The Firing Line Forums

Go Back   The Firing Line Forums > The Skunkworks > Gear and Accessories

Reply
 
Thread Tools
Old September 14, 2013, 09:37 PM   #1
FoghornLeghorn
Senior Member
 
Join Date: September 2, 2011
Posts: 537
A question re sighting in a scope.

I read a theory about sighting in a scope. This particular theory says to sight in the scope at 200 yards. If you have a shot at 100 yards, aim dead on. The bullet variance will only be about 1 inch. If you have a shot at 300 yards, aim dead on. The bullet drop will only be about 1 1/2 inches.

The idea being that in that scenario, regardless the range, the shot will still be in the kill zone for a deer or elk sized animal.

Does this have any validity?
__________________
"I say, boy, I say, you're doing a lot of choppin', but no chips are flyin'."
FoghornLeghorn is offline  
Old September 14, 2013, 10:08 PM   #2
Sierra280
Junior member
 
Join Date: July 29, 2013
Location: Gardnerville, NV
Posts: 569
That sounds pretty close, I'm guessing you are talking about a moderate velocity .30cal round, it will change with bullet weight and velocity.

When I sight in a rifle I always start with the 25yd 1 shot sight in, then go out to whatever i want my zero at. It's a little high at 100 and close to dead on at 200.

--shouldn't this be in a different section of the forum??
Sierra280 is offline  
Old September 14, 2013, 10:55 PM   #3
Jim Watson
Senior Member
 
Join Date: October 25, 2001
Location: Alabama
Posts: 10,984
That is very optimistic.
The flattest thing in my old chart is .300 Win Mag.
Zeroed at 250 yards, it is 2.9" high at 150, 3.5" low at 300.
No doubt there are flatter loads now, but I doubt THAT flat.
Jim Watson is offline  
Old September 14, 2013, 11:17 PM   #4
Nathan
Senior Member
 
Join Date: July 1, 2001
Posts: 1,893
I get
100 +1.5"
200 0.0
300 -7.0

For 180 gr 30'06.

Your numbers must be for something hotter. I like to 0 +2.5" at 100 for:

100 2.5
200 1.79
300 -4.3
Nathan is offline  
Old September 14, 2013, 11:50 PM   #5
FoghornLeghorn
Senior Member
 
Join Date: September 2, 2011
Posts: 537
I asked the same question elsewhere.

A poster gave me this link.

http://www.rmvh.com/MPBR.htm

Interesting info.
__________________
"I say, boy, I say, you're doing a lot of choppin', but no chips are flyin'."
FoghornLeghorn is offline  
Old September 15, 2013, 12:04 AM   #6
Theohazard
Senior Member
 
Join Date: April 19, 2012
Location: Western WA
Posts: 2,131
Quote:
Originally Posted by FoghornLeghorn
Does this have any validity?
Yes, it's pretty common. Hunters often refer to it as your "point blank range" and the military (or at least the Marine Corps) refers to it as the "BZO", or "battlesight zero". The idea is that if you always aim your rifle at center mass, up to a certain range the bullet will never be more than several inches too high or too low.

In the Marine Corps we would zero our M16A2s at 36 meters, which also zeroed the rifle at 300 meters (the bullet crossed the sight line at 36 meters on its upward arc, then came back down and crossed the sight line again at 300 meters on its downward arc).

So with our M16s we didn't have to account for elevation when shooting up to about 350 meters or so, we could aim center-mass at any target and be sure to hit no more than several inches too high or too low.

This is the same principle hunters often use when zeroing a scope, but the maximum distance you can shoot without adjusting for elevation (your max point-blank range) changes depending on several factors, most important are the cartridge used and how large the kill zone is on the animal you're hunting.
__________________
0331: "Accuracy by volume."
Theohazard is offline  
Old September 15, 2013, 12:06 AM   #7
Theohazard
Senior Member
 
Join Date: April 19, 2012
Location: Western WA
Posts: 2,131
Quote:
Originally Posted by FoghornLeghorn
I asked the same question elsewhere.

