Few questions regarding restoring an old 8 bore gun.

Discussion in 'The Gun Builder's Bench' started by Ironoxide, Sep 5, 2019.

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  1. Sep 5, 2019 #1

    Ironoxide

    Ironoxide

    Ironoxide

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    I have this 8 bore Belgian smoothbore muzzleloader. I described it in more detail and there are pictures of it in the thread I started in Firearms Identification forum.

    Although I'm still waiting for a book of 19th century Belgian gun catalogues to identify the maker of the gun I'm pretty certain I'll confirm the historic value of the gun is pretty minimal so it is a prime candidate for a restoration.

    The main focus of the restoration will be the stock, I also plan to make some new screws to replace the non-matching ones and I still haven't decided what would be the best way to restore a slightly better look to the barrel. I'm starting this thread to get some advice regarding it.

    I expect the restoration will take a while as I plan to proceed quite slowly not to mess things up.

    Regarding the barrel, it is an octagon to round. At the bottom (I assume)original bluing is present with proof marks and the edges of 3 bottom flats are nicely sharp. Unfortunately it looks like someone "polished" the top of the barrel incorrectly rounding up the edges of 3 upper flats slightly. The radius of curvature is in the region of up to 10 thou (0.25mm) so it should be possible to fix the edges by removing up to 10 thou of material per flat. I've never done anything like this to a gun barrel so I'm after some advice from anyone who has done something like that, or seen it done. Is a procedure like this worth doing? Not in a monetary sense, but is the usual end result worth removing material from an original barrel to improve how it looks like?

    Also, the barrel has some marks on the surface towards the muzzle. The marks look like scratches, maybe some shallow rust pitting. I definitely don't want to remove material from there as near the muzzle the barrel walls are quite thin. Is it worth to rust blue a barrel with scratches, dings and some pits or will it look even worse when blued?
     
  2. Sep 6, 2019 #2

    billraby

    billraby

    billraby

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    Draw filing should sharpen up the edges. It is pretty easy to do. Go ahead and take out scratches near the muzzle if they are not too deep. Or maybe just lighten them up a bit. Draw filing will give you a smooth, fresh surface. Rust blue does remove metal and does a good job of smoothing out minor scratches. All depends on how thin the muzzle is and how deep the scratches are.
     
  3. Sep 6, 2019 #3

    Ironoxide

    Ironoxide

    Ironoxide

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    Thanks for the suggestion. I saw some youtube videos showing draw filing. I'm wondering how much better or worse would it be to use the same draw filing motion, but using flat wood backed sandpaper. It may be a more gentle method. However, my favourite would be to just stick the barrel to a magnetic table of a surface grinder... Unfortunately the nipple drum and fence prevent access of a grinding wheel from the top to two flats :( I have to try draw filing on a piece of scrap first to see how much material it removes.

    Regarding slightly deeper marks near the muzzle I can always remove them later(after bluing and reblue) if they look bad. I think I'll leave them for now. I don't mind thinning the octagonal part by up to 10 thou, but the muzzle end is only about 100 thou. I know there are guns that are half this thickness at the muzzle, but I like to have the extra strength in case of mechanical damage if I can.

    Also, I have a question regarding re-proofing the barrel. It was discussed briefly in the Firearm Identification forum thread. Previously I intended to make a wooden stand for the barrel to test it on, but considering the amount of extra work this will require to attach and align the lock properly etc I'm leaning towards proof testing in stock but suspended on ropes so the gun can recoil freely. The stock has a badly glued partial crack in the wrist. Still I think shooting it with a light load wouldn't break it. I'm hoping the force exerted by recoil during proofing when suspended and allowed to swing back will be similarly small. Does anyone have any tips regarding this method?
     
  4. Sep 12, 2019 #4

    Ironoxide

    Ironoxide

    Ironoxide

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    Re-proofing of the barrel was successful :)

    I thought I'll update this thread in case anyone looks for information about (re)proofing barrels and finds it. I ended up making a wooden contraption consisting of one 10 inch wide, 1.2 inches thick, board about 5 inches longer than the barrel. The barrel was placed in the middle of this plank and one additional plank was placed on each side of the barrel. Those side-planks were planned so they were the same height as the barrel. Another piece of wood was placed behind for the recoil force, and three planks screwed on top of two previously mentioned planks lying alongside the barrel so the barrel couldn't move. The wood was pine and the whole thing with the barrel weighted close to 45 pounds (20kg). I also decided not to mess with installing a caplock, but to use a fuse to initiate the test and compensate for the lack of the nipple by increasing the charge.

    The barrel uses a patent breech with a flash hole in the center so looking from the inside of the barrel with a borescope it looks like a funnel. The diameter of the hole appears to be slightly under 80 thou (2mm) so not dissimilar to touch holes used on flintlocks. I read somewhere an opinion of someone who had a convertible flintlock/caplock rifle that he has to use 5 grains more powder to get the same muzzle velocity when using the rifle as flintlock. As he was using a smaller caliber rifle (50 cal if I remember correctly) I decided to up the load by 10 grains to make up for it.

    Also while testing various nipple threads I noticed the thread in the nipple seat has no problem marring silver steel. Although the silver steel rod was in annealed state it is still made of modern chrome vanadium steel and if it is so easily damaged by the existing thread it suggests the barrel steel is at least stronger than annealed silver steel which has yield strength of 45-55 kpsi. In a barrel of this size the pressure would have to be in excess of 25000 psi for the stress on the inside wall of barrel to exceed 45 kpsi (based on Hoop stress formula).

    Therefore being confident the barrel can take it if the steel is not damaged I decided to re-proof it with 210 grains of 3F, 0.6 inch of cork wads, 2 ounces of shot and another 120 thou thick cork wad. The nipple was removed and a 3 inch green fuse(used for model rockets) was inserted into the flash hole. The recoil made a quarter inch deep impression of the breech lug in the wooden plank, but the whole contraption didn't move.

    I'm pretty happy with the result. Now I have to wait for the epoxy I ordered to arrive and once it is here I'll be able to fix the stock. Based on many positive online opinions I decided to order Brownells Acraglass Gel. It takes 3 weeks to have it shipped to Europe, but it is supposedly worth the wait.
     
  5. Sep 12, 2019 #5

    Dphar1950

    Dphar1950

    Dphar1950

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    I am curious as to the "rust blue removes metal" comment. If it does its at the microscopic level and would be impossible to detect with a micrometer and in fact the slight built up of oxide on the part should make it slightly larger instead.
     
  6. Sep 12, 2019 #6

    Dphar1950

    Dphar1950

    Dphar1950

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    Use 1/4" plexi-glas and attach the abrasive paper with double stick carpet tape when polishing flat surfaces. Just don't flex the plexi-glas. For rust blue do not go finer than 320 grit and 220 might be fine as well. A fine polish makes it harder to "wet" the surface with the first coat of solution.
     

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