Large bore rifling (50mm)


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Ferrothorn
November 14, 2012, 07:38 PM
Me and a couple of university friends are building a black powder cannon. (We've made sure to follow ALL applicable laws, no further discussion about that.) Still at the planning, computer simulation and CNC programming stage

Now for the hard part.

How do you rifle a barrel that big? Inner diameter 50mm, roughly 2". There are no tools for it. Can't find a machine/tool combination in our entire multimillion dollar educational workshop to do the trick.

The only ones who actually work with those diameters are mil. contractors and you can't exactly walk up to Bofors and ask them to rifle the barrel.

And yes, we DO want rifles for the barrel (or at least I do) because they make the gun look more beautiful.

For legal purposes, the "gun" will never actually fire any projectiles, only black powder salutes.

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Jim Watson
November 14, 2012, 07:43 PM
I daresay you could get the appropriate Foxfire book and scale up an old fashioned rifling bench from .50 cal to 50mm. They were nearly all wood except for the cutters.

But actually, I think you are nuts. You would quadruple the work on a blank popper just because you like the looks at the muzzle? OK, sit down with a cardboard template and a sharp new file and cut a dozen or so evenly spaced notches into the muzzle. It will LOOK like rifling without the trouble of building and operating the machinery.

25cschaefer
November 14, 2012, 10:52 PM
Rifling can be an exhausting process, every groove can take more than 80 passes in a small rifle, I would assume in a bore that big you would have either 10 small grooves or 5 big grooves.

If all you want is looks and it will NEVER fire a projectile, just for looks; you could weld a plate with the dummy grooves on the front. Don't think flat plate, you could contour it.

paintballdude902
November 15, 2012, 01:07 AM
id just do the first 6 inches if just want it to look sharp(pun not intended)

blarby
November 15, 2012, 02:49 AM
CNC programming stage

If you are at a university with CNC machines, certainly you have access to a large format laser cutter ?

That would be my first thought......

If you really only wanted it for show, and not actual rifling...that would be very easy to faux into the first few visible inches using standard CNC machining.

rcmodel
November 15, 2012, 11:34 AM
IMO: It would be counterproductive to rifle a blank firing cannon just for "looks".

It will make bore cleaning much more difficult & time consuming after every firing.

I'd lap the bore smoother then a baby's bottom and call it good.

Your friends will thank you when it come cleaning time every time you fire it.

rc

Jim K
November 15, 2012, 03:05 PM
I agree with rcmodel, but if you want to do it anyway, get a piece of round aluminum that is a slip fit in the barrel. Cut a groove in it at a slight angle. Insert into that groove a very hard scraper (tool steel) that will protrude just a bit. Push or pull the cutter through the barrel. Make a guide to keep the cutter on track and turn it at the rate you want. Most rifling machines are made with the idea that the barrel is fixed and the cutter turns, but for a large bore, you would be better to do it the other way.

Normally, a scrape cutter will make one pass around, then it is shimmed and goes around again, and so on, but with some time it is possible to fully cut one groove, then remove the shims and set up to cut the next, and so on.

Jim

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