A poster gave me this link.

http://www.rmvh.com/MPBR.htm

Interesting info.
Never mind, it looks like someone already answered your question before I did.
__________________
0331: "Accuracy by volume."
Theohazard is offline  
Old September 15, 2013, 08:50 AM   #8
wogpotter
Senior Member
 
Join Date: September 27, 2004
Posts: 3,002
You're thinking of something called "Mean Point-blank Range".
What it does is to factor in the following:
Target dimension (vital area for a hunter).
Trajectory of the bullet.

& combine them into a range at which that bullet, fired at that velocity, will strike the target (vital) area with a dead on hold.

Each change to the parameters, bullet wweight, bullet shape, velocity, bullet's BC & animal size, will change the set zero. For example my 165 Gr .308 at 2650 FPS will be good from 100 (4.3" high) to 350 yards (6.35" low) with a 275 yard MPBR for a target with an 18" vital area.
__________________
Allan Quatermain: “Automatic rifles. Who in God's name has automatic rifles”?

Elderly Hunter: “That's dashed unsporting. Probably Belgium.”
wogpotter is offline  
Old September 15, 2013, 07:20 PM   #9
Jim Watson
Senior Member
 
Join Date: October 25, 2001
Location: Alabama
Posts: 10,984
I saw an old American Rifleman article in which T.K. Lee, maker of the Lee Dot scope reticle, discussed the approach in a graphical way.
Tell him what caliber and load you were shooting and he would put a dot reticle in your scope to suit its trajectory over the "point blank" range.
Zero correctly and out to its maximum usable range, your shot would strike someplace under the dot on the target.

If the dot covered more than the vital area of the game, it was too far away.
Jim Watson is offline  
Old September 16, 2013, 10:53 AM   #10
George Hill
Staff Alumnus
 
Join Date: October 14, 1998
Location: North Carolina
Posts: 11,547
I've been pushing my zero ranges on magnum rifles out to 300 yards with good results. Specifically with my 7mm Rem Mag.
__________________
MAD OGRE
George Hill is offline  
Old September 23, 2013, 07:30 PM   #11
Kirby8604
Member
 
Join Date: March 14, 2013
Location: St. Paul, MN
Posts: 61
As mentioned, it depends on the round/velocity, but the stated numbers are in the correct range. If you can pretty well guess the distance of a shot while hunting, you may as well aim where you know your bullet will land (if you sighted at 200 and shooting at 300 aim 1.5" higher or whatever is the case for your gun/round). This requires you to know how your gun and the particular ammo you're using behaves at distance, which requires range time.
Kirby8604 is offline  
Old September 24, 2013, 05:27 AM   #12
jmr40
Senior Member
 
Join Date: June 15, 2008
Location: Georgia
Posts: 5,870
At one time something similar was very common. Lots of guys still use the concept to one degree or another. With today's flatter shooting rifles, range finders and scopes with long range dots and adjustable turrets more and more people are just using 100 yard zero and letting the technology take care of sight adjustment at longer ranges. Used properly it works much better.

The biggest problem with a 200 or 300 yard zero is that your bullet will be quite a bit higher than you point of aim at 50-150 yards and you may have to remember to aim low at close ranges. This complicates things at exactly the ranges 95% of shots are taken while only offering a very slight advantage at ranges beyond 300 yards where shots are rarely taken.

I use a 100 yard zero. This means my bullet will never be more than 1/2" higher or lower than my aiming point from 50 yards to about 130 yards. Less than 2" low at 200 yards and I can still make hits at 300 yards with the crosshairs holding on the top of a deer's back. Beyond 300 yards I use the dots on the crosshairs as aiming points.

It is completely unnatural to have to remember to aim low, especially when close shots usually happen fast. Much easier to aim a little high on longer shots where you usually have a lot more time to set up the shot anyway.
jmr40 is offline  
Old September 24, 2013, 08:33 AM   #13
kraigwy
Senior Member
 
Join Date: June 16, 2008
Location: Wyoming
Posts: 9,398
There are variables one must consider. The rifle, and the target, being the main two.

