The Firing Line Forums

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

Reply
 
Thread Tools
Old September 9, 2012, 01:13 PM   #1
BoogieMan
Senior Member
 
Join Date: April 4, 2012
Location: South Jersey
Posts: 1,287
Scope education needed.

I would like a little scope eduction/explanation

MOA- Moment of angle, How does this effect my shooting? What does it mean with a scope -vs- red dot?
Paralex- What exactly is this?

I wantr to upgrade my 30-06 with a decent scope. Currently wears a simmons 3-9x40. I am considering the Nikon buckmaster 4.5-14x40. Any cons to Nikon? Is there a better buy below $300?
__________________
Concentrated power is not rendered harmless by the good intentions of those who create it.
Milton Freidman
BoogieMan is offline  
Old September 9, 2012, 01:42 PM   #2
Doyle
Senior Member
 
Join Date: June 20, 2007
Location: Starkville, MS
Posts: 5,090
Google will give you more complete answers but here is the simple version.

MOA - Minute of Angle. It is a measurement of a portion of a circle. A circle is divided into 360 degrees. Each degree is divided into 60 subparts called minutes. One MOA is one of those minutes. In shooting, MOA gets translated into a linear distance. One MOA worth of angle difference, when measured at 100 yds is pretty close to 1 inch (not exactly but close enough for our discussion here). At 200 yds, that one MOA becomes two inches. Etc. With scopes, the ability to adjust the crosshairs is measured in MOA. A 1/4 MOA adjustable scope means each click of the scope adjustment will result in a POI (point of impact) change of 1/4 inch. In a red dot scope, there is also a MOA measurement for how large an area the dot covers. A 5-MOA dot will cover an area of 5" at 100 yds.

Parallax - this one is a bit harder. Think of the relationship of the crosshairs to your target as you are looking down the scope with your eye perfectly centered in line with the crosshairs. Now, imagine moving your eye slightly off that line of sight. Parallax is the movement of the crosshairs in relation to the target as your eye shifts off the centerline. Scopes are designed to be "parallax free" (i.e. no movement) at a certain distance. Scopes designed for a rimfire (i.e. fairly short range) are typically set at 50 yds. Scopes that are designed for centerfire calibers are either set to be parallax free at 100 yds or they are user-adjustable. The poorer the quality the scope, the more noticable the parallax change will be as you get away from that parallax-free distance.
Doyle is offline  
Old September 9, 2012, 01:48 PM   #3
SamBo
Junior Member
 
Join Date: August 26, 2012
Posts: 5
MOA is the Minute of Angle. It is the angular degree difference of the center line of the bore to the center line of the scope. The further the distance, the greater the angle.

Parallax can be defined appropriately to rifle scopes as the apparent movement of objects within the field of view in relation to the reticle.
http://www.6mmbr.com/parallax.html
Attached Images
File Type: jpg Parallax-1.jpg (8.6 KB, 10 views)
SamBo is offline  
Old September 9, 2012, 03:25 PM   #4
BoogieMan
Senior Member
 
Join Date: April 4, 2012
Location: South Jersey
Posts: 1,287
So I have a cheep scope on my SR22 (rfle) I think its a barska. It is very sensitive to the distance and angle at which I can actually see through it. Is this an issue of eye releif distance or paralex?
__________________
Concentrated power is not rendered harmless by the good intentions of those who create it.
Milton Freidman
BoogieMan is offline  
Old September 9, 2012, 06:13 PM   #5
Doyle
Senior Member
 
Join Date: June 20, 2007
Location: Starkville, MS
Posts: 5,090
Quote:
I think its a barska
That alone is enough to describe your problems.
Doyle is offline  
Old September 12, 2012, 08:52 AM   #6
bumnote
Senior Member
 
Join Date: October 13, 2008
Location: Northern Virginia
Posts: 374
Quote:
Is there a better buy below $300?
I have a Mueller Eraticator, 8.5-25x50 and I've been happy with it. Eye relief leaves a lot to be desired...but for the price range it's a good scope. I shoot iron sights 90%, so I didn't want to spend a lot on a scope. I have it mounted on a 308, it holds a zero, has a good warranty and for under $300 I'd have a hard time doing better. The paralex is adjustable and has an MOA of 1/8".
__________________
"And remember, Abraham Lincoln didn't die in vain, he died in Washington D.C." - Firesign Theatre
bumnote is offline  
Old September 12, 2012, 08:04 PM   #7
big al hunter
Senior Member
 
