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

[Cadillac STS]

If I put the primer (and powder) in then try and press the projectile in the air pressure builds up huge in the chamber and either pops the primer out or prevents me from fully seating the projectile I'm pressing the projectile in 1 inch, that's compressing the chamber from 0.666cu in to only 0.05cu in! I'm not sure how to calculate what the air pressure inside would be at the end but I assume it must be pretty high. I also know when you're compressing air that much it gets very hot, if I compress it too quickly it might get hot enough to ignite the powder = boom.

If I'm pressing the primer in as the last step I can't figure out a way to use a pressure release bushing. With the press holding both the projectile in as well as the primer, wouldn't the actual case/hull explode?

-Jamie M.

To avoid too much pressure when pressing in the projectile make a very small slot up to about the last 1/4 inch of the projectile so while pressing it most of the way pressure escapes then the last 1/4 inch it seals and puts in a little pressure.

The smallest of slots like scratching of a pin just to let the air out. Then maybe one on each side in case the pressure release at firing would be uneven.

 

[toysareforboys]

To avoid too much pressure when pressing in the projectile make a very small slot up to about the last 1/4 inch of the projectile so while pressing it most of the way pressure escapes then the last 1/4 inch it seals and puts in a little pressure.

The smallest of slots like scratching of a pin just to let the air out. Then maybe one on each side in case the pressure release at firing would be uneven.

Nice, that could work!! I thought about making a slot but I wanted to keep 100% of the pressure in the case until the projectile is well on its way (1 inch) down the barrel (to reduce the pressure spike that the barrel/barrel chamber will see). I also figured a slot would reduce the re-usability of the projectile because the hot gas escaping through the slot would erode it quickly.

I still might use your idea though because pressing a primer into the cup while the gunpowder is in there is scary

Thanks for sharing and the good photography!

Glad you like it Hopefully I'll have some videos to share shortly too.

-Jamie M.

 

[derf]

Instead of machining all those projectiles, you could make a mold and cast them from polyurethane. Much faster and not to mention less expensive.

Alumilite - Mold Making & Casting Resins

www.alumilite.com

 

[toysareforboys]

Instead of machining all those projectiles, you could make a mold and cast them from polyurethane. Much faster and not to mention less expensive.

Alumilite - Mold Making & Casting Resins

www.alumilite.com

If they turn out to be as not as reusable as I'm thinking, I'll probably go that way, thanks!

-Jamie M.

 

[Cadillac STS]

One thing to consider to make things easier is using your lathe to make a custom holder for the press.

3.5 inch steel round stock 6 inches long or so.

Bottom bore out an inch or so that will just fit your jack ram. Top bore out just big enough to insert your cartridge including the projectile so it goes in straight.

Also gives some blast containment.

So then you have a stable method to do it, not balancing it with pressure risking it going the wrong way.

 

[Tozguy]

Just to be clear, there should be no attempt to contain the blast as pressure will find its way out somewhere somehow.
Any holder or chamber that would be pressurized as a result of a mishap should be adequately vented in a safe direction.

 

[Cadillac STS]

Explosives are dangerous. be Very careful. Especially with a hand held devise. To me not worth the risk.

 

[toysareforboys]

First range trip was a success! Still have all my fingers and both barrels survived without issue (barely). They didn't allow pics or video unfortunately. And boy does smokeless powder really take the fun out of launchers. No smoke? NO FIRE? lol. Not sure why I was so afraid of smokeless?? With 7 grains of Trail Boss it felt like shooting a .22LR (both noise and recoil), vs. 55 grains of Triple Seven FFg felt and sounded like a 12ga (it probably detonated, see the primer bulge pic below)!

Note to self in case I forget: Mount the M203 sight higher so I can keep the gun against my shoulder easier when aiming/firing.

I shot the 7 grain smokeless one first, out of the 12" barrel. Almost zero dirt/residue in the hull, barrel chamber or barrel, sweet. Landed 4ft low at 50 yards using the M203 sight set to 50. I was unable to extract the case from the barrel so for the next shot I just swapped barrels. The projectile took a funny bounce off the floor/backstop and and hit the 45 degree armoured steel baffle near the ceiling and shattered. I could see the blue scuff on the baffle and used that mark to know where to dig in the backstop to find as many pieces as I could:

