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

[Tozguy]

Just wondering if the tail would survive better if it was rounded (or maybe boat-tail shaped) like many copper bullets.
The tail is most exposed to heat and pressure so that would make a sharp corner prone to erosion.
The bottom edge of the body seems to seal quite well and have survived OK.

b) not make the round such a tight fit in the chamber/barrel.

Based on how clean the aluminum is on the outside of the hull I bet that your idea is worth a try.
Cutting a slight taper to the hull might make it easier to extract without promoting blowby.

 

[toysareforboys]

Both great ideas, thanks! I'll try boat-tail shaped on the last 1/4" on the new longer tail, and one that's cupped as well, see how each one does.

I like your idea of the taper too, or at least not ALL of the hull has to seal in the chamber, just make a 0.5" sealing band near the base, might work. It'll be easy to see if I'm getting blowby with smokeless as it'll leave white residue on the black receiver face.

If I get blowby with the small sealing ring I might try an o-ring or two, more difficult to insert but should extract very easy.

Thanks again.

-Jamie M.

 

[Cadillac STS]

What is the compound that is used for tracer bullets? Might add some of that to be able to view the path of flight.

 

[toysareforboys]

What is the compound that is used for tracer bullets? Might add some of that to be able to view the path of flight.

Tracer rounds are prohibited at the indoor range (due to the rubber backstop I assume)

My friend has a super nice highspeed camera but he says the lighting in the range is so crappy it can probably only do 240fps or so at 1080p, probably not fast enough to see it.

-Jamie M.

 

[toysareforboys]

Did someone say ROUNDED? Woot

I made it from the normal projectile I shot it today:

[video]

With the rounded nose it's much much easier to insert into the barrel (to push the hull grip clips out of the way)!

I also reloaded it into the hull I shot today! Everything went back together perfectly, another 12.5 gains of triple seven FFg (by weight).

Won't get to launch until Thursday probably

-Jamie M.

 

[Tozguy]

Just wondering what approach you used to cut the nose round.

How does the round nose stand up to the impact on the baffles?

Also how did you solve the fired hull extraction problem mentioned earlier?

Thanks for the video, nice work.

 

[toysareforboys]

Just wondering what approach you used to cut the nose round.

I used this 3/4" radius router roundover bit clamped in my normal tool holder with a couple washers underneath to get the height centered: https://www.busybeetools.com/products/r-bit-roundover-2in-x1in-x1-2in-shank.html

I ran my lathe in reverse and cut it "from the back".

The only trick to using it is you have to keep the surface temperature of the Delrin under control otherwise it'll get gummy and grab the bit/rip it out of the chuck. I found that holding an ice cube against it while cutting worked perfectly (you only need one hand to do the cutting anyway).

How does the round nose stand up to the impact on the baffles?

I have not fired the round nose version yet but I should get to on Thursday.

The 45 degree angled backstop is made out of recycled car tires all chopped into tiny pieces so it's fairly fluffy/soft so as long as it lands in the backstop any projectile should receive zero damage. The problem is if it bounces off the backstop and hits the armour plate on the ceiling (baffles). I believe if the velocity is too high it bounces off the backstop.

Also how did you solve the fired hull extraction problem mentioned earlier?

I have two barrels, the hull got stuck in my spare 12" barrel, the one in the video in my last post is the 9" barrel that came with my launcher.

I have not extracted it yet. I've made a jig out of delrin to hold the barrel in my 50 ton press so I can press out the stuck hull (the jig has space for the hull to push out the bottom), should be pretty effortless.

The reason I have not extracted it yet is because I don't want to see the disappointment of the inside of the barrel being damaged. Barrels are next to impossible to get in Canada (they are a controlled part usually, for some reason LMT barrels can get here but not Colt) and are $$$. In my mind, if I haven't seen the damage yet, it isn't damaged. When I wipe away the tears I'll get it pressed out. Not sure I'll have pics or video of that, don't need to be reminded.

Thanks for the video, nice work.

Thanks! Glad you like the video. My range prohibits phones/cameras and video and pictures so it's tricky to record them

-Jamie M.

 

[Tozguy]

Ice cube...I would never have thought of that!

 

[toysareforboys]

I figured the only part of the projectile that would wear out when re-used a lot is probably the rifling engagement band so I will try out replacing it with a high temperature o-ring instead (specs of o-ring shown in photos for testing are ID: 26mm, OD: 36mm, Cord Diameter: 5mm). Very cheap (26 cents US or 34 cents CAD each shipped), user replaceable if it wears out and should provide a nice projectile to barrel seal and give good grip to the rifling.

I didn't round off the nose of the o-ring projectile because I already know the flight path of that one and I want to see what changes with the o-ring.

It's pretty stiff to get it into the chamber (especially with no lube) and then push the round all the way in (o-ring drags heavy on the chamber). If that gets too annoying I have an idea where I can use t-bolt hose clamps to compress the o-ring and squeeze it inside the hull!! Then it'll be super easy to push the round into the chamber/barrel and as soon as it fires and the projectile moves forward a quarter of an inch the o-ring will expand to engage the rifling. That's how I think it'll work anyway. Once the rest of my order of the hulls arrive I'll set up a bunch of different setups and test them all.

-Jamie M.

 

[Tozguy]

Is the o ring groove square? Seems to me that lube would help the o ring slide into the chamber.