Surcouf Guns

Discussion in 'Weapons & Pneumatics' started by JustinScott, Oct 26, 2022.

  1. Beaver

    Beaver 2020 Rookie of the Year Admiral (Supporter)

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  2. JustinScott

    JustinScott Well-Known Member

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    Next revision of the guns! I think I took all feedback into consideration, please let me know if I misunderstood or missed anything!!!

    The square hole next to the piston is for the magnet that beaver recommended; which are now on their way to me!

    Updates:
    - Feed tube has 1 degree down angle, except at the piston which is 20 degrees
    - All tubes are now on one plane for easier printing
    - I tried printing the threads in this orientation, and it seemed to work out.
    - I'm estimating I'll have about 40 rounds per cannon. :)


    Screen Shot 2022-10-31 at 3.31.20 PM.png
     
    Last edited: Oct 31, 2022
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  3. darkapollo

    darkapollo Well-Known Member

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    How long are the tubes? Is this for fast gun or big gun?
     
  4. Kotori87

    Kotori87 Well-Known Member

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    Much better than the first version. The slope and curves should help feed quite a bit. A few additional thoughts.
    Take a look at the piston region geometry in my cannons. I'll send you the files as soon as I can. That section needs to be very smooth, no printing imperfections or excessively thick layers or the piston will be prone to jamming. I also recommend sloping the edges, so you don't have a sharp 90-degree angle in there. That shape requires supports, which are messy to remove and often cause printing imperfections. A 45-degree should eliminate the need for any sort of support. You can see what I mean in the examples I'm sending.
    Some experimentation may be required with the magnet size/strength/position, but I have generally found that it doesn't need to pull down or anything. You just want it closely aligned with the ball that's currently in the chamber and ready to shoot, as close as possible to maximize the magnetic strength. There's no need to offset it down low to pull the round into the piston or anything like that. It's not strong enough to unstick a jammed piston, so you're really sacrificing magnetic pull for nothing.
    The magazine pressure line seems pretty long. You're 3d-printing this thing, so think in three dimensions. Since you're not trying to do a 10-round-per-second magazine dump, you don't need the magazine pressure line to blow on the very last ball. You could, for example, run the line out to the side of the cannon, then up to the first bend. You'd still be blowing rounds down the magazine, but you'd gain a much shorter flowpath with less resistance to flow.
    I am not a huge fan of the ultra-coarse sideways-printable threads. I prefer to use standard machine threads, printed in a favorable orientation on the print bed. See my example files. The 1/8NPT bottom plug and 1/4-20 magazine plug are both oriented to print as part of the main cannon, but the breech threads cannot be. So the breech is printed as a separate part, in a favorable orientation, and solvent-welded together afterwards. The finer threads give more precise, repeatable adjustment when tweaking the cannon than coarse threads, for obvious reasons.

    Overall this looks like a functional cannon. You can certainly print what you've got right now and I bet it'll work.
     
  5. darkapollo

    darkapollo Well-Known Member

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    Here is an example of one of my prototype cores for a bulk magazine, and what it looks like with the outer shell. I am going to redesign it for more of a 'dead drop' than the swoop. It will not have as many 'at the ready' but I am hoping to make it more compact to where I can fit it side-by-side as duals. Right now it fits perfectly inside of my Derf barbette (2.5" barbette) and I have managed to fit a -slightly- modified version into a predreadnaught barbette (under 2"). The hopper has been capacity tested and I can over stuff it, holding in excess of 60rds (which leads to inconsistent feeding until there is room) 55 rounds would be the max (50 in to battle, plus a few for testing). The balance tube acts less of a blow forward tube and instead acts as a ball 'popper' (like those kids toys) tossing the rounds and helping to break up any jams. I have rapid fire tested it and it kept up with my slow trigger fingers.

    upload_2022-11-1_7-32-34.png upload_2022-11-1_7-33-8.png
     
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  6. JustinScott

    JustinScott Well-Known Member

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    Revision #3 -

    With @Kotori87 's suggestion that I don't need to take the air the whole way to the end of the magazine; that means I can extend the magazine and carry more rounds! The cannons should now be up to 46 rounds each! I think nearly 100 rounds is pretty good & holds true to her original intention of a CRUISER submarine! :)

    @darkapollo - I'll be fighting her in Big Gun; however I don't see any reason she wouldn't be legal for Fast Gun too... other than I wouldn't be able to fully arm both cannons! I'm trying to keep 'both formats' in mind, and will re-read the IRCWCC rules since I am only going off a decade old memory.

    Screen Shot 2022-11-01 at 9.55.04 AM.png
     
  7. Xanthar

    Xanthar Well-Known Member

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    Nice! I've been working on something very similar :)
     
  8. darkapollo

    darkapollo Well-Known Member

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    What caliber does she run?
    For FastGun, she is listed as C1/ 1.5U, so you have your 1/2 U pump and class 1 and 2 are allowed to split the remaining unit into 1/2 units so you could have dual bow guns at 25rds each.
    upload_2022-11-1_11-56-27.png
    Also, just from a design point of view, you do not want a dead stop at the load port. I know there is a slight angle there, but from past testing, you want it to pour the rounds in. You will want to make that transition a lot smoother.
    Back when I was still working on printing coil based magazines, I found that even a smooth 90* elbow would cause loading jams. That is one big reason I went to a bulk magazine style, plus being more compact with a shorter run to the firing chamber.
     
