Yesterday I shot about 300 rounds with BDM and the originall 10 rd insert mags.  I got about 4 or 5 stove pipes and 2 or 3 FTF with the rounds diving low.  The thing I'm most worried about was that it doubled 3 or 4 times.   None of the malfunctions really occured with the same mags so I'm thinking the kit needs to be tuned.  I was using Federal bulk and originally was running it a little dry then added some oil during shooting.

I have the M-261 kit in a 11.5" upper w/ a 5.5" flash hider.  I'm using a DPMS hammer and standard springs.  I polished the barrel on the M261 just like the tutorial in the Spikes Industry forum.  The barrel doesn't have a gas port and was a 1 in 12 A1 barrel cut down for me by KKF.  The rifle is my dedicated 22LR set up so it only needs to function with the M261 and not with 556 rounds.  

I was thinking of replacing the hammer spring with a reduced power spring.  Will this spring help with the doubling and will it cause light strike problems with the DPMS hammer?  Should I cut the 'tail' off the hammer or replace it with a speed hammer?

Any help is appreciated.  Thanks!

It should shoot quite well with the barrel setup you've described.

There's a post sticky'd above about M261 Mags that may give you some insight. If you haven't already been there. I've never had much luck with reduced power springs for me they usually leave light primer strikes but it may work for you. I sold all my M261's and stick with the Atchesson Design (Spike's/Ciener/CMMG) because I have found them to be so much more accurate (JMO). The M261's that I had were 100% functional at feeding Federal Bulk after I did the minor mag mod to the BDM Mags. Never had doubles.
Good Luck

Check to see if the bolt is dragging on the mags.

My 261 runs best with CCI Standard, Federal Auto Match might be good too  (if you don't get the same bad lot I ended up with).  I prefer to run SV in my 261 and Air Force conversions as I believe that is what they were set-up to use.  Some lots of Federal bulk, especially lately, have been very inconsistent.

YMMV

Check the back button screw holding that little plate on there.  Not sure what it is called.  Had mine loosen up after a couple thousand rounds causing multiple FTF's and left me scratching my head.  Someone else also mentioned to me about that little tab getting flattened out would cause feeding issues too.  Also check the firing pin channel for gunk and build up.  That gray paste seems to work itself into everywhere shooting .22's.
HTH
JestersHK

I checked the plate and it's good.  I finally decided to break it down as much as I could.  The only thing I couldn't figure out was the extractor.  The firing pin wasn't too bad but there was some crud on the M261 barrel.   I cleaned it up and put it back together but I noticed how rough the machining is on some of the parts.  I also found a little rust under the rail/bar.  I did end up replacing the hammer spring with a reduced strength spring.  Hopefully I can get to the range soon to try it out.

Anyone have a link to an online manual for the M261? - Thanks

I downloaded a PDF from Oly's site.  Their rim fire adapter is a identical clone of the original M261 kits.  Its about halfway down this page.
http://www.olyarms.com/index.php?option=com_docman&task=cat_view&gid=22&Itemid=30
Hope this helps and good luck.
JestersHK

Try different ammo and clean/lube the kit good to start.  Carry a can of brake cleaner and CLP to the range with you and rinse/relube every couple hundred rounds.  Try different host mags for the inserts - I always have problems with 20's, but USGI 30's in good condition work well.  Dont have any BDM mags yet, so cant help you with that one.

I had really bad problems with mine at first. My chamber insert blew in two!

I had double, triple, get but rape in federal prison full auto issues really bad to the point were I stopped shooting it.

My fix was to order replacement springs from Compass Lake. I cut a spring down about 3/8". No more slam fires!

Feeding was a problem but not as bad. I had to tweak my Black Dog mags a little bit and they had to be broken in really good.

Now after about 2K+ rounds of pain in the a@@ it has been 100%.

Do not clean the surface of your .5.56 chamber, and do not clean the outside of your 261 chamber insert. The build up helps prevent blow by and helps keep the pressure up.
I almost got to the point of chucking up one of my inserts into a lathe and turning it down on the chamber face shoulder to help it form a better seal. I also thought about adding o-ring groves and o-rings.

Stay away from the hot stuff or you risk splitting your adapter.


Samuel

If only we could get Spikes to churn us out a couple of their nifty oring fitted chamber adapters for our M261 kits.  The stars would align and probably clear up a few issues with these kits.  Has anyone compared the CLE chamber adapter to the Oly or original M261 unit?  On my Oly kit there is not enough material on the chamber adapter to put a nothc or 2 to support a oring me thinks

Compass Lake used to have the extra barrels/chamber inserts for sale.  They use their own barrel that had the chamber adapter built in and didn't have a use for original M261 inserts.  I bought a few as spares a while back.  I think they still have them for around $20 if you wanted to experiment to get an O-ring on.

I checked their website for extra recoil springs but couldn't find them.  Does anyone have a source for the recoil springs or extra firing pins?  Sarco has the other parts but not those two parts.

Compass Lake has everything. They have their own firing pins. I bought two but they told me I should never have a problem and was told one will never wear out. I bought three inserts 2 firing pins 2 extractors 4 recoil springs 2 extractor springs 4 chamber insert pins, 4 little spring plates, and a guide rod a couple of years ago. Total was like $100.



Samuel

Sarco still offers spare parts. "Barrels" are $75.
There's a "support kit" with some springs and things for $26.

FWIW, Sarco's "Spares Kit" gives you more than the listing says.  I've ordered 4 of them now, and it's true of all of them.

Here's a pic of the latest kit I got from them (just last week).  Notice the recoil spring.  It's not listed separately anywhere on their site.



Note: that's not rust on the extractor, just a reaction to the flash.