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5/28/2020 10:18:12 PM
Posted: 1/9/2003 12:20:38 PM EDT
Just doing some playing around with options here.  I have an ARMS#38, with which I use an Aimpoint and ARMS mount.  I had thought about selling the #38 and getting a #40 so I could also mount an ACOG.  But that may not be necessary.  For those of you that know, a lot of the militar have switched to a SIR type interface.  Since it's rail is essentially the same as the #38, do they just mount the ACOG as it it was going directly on the upper?  Does it make any difference that would sit 1/2" higher than intended?  If it doesn't make any difference, I'm not going to change my gear.
Link Posted: 1/9/2003 1:26:51 PM EDT
Link Posted: 1/9/2003 6:27:33 PM EDT
I have a SIR with ACOG mounted on my Bushy. I used the ARMS #19 ACOG mount. I also have the ARMS #40 BUIS installed. I like the setup and don't have any problems with the slightly higher cheekweld. If you do get the SIR, make sure you get the ARMS #40. It fits perfectly on the flatop of the rifle with the SIR butting up against it.
Link Posted: 1/9/2003 6:48:00 PM EDT
The ACOG mounted and issued in the SOP MOD kit, mounted in the issue carry handle is higher that when mounted on the SIR. When the ACOG is mounted via the throw levers on the SIR, it is about 3/8" lower than when in the carry handle. How anyone can think it might be too high on the SIR hasn't been familiarized what has been optimum and issue, or to the fact that optics for military operation are better utilized better up than way down low./ Just look at the hts. used by US, Russian, German, IDF, Canadian, troops, etc. of scopes measured off the center line of the bore. THe Ht. of the SIR puts the optics at optimun ht. and alsop allows a more stable platform as it allows you to use lower more stable rings, than coming off the naked flat top.
Good Shootin, Jack
Link Posted: 1/9/2003 7:49:50 PM EDT
Link Posted: 1/10/2003 1:03:39 PM EDT
I'm by no means an expert on this topic, but what about height-above-bore?  For any of the ACOG series w/ ranging reticles, height-above-bore can really become an issue as the distance to target increases.  According to Trijicon, the scopes are calibrated for certain heights-above-bore.

Take the NSN, for example.  It's calibrated for mount directly on the M4 flattop.  What does the SIR do to that calibration?

Same for TA11, TA31, both of which (according to Trijicon) are calibrated for height-above-bore when mounted on a standard A2 carry handle.

I'd love to see the ballistic comparison for various heights-above-bore w/ the ACOG scopes.  For those tech-minded guys w/ lots of time, it's a good extra credit project.  Make particular note of POI beyond 200 meters.

Link Posted: 1/10/2003 3:48:52 PM EDT
bore height should be a BDC issue.

height above the bore axis has the most to do with shot dispersion (closer the sights are to the bore- the closer your shots will be at all ranges to the target {IE shoot a M-4 at 3ft and then shoot a enfield bolt gun at 3 ft (the M-4 will hit about 2 inches low while the enfield will be less than half of that.

THIS IS MAGNIFIED when the sights are mounted on the carry handle as TILTING then becomes a serious issue [shoot this setup on an accurate Ar halfhazardly and you will see half-moon groups appear on the target.
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