 144 yards, It reaches it's dead zero range at 258 yards and then reaches it's maximum point blank range of minus 4" at 304 yards. With this sight in the bullet never rises above or falls below 4" out to the range of 304 yards. The difference between this bullet weight and the 200 grain bullet is only 4 yards. The charts show the trajectory of 60 calibers in various bullet weights. The 304 yard max ppr is quite a bit different than the 368 yards you show.

That's the one. thanks. I have it some where. Of course being able to do it on-line is cool also. tom

Not entirely true.

1.5" is taken (blindly) as "normal," but the actual heights with today's variable scopes and large objective bells are very often higher.

Measure
(a) the diameter of any part of the scope
(b) the diameter of the barrel directly below (a)
(c) the distance between the scope at (a) and the barrel at (b)

Add 1/2 the scope diameter at (a), 1/2 the barrel diameter at (b), and distance (c). That's the height of your scope's line of sight above the bore axis of your barrel.

You can also measure the distance from the bottom of the barrel to the top of the scope at any point, then subtract half the diameter of the scope and half the diameter of the barrel at that point to get the same "scope height" distance.

Maybe it's 1.5" -- but don't be surprised if it's higher.

The higher it is, the farther from the muzzle your bullets will cross the line of sight, both as they rise (seldom as close as 25 yards -- another myth) and as they descend -- making your zero and point-bank ranges a tad longer for any given "kill zone" diameter.

Pumpgun, now get some target turrets on that scope and go kill stuff <img src="/ubbthreads/images/graemlins/wink.gif" alt="" /> Sticks method is MUCH easier to use the PBR. To verify your drop, shoot at targets at said ranges to make sure all is up to snuff. I still like target turrets much better <img src="/ubbthreads/images/graemlins/wink.gif" alt="" /> Flinch

Flinch, no can do I would have to buy one of them loopie scopes to get target turrets. lol. tom

Pumpgun,

Why would you use a 5" vital diameter for elk? Mever shot an elk, but a nice sized whitetail in our neck of the woods has a 18" chest. To keep the shot in the middle third of the animal, roughly considered as the vitals, that gives you a 6" diameter. On an average moose, somewhat larger than an elk, I guess, the chest is around 30 inches in average, and as much as 36 inches on a large one. Again, a third of that is 10 - 12 inches. So would an average elk would go what, 24 inches? Make your diameter 8 " and that gives you a more useable range for the Point Blank.

shootist, I considered that, but the range was far enought all ready to get out beyond where I would ever take a shot. tom

Pump, how dare you hunt elk with anything but a Leupold <img src="/ubbthreads/images/graemlins/wink.gif" alt="" />

250 yard zero.

300 yards, hold 5 inches high, or shoot directly at animals center chest.

400 yards, shoot at backbone with verticle cross hair in line with the front leg. You never take cross hairs off of fur (do not hold over animals back....big mistake that is often made). Worked for me, before sucumbing to the "dark side" <img src="/ubbthreads/images/graemlins/laugh.gif" alt="" /> Flinch

Tom, Keep in mind that with something like 3.3 inches over at 100, it'll go up from there for a bit. I've watched my hunting partner shoot over bucks a couple times (nice ones!) because he had a quick shot at 150 and didn't hold low. Easy to do under pressure.

I like hunting with it about 2.5 over at 100. Depending on the rifle, that'll give me about a 275 MPBR. If the critter is 300+ I'm usually not shooting unless I've had time to range it and check the drop/wind chart I stick to the stock. I REALLY like to take my time with any shots over 300 to make sure it's going to be a slam dunk.

That's my $.02.

MS, 3 to 3.5 incvhes high @100 has served me well for years even on them dinky little texas whitetails have not shot over one yet.

Flinch, I used the money I save by not buying them loopies to get a range finder lol. tom

I used to use 3-3.5 high @ 100 yds., but I found on shots in the 200 yd. catagory on a coyote, for instance, and I'd shoot over him sometimes. Now I stay with 2-2.5 inches, and make very sure it is on the money from a field position.
One of the great things about target style elevation knobs is that I can go for precision at closer as well as longer ranges. For instance, if I reset for 300 yds., my range estimation can be 50-80 yds off and still make the shot. Not so if I hold over. E

I have the article and yes, it is a plus/minus 4 inches for point blank range. Very effective.

Holy crap this is an old one!

With a 1.5 sight(scope) height and 2800fps muzzle velocity:

100yds = +3.0"
200 = +2.5"
250 = O
300 = -4.1"
400 = -17.8"

I use this type of zero for 225 .338's, 180 grain '06, 100 grain .243, and 200 gr in a 300 mag.

For a 225 grain .35 Whelen/180 grain .308 I zero 3.5" high.
I then shoot them at 200 and 300 yards. It appears to be pretty close and as far away as I want to shoot except for a stand with a very good rest.

I have drop tables and a laser range finder for the longer shots.
Seems to work pretty well.

But it isn't common with modern scopes that have objective rings 'way over an inch in diameter.

Measure a few before you assume an inch and a half as a default. You'll find that an inch and a half is not that common these days.

Measure!

Half the diameter of the objective ring of the scope
plus
half the diameter of the barrel right under the objective ring of the scope
plus
the vertical distance between the objective ring and the barrel
equals
scope-axis height above bore axis (SAHABA).

And the higher the SAHABA, the farther out the bullet crosses the line of sight, both as it rises and as it curves downward out beyond the sight-in distance.

FWIW, I use a three-inch-diameter kill zone to calulate the MPBR for my prairie-dog rifle � and the SAHABA, IIRC, is something like 1.75 or 1.8 inch. (Gotta go measure it again one of these days!)

Right as usual, Ken.
An old post. I was hoping Tom was posting again. He's a good guy to have around. E