Earlier this year I bought an Olympic Arms Partner 22 upper from Midway USA. I wanted a dedicated upper that closely replicated the A2 style carbine upper I had already.
I had to get the tools out straight away because the Oly upper receiver lugs didn't quite match the pin spacing of my Stag Arms lower. I enlarged the hole through the lug for the takedown pin just enough to get the upper to mount onto the lower. I also switched to a DPMS hammer so there was no notch to interfere with the 22 bolt.
For a while the mean rounds between failure was dismal.
Problem #1 they put a phosphate finish on all the internals. The surfaces hold onto the waxy fouling generated by 22s and bog down the kit. Polish everything (breech, bolt, firing pin, rail) to minimize the build-up of crud where parts contact each other.
Problem #2 the firing pin travel is too limited. Obviously they want to keep the end of the pin from peening the breech. The pin was not making a deep enough impression to reliably fire the ammo. I relieved the shoulder on the firing pin to allow more travel but not so much that the tip could go beyond the impact face of the bolt.
Problem #3 The headspace was a bit too generous which contributed to the light strike issue. Since the mouth of the chamber is chamfered, the rim can sit pretty deep in the breech.
To fix the headspace, I ground some material off the impact face of the bolt and polished the bolt and breech faces.
Problem #4 The bolt interfered with the BDM magazines. I had to relieve a spot on the underside of the bolt and soften the leading corners of the rail where it meets the bolt face. The corners when sharp were marking up the feed ramp that's built into the magazines.
Problem #5 There is a wire component of the bolt called a cartridge retainer. It is supposed to work opposite of the extractor and keep the shell on the bolt face until the ejector can kick it clear. The one that came with the upper didn't do this very well and made manual extraction troublesome. I mothballed the original and bent up a piece of music wire into a similar part but positioned the bend so it would keep the shell where its supposed to. I had to reshape my replacement wire several times to get it to work properly but it really does the job now.
Problem #6 The extractor was not grabbing some of the shells. Not knowing what would run this upper I fired some ammo that didn't even cycle the bolt. Manually retracting the bolt via the charging handle wasn't always effective at clearing the chamber. The extractor was sharp enough but where the extractor cut met the chamber, it wasn't blended well enough to allow the extractor to really grab the rim. A few careful licks from a needle file at the extractor cut put this right.
Problem #7 The M261 BDM magazines that work with this upper have an integral feed ramp that only works with some bullet profiles. The Winchester 555 hollowpoints would nose down and snag inside the magazine. Reshaping the feedramp (on each magazine) seemed to be the best way get a smooth transition to the mouth of the chamber. No more nose down or nose high jams.
So after all that, the upper can handle Federal Bulk (works great), Remington Golden Bullets, Win 555 (sometimes too weak to cycle), Win Xpert (works but fouls quickly).
These aren't the greatest photos but they should give a fair idea of what's going on. Some of the notes are redundant but shown from different angles:
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Originally Posted by Wildcat
in several places now. There were some other minor annoyances that required attention but what I posted are the basics of what it took to get this one running. Definitely not for the faint of heart.
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