enduroshot

First I've read about this and the evolution of the M3. Thanks!

So I found info on Brownells website which seems to confirm the SL180 version but says it was the "Benelli second generation" and includes dimensional information. I'm copying and including a pic for anyone that might stumble on this thread later. I also called Carlson's who told me they don't offer it and to call Brileys. Brileys doesn't stock it and it would be basically a custom order. But they have all the information and history on it. $95 for extended choke and $75 for regular flush. I went ahead and ordered another M1 from a private seller out if state and am waiting on it to arrive at my local FFL. Really excited but wish it was a pre-ban. I'll still go take measurements of the one at the local store after it arrives if it's still available. Thanks to everyone that responded! Maybe this info will help someone else with the same question one day. From Brownells website... Benelli choke tube systems. There are three known choke tube systems that have been used on Benelli shotguns commonly encountered in North America. They are as follows: First Generation: External Thread System. This is the earliest of Benelli choke tube systems and is typically found on the SL-80 Series: Models 121 and 123, from 1960 through 1986. The thread is on the outside of the barrel and the choke tube has a female thread. These chokes are very much like the old Weaver choke tube system. This requires a special spanner to remove and install the tubes. No current source for these is known at this time. Second Generation: Internal Thread System. This system was used on models imported by Heckler & Koch U.S.A. from 1986 through 1995. The barrel is internally threaded with a male thread on the choke tube. The threads are square and are located on the muzzle end of the tube. The major diameter of the threads is .810". The tube has a nominal overall length of 1.888". Included in the overall length is a collar with a nominal length of .118". (1.77" length from face of barrel muzzle to breech end skirt of the tube) This collar extends from the muzzle of the barrel and uses slots for the tube wrench. Third Generation: Internal Thread System 1995 to present. This barrel is internally threaded with a male thread on the choke tube. The threads are square and are located on the muzzle end of the tube. The major diameter of the threads is .810". The tube has a nominal overall length of 2.050" from the face of muzzle to the breech end skirt of the tube. This system is interchangeable with the Beretta Mobil Choke style choke tube system.

Thanks for all the thoughts. I don't think it's a thread issue. The choke bottoms out on the internal ledge of the barrel counterbore for the choke. We confirmed this visually and by running a finger down the choke and into the barrel.its a smooth transition. The idea that the end of the barrel was cut back is a good one. I actually got a line on a good condition private sale M1 with box, manual, and chokes. So actually planning to purchase that one now instead. My curiosity is peaked now though so I will probably go and compare the two or do the dowel suggestion to verify length. But will need to go through FFL transfer so might take some time. Thanks again!

New member, but been lusting after an M1 or M2 for a while. I'm very interested in a 1988 year HK import Benelli M1 Super Sport at a local store near me. Good condition but is missing the choke. The store had quite a few Mobil style chokes that we tried but they all appeared to bottom out on the interior land of the barrel before the choke was fully threaded. I was only able to turn the chokes in about 1.75 turns. Just didn't seem right even though I've only ever used plain bore double barrels. Anyways, is there a special length choke for the early HK imports? It didn't appear to be a thread pattern issue as the choke fully seated. I've attached some pics, but decided to hold off buying until I figure out the choke issue.