Rifling simulation and scopes

[Jerry Carducci]

Hello all. Two questions

• What is the current thinking/ solution for simulating rifling in a main gun barrel; I've heard of various inserts- 3D printed or rolled metal

• Is there a supplier for AFV optical equipment or is each up their own design? I've simulated these in smaller scale but here more detail in needed

I read a thread where a fellow approached a gun maker ostensibly to cut actual grooves in a barrel but it was deemed impractical, Why? It would seem
a short plug broach could be made, likely more than one to cut shallow (very shallow) grooves for a short length of the barrel. Using a PaK 75 as an example having 32 grooves and a progressive twist (I believe anyone could be forgiven the progressive part in a model!). I don't have the exact groove depth of the original to hand but a few thousandths of an inch for a model should be sufficient.

Thoughts?

Be well.

Jerry Carducci

[Robert E Morey]

Hi Jerry
I think the 3D printed rifling insert is most practical. The ease of modeling the insert and printing the insert with high accuracy are the two biggest factors. The inexpensive resin printers available now can do just that. If you don't get your first design just right - its easy to tweak the model and print another.

But some folks don't like plastic parts on metal models, so other methods could be explored. Could you rifle the barrel - sure if you have the equipment and know how. Could you make a tank barrel from a large bore rifle barrel - probably, may not be scale and involves a lot of machining. The late Mike Stannard and perhaps others experimented with flat photo-etched rifling inserts that were then rolled and glued in the barrel. This option does solve the metal material question but creates new challenges -getting a flat sheet round and to the correct size. All possible with fiddling. Perhaps if you must have metal part - creating a rifled plug insert (instead of the entire barrel) would be another possibility.

I suppose it depends on how accurate you want it to be and what purpose it would serve once complete. The 3D printed part will look just like the real thing once painted and weathered, so in the end that is the most practical for me. For my needs there is no need for a fully rifled barrel that no one would really see.

There are several members which have used FPV for steering tanks - I don't know if that answers your "optics" question.

Best regards,
Bob

[Stephen White]

This is where Mike Stannard got the idea for barrel rifling.

http://www.armortek.co.uk/Forum3b/viewt ... &start=450

I milled the lands but I think now I would use photo etch.

I also bored out the kit muzzle to accommodate the thickness of the insert material, giving an accurate calibre weapon.

[Jerry Carducci]

Thanks for the insight into simulating rifling grooves. A rifle barrel wouldn't do to simulate a large bore as just the groove count alone
wouldn't be close.

Apologies for the lack of clarity surrounding the optics question. By optics I meant episcopes/ periscopes, vision ports and other optical
glass items used in a tank.

Jerry

[Adrian Harris]

Various people have made resin optics for cupolas etc, but I believe it was only Mike Stannard (FOA) who made optically reflective prisms in this scale.

Adrian.

[Robert Reid]

• Is there a supplier for AFV optical equipment or is each up their own design? I've simulated these in smaller scale but here more detail in needed

Jerry Carducci

viewtopic.php?f=50&t=7752&hilit=mirbat&start=30

I did my own optics, simulating the lenses with German Silver highly-polished and clear epoxy.

Cheers,

RPR

[Jerry Carducci]

• Is there a supplier for AFV optical equipment or is each up their own design? I've simulated these in smaller scale but here more detail in needed

Jerry Carducci

viewtopic.php?f=50&t=7752&hilit=mirbat&start=30

I did my own optics, simulating the lenses with German Silver highly-polished and clear epoxy.

Cheers,

RPR

Interesting approach to the simulation of optics, thanks for that. Marvelous work on the 25 pounder.

In terms of simulating rifling with some type of insert what length seems to work best? That is, how far back
from the muzzle does the insert need to extend to have a good appearance? I seem to recall Per mentioning
something about a rolled photo etch piece he experimented with.


Jerry

[Adrian Harris]

The ones Vince designed for the Chieftain are 25mm long and 20mm in diameter.

I haven't seen one painted black but I would imagine any longer and the grooves would be invisible.

The bigger the bore, the longer the plug would need to be. A muzzle brake makes the rifling all but invisible, except through the side vents.

Although machined and rolled metal sheet means you are not adding plastic to the kit, I do think the grooves can cause the metal to deform as it is rolled, leading to a plug which is no longer nicely cylindrical.

Adrian.

[Christoffer Ahlfors]

In terms of simulating rifling with some type of insert what length seems to work best? That is, how far back
from the muzzle does the insert need to extend to have a good appearance? I seem to recall Per mentioning
something about a rolled photo etch piece he experimented with.

Jerry

Hello Jerry!
This is the insert Per Sonnervik made for his hunting tiger. It's made of copper and as far as I know, Mike Stannard used nickel silver. Presumably then, Per "rolled his own" so to speak, but I am pretty sure that Stephen's idea is what spawned this.

In terms of getting it properly cylindrical, this is how it came out. He used a roller similar to that in Stephen's article and fitted it to the plug in this picture:

It has a slip fit in the barrel:

The length of this insert is 37mm.

Hope this helps!

[Christoffer Ahlfors]

I see now that the boys need to clean the barrel out properly. Amazing how revealing a photo is!

[Jerry Carducci]

I must look back on my email from Per. I do recall when he told me about that insert. I though at the time it was a clever solution. I also had a reference to the 128mm PaK that described the rate of twist and number of grooves however I can't locate it presently. This is good information as I'm on the list to receive a Jagdtiger kit!

Jerry

[Adrian Harris]

Armortek have supplied details of the JT barrel so plans are afoot for a 3D printed plug.

The Andrew Dewey book has all of the details apart from the rate of rotation, so if you did find that reference it would be most helpful.

Adrian.

[Robert Reid]

Rate of rotation for most artillery (large bore guns) is 1:15 - 1:20 calibers....

So if you have a 100 mm gun, you are looking at a twist rate of 1 turn in 1500 MM to 1 turn in 2000 mm.

Tends to be a slower twist rate with larger bores. So if you are trying to do a large-bore 128mm PAK-type Maus cannon, you are probably looking at a twist rate if one turn in about 2.5 meters.

This is a guideline.... But as I collect, restore and shoot large (live) artillery (including making my own shells)... I can say this guideline pretty much applies. Of course, these days, smooth bores and fin-stabilized sabots are sort of the rule. But in the good 'ol days, this formula gave a general guideline.

As for count of lands/grooves... someone needs to visit the Tank Museum or Aberdeen MD and start counting!

Hope this helps!

Cheers,

RPR