Hey guys,

I am kinda new to the world of ARs so forgive me if this is a dumb question. Does the cmmg conversion kit cause any extra stress or damage to your barrel? With the long cylinder on the front of it does it come into contact with the rifling on your barrel and if so does that or the 22 ammo itself cause any extra wear compared to shooting 556? Also my ar has a carbine milspec spring with an H buffer. Will I have to change that at all to shoot 22 out of it?

Thanks in advance.

You have nothing to worry about.  The system is proven from about 10 different manufacturers.
Johnathan Arthur Ciener put it on the map over 30 years ago.
A feller by the name of Max invented it.

A Taccom pressure plug is a must.
It uses the buffer spring pressure, to jam the chamber insert forward.
The neck tapers are forced to seal the system.
And it works gangbusters.

It REALLY made sense before ammo was .30 cents a round.
The 1/9 twist barrels work a little more accurately the 1/7 twist.

The dedicated. 22 are the most accurate.
But as an accessory to a standard 5.56 AR, they are decent.

Nope, no damage. You'll get a little crud in the gas tube, removed by firing a 5.56. Although I've not noticed it, there are reports of leading, again easily removed. Oh yes, .22s are dirty so you'll need to clean it after shooting. Other than that, good to go. You do not need a receiver extension, buffer, or spring at all--the bolt has the recoil spring contained within it. It IS good to have your buffer installed as the bolt likes some back pressure. So, remove 5.56 bolt, drop in .22 bolt, close it up and you're ready to go.

I love mine. My only complaint is rimfire ammo not being as reliable (and I am shooting up all my old Winchester white box first) and it gets stuck so I have to drop the mag and use a pic to remove it every so often.

I have the conversation kit. It works well. If I could do it again,  I would buy the dedicated upper to avoid any possibility of the gas orifice clogging up. That way it would have 1 in 16" rifling and should be more accurate.

Uh, the Air Force was using it long before Ciener brought it to market.

That isn't anything like a CMMG.
OP asked about the Atchison type.

I have the CMMG and was using the Ciener before it. They are most accurate naturally in a dedicated .22 upper. Out of the 1/7 1/8 1/12 the most accurate I have seen and I have tried all 3 is a 20" 1/12 I am very pleased with the accuracy out of the 20" 1/12 not so much with the others.

They are nice to carry in a range bag to be able to switch over as they used to be cheap to shoot. Hopefully someday again still cheaper to shoot than 5.56/.223

I ended up building a couple of dedicated .22 uppers that I use the CMMG kit using the adaptor collars. This way I just leave the conversion in the upper and if I want to switch over I can easily remove the collar and reinstall in the 5.56 rifle. This way I can get more accuracy and less crud in my 5.56 upper but keep the option of being able to switch back.

Anyone know where I could find a left-handed collar?

It looks like you'd have to buy a full kit, or maybe call stag arms or cmmg and see if they have one.

This.  A dedicated 1:16 upper is the way to go if your budget isn't tight.  Faster, easier, more accurate, but more expensive.

Forgiven

Get rid of your Winchester 22lr ammo!! Also, if you have any Remington 22lr, throw it away or give to someone you don't  like. CCI or Federal run great.

I've had no experience with conversion kits, but I do have a dedicated upper. I decided to get the dedicated because of the twist rate (1:16). I was told that the higher twist rate of a 5.56 will cause lead fragments from the bullet to build up in the chamber, barrel and the gas port. It made sense to me because my understanding is that the conversions have accuracy issues due to that leading. It seems to me that build up in those 3 areas could cause failures. Just my $0.02

The accuracy issues w/ faster twists is not from excessive lead buildup - it's from the cheap nature of .22 LR bullets, such that the center of gravity of most of em is ever so slightly off.  If you spin them from a 1:16" twist bbl, they have just enough spin to travel accurately to the target.  The faster you spin them, the more the slightly off center bullet assumes a spiral trajectory - 1:7" twist bbls are known to pattern .22 LR, rather than shoot it.  1:9" is a decent plinking compromise, but you'll not see great accuracy from a conversion kit.  The Air Force qualified Airmen w/ M-16A1 1:12" twist bbls shooting .22 LR.

This same center of gravity issue is present in M855 - which is why M855 tends to be more accurate from 1:9" twist bbls than the issue 1:7".  The problem is in the manufacturing process when the lead bullet is formed around the steel penetrator core.  This issue was resolved w/ the new M855A1 round w/ its exposed penetrator, which allows more precise manufacturing.

If you really want to have fun w/ twists, shoot 35 grn varmint bullets from a 20" 1:7" twist bbl - they'll go poof before they hit the target, I'm told.  The spin is so fast the thin jacket can't hold the bullet together & it explodes into a lead mist.