Ever since I got my Arsenal SGL21-61, the rear sight has been tilted to the left. IOW, the right side was higher than the left, throwing my shots left no matter how far I cranked the post. I thought at first it was a bad rear leaf. I ordered a RPK rear sight from Soviet Military dot com, and slapped it on. Sight was still tilted left. Well, I had it at work showing it off to one of the guys in the fab shop. He looked at it, and said his WASR was the same way. We took it in, did a few measurements, and sure enough the entire rear sight base was off 1.5mm left. Doesn't sound like much, but equates almost 2-3" at 100 yds. Here's how he fixed it.
1. Field strip the rifle and remove the lower handguard.
2. Drive the pin out of the rear sight base from right to left. Mine had a tapered pin.
3. Clamp the receiver in a padded vise. Use just enough clamping force to hold the rifle steady
4. With a soft face mallet, move the RSB until it is center. It takes a little force to move it, but once it moves, it moves. Both sides should be square with the trunnion.
5. With a small file, drill bit, or end mill, redress the notch in the barrel. You will see the "rise" through the pin hole. Dress the side with the rise ONLY, or bore for an oversize pin entirely, boring from the side with the rise.
6. Gently drive the pin back in from the side you dressed. If you have a tapered pin, the taper will compensate for the dressed area.
7. Touch up paint if desired.
In the pic, the red arrows are the edges that should be square. The gap at the green arrows should be the same, or fairly close, on both sides depending on the machine work. You'll notice mine is touching on the right side. My RSB was also off because the hole for the barrel attachment point isn't bored square. The RPK sight helps compensate for this.
And here's the unissued RPK sight I got.
You do lose the 300M Battle Setting with this sight, but it's a small sacrifice to have the windage adjustment. The sight also sits slightly higher than the stock sight, so slight adjustment of the front sight post is in order. Now maybe I can properly zero this thing.
ETA: Got it out to the range, and re-centering the RSB made a huge improvement. Now, the rifle is dead on, meeting the Ruskie "16 in. circle" spec out to 200 yds. I also learned that trying to make sighted shots after a double mag dump is a toughie. Nature of the beast, I was told. Here's a pic of my target. The backer is 16"x22" and the paper plate is 7". Range Fudds give you dirty looks shooting B27's at that distance, so I improvised.
As you can see, the hotter the barrel got, the more the spread. 2 shots landed on the left side of my AR target(and, yes, I know my AR sights are off high for 100 yds). This target was shot after dumping 60 rounds and having a barrel too hot to grab.