  9. JustinScott

    JustinScott Well-Known Member

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    This thing is such a PITA to print....

    Thinking outside the box... what would happen if I designed it like this? Would this style design work? Screen Shot 2022-11-03 at 7.03.54 PM.png Screen Shot 2022-11-03 at 7.05.16 PM.png
     
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  10. darkapollo

    darkapollo Well-Known Member

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    Yes but you will wan much more of a feed in angle on the ramps. As is the next round will be shot away from the chamber and the relatively low slope angle means it will take a ‘while’ for the next round to chamber.
     
  11. JustinScott

    JustinScott Well-Known Member

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    And it’s too much depressurization for the accumulator…
     
  12. Kotori87

    Kotori87 Well-Known Member

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    I have always been curious how this type of muffin magazine works. I understand the basic idea, but how do you prevent stacking jams? How do you ensure rapid, reliable feeding? How do you ensure the correct amount of ammunition in the magazine? Is it just a bunch of guess-and-check, or what?
     
  13. JustinScott

    JustinScott Well-Known Member

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    Was able to test fire the Surcouf cannons for the first time today! Total fail.

    The design that worked the best so far was Mk3 above, printed down the middle long ways. IE one of the first photos where I would only need to print twice for the whole ship.

    The parts that failed:
    The Mk3 print was the right side, which was a mirror. Which meant the threads were mirrors too. No problem, so I printed right side parts. All was good until I forgot which way was which and threaded it too far and cracked the plastic. ;(

    The air port printed too wide, so the air tube would not glue in place. I eventually just tapped it and used a clippard nipple.

    The wall in the aft was so thin that a hole was formed. I have to shorten the magazine.

    Only the barrel threaded. All other thread parts just didn’t turn. I’m not sure what happened. It’s like I need more tolerance between them. I’m going to play around with off the shelf replacements.

    The battlers connection tight tolerance barrel isn’t wide enough for the BBS to pass!!? IDK what I’m supposed to do with that. I could drill them a bit? I don’t think they make different size BBs…. Now with multiple issues, and no response from them, I’m really disappointed with BC product so far.

    What worked well:

    the magazine worked fantastic after I pushed a 3/16” bearing through it. Afterwards, the BBs flowed perfectly!!

    The barrel thread, even printed horizontally was perfect.

    Overall I think of it as a successful first test. Still would have been happier if a BB would have fallen out of the BC rifle. That said, I have next steps and that’s all an engineer needs.
     
    Last edited: Nov 5, 2022
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  14. Kotori87

    Kotori87 Well-Known Member

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    What do you mean the BC tight-tolerance barrels wouldn't pass bbs? I've been slinging cheap-o walmart bbs through BC stainless barrels for years now. As long as you're using .177" (4.5mm) bbs, you should be fine. I use a .180" extra-long drill bit to remove the burrs from the safety pin holes. Are you sure you didn't have a few 3/16" ball bearings mixed in there as well? Glad to hear the magazine feeds well, though. That's important.
    I learned to add threads as one of the last steps in cannon design, after I have mirrored the main design. That way the threads go on right-way-around every time. But yeah, I broke one cannon last year by over-tightening it during tweaking. Turns out the o-ring fell out, and that was why it was weak.
     
  15. Bob Pottle

    Bob Pottle Well-Known Member

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    While still active in the hobby I'd found slight variations in copper BB size so a small percentage wouldn't pass through my homemade tight tolerance SS barrels. I used a spare barrel to weed out BBs that were too wide.
     
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  16. darkapollo

    darkapollo Well-Known Member

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    Which one was the MK3..?
     
  17. Commodore

    Commodore Well-Known Member

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    FYI, not all BBs are the same. The Daisy bb's are a touch larger than the Crosmans. I think it was something like .174-5 vs. .172-3. And yes, sometimes that little bit is all that matters. These days, I prefer a certain other brand which has given me great consistency, and they're also about the same size as the Crosmans which I preferred in the past, before their QC went to heck. I'd rather have to tweak a little vs. having something jam in the magazine or barrel.

    (And a couple of mine, specifically the Bismarck's double sterns are the BC/Charley extra special barrels where if you put your finger over the end, you can hear the BB roll slowly down the barrel. I definitely don't want to jam those up with crappy BBs)
     
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  18. JustinScott

    JustinScott Well-Known Member

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    My post above which starts with “revision 3”
     
  19. JustinScott

    JustinScott Well-Known Member

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    Mark V guns are ready to print!

    Changes:
    - Magazine has been shortened because the aft wall was too thin & popped a leak.
    - All threads have been increased in size. This is for comfort as well as the thinner threads just didn't twist in place.
    - The piston diameter was also increased to compensate for the larger port, but for no other reason.
    - Moved the air port to lower in the magazine so the bearing wouldn't impact during sizing.

    Screen Shot 2022-11-07 at 3.27.07 PM.png





    - I'm moving forward with printing it as one unit on its side, since I had reasonably good success with Mk3

    Screen Shot 2022-11-07 at 3.31.55 PM.png
     
  20. Xanthar

    Xanthar Well-Known Member

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    So... I'd cut that half in to two quarters and print them one at a time. You'll save your self a lot of time+plastic and catch any problems in the internal passages, right away, because you'll be able to see them.
    I'll also suggest using octagonal cross sections instead of circular ones wherever you can, again. It will bridge easier and your model will have a lot less points and surfaces to deal with.
    That would help avoid crashing fusion and make slicing faster + easier to examine your layers.