GlockTalk.com
Home Forums Classifieds Blogs Today's Posts Search Social Groups



  
SIGN-UP
Notices

Glock Talk
Welcome To The Glock Talk Forums.

 
  
Reply
 
Thread Tools Display Modes
Old 07-31-2011, 20:27   #1
TheBelly
Senior Member
 
TheBelly's Avatar
 
Join Date: Jan 2004
Posts: 1,211
Blog Entries: 4
POA/POI shift between 100yds and 200yds

OK here's the question and it may be a bit long/complicated:

All others thing being equal, and using a 0 MOA base for a .308 Win, will the POA/POI shift between 100 and 200 yds be different? if so, which way?

Will this difference be magnified using a 20 MOA base?



@ 100 yds, the POA and POI are the same, will the POI be higher, lower, or the same at 200 yds? how will the difference be magnified using a 20 MOA base?
__________________
Family Values and Traditions

So 'true'. Nothing 'false' with a dog.
Either they love you, or they can't stand you.
RIP Lilly
TheBelly is offline   Reply With Quote
Old 07-31-2011, 23:56   #2
Zak Smith
3Gunner
 
Zak Smith's Avatar
 
Join Date: Aug 1999
Location: Fort Collins, CO, USA
Posts: 692
The 20 MOA base, provided the scope center over bore center axis is the same, does not change anything about the ballistics. All it does is offset the erector assembly when you have your zero so it has more "up" travel before it "bottoms" (or "tops") out in the scope tube as you turn the turret.

If you have a 100 yard zero, you will typically be 0.4 - 0.5 mils low at 200, depending on your load.

The inclined base does nothing to this.
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 signatures.
.
To view links or images in signatures your post count must be 10 or greater. You currently have 0 signatures.
.
To view links or images in signatures your post count must be 10 or greater. You currently have 0 signatures.
.
To view links or images in signatures your post count must be 10 or greater. You currently have 0 signatures.
Zak Smith is offline   Reply With Quote
Old 08-06-2011, 16:44   #3
TheBelly
Senior Member
 
TheBelly's Avatar
 
Join Date: Jan 2004
Posts: 1,211
Blog Entries: 4
If I zero a scope for the 0 MOA base, but then switch to a 20 MOA base, the POI will be a lot higher, is that correct?

I didn't think that the .308 started dropping between 100 and 200 yards. Or, more accurately perhaps, I didn't realize that 100 yards was the actual highest point of the path of the bullet.

I understand your point about a 20 MOA base giving more 'drop' in elevation to be able to reach out and get the longer distances. I just thought that, given a 20 MOA head start in the upward angle (if the line of sight was parallel to the ground), that the bullet wasn't going to be heading upward still between the 100 and 200 yard marker....

does that make sense?
__________________
Family Values and Traditions

So 'true'. Nothing 'false' with a dog.
Either they love you, or they can't stand you.
RIP Lilly
TheBelly is offline   Reply With Quote
Old 08-07-2011, 11:28   #4
Zak Smith
3Gunner
 
Zak Smith's Avatar
 
Join Date: Aug 1999
Location: Fort Collins, CO, USA
Posts: 692
Quote:
If I zero a scope for the 0 MOA base, but then switch to a 20 MOA base, the POI will be a lot higher, is that correct?
If the mounts were otherwise identical and no other error was introduced-- and you didn't adjust the scope knobs-- yes.
Quote:
I understand your point about a 20 MOA base giving more 'drop' in elevation to be able to reach out and get the longer distances. I just thought that, given a 20 MOA head start in the upward angle (if the line of sight was parallel to the ground), that the bullet wasn't going to be heading upward still between the 100 and 200 yard marker....

does that make sense?
No. There is no head start. It just changes where the erector assembly is physically in the scope. If you have a 100 yard zero with a 0 moa base and a 100 yard zero with a 20 moa base, you have the same zero and the trajectory is identical.
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 signatures.
.
To view links or images in signatures your post count must be 10 or greater. You currently have 0 signatures.
.
To view links or images in signatures your post count must be 10 or greater. You currently have 0 signatures.
.
To view links or images in signatures your post count must be 10 or greater. You currently have 0 signatures.
Zak Smith is offline   Reply With Quote

 
  
Reply

Thread Tools
Display Modes

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 -6. The time now is 23:13.




Homepage
FAQ
Forums
Calendar
Advertise
Gallery
GT Wiki
GT Blogs
Social Groups
Classifieds


Users Currently Online: 770
183 Members
587 Guests

Most users ever online: 2,672
Aug 11, 2014 at 2:31