Next was the 55 grains of Triple Seven FFg out of the 9" barrel. Almost too much smoke for the range but they said if I limited myself to 1 shot every 5 minutes it would be allowed. Recoil was crazy, felt just like a 12ga slug, my wrist and shoulder hurt pretty good. Lots of noise and fire. Makes quite a mess in the barrel and the hull is dirty inside and out but for sure not as sticky/gummy as Goex black powder and cleaned up easy with soap and hot water then wiped it down with WD40. Projectile landed 6 inches high at 50 yards, pretty much right on target, and landed softly in the backstop, no bounceback. Upon recovering the projectile I noticed the tail was missing. On the shooting table just in front of the barrel were little blue plastic pieces so I'd have to assume that the tail broke off or shattered on launch, not really sure what could have caused that, maybe too much pressure on ignition and it shattered the tail instantly? Maybe the powder wasn't packed tight enough and it detonated? That would explain the nutty recoil and the primer cap being bulged and molded into the shape of the firing pin hole!! I looked and looked, all over the range floor, the backstop, for the tail or peices thereof, nothing. The hull extracted from the barrel without issue. I used my micrometer to measure the barrel diameter and checked it from front to back, no bulging, impressive! I find it pretty amazing that it survived that much overpressure (having a projectile that light helped of course).

Check out that primer bulge

Before I packed up to head home I figured I'd try and get the smokeless hull to come out of the 12" barrel and boom, it slid out perfectly easy... what the fudge?? My only guess is that it's such a close fit that once the shot goes off and the case gets warm it expands slightly making it impossible to remove, then once it cooled down it came out fine. Just a guess.

All in all a great trip, lots of info/data to go on. I think from this point forward I'll stick to smokeless, even if it's less fun it seems much safer.

-Jamie M.

 

[toysareforboys]

Alright, second version of the smokeless setup.

And finished (I shaved .001 off of most of the hull to hopefully help extraction after firing):

Same aluminium cup, projectile tail shortened from 1" to 0.75", 10 grains of Trail Boss smokeless, and oversized the tail 0.040! Yikes. Made some creaking and groaning noises pressing in but she did it. Hopefully that'll get me more combustion of the smokeless.

Should get to light it off tomorrow (Monday), will try and sneak in a camera.

-Jamie M.

 

[toysareforboys]

The new smokeless setup worked AMAZING!!! Flawless combustion, a TON of power, wow. Not quite as much recoil as the detonation of the triple seven yesterday but close! The lady that was shooting .22LR on the handgun range across the hall (I was on the rifle range) came over to make sure everything was ok, lol. She said it was so loud she almost dropped her gun, she was just getting ready to shoot, and then she had to put it down for a while because she was so shaky. I think the smokeless is working good now

My first pull of the trigger was just a click, looked like a light primer strike (was pretty off center too, weird). My guess is that because the hull is such a tight fit in the chamber that the spring pin in the barrel that's supposed to keep the hull tight/flat against the receiver face isn't able to do its job, so the hull was sitting a hair off the receiver face so the firing pin had to travel too far to hit it. I solved this on the second try by not seating the round as far into the barrel (I did, but used my knife to pry it back a bit) and closed the barrel very slowly and only until the latch clicked, as to keep the hull tight against the receiver face. Worked fine that time.

To avoid the light primer strikes in the future I can a) make the extraction rim on the hull thicker so the barrel better holds it tight to the receiver face and/or b) not make the round such a tight fit in the chamber/barrel. Option b might be required because once again, after firing the round, I couldn't get the hull out of the barrel until I let it fully cool down

I think I'll go back to 7 grains or less now that I have good combustion, 10 grains is pretty insane, lol.

Once again the projectile hit the steel baffle on the ceiling, put a big scuff in the front of the projectile but didn't shatter it this time. It's probably reusable but might not fly very straight. Next time I'll have to put a camera down at the backstop to see what's going on down there. If I can get my projectiles to land in the soft backstop they'll be very reusable, not so much when they hit the metal baffles.

I was able to sneak in a camera, sorry for the horrible audio as I was right beside where the main ventilation fans are. Headphones users use caution

[video]

Check out those impressions from the receiver face, and that dent from the extractor push pin! That must have been some serious recoil

When I went to clean the barrel I noticed it was full of lots of plastic debris (it was spotless before the shot), could it all have come from just this little chip on the tail? There's no other plastic missing from the projectile other then where it looks it hit the metal baffles?!? Very strange!

Can't wait for my next trip, I'll have a bunch of rounds loaded up including some with perfectly round noses (maybe they'll survive hitting the baffles better)!

-Jamie M.