Mirror alignment using 12 ga shot gun shell

So I’ve been frustrated with the normal method of aligning mirrors from tube to lens while burning tape along the way. You can easily get it to work in one spot but more difficult over the entire range.
I noticed an alternate method of replacing the lens with a laser pointer and align from lens to tube without burning tape. My third mirror/lens has a lens tube that just happens to be at the same diameter at a 12 ga shot gun shell. Amazon sells laser target shells that fit perfectly where the lens tube goes. Pictured showing red beam against mirror three.
I’m not going to get into the entire process but it worked perfectly. What was really fortunate is that the laser beam bounced off the laser tube cover. Not sure what it’s made of but not glass. And reflected back to mirror three allowing me to perfectly align mirror one.

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There’s at least one commercial version of this out there… replaces the lens tube I think…


To get a good alignment, you have to go from the tube to the table.

The problem is there is no way to align your led pointer to that of the tubes beam… for this to work, they need to be square in all three dimensions.

It’s been debated, quite frequently, how useful this technique is…


Generally if you’re having issues with alignment, something in the process or thought about how it’s working isn’t correct… this should become more simple the more you do it…

I’ve never complained about success, so if it works for you, great…


And I’d ask you post a link to the 12g laser you used… I can thoroughly understand frustration :wink:

Nice touch, using the 12g laser… I’m sure the 12g laser is lower cost… ?

:smile_cat:

Thanks for the feedback Jack.
Here is the Amazon link:

MidTen Bore Sight 12 Gauge Laser Red Dot Boresighter with Three of Batteries Amazon.com

At laser parts go this is a great deal and it’s a solid brass well made body that just happened to fit my setup perfectly.

What makes this method work so well is that my laser tube has a front cover (deep inside the opening) that reflects the pointer beam. So traveling from mirror to mirror are TWO red beams. The beam traveling to the tube and a reflection of that beam off the tube landing back on that third mirror.
So after the beam is centered and stationary over a range of motion on each mirror you simply adjust the first mirror the drive the reflected beam to the center of the third mirror. Your reflecting the beam back on itself.

Again it works flawlessly and very quickly. I’m surprised there is only one commercial unit available. I test fired the laser on to tape attached to the end of my nose cone (my normal alignment check) and it’s spot on in all bed locations. Also ran cutting tests.

I think I’ve seen more than one type out there.

It’s great it’s working for you…

Thanks for the link… :wink:

Good luck

:smile_cat: