Recently purchased the pistol and am reading lots of posts noting how poorly the short buffer tube works.  I've been  experiencing porblems similar to those stated in posts about the flaws ( failure to strip next round, failure to close the bolt)  I've been impressed by the modularity of this platform.  I've purchased a seperate upper with a 16" barrel and my intentions are to create a case to hold my gun/s.  For simplicity i wanted to use a rifle stock buffer tube with the stock removed while using the pistol upper and then just add the stock when i put the rifle upper on.  I'm a big guy and wanted to use the SOPMOD stock as it's got the longest LOP and i've read it fits on the mil-spec tube ergo...

Will the mil-spec tube work for a pistol barrel?

What is the difference between a carbine milspec tube and a rifle milspec tube other than the obvious: length, and number of positions.  Do they function differently?

Has anybody an opinion on the Professional Ordinance brand?  I've had quite a bit of problems with it really and have just chalked it up to poor maintenance.  Besides the errors previously mentioned: failure to close bolt, failure to strip next round from magazine... the extractor snapped off at where it meets the vertical pin that turns it to the side to eject the spent cartrige...THAT was a bummer weekend :/....Anyhow...I'm new to the forum and would like some opinions.  Thanks.

If I recall correctly the older Professional Ordinance (pre Bushmaster) pistols have a
proprietary thread pitch for the recvr ext tube (buffer tube) so a standard tube will not
thread on properly ?  

Do you know of any resources on this particular weapon?  I can't get ahold of the company (I assume they are out of business)  Do i have any options other than sell it and buy a different gun?

I was told that Bushmaster bought them.
Bushmaster has refined the product and now markets them under their name.
The Carbon 15 Pistol line has several models.
Carbon 15 9mm Pistol,  Carbon 15 Type 21 Pistol,  Type 21s,  Type 97 and  Type 97s Pistols.

A link to Bushmaster is at the very top of every page in the middle on this website.

I hope this helps

Doing some more reading found that there were several shortcomings and slight differences between the Pro Ordnance and the rest of the gang...wishi I hadn't bought this thing and had just gotten an AR-15...Does anyone have any reference on what all will not interchange?