A friend recently dug out a NIW M261 conversion kit that had been in his safe for a number of years. The unit is unfired and is complete with three 10 round mags still wrapped in foil paper and the original unopened operator/maintenance manual dated 1978.

How well do these work in full auto as compared to my Ceiner kit?
Will this conversion kit run using the Ciener 30 round mags I own?
Does this kit have any value as a collector item, or is it simply a nice accessory?  

1.  they're not made for full auto fire
2. no, they won't accept the mags
3. no collector value

SARCO sold the setup exactly as you describe as recently as 1999 for $125. (That's when I bought mine.) Now they say they have discovered "a few more" and are selling them with two mags and no manual for $175.

No particular "collector" value, but they are valued as shooters. They work well and nearly everyone who has one seems to like it. I like mine.

Don't you have to have a 1/12 twist barrel ala A1 to get decent accuracy out of any of those .22 Kits? I'd assume a 1/9 or 1/7 would just spin those 40gn rounds into oblivion.

Thanks for the speedy replies and information! According to the invoice, this one also came from Sarco and was priced at $124.75 plus shipping. I've got a full auto Ciener kit so I have no use for this conversion if it's semi auto only and the 10 round mags are almost worthless except for use in semi auto fire. I suppose in the time it's taken me to inquire about this kit, I could have retrieved mine from the safe and compared the two side by side. I was reluctant to remove the M261 from it's packaging in case this NIW unit had some collector value.

Quoted: Don't you have to have a 1/12 twist barrel ala A1 to get decent accuracy out of any of those .22 Kits? I'd assume a 1/9 or 1/7 would just spin those 40gn rounds into oblivion.

Nope.  My 1/9 RRA barrel does fine with .22s through an M261.  The little bullets are solid; they don't disintegrate as a jacketed bullet can, though they may change shape in the process of moving from muzzle to target.  At 50 yards the holes are still the same size as .223 bullets make.

A 1/7 can spin a thin-jacketed 40gr at 3300fps+ apart.  The .22LRs at <1000fps hold up just fine.  Accuracy seems to (usually) be better from 1/12 barrels though.

Accuracy with .22 conversions seems to be hit or miss. I have one 1:12 barrel that shoots them superbly, one that shoots them pretty well, and one shoots some tight groups and some turds. When I tested my unit in a 1:9, accuracy was pretty bad (compared to real .22 rifles) with most brands, but others here have reported decent results with 1:9 and even 1:7 barrels. All depends on the luck of the draw, I guess, as well as what you consider "accurate enough."

Based on what I've seen and read, though, I'd say your chances of getting usable accuracy are better with a 1:12 barrel than with a quicker twist.

I can get 3/4" groups at 25m with a 1/9 barrel shooting Winchester Dynapoints 40gr.