Lets look at hunting. You need a ballistic chart for your rifle/ammo combination. Then you need to determine MPBR (Max Point Blank Range) for that combination.

Before you can find your MPBR you need to know the size of the target, not the critter, but the vital area of the critter.

Here's an example: The average size of vital, or heart lung areas.

Antelope 8.5
Deer 10.5
Elk 15

So taking the above into consideration, lets say we are hunting antelope. You need a MPBZ that, when aimed at the center of the target you are never 4 inches high, or 4 inches low.

Lets look at a 130 Gr SST bullet with a MV of 3000 fps. If we sight this rifle/ammo combo in at 275 yards, the highest point of the trajectory is about 150 yards (3.3 in high) and it drops below the magic 4 inches at 325 yards.

You need a ballistic program, the BC of your bullet, and the velocity, then you can compute the MPBR for what ever critter you're hunting.

This is just a guide, after you get it figured out, you need to set targets out at varying range to confirm what your Ballistic programs said.

This is pretty much what the military does in considering Battle Sight Zero's (BSZ). The odd part on military shooting is getting the target to expose itself by standing up so you can take advantage of the BSZ. That is not likely to happen, but for hunting, the above will work pretty well.

Also one much quickly determine the range of the critter. That's why I like MIL Dot scopes.

Using the above antelope, which the average body size is 14 inches from the top of its back to the bottom of its stomach is14 inches, we look at that in the scope and if its covers no less then 1.2 MILs its in range of your MPBZ.

Its all about knowing your rifle/ammo combo. You cant just say, 2 inches high at 100 and you're good to go for any rifle, any target. It just don't work that way.
__________________
Kraig Stuart
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071
kraigwy is offline  
Old September 24, 2013, 09:56 AM   #14
Jim Watson
Senior Member
 
Join Date: October 25, 2001
Location: Alabama
Posts: 10,984
The usual MPBR drill does not take into account the grouping capability of the rifle. If in that example, your nominal drop takes you 4" low at 325 yards, that is for the average shot. If you have the proverbial MOA rifle (+load +position +hold) then you might well strike another 1.7" lower still; 5.7" off center. Does that matter to you? (Yes, I know you might strike that much higher and be closer to center, too; but you have to figure the worst case.)
Jim Watson is offline  
Old September 25, 2013, 08:53 PM   #15
603Country
Senior Member
 
Join Date: January 6, 2011
Location: Thornton, Texas
Posts: 2,248
I sight my rifles in at 200 yards. For a 270 and a 130 gr bullet at 3000 fps, you'll be down about 7 inches at 300 and 20 inches at 400. That's as far as I'll normally shoot anyway. For my 220, the 300 yard drop is more like 5 inches and 15 inches at 400. If that's all the distance a fellow is going to shoot, there's no need for fancy target turrets.

I will admit that occasionally that sighting method will give me trouble. I hunted for years with a 35 Remington and I had gotten in the habit of aiming just below the top of the back. That aiming at the top of the back, once or twice or thrice, caused me to shoot over deer with my 270 when I was in too big of a hurry. I guess my shooting instincts with the 35 can't be unlearned in split second shooting.
603Country is offline  
Old October 8, 2013, 02:45 AM   #16
Bolinger
Junior Member
 
Join Date: October 7, 2013
Posts: 7
Agree with Nathan and Kraigwy - check your bullet grain as all brands and grains will need slight compensation - people usually forget when they change ammo and different grades, or even move up in Altitude your zero will be slightly different. Having said that, your in the ball park going off my quick calcs. Cheers.
Bolinger is offline  
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 06:08 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
This site and contents, including all posts, Copyright © 1998-2014 S.W.A.T. Magazine
Copyright Complaints: Please direct DMCA Takedown Notices to the registered agent: thefiringline.com
Contact Us
Page generated in 0.09933 seconds with 9 queries