Anyone have any experience changing out the rear sight aperture?  I have a ghost ring sight on my Marlin 45-70 that is just too big for my tastes.  I'd like to switch it out for something smaller to improve accuracy.  Is this even possible?

I have one of the BAR11... sights on my Benelli M4, I replaced the ghost ring with a tritium ghost ring.  Replacing it is surprisingly easy, just back out the windage screw and the sight lifts right out.

According to their website, your sight comes with a **D4 standard diopter.  They also make a **D2, **D3, **D5, and **D7 diopter for it as an option.  I'm guessing that the **D2 and **D3 have smaller apertures while the **D5 and **D7 have larger ones.  I'd contact their American distributor at (941) 485-2579 to see what the sizes of the other apertures are and how you can buy a smaller one.

To get an idea of what size you might want, I'd suggest a simple test rig to try different sizes.  You can make it by taking a piece of black electrical tape and covering the aperture on your sight then using a nail of the appropriate size, punch a hole in the tape.  That way you can see what the sight picture through the smaller aperture will look like on your rifle.

I find that peep sights mounted on the rear of the receiver or tang sights on my leverguns and used for precision shooting usually work best with a .042" - .060" aperture assuming that your eye is held close to the rear sight. The National Match apertures on my M1 Garand and M1A are .0520" (I chose the smaller option on them as a .0595" aperture as standard) while the target aperture on my Mini-14 is .042".  For comparison, the aperture size on a standard M1 Garand / M1A rear sight is .069".  If you want it for hunting, you'll likely want to go a bit bigger than the target apertures, say .070" - .080".

Awesome.  The D7 they make is 2mm or 0.78", I'm going to try to see if I can purchase one.

I just put one on order, they are $19. The D7, 2mm, is the only one that is a different/smaller size. The other options are all the same size and all seen on the website.

That sight looks nice.

Smaller means less light gets through and a darker image.

Minor technical correction - 2mm is 0.079", not 0.78"  (which would be very large for an aperture, )

Exactly, what we need!

Mine are on a deer gun and I am guessing the 45-70 is also. The standard aperture is great for night time tactical CQB, it's VERY large. No so good for deer hunting in the daytime!

Take a look at the Ranger Point ones. Absolutely love them on my new Marlin 94.

https://www.rangerpointstore.com/cloverleaf-adjustable-aperture-peep-sights-marlin-and-henry-brass-black-stainless/

And look at the Skinner rear sights, especially the "winged" version.    http://www.skinnersights.com/tactical_sights_14.html



It's shipped with a .096" aperture but you can get other sizes: