7.62x40 WT

[Hawk]

So those are tin oxide swirls. This mold has made me jack the temp on my furnace up to levels I have never used before.
Got the furnace set to 700-710 Degrees.
I'm running the mold really hot and fast. Have to use a fan to cool the sprue plates. Bullets are frosted in the middle and bases, but not so much on the nose.
If I don't run this hot and fast, I get wrinkles in the nose.
I want my bullets to look like Ben's. Bright and shiny

 

[Hawk]

At least I figured how to get the picture upright!

 

[Ian]

I think Ben must cast with his moulds on the ragged edge of too cold and often, if you look close, he gets rounded driving band edges on one side or sometimes even all around. That's the razor's edge between fillout and frost. You can ride that line (which often takes a lot of tin in the alloy or an iron mould), or go way past it. With aluminum moulds I find it much easier to run the alloy at 725°F and pour a smaller sprue puddle, plus use a fan to cool the sprue plate so the sprues can be cut sooner. This will encourage heat sink into the bottom of the blocks. The danger here of running a mould this hot and fast is that you can begin to get "shrunken bullet syndrome", where the middle of the bullet is undersized. Dan wrote an excellent article on the subject which can be found at the Mountain Molds website. Others may have success with other methods, but with aluminum, I generally run a hot alloy and brisk pace to keep the heat up.

And here's what they look like: Far left and far right are straight clip-on WW alloy, two in the middle are 50/50 soft scrap and clip-on WW with 1% tin added.

 

[Hawk]

Excellent bullets, much better than mine.
Do you flux a lot to keep the tin from oxidizing or keep a layer of something on top of the alloy?
I've just got a 10 lb lee furnace, so I don't get a lot of bullets before having to replenish my alloy.

 

[Ian]

Here's the problem Creeker was dealing with recently with an aluminum mould someone sent him to diagnose, and his solution was merely to apply his experience to find the temperature that the mould liked. Once he hit that, with no other mods to the mould (including no cleaning or anything if I'm right), he got perfect fillout with no added tin. He did comment that the bullets were coming out lightly frosted when they started to sharpen up, which is typical of low-tin alloy such as what he and I tend to use.

 

[Ian]

Excellent bullets, much better than mine.
Do you flux a lot to keep the tin from oxidizing or keep a layer of something on top of the alloy?
I've just got a 10 lb lee furnace, so I don't get a lot of bullets before having to replenish my alloy.

I don't flux much at all in my pot (20lb Lee). Sometimes, when it doesn't matter much, like casting high-volume pistol bullets, I'll throw back the sprues as I go and that tends to build oatmeal on top of the mould and eventually carry oxides to the bottom of the pot where they find their way into the mould. When doing that, I stir vigorously about twice during the session, let the oatmeal rise to the top, and skim it off. When I replenish the pot with ingots and culls, I add the skimmings back and do a little sawdust flux to recover the oxidized metal.

 

[fiver]

I see that same thing with my accurate mold.
when I see it right in front of the front drive band I know I'm in the proper heat zone to keep everything within about 1/2gr easily.
it's also where I want to be for sizing.
if I get any heavier than 166.9 grs the sizer will wipe the tapered front section of the boolit telling me I went too big.
if I go under 166.4 grs I have a void somewhere or incomplete fill out. [usually on the base]
I weight sort into .4.5.6 and .7.8.9
the vast majority of them come in at 166.6 once I see that little bit of frost look and keep the mold there.
I can also tell in the sizer.
the boolit enters the die and has the slightest amount of resistance so the gas check is pushed on square as it's squished into place on the shank.

 

[Hawk]

Finally got out this weekend to shoot some of the PC coated bullets out of the 31-155W Mold.
19.0 Grains AA1680
rem 7-1/2 primers
OAL 2.05'
No gas checks

IIRC Accurate Arms lists around 19.7 grains 300 BlkOut with a 165 grain Jacketed projectile.
My PC coated boolits weight about 159 Grains.

Just trying to fire form some brass, so I started with a light load.
Ejected the round, but wouldn't pick up the next round or lock the action open on the last shoot.
All rounds went into 1-1/2" at fifty yards. Had several five shot groups go into 1/2" to 3/4" at fifty.
Had to stop after about 40 rounds, because I had a stuck failure to chamber on a round and didn't have a rod to drive it out. Appears to have hung up on the shoulder.
I'll have to get some measurements and figure in out. might have the crimp set too low and did a little crush on the shoulder.
It was so hot, I couldn't fire but 15 rounds before I had to quit and let the barrel cool.
When I get all 100 rounds fire formed, I'll start trying to work up a good load and chrono some. The Chrono is hard to set up at a public range on the weekends!
This bullet really wants to shoot!

 

[Ian]

Not to sound like a MagnetoSpeed salesman...buuttttt....