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1/25/2018 7:38:29 AM
Posted: 3/17/2006 6:19:56 AM EST
[Last Edit: 3/17/2006 10:07:49 AM EST by weasel_2002]
I usually don't post alot because I'm browsing and absorbing other's information and views, but since I often get my ideas from seeing how others do certain things, I thought I'd post a sample of a recent modification which may enlighten others.

I read all the good/bad views about an adjustable BUIS. So when I picked up a RRA Dominator Mount on trade to be used for a new Eotech-equippped carbine build, I couldn't decide if I really needed/wanted an elevation adjusted rear sight plus I always have liked the sight adjust on my A1/C7 upper. So I morphed an A1-Style RRA Domininator Mount.

The only modification to the original RRA mount are two thru tapped 4-40 holes on the main frame the under the A2 upper sight block. Other than that no modifications have been done and the sight can be converted back to OEM style in about 10 minutes, if your good with a punch and bunch of ball bearings/springs.

The only parts needed were an A2 slight block, an A1 windage drum, an A1 windage drum detent and (2) 4-40 screws, which I had luckily stripped from other projects. The A2 sight spring was slightly modifed to provide the spring force for the A1 drum detent and the A2 windage screw was cut a little shorter to match the hub of windage drum. A little layout work and mill work and it was an A1-Style RRA Domininator Mount.



Link Posted: 3/17/2006 7:27:20 AM EST
Could you have done this without removing the elevation drum? I like the A1 windage much better, but don't have any issues or concerns with the elevation drum.

Thanks for the input.
Link Posted: 3/17/2006 8:09:26 AM EST
[Last Edit: 3/17/2006 10:17:07 AM EST by weasel_2002]
Yes, you could modify the A2 sight block and keep all the elevation adjustment. That was my original intent but the extra A2 sight block I had was a DMPS and had a different thread pitch and height as compared to the RRA A2 block so it wouldn't have worked. I figured I could modify the original RRA A2 slight block down the road now that the guinea pig test was out of the way.

The modification steps involved counter boring aboput 0.030" by 0.375" diameter into the windage drum sight of the block. This removed most the A2 adjustment dimbles and was needed to get the correct distance from the shoulder of the windage screw to the windage drum roll pin cross hole.

The only major issue was that you do not have room to drill the 0.125" diameter hole for the drum detent spring and plunger. It needs to be on the circular path around the drum but if you drill at the lower portion of the block you break thru to the relieved area where the aperture spring rests. There was no great way to hold the spring and plunger in so I eliminated the detent spring and used the aperture spring to help provide the required spring force for the detent pin. I drilled the detent hole, 0.125" diameter, back into the sight block about the length of the detent pin, 0.235" I believe. This hole broke thru the relief area of the aperture spring area and left a groove about 1/2 the diameter of the hole. I then cut a 45 degree angle of the original spring end of the detent pin and this rides under the corner of the aperture spring. I then cut a slit in the aperture spring to provide a slightly lower spring force to the dentent pin as it hits the 45 degree area of the pin. It's like the multiple fingers on the sear spring of a 1911 pistol. This seems to work good. Nice tight spring force and no way the detent pin can be removed without removing the drum first and the spring force to the aperture is minimally affected. Obviously, time will tell if it works as planned.

Hope this helps explain it a little, in the long-winded fashion. hanks
I modified the above picture to show the modified components. Another thought was that you could change the design a little to allow modification to be completed with simple drill press, or hand drill if your really good.

You could eliminate the need to counterbore the sight of the sight block by remove material from the back side of the sight drum. This amount would be dependant on the thickness across the outside ears of the sight block. You would think they all were the same but look at all the different thread pitches. If you couldn't remove quite enough material then the cross hole in the windage adjustment screw would need to be relocated. You can leave the A2 Screw length alone but it sticks out past the A1 sight drum about 1/8".

Then, the only drilling mod is the hole for the drun detent. Careful layout and manipulation could get this done without the use of expensive tools. The angle on the detent pin could be filed with a little trial and error.

The slit in the aperture spring is simply cut with a thin diameter cut-off wheel in a rotary tool.

Food for thought ***
Link Posted: 3/17/2006 8:50:50 AM EST
This is slick - good idea.

My vote for best Optics Forum Post this year.
Link Posted: 3/17/2006 9:12:00 AM EST

Originally Posted By Forest:
This is slick - good idea.

My vote for best Optics Forum Post this year.


Link Posted: 3/17/2006 9:43:01 AM EST
pretty neat...

Link Posted: 3/17/2006 2:25:09 PM EST
I hope RRA is paying attention.
Link Posted: 3/17/2006 3:50:12 PM EST
Link Posted: 3/17/2006 5:52:32 PM EST
nice bit of fab work there!

Funny, I always thought YHM should make their EOtech riser intergal to there BUIS
(Since they have an A1 flip-up) but I love the stoutness of yours!
Link Posted: 3/18/2006 2:12:34 PM EST
Great work! How about a same plane aperture model?
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