Marvel Conversion Barrel wanted

I'm interested in a late model Marvel Conversion Barrel for dimensions. Condition not important! Beat-up OK! I intend to unscrew the barrel from the mounting block, my interest is how the threads are done. I want to see if it is the same as the Nelson. If it is, I see a possible problem. Nelson only has one screw in the barrel the other is in the mounting block but Marvel as 2 screw in the Barrel Over time that may become a problem! The barrels I have, one is older version other is from a friend of mine that can't be disassembled, used for assembled dimensions only!
 Would be interested in photos to see where screws are located if barrel not available for sale.

Please excuse my ignorance, what is the problem with either the marvel or the nelson design? I have extensive time behind both and have not experienced any issues related to the barrel block and barrel interface.

Don't know anything about Marvel, haven't disassembled one yet but noticed a difference between older model I have and the newer version from my friend.
 Nelson barrel is threaded 3/8"-40tpi Left Hand. Bottom of the threads on 3/8"-40tpi is .350" diameter. However at the junction where the barrel meets the mounting block there is an gap that's about .10" wide and .330 in diameter. Subtract the grove depth diameter .223" that .107" so thickness of the wall is .054" Quite thin! One Nelson scope mount screw is the mounting block, therefore the scope mount will add to strength. If Marvel is done the same the scope mount in on the barrel only so no added support. Weight of a Red Dot, scope mount and barrel might bend and eventually crack the Marvel barrel. Might be a good idea to add another screw. I'll get a barrel I unscrewed from a Nelson and make a photo. When I re-barrel a Nelson (didn't do any Nelsons yet) I counter bore the end with 10mm carbide end mill .01" deep. End mills will tend to cut slightly over-size by a thousandth or 2, I then check the hole size with pin gauge, when I thread the barrel I don't an an under-cut it's over-size by .019" so now wall thickness is .085" and the screw in the mounting block on a Nelson will add support. Better .085" them .054" Maybe on the next Nelson re-barrel I'll 13/32" end mill. That will increase wall to .092"

Ok, let me rephrase my question, what measurable improvement can be made? I have personally used (arguably some level of abused) several marvel and nelson conversions with no issues with either a metallic rib or a combo rib with a heavier optic. Each conversion configuration will group x ring and function flawlessly when correctly maintained and using reasonable ammo. I still don’t understand the potential improvement potential.

Creating a better mousetrap.

Simply put the metal thickness of the Nelson barrel at the junction of the barrel and mounting block is .054" thick. Maybe less. Being the Nelson scope mount is steel combined with the screw in the mounting block the scope mount adds to the strength but in the Marvel having all screws in the barrel there is no additional support. I would think that adding a 3rd screw in the Marvel so the scope mount is attached to the mounting block will add support.
 My slight change to the barrel mounting also adds support to the re-barreled Nelson. However I have never disassembled a Marvel.
 Therefore I want a Marvel barrel to see what actually exists. For my friends gun a one piece barrel is being made, His existing barrel is about 3/4" longer than the Standard Nelson to which he intends to add a silencer or muzzle break. Currently the Marvel barrel is not threaded on the end, just want info so as to tell him of the problems of added weight and length might add.
 Photo of Nelson Barrel I'm making for Adam, one for my friend is similar and longer.

Froneck wrote:Simply put the metal thickness of the Nelson barrel at the junction of the barrel and mounting block is .054" thick. Maybe less. Being the Nelson scope mount is steel combined with the screw in the mounting block the scope mount adds to the strength but in the Marvel having all screws in the barrel there is no additional support. I would think that adding a 3rd screw in the Marvel so the scope mount is attached to the mounting block will add support.
 My slight change to the barrel mounting also adds support to the re-barreled Nelson. However I have never disassembled a Marvel.
 Therefore I want a Marvel barrel to see what actually exists. For my friends gun a one piece barrel is being made, His existing barrel is about 3/4" longer than the Standard Nelson to which he intends to add a silencer or muzzle break. Currently the Marvel barrel is not threaded on the end, just want info so as to tell him of the problems of added weight and length might add.
 Photo of Nelson Barrel I'm making for Adam, one for my friend is similar and longer.

