Plaster casting .408 cal

[mouz]

oh my god..... what is wrong with your shock pump?!?!?!?!?!??!? it seems to be alway dieing. what pressure did it go to? mine goes to 400 psi (28 bar). the thing is my copper barrels are very thin and i wasn't sure if they could take it, but recently i had a good look at some rifling on a pistol and it was very shallow. i think i might have to harden the steel of the hex nut for copper, and i will spend more effort to make a nice sharp bead.

[FighterAce]

I have no idea what was wrong...  I know what pressures it can reach, I have the same one as you do  Maybe I went 2 or so bar over the pressure gauge limit here and there but thats not enough to brake the pump like that... must of been bad quality control on the batch or something

If you keep the grooves shallow enough you'll have no problem with rifling copper. The problem is getting the bullet to catch those shallow grooves.

I wanted to use 13mm copper too for my sniper because I found a way to make a very nice full metal bolt action using the 13mm as the barrel, 22mm as the bolt and 3/8 connectors as the spacers. At the end I switched back to PVC barrel because of the weight issue. It would be way too heavy with a copper barrel to carry in the field... every ounce matters when you gotta hump it around all day    You learn that real fast when you start, believe me.

[BoyntonStu]

I have no idea what was wrong...  I know what pressures it can reach, I have the same one as you do  Maybe I went 2 or so bar over the pressure gauge limit here and there but thats not enough to brake the pump like that... must of been bad quality control on the batch or something

If you keep the grooves shallow enough you'll have no problem with rifling copper. The problem is getting the bullet to catch those shallow grooves.

I wanted to use 13mm copper too for my sniper because I found a way to make a very nice full metal bolt action using the 13mm as the barrel, 22mm as the bolt and 3/8 connectors as the spacers. At the end I switched back to PVC barrel because of the weight issue. It would be way too heavy with a copper barrel to carry in the field... every ounce matters when you gotta hump it around all day    You learn that real fast when you start, believe me.

Heft a 38" length of 3/4" Type M copper tubing.

It light as a feather, and I have had it to 600 psi.

Compare that to your PVC barrel.

[FighterAce]

I dont need copper for air tank so it doesnt matter how much it can take... and in Croatia we dont have type M, L, etc. we just have designations by OD so its 15, 18, 22 etc.

btw. all copper pipes have a 1mm thick wall... how does that compare to Type M?

[mouz]

the copper pipe i have sure isn't that thick. its more like 1/2 mm.

[FighterAce]

I finally got a digital scale and some RTV silicone rubber for mold making.
After 3 tries and 2 wrong ratios because of the faulty instructions I came up with this...



I know it isn't perfect but it works 

Heres how the plaster bullet looks like...





I decided to use electrical tape as a seal for now...







The weight is 8.5 g atm but it will get lighter as the water evaporates and glue hardens.

Now I just need to find whats the SG of the electrical tape to get a barrel with a right twist rate and then get some groupings 

[Forum Admin]

Now that's a nice bullet casting setup. They'll be pretty spectacular to shoot against a hard object. Have you considered putting a nail inside? 

[FighterAce]

Hold your horses 

Just had an interesting chat with guys @ spudfiles... apparently I need a 1 in 3.2 twist rate witch would produce 160 000 RPM and plaster just cant take that...

Yes I have considered a nail inside but right now I'm dead in the water with this bullet.

[FighterAce]

I just might get lucky with cement... not sure but I think it could survive.

[Forum Admin]

A nail will bring up the mass and lower the twist rate, not sure by how much, though.  Fishing sinkers would do even better. Of course, anything put inside would have to be centered for good flight.

[josephlys]

Wow thats a very good looking bullet you have there, very nice bullet casting setup indeed.