Go Back   CMP Forums > CMP Sales > M1A/M14
Register FAQ Members List Calendar Mark Forums Read

Reply
 
Thread Tools Display Modes
  #1  
Old 05-01-2020, 02:30 PM
Pirate69 Pirate69 is offline
 
Join Date: Nov 2009
Location: Greenville, NC
Posts: 44
Default Re-purposing a 3rd Gen Scope Mount

Bought a used mount years ago and finally decided to mount it. Running into some problems. For some reason it is shooting extremely high at 100 yds. Was able to adjust the mount windage and get it on paper but it is shooting at least 3 feet high at 100 yards with the scope elevation bottomed out. Scope mounts look good (installed level) and the two mounting bolts line-up proper.

Has anyone seem a problem like this before? Thanks in advance for any suggestions.
Reply With Quote
  #2  
Old 05-03-2020, 08:51 PM
M14 M14 is offline
 
Join Date: Jul 2011
Location: south mississippi
Posts: 835
Default

What receiver maker?
What barrel maker?
What barrel length and profile?
What scope?
What rings?

I assume you mean an SAI scope mount from your gen 3 reference?

I have seen this before but not quite that high. The guy was using ring inserts that are adjustable and had them installed the wrong way. Also, what is the center of the scope height from the bore centerline?
Reply With Quote
  #3  
Old 05-05-2020, 07:42 AM
Pirate69 Pirate69 is offline
 
Join Date: Nov 2009
Location: Greenville, NC
Posts: 44
Default

What receiver maker? SAI

What barrel maker? SAI

What barrel length and profile? 22" SS Loaded Model

What scope? Cheap Chinese scope; but proven to hold accuracy and adjustment. 2.5" above bore. Another scope aligns the same way.

What rings? Unknown, set of SS Weaver type that I had in my drawer.

Yes, SAI 3rd Generation Mount.

What I do know at this time. Checked barrel, mount and scope top level relative to each other. Top of mount is +0.5 degree from barrel. Top of scope is +1.5 degrees from barrel. Think this is the problem. Need to figure out how to shim the scope.
Reply With Quote
  #4  
Old 05-05-2020, 08:13 AM
M14 M14 is offline
 
Join Date: Jul 2011
Location: south mississippi
Posts: 835
Default

Quote:
Originally Posted by Pirate69 View Post
What receiver maker? SAI

What barrel maker? SAI

What barrel length and profile? 22" SS Loaded Model

What scope? Cheap Chinese scope; but proven to hold accuracy and adjustment. 2.5" above bore. Another scope aligns the same way.

What rings? Unknown, set of SS Weaver type that I had in my drawer.

Yes, SAI 3rd Generation Mount.

What I do know at this time. Checked barrel, mount and scope top level relative to each other. Top of mount is +0.5 degree from barrel. Top of scope is +1.5 degrees from barrel. Think this is the problem. Need to figure out how to shim the scope.
Yes, a small difference there is greatly compounded at distance, for example: I do a lot of 1000yd. Shooting and I needed a 20 MOA rail under my Athlon (inexpensive ) scope to have enough adjustment to reach the target when dialing it.

I ordered one and when it arrived I measured it. The back was 1/8" taller than the front in only 5 1/2" of overall length. I'm not a math major and I couldn't believe it would work with that small change. It did.

I'm not familiar with SAI mounts, but are they Weaver as well? If they are picattiny and you are using Weaver rings, this could also cause problems. The two are not compatible, no matter how many vendors plaster all over their websites that our product will fit Weaver or picattiny rails. The blueprints are different.

I assume with a loaded that it has a NM reamed flash suppressor? I ask because one of my customers had bullet strike at his, which caused high impacts. He was using an original, non-reamed one that was not only bent, but loose. May want to check for signs of copper residue there.

One last thing, not meaning to insinuate anything, but check to make sure you are adjusting the scope the right way. Make certain elevation turned counterclockwise is up and windage turned clockwise is left. Try taking everything off the scope that you had dialed, going back to center both ways. Count all your elevation clicks and center the scope to half that, same with windage. After getting your degree discrepancy fixed, try shooting it at 25 yds, meters, whatever, just close.

Let us know how it turns out, it may help someone else with similar problems if we can nail this one down.
Reply With Quote
  #5  
Old 05-05-2020, 12:24 PM
Pirate69 Pirate69 is offline
 
Join Date: Nov 2009
Location: Greenville, NC
Posts: 44
Default

"I ordered one and when it arrived I measured it. The back was 1/8" taller than the front in only 5 1/2" of overall length. I'm not a math major and I couldn't believe it would work with that small change. It did."

The 1/8" rise on the 5.5" rail is a 1.3 degree rise. It equates to a 817" rise at 1000 yards. Looks like I am seeing a 0.3 degree rise with my scope mount. My ring contact points are 4.5" apart on the mount.

If I can get a 0.03" shim between the mount and the front ring, I can lower the impact 22" at 100 yards. Since I am 18.5 inches high, at 100 yards, with the scope elevation bottomed out, this should give me 3.5" low at 100 yards with the scope elevation still bottomed out. A little room to move it off the bottom. Sounds good on paper, right? Lets see if I can shim it.

Already performed the other checks. Shot at 25 yards at time scope was mounted. First indication that I had a problem. Not seeing any copper on flash suppressor.

Last edited by Pirate69; 05-05-2020 at 03:01 PM.
Reply With Quote
  #6  
Old 05-05-2020, 08:38 PM
M14 M14 is offline
 
Join Date: Jul 2011
Location: south mississippi
Posts: 835
Default

Good deal, sounds about right. Thx for the trig touch up.
When I was using shop mills and lathes way back I could stay fresh on my math skills, but like anything unused, it suffers. Let me know how the plan works in practical application.
Reply With Quote
  #7  
Old 05-06-2020, 06:46 AM
Pirate69 Pirate69 is offline
 
Join Date: Nov 2009
Location: Greenville, NC
Posts: 44
Default

Will do. It will be a few days before I can get back to this project.
Reply With Quote
  #8  
Old 05-14-2020, 09:22 PM
Pirate69 Pirate69 is offline
 
Join Date: Nov 2009
Location: Greenville, NC
Posts: 44
Default

I think I have found a solution. I glued a 0.062" SS rod to the top of each side of the front of the mount rail. This gave me just enough clearance for the mount claw to still grab the bottom of the mount rail. This change in elevation of the front scope mount allows the POI and POA to match without the scope elevation to be bottomed out.

Seems to be a solid mount . After zeroing at 100 yards, I shot a 10-shot group at 300 yards. Ten shot group of 8". Eight rounds within a 5" circle. This was shot with 168 grain Nosler CC; not milsurp.

Satisfied so far.
Reply With Quote
  #9  
Old 05-22-2020, 02:49 PM
tanker trash tanker trash is offline
 
Join Date: Dec 2009
Location: Burnet ,Texas
Posts: 332
Default

reverse the scope rings. of course then it may shoot low.
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



All times are GMT -5. The time now is 06:27 PM.