Frank I own one that I bought from Bob at Perry the last year he had a shop on commercial row at Perry.
It has three screws that hold the scope rail or open sight rail on the barrel. the barrel is about 3/4"s longer than the slide and has a hole in the bottom that is tapped for the recoil compensator that Bob had installed on the barrel. I have the comp somewhere in a box. I took it off because it made it muzzle heavy. 
The rear screw is about .265" in front of the barrel block in the barrel I said about because that is as close as I can measure it mounted on the frame of a DCM 1960's $5 1911 frame, I also have the rest of the 1911 in the bag the conversion came in. Mine also has a Micro groove barrel that shoots exceptionally well.

Here is a photo of late version of the Nelson barrel removed from the mounting block. The under-cut as measured with Starrett 486 Blade micrometer is .368". Older version that I did my first re-barrel  was .350". I do have a few removed Nelson barrels so when I have time I will check them to see what under-cut sizes might be
 Keep in mind unfits in the threaded hole with a slight lead-in countersink so there is a bit of a gap between the barrel and block at that point.
 If a micro red dot sight is added the low weight may not be a problem but if a heavy red dot like a Aimpoint 9000 there use there might be some issues.
 Rodger; can you attach a photo or message me a photo? As you can see in the the photo where the rear screw is located on standard barrel.

Frank if the hole in the blued portion of the barrel is for the scope mount it is 
way out in front of the barrel block where the original is just about .265" as I measured it with a Starrett caliper.

Send me an e-mail and I'll try to get some pictures for you, the best I can see without taking it off the frame there is no mounting screws for the rails in the barrel block.

Hole you see in the blued portion of the barrel is not a screw hole, it's for the pin between the screw holes. The center distance between the screw holes is 3.250" the pin hole in between them at 1.625". Interesting, though I don't have the Marvel here with me, the screw in the barrel is about that distance. I didn't remove the scope mount from my friends barrel so the distance is a guesstimate.
 Can't find your e-mail, mine is FSCO@pa.net

If there is a big concern about screws shearing off or some other screw hole  problem, why not drill and tap a new hole wherever you feel comfortable with the location?

Not that I'm concerned with screws shearing off, it's there is no screw. A I mentioned and shown in the photo the wall thickness at the point the barrel .625" diameter meets the mounting block the wall thickness is very thin. The Marvel barrels I have the 2 screws attaching the scope mount to the barrel are only in the barrel yet all the Nelson barrels I have one of the 2 screws is in the mounting block as seen in the threaded section of the barrel. Thought I think it a poor way to fit the barrel, the Nelson having the screw in the mounting block will help. If a screw is to be added it should be in the Marvel. But Rodger stated that his long barrel Nelson has the 2 screws in the barrel very similar to the Marvel. In addition the Marvel barrel from my friend is the long barrel, dam near a copy of the Nelson except for the screw location and the ejector. The ejector is exactly the same except it's .050" thick and Nelson .070 thick. I've talked to Larry Nelson, he would like to make a one piece barrel. Making it on a CNC machine would be easy except he can't find any of the companies that rifle barrels to rifle his blank. I did get a a 2" diameter blank from Lilja, it was over $240 more than the standard diameter in addition the increased weight increased shipping cost!. You can see in the first photo the amount of material that had to be removed, looking at the lower right projection the bottom radius is the original barrel blank. Larry was right making a barrel from a 2" blank would add quite a bit to barrel cost!
 Simply put my thoughts that after quite a bit of shooting that thin section may become weak especially in the Marvel. I have re-barreled quite a few Nelsons, those that were shot quite a bit, the barrel unscrewed with little effort yet 2 I had that were never shot were very difficult to unscrew. To me it implies that shooting is loosening the barrel attachment.
Hi have one one older Marvel barrel to disassemble and another Marvel from my friend I can't disassemble. I would like to buy a few cheap beat-up Marvels to disassemble them.
 As to adding a screw, I have the Nelson conversion plus I'm making solid barrels plus a complete modified version that that has a sleeved solid barrel and Lija solid barrel in the works. My thoughts are for others to think about.
 However it's my thoughts and I could be wrong! Time will tell!

Was doing some work on my barrels. I found I made a mistake on my Previous post! My friend's late model long barrel Marvel does have the second screw in the mounting block. The other Marvel also a long barrel has the 3 screws in the barrel, 2 screws are near the muzzle and one a short distance from the mounting block. My friend's has iron sight only rail and the other a scope mount rail. I'm interested in seeing what others have. Please post photos of Nelson and Marvel long and short barrels.