I'm wondering what ammunition is recommended for an SLR-104 so that the rear sight is calibrated at the various distances.

7N6 preferably.

If you can't get a hold of any 7n6, just use 55g bullets

there are several:
surplus which requires proper cleaning
http://www.sgammo.com/product/surplus/1740-round-crate-545x39-fmj-7n6-surplus-ammo-russian-made-1974-75

new, non-corrosive
http://www.sgammo.com/product/wolf-performance-ammunition/750-round-case-545x39-fmj-60-grain-steel-case-polyformance-wpa-w

http://www.sgammo.com/product/wolf-performance-ammunition/1000-round-case-545x39-60-grain-fmj-wolf-ammo-old-stock-2010-mfg

http://www.sgammo.com/product/silver-bear/750-round-case-545x39-fmj-60-grain-silver-bear-non-corrosive-ammo

they also have a deal on mags
http://www.sgammo.com/product/surplus/10-pack-30-round-ak-74-545x39-military-surplus-magazine-bulgarian-factory-21-black-n

I love this stuff.  Very easy to clean.  A good alternative to 7N6, which is not as easy or cheap as years ago.  

http://www.ar15.com/forums/t_4_64/155262_My_first_time_using_Red_Army_Standard_5_45__pics_.html

I've read some reviews online that the 55 gr rounds are too short and cause feeding problems.  

My objective is to find a round other than 7N6 that will allow me to use my rear sight at the various settings.

Edit:  After playing around with the ballistics calculator at handloads.com (http://www.handloads.com/calc/) it seems like there is hardly any difference between 60 gr. at 2800 fps and 53 gr. at 3000 fps, at least for my purposes.  I'll probably just end up picking up some 60 gr. ammo.

Compared to the other options, I would say silver bear is your best bet.

I've used most of the Barnual stuff;  WPA 60g  FMJ, WMC 60 gr FMJ, Silver bear 60 gr FMJ and the WPA 55 GR HP and have had 0 issues.  Also, I have used the golden tiger with the same results.

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If you can't get a hold of any 7n6, just use 55g bullets

I've read some reviews online that the 55 gr rounds are too short and cause feeding problems.  


That applies to 5.45 AR uppers.  Never had any problems with 55 gr. (which were HP & SP) in any '74 platform.  Bulgarian, Romanian, Polish, Saiga, etc.