Tuesday, January 29, 2013

Conversion Kit (Caliber .22 Rimfire Adapter) M261


Sometimes a person gets lucky.   Sometimes, rarely, it's a special kind of good luck that keeps a man smiling the rest of the day.  Yesterday was that day for Carteach.

Perusing the local Craigslist, what should appear in the 'sporting' section but this.... an AR rimfire conversion kit!

Not just any, but an original 30 year old US army M261 conversion kit, with no less than three magazine inserts, and the operator manual as well.   Yes, I bought it.  I would have bicycled through three feet of snow to be there first, cash in hand.

There are any number of rimfire conversions on the market for the AR platform, and even more rimfire versions of the rifle itself.  Not only are such pip-squeaking shooters a lot of fun, but they make excellent training aids.

The US military is not unaware of this.  They have been buying rimfire rifles and rimfire conversions since the early 1900's, taking their cue from both the British and the Germans who did exactly the same thing.  Today, an early rimfire conversion for a German Mauser, in it's original case, is an exceedingly rare collectable.  The rimfire versions of the full sized military rifles, only slightly less so.

The .22lr chamber, which inserts into the 5.56 chamber
Given the M-16/AR-15 family of rifles already having a bore of the correct size to handle .22 rimfire bullets, the chore of building a rimfire conversion for it is really quite easy.  All that's needed is something that replaces the centerfire bolt, and extends far enough into the 5.56x45mm chamber to give a rimfire cartridge a home.  Also, a magazine compatible with .22 Long Rifle to replace the one fitted to .223 sized cartridges.

Upper, and AR-15 bolt.  Lower, the M-261 conversion bolt
The recoil of the rimfire cartridge is slight enough that a simple blowback action is sufficient, and both bolt and recoil spring can be housed in the space normally taken up by the centerfire bolt alone.

To use the US Army conversion kit, the rifles centerfire bolt is removed (10 seconds), and the rimfire bolt is slid home in it's place (another 10 seconds).  That's it.... the rifle is now ready to shoot inexpensive rimfire ammunition instead of full power 5.56 centerfire ammo.  Simple.

The Army magazine insert, ready to be installed.
The magazines..... slightly less simple.  Not difficult, but still taking a moment or two to prepare.  This difference is what separates the Army conversion from the Air Force version of the same kit.  The Air Force model uses special .22 long rifle magazines sized to fit the AR receiver, and the Army model uses 10 round magazine units that insert into 5.56mm AR magazines, using the centerfire magazines as adapters in a way.

To use the Army style rimfire conversion magazines, one is simply inserted into the top of a standard magazine, depressing the follower and spring, and then slid back home under the standard magazines feed lips.   That's it..... a standard 5.56 magazine has now been converted into a rimfire magazine.

In use, the M-261 conversion kit seemed problematic.  It's quite ammunition specific, feeding some and not others, and firing some and not others. 

Once the unit was stripped and given a thorough lubrication with magic unicorn tears  (That's for another article...), the unit began to feed quite reliably.  Firing uniformly was another story.

Note the size of the firing pin!
The issue seems to be the massive firing pin in the bolt, along with it's very strong rebound spring.  The firing pin is large and heavy, and contacts a huge portion of the rimfire cartridge in use.  Couple that with the heavy spring, and it takes a very solid whack from the AR's hammer to make the unit fire the rimfire cartridge.

However, one brand and type of ammunition tried seemed to have a more sensitive priming compound, and that was Federal's High Velocity Match ammunition.  With the Federal offering, the conversion kit equipped AR-15 settled down and began functioning perfectly.

Accuracy wise, the converted rifle proved to be a shooter, with groups easily matching those of a S&W M&P 15-22.  One inch groups at 25 yards were not difficult in either case.
Upper, 25 rounds from the M&P 15-22, lower group is 6 rounds from the M-261

So..... the kit is kewl.  Very kewl.  Even more since it's a piece of military history that can still be used with great enjoyment.  That said, is a conversion kit worth owning?

There are varying points of view to that.  Some would say yes, certainly it is.... if it works well.  The ability to switch the centerfire AR into a rimfire at will is a certain money saver, and allows shooting on ranges that often don't work well with the bigger round.

The other view point..... instead of buying a conversion kit, just buy a whole new rimfire dedicated upper, or even a strictly rimfire rifle like the M&P 15-22.  That notion has a strong following of it's own.

Now, having had both rifles side by side on the  range..... The Fat Man is still undecided. The kit equipped AR just feels different than the lighter M&P rimfire.  It handles different.   

That said, I can understand the idea of having two entire rifles, instead of one (plus an extra thing to make it different).  On the third hand..... if possible, why not have all of it?

No matter what, there is certainly a great value in having a rimfire trainer, no matter how you choose to arrive there.

What will Carteach's choice be?  It's hard to say.  Hell, given today's insane market, maybe he'll sell the whole batch at crazy high prices and switch over to muzzle loaders.   Especially given the state of home finances.

Maybe... for another day... but for now, there's .22 that needs used and cans that need plinking!


Old NFO said...

The only negative I've heard on those is how dirty the gun gets, and the problem of keeping the gas tube clean... Nice find though!

Old NFO said...

The only negative I've heard on those is how dirty the gun gets, and the problem of keeping the gas tube clean... Nice find though!

Carteach said...

I had not considered the gas tube angle. I have some extra cleaning to do tomorrow... sigh. I need me some more pipe cleaners...

Kevin Highland said...

I've also heard cleaning the gas tube is as simple as shooting about 3 rounds of .223 through it.

Bruce S. said...

I must say your accuracy is much better than what I have been able to achieve with my CMMG .22 conversion in a Colt HBAR. I have not tried every brand of .22 on the market but my usual fodder produces a 6-8 MOA group at best while feeding "most of the time". This same ammo in my 10/22 gives 1-2 MOA consistently. Could the twist rate be the difference? The Colt has twice the twist rate of the Ruger. A dedicated upper would be really great--if you could find (and afford) one right now.

Ryan said...

Neato! .22 conversion kits are a handy thing for an AR owner to have both for economic shooting and potential survival needs. That it is a cool old piece of MILSURP gear makes it all the better.