Join Date: March 12, 2011
Location: Washington state
Posts: 953
What Doyle said, both times. The problem you describe with the barska is eye relief. The distance between the ocular lense (the one you look through) and your eye is eye relief. Better scopes will have more range of relief.
__________________
You can't fix stupid....however ignorance can be cured through education!
big al hunter is offline  
Old September 15, 2012, 10:07 AM   #8
dmazur
Senior Member
 
Join Date: July 5, 2007
Location: Pacific NW
Posts: 1,310
Quote:
MOA is the Minute of Angle. It is the angular degree difference of the center line of the bore to the center line of the scope. The further the distance, the greater the angle.
Here's a link to an interesting discussion on MOA -

http://thefiringline.com/forums/showthread.php?t=31171

...while the above definition of MOA is interesting, it doesn't agree with the accepted definition in shooting (or geometry).
__________________
.30-06 Springfield: 100 yrs + and still going strong
dmazur is offline  
Old September 18, 2012, 06:31 AM   #9
BoogieMan
Senior Member
 
Join Date: April 4, 2012
Location: South Jersey
Posts: 1,287
My 30-06 currently has see-thru mounts on it so that I can also use the irons. from what I understand this would have a negative effect in the MOA. Am I understanding correctly? Or is it just a matter of there being a point were the point of aim and point of impact intersect? It would seem to me that the greater the difference between the center of the scope and center of the bore= smaller "sweet spot".
I woods hunt so I sight in at 100yds and figure I am good between 30-200yds. I think I need to do some research with this particular rifle and see how and where the bullet changes from an upward trajectory to a dropping trajectory.
165 Sierras BT from a 30-06 carbine. Any idea where I should start to look?
__________________
Concentrated power is not rendered harmless by the good intentions of those who create it.
Milton Freidman
BoogieMan is offline  
Old September 18, 2012, 07:50 AM   #10
dmazur
Senior Member
 
Join Date: July 5, 2007
Location: Pacific NW
Posts: 1,310
Quote:
My 30-06 currently has see-thru mounts on it so that I can also use the irons. from what I understand this would have a negative effect in the MOA.
Not directly related. The rifle / load combination have a certain accuracy, which can be measured as a group size in MOA. (MOA is just a short way of expressing accuracy...not related to POA or POI or any measurement on the rifle.) When shot from a bench rest, the accuracy is assumed to be mostly the result of the load and not the shooter.

However, when shooting in the field, issues such as cheek weld can ruin accuracy that was quite good at the bench. So, since see-thru rings can make it difficult or impossible to get a good cheek weld, they are generally considered a poor choice. Yes, this can result in larger groups, but the rifle's "MOA" didn't change.

Quote:
It would seem to me that the greater the difference between the center of the scope and center of the bore= smaller "sweet spot".
The scope has a line of sight, which is straight, and the bullet follows a curved path, the trajectory. These are going to intersect at two locations.

Here are two "runs" of a ballistics calculator -

+---- Bullet Inputs -----+----Atmosphere Inputs ----+-------Sight Inputs ------+
| Caliber: 0.308 inches | Temperature: 59 degrees | Sight Height: 1.5 inches |
| Weight: 165 grains | Pressure: 29.92 inHg | Zero Range: 100 yards |
| G1 BC: 0.397 lb/in^2 | Humidity: 0 % | Look Angle: 0 degrees |
| G1 Form Factor: 0.626 | Density: 0.07647 lb/ft^3 | |
| MZL Velocity: 2700 fps| Wind Speed: 10 mph | |
| | Wind Direction: 3 O'clock| |
+------------------------+--------------------------+--------------------------+


