The Firing Line Forums

Go Back   The Firing Line Forums > The Hide > The Art of the Rifle: General

Reply
 
Thread Tools
Old November 27, 2006, 05:40 PM   #1
SlimWallet
Junior Member
 
Join Date: November 2, 2006
Posts: 3
Question on sighting a 308

Gents,

Check me out on this......Gonna help sighting in a new Savage 308 for my daughter's boyfirend.

To get a 200 yard zero the group should be about an inch high at 50 yards. Is that right? ... and then about 2 inches high at 100 yards....?

Thanks,

Slim
SlimWallet is offline  
Old November 27, 2006, 06:14 PM   #2
Unclenick
Staff
 
Join Date: March 4, 2005
Location: Ohio
Posts: 10,226
Two inches high at 100 yards is Jeff Cooper's standard approach and works quite well. At 50 yards, however, it is likely to be more like half an inch or so. It is too close to the "point blank" range, meaning the point at which the bullet passes through the line of sight of the scope on its way upward in its trajectory. The reason is the height of the scope axis above the bore means the trajectory has to climb a bit to cross that line of sight.

If you want an exact number, you need to provide measurements of the height of the center of the scope above the center of the bore and the length of the barrel, then provide bullet weight and muzzle velocity (published is OK for a commercial load, though it presumes a 24" barrel for .308 specs; add about 20 fps for each inch of barrel beyond that to be in the ballpark for muzzle velocity). Usually you will find out that the point blank range is somewhere around 30 yards or so, while exact 200 yard zero puts you 1.5 to 2" high at 100 yards, depending on the bullet weight (heavier is higher, and Cooper favored the 180 grain bullets). It is too small a difference from exactly 2" for most gun and ammo combinations to care. If you get a lighter bullet and you sight it 2" high instead of 1.5" at 100 yards, it will climb another quarter inch or so at around 220 yards, but then stay in a 4" kill zone circle out a little further.

You just want to get 10 or 20 shots to average 2" high at 100 yards. If you can put the gun on sanbags or in a cleaning vice and take the bolt out, you can line the bore up with the center of the target. Depending on your scope height, you want the scope to be looking about 2 inches low on the target at 100 yards when the bore is sighted dead center. That will get you close to where you need to be before you shoot.

Nick
__________________
Gunsite Orange Hat Family Member
CMP Certified GSM Master Instructor
NRA Certified Rifle Instructor
NRA Benefactor Member
Unclenick is offline  
Old November 27, 2006, 06:25 PM   #3
SlimWallet
Junior Member
 
Join Date: November 2, 2006
Posts: 3
Nick,

OK thanks....... that's what I need to know..... get it about a half inch high at fifty then shoot hundred yards and fine tune it.

Thanks,

Slim
SlimWallet is offline  
Old November 27, 2006, 06:37 PM   #4
Unclenick
Staff
 
Join Date: March 4, 2005
Location: Ohio
Posts: 10,226
Right. Give me your scope height and bullet and muzzle velocity and I can give you more exact trajectory numbers. Otherwise, if your scope is, say, 1.5" above the bore axis (pretty typical), just sight to dead zero at 25 yards range (if you have that available), and you will be just about right there.

Nick
__________________
Gunsite Orange Hat Family Member
CMP Certified GSM Master Instructor
NRA Certified Rifle Instructor
NRA Benefactor Member
Unclenick is offline  
Old November 28, 2006, 12:10 AM   #5
T. O'Heir
Senior Member
 
Join Date: February 13, 2002
Location: Canada
Posts: 3,212
Sight in 4" high at 100 and you'll be in the kill zone of a deer out to about 300 with no hold over using a 165 grain bullet.
T. O'Heir is offline  
Old November 28, 2006, 02:07 AM   #6
Twycross
Senior Member
 
Join Date: January 26, 2005
Location: Montana
Posts: 1,187
If you want exact numbers, you can go to a ballistics calculator (this is my favorite one). You can play with the numbers and get pretty much the exact POI at any given point.
__________________
The test of character is not 'hanging in' when you expect light at the end of the tunnel, but performance of duty, and persistence of example when you know no light is coming.
- Vice Admiral James Stockdale, USN (ret.)
Twycross is offline  
Old November 28, 2006, 06:20 PM   #7
snolden
Senior Member
 
Join Date: January 25, 2006
Location: N. E. AZ
Posts: 266
I prefer a 300 yard zero myself.

My drops for 165/168 gr black hills are +3 @ 100 yards +1 @ 200 yards and -4 @ 300 yards. So it is kinda like a 250 yard zero actually.

this is for an FAL @ around 2700 fps muzzle velocity

each gun is slightly different so use some common sense and shoot it with what you are gonna use.
snolden 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 09:32 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 0.07973 seconds with 9 queries