large SXS rifle build

So I got the mono block finished today. It went well and seems like it's going to work just fine.

I bored the block straight though so the barrel bores will be parallel to each other. It made muzzle end of the mono block off center. The shotgun barrels would have crossed over the point of aim at some point.

The threads are 13/16-20 (0.812" od) and the counter bores are .850". The threads are 25mm long.

After facing, boring and tapping on the mill I switched to the lathe to bore the counter bores.

I turned a chunk of steel, then threaded it for the mono block. Hand tightened the mono block on it and bored with the lathe. Pretty much will guarantee the threads and counter bores are inline.

I could have bored and tapped the mono block from the muzzle end in the mill but I figured this was has less potential for unforseen issues having more then 1 setup. Time wise it took longer to do it the way I did.
 
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Thanks, its an 1938 Clausing 100 series mk1 "dual" 12x36" it has 2x Timken taper bearing in the head stock opposed to the Babbitt bearings like my Myford ml7.

and for the off set, the shotgun barrels made a very narrow "V" so the should shoot at the same point of aim after a set distance.
the center of the bore at the chamber end was 26mm and the center of the bore at the muzzle end was 19mm

now the chamber end is 26mm center to center and the muzzle end is 26mm c-t-c so the barrels are now parallel to each other, and ideally no matter how far away i shoot the bullets should never cross paths and hit about an 1" apart.

i plan to thread the barrels in and then solder the everything as one
 
today i turned and threaded the barrels for the mono block. it went well, i left 0.0025" per side for solder in the counter bore.

the barrels are fairly straight, after threaded in and torqued up the muzzle ends of them are 30mm ctc but they should be 26mm ctc so ill need to make a small section of material for near the muzzle to go between the barrels to solder to so i can make them 26mm ctc

i had to hold the OD of the barrel but use a center on the chamber end to machine them so they aren't perfect but easily manageable. its only a 4mm over 711mm (28")

I'm thinking I'm going to set the barrels parallel and make sure they are even up and down and solder a block between the barrels holding them in place about 8" for the muzzle, then i will make and install the bottom and top ribs and solder them on to around the same 8" form the muzzle.

that way i can get the fore arm installed and rear sight on. before dealing with regulating it

i plan to regulate it at 50 meters, ideally I can get both bullets within 3" of each other.

the issue,
the barrel is thin near where the end of the mono block is. there is 0.130" wall thickness (thicker then the smokeless 16g barrels at the same point) at the transition from the mono block diameter to the barrel diameter. its about .75" into the rifling so its ahead the chamber. i think it will be fine but i believe I'm going to proof it 70gr of FFFg and then run 70gr of FFg as the main load. i do not care about velocity at all and would be 100% fine with even 1000 fps

if this was a modern barrel i wouldn't even blink an eye at that wall thickness after seeing my factory 45-70 double wall thickness, but they are cast barrels from a 577 snider Enfield (1866 and 1867) so i am a little nervous. i wish i built this a large bore on a 12g action, not for the action strength but for the barrel diameter.

knowing what i know now, i would have used a 12g sxs for the .577 OR i would have use modern barrels. although i have a feeling with ffg black powder it will not be a concern and I'm over thinking it, i read the snider operates around 5500 psi


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Evanguy said:
so i bought the French under lever hammer gun for this project, i was back and forth on what shotgun to use but realized when i couldn't find it for sale any more i was rally disappointed, only to realize i was in the 12g section lol. so clearly i wanted this one.

its funny i bought a Merkel sxs (cross bolt with side clips) for this exact reason about 6 years ago although at the time it was going to be 43 Mauser sxs. but the gun shoots so well as a shotgun i couldn't bring my self to touch it. it just hits what ever I'm looking at when i shoulder it.


and about regulating the barrel its not that hard just takes a lot of shots and soldering, i have a double rifle in 45-70 i need to regulate after i find a load for it. ill post lots on it when its happening


here is the rifle

https://intersurplus.com/collections/side-by-side/products/st-etienne-sxs-in-16ga-1

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Did you alter the cast on the stock? Or, am I observing an optical illusion?
 
Thanks guys. I'm pretty excited how's it's coming along. I hope to use it for back bear this spring or black tail this fall.

The barrels do add some weight. It was an even 6 pounds, I can see it being 8 pounds when done. If the balance is too off after the ribs are installed I'll have to add weight to the butt stock. I'm willing to sacrifice weight for handling and feel.

bluelynx said:
Did you alter the cast on the stock? Or, am I observing an optical illusion?
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Nope that the pic right from intersurplus. And in had it feels very much like all my other guns, points very well and handles nice. I assume it's an illusion.

Although it may have been built for a left handed shooter as the rear trigger has been pulled 1000's of times more then the other, and the left firing pin is even totally warn out from a million fires or dry fires. I had assumed a left handed shooter owned the gun honestly. Maybe it is an odd cast on the stock.

I do like the feel of it though I believe I'll be able to shot it fine.
 
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threecentsolution said:
What's the plan for extractor/ ejecters
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I'm just going to remake the faces of them. I need to machine the barrels inserts away to make room for the ejectors, but also counter bore for the case rim and that will involve cutting the chamber deeper. then i will make new ejector faces and cut them on the mill for the case and rim size. ill use a boring head and bore the case diameter in the injector face and then counter bore to depth the rim depth.

bluelynx said:
What are you going to use for a pressure test?
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well i wish i had modern barrels so i wouldn't even have it think about it, but i might load the 480 gr bullets i have with 70gr FFFg black powder and remote firing it a few times and check it over, if all is well then just loading 70gr FFg with the same 480gr bullet and shooting it.

im not sure though i may "proof" it with H777 FFg then using real black powder FFg (15-23% less energy?)

jamesharrison said:
You're essentially "sleeving" the gun, albeit you've added threads to the barrels & stubs.
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Thanks Jim, i have my terminology mixed up. I had assumed sleeving barrels was the same as lining a barrel. I had thought a sleeve and a liner were the same thing.
 
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