+----------------------------- Program Output ---------------------------------+
Range Velocity Energy Trajectory TOF Drift
(yards) (fps) (ft-lb) (inches) (sec) (inches)
0 2700 2671 -1.50 0.0000 0.00
10 2677 2625 -1.12 0.0112 -0.01
20 2654 2580 -0.79 0.0224 -0.03
30 2631 2535 -0.51 0.0338 -0.08
40 2608 2491 -0.28 0.0452 -0.14
50 2585 2448 -0.10 0.0568 -0.22
60 2562 2405 0.03 0.0684 -0.31
70 2540 2363 0.10 0.0802 -0.43
80 2517 2321 0.12 0.0921 -0.56
90 2495 2281 0.09 0.1040 -0.71
100 2473 2240 -0.00 0.1161 -0.88
110 2451 2200 -0.15 0.1283 -1.07
120 2429 2161 -0.35 0.1406 -1.28
130 2407 2122 -0.61 0.1530 -1.51
140 2385 2084 -0.94 0.1655 -1.76
150 2364 2047 -1.32 0.1781 -2.03
160 2342 2010 -1.77 0.1909 -2.32
170 2321 1973 -2.28 0.2038 -2.63
180 2299 1937 -2.85 0.2167 -2.96
190 2278 1902 -3.49 0.2299 -3.31
200 2257 1867 -4.20 0.2431 -3.68

+---- Bullet Inputs -----+----Atmosphere Inputs ----+-------Sight Inputs ------+
| Caliber: 0.308 inches | Temperature: 59 degrees | Sight Height: 3 inches |
| Weight: 165 grains | Pressure: 29.92 inHg | Zero Range: 100 yards |
| G1 BC: 0.397 lb/in^2 | Humidity: 0 % | Look Angle: 0 degrees |
| G1 Form Factor: 0.626 | Density: 0.07647 lb/ft^3 | |
| MZL Velocity: 2700 fps| Wind Speed: 10 mph | |
| | Wind Direction: 3 O'clock| |
+------------------------+--------------------------+--------------------------+


+----------------------------- Program Output ---------------------------------+
Range Velocity Energy Trajectory TOF Drift
(yards) (fps) (ft-lb) (inches) (sec) (inches)
0 2700 2671 -3.00 0.0000 0.00
10 2677 2625 -2.47 0.0112 -0.01
20 2654 2580 -1.99 0.0224 -0.03
30 2631 2535 -1.56 0.0338 -0.08
40 2608 2491 -1.18 0.0452 -0.14
50 2585 2448 -0.85 0.0568 -0.22
60 2562 2405 -0.57 0.0684 -0.31
70 2540 2363 -0.35 0.0802 -0.43
80 2517 2321 -0.18 0.0921 -0.56
90 2495 2281 -0.06 0.1040 -0.71
100 2473 2240 0.00 0.1161 -0.88
110 2451 2200 0.00 0.1283 -1.07
120 2429 2161 -0.05 0.1406 -1.28
130 2407 2122 -0.16 0.1530 -1.51
140 2385 2084 -0.34 0.1655 -1.76
150 2364 2047 -0.57 0.1781 -2.03
160 2342 2010 -0.87 0.1909 -2.32
170 2321 1973 -1.23 0.2038 -2.63
180 2299 1937 -1.65 0.2167 -2.96
190 2278 1902 -2.14 0.2299 -3.31
200 2257 1867 -2.70 0.2431 -3.68

Strangely enough, the 3" sight height results in less difference between POI and POA (the sight line) at 200 yds than the 1.5" sight height.

You might consider using a 200 yd zero (which is similar to adjusting for a POI 1.5" higher than POA at 100 yds.) Then you are hitting within 1.5" of where you aim all the way to 200. With a 100 yd zero, you are closer to POA to 100 yds, then POI falls off quickly.

In practice, the differences are very small. The main concern, IMO, is that see-thru rings make it difficult to consistently position your head behind the scope. And, unless the scope has zero parallax (unlikely), accuracy will suffer.
__________________
.30-06 Springfield: 100 yrs + and still going strong

Last edited by dmazur; September 18, 2012 at 08:10 AM.
dmazur 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 09:44 AM.


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 0.09190 seconds with 10 queries