How to machine the end of a 1.5" dia rod perfectly round?

[toysareforboys]

I reload 45 LC using about 1/2 a case of Trail Boss.
Trail Boss is a powder that has been designed to occupy a large space (with little weight) and still burn <relatively> slowly.
The typical 8 pound canister only holds 5 pounds.

You might get enough umph out of TB for your project.
And there is basically no way to have so much that something goes boom.

Wow, neat powder! Never seen it for sale in Canada but I'll look extra hard. How's the smoke with it?

Thanks!

-Jamie M.

 

[cjtoombs]

Also, if you don't need it for looks, I don't know that at the velocity that those will shoot that the nose of the projectile will make much difference to performance, that truncated cone you did on the lathe may be just fine for your purposes. They make bullets that are basically that shape for pistol cartridges anyway.

 

[682bear]

Smokeless powder will detonate... especially with light loads in large cartridges...

Several years ago, I played around with some Trail Boss while experimenting... trying to see how accurate I could get 160 grain cast lead bullets to shoot out of a 30.06... the trail boss didn't prove to be a very accurate powder.

IIRC, my load book said you could take practically any standard metallic cartridge, fill it full, then weigh the charge, and that would be 'max load' for that cartridge...

-Bear

 

[Tozguy]

Considering that you are cutting Delrin, I would consider using one of these to cut a round nose on a lathe.
https://www.amazon.ca/Kempston-3014...=2025&creative=165953&creativeASIN=B0013KRS1K
It should be straightforward to mount the bit in the tool post on center.

 

[Tozguy]

About the reloading, based on my experience with shotgun and light pistol loads for smokeless powders, I would go to the trouble of packing the case if only to get consistent combustion during your trials. I don't know how well read you are on pistol loads but there is a lot of info in that niche on using smokeless powders with short barrels at low pressures.
Trail Boss would be my first choice to try.
Do you have a bullet trap? Using smokeless powders it is often possible to see the bullet fly at low velocities.

 

[Cadillac STS]

With Delrin what about getting it close to round on a sanding wheel or sanding belt then put it in the lathe to finish out with various levels of sand paper (Maybe files) to smooth. Lathe will keep it concentric.

Wouldn't need a ball turner on the soft material.

 

[cjtoombs]

Smokeless powder will detonate... especially with light loads in large cartridges...

Several years ago, I played around with some Trail Boss while experimenting... trying to see how accurate I could get 160 grain cast lead bullets to shoot out of a 30.06... the trail boss didn't prove to be a very accurate powder.

IIRC, my load book said you could take practically any standard metallic cartridge, fill it full, then weigh the charge, and that would be 'max load' for that cartridge...

-Bear

To be technical correct, most smokeless powder (except for some propellants tried by the military) will not "detonate". That doesn't mean they won't blow you're gun up, but a detonation, in technical terms, is a very specific thing. A deflegration explosion is what you see in gun failures, when the gun breech or cylinder explodes in a few large pieces. This is due simply to the pressure inside increasing slowly (relative to a detonation) until the strength of the containment is exceeded. A true detonation produces small fragments due to the detonation wave propagating around the cylindrical body and producing rarefaction waves that tear the container apart, these waves bouncing back and forth inside the pieces and tearing them apart in turn, until there is not enough energy to further tear the pieces apart. I suspect that these low load gun failures are related to the poor propellant bed ignition I discussed above, if they exist. Discussion of them has been around since the 1950s, P.O. Ackley attempted to replicate them and failed. I have shot reduced loads and never had a problem. If it does exist it is only in very specific loads and then under very specific conditions.

 

[toysareforboys]

Considering that you are cutting Delrin, I would consider using one of these to cut a round nose on a lathe.
https://www.amazon.ca/Kempston-3014...=2025&creative=165953&creativeASIN=B0013KRS1K
It should be straightforward to mount the bit in the tool post on center.

Ahhhh, neat idea!! I think I'll give that a try, thanks!

I found some Trail Boss powder locally On the 37mm/40mm forums they said they use up to 20 grains. I'll start with 5 grains and work my way up. Should be fun!

-Jamie M.

 

[toysareforboys]

This Trail Boss powder is weird, you pay for 1LB of it but you only get 9 ounces! lol

It's absurd how light/less dense it is vs. goex or triple seven. 20 grains just about fills the whole case not leaving much room for a tail on the projectile. If I end up eventually using that much I'll have to increase the diameter of the chamber.

Thanks again guys for all the help, even with the non-machining info. Can't wait to give it a rip.

-Jamie M.

EDIT: I decided to spin up another prototype hull/case with a 7/8" diameter chamber instead of the 1/2" one above. That'll give me 98.5mm³ of chamber volume instead of 32mm³, nice. I'll try and get it finished tomorrow

 

[rwm]

This looks pretty cool. Can you tell me more about the projectiles and intended use? Do you recover the blue projectile? Why round instead of stock? Do you launch other objects in front of it? What other kinds of load does this use. (aside from grenades!)
Robert