Improving A Mould's Base Fillout

[462]

A NOE 311169 (Lyman 311291) five-cavity mould has been tormenting me with incomplete base fillout. I’ve read that using a file to just cut the top of the cavities’ sharp edges is the fix, but thought I’d try a different approach.

Not wanting the NOE mould to be the guinea pig, I decided to sacrifice a Lee two-cavity. Using an RCBS deburr/chamfering tool and lightly applied pressure, I gave the tool a half turn. Instant success.

It worked so well, the NOE received the same treatment and is dropping bullets with nice, sharp, completely filled out bases.

The reason for using the deburring/chamfering tool is that it should give a uniform trim, whereas a file may not.

 

[yodogsandman]

Ha, ha, ha, LOL....I've been having a hard time tonight and for the last few nights with a barely used 2 cavity NOE 311291. Same problem, base fill out. Plus others (sticking in the mold, worm lines). Mine responded good to increasing the lead flow. I've heat cycled it four times now. I tried breaking the top edge of the mold with a stone and making sure the sprue plate was adjusted right. Made sure to pour a big sprue puddle, too. Even resorted to smoking the cavities (solved the other stuff).

I had thought of trying a deburring/chamfering tool, like you but, wanted to try all other options first. I'll have to go and try that tomorrow night. Thanks for your post, it's very relevant!

Did you run a stone lightly, on the flat of the bottom of the sprue plate after?

 

[Ben]

If your mold is not offering good bullet base fill out and you are satisfied that your alloy and mold blocks are hot enough & your mold is 100 % free of oils and you continue to have " rounded bullet bases ".....this technique will remedy the problem. Often , air has a problem escaping from the area of the juncture of the sprue plate and the tops of the mold blocks. This air that can't escape can interfere with proper bullet base fill out.
Sometimes this can be remedied by simply loosening the sprue plate hold down screw and putting less tension on the sprue plate. This act of putting less pressure on the sprue plate will often times improve the escape of air and improve the bullet base fill out. If you try this and it doesn't help, it is time for a very slight amount of metal removal.

You take a FLAT FINE CUT SWISS FILE and remove a VERY SLIGHT amount of metal, - - - - Let me repeat A VERY SLIGHT AMOUNT OF METAL , in the areas where the red arrows are pointing. This metal removal is done on both of the mold halves.

If you fail to follow the directions and remove too much metal, you'll end up with fins on the bases of your bullets.
( Not a real big problem as your sizer die will break off the fins, but it is something that can easily be avoided , if you work slow and test your molds for proper base fill out )

Don't over-do this metal removal with your fine cut Swiss file.

When the work is done properly, this BREAKING OF THE EDGE, allows air to escape and greatly improves base fill out on your mold .

Ben

When I 1st purchased this mold and began to use it this particular Lyman mold wanted to offer about a 70% rate of proper bullet base fill out. Once the work that you see above was done, that changed to 99.5 % near perfect base fill out as you can see in the photo below.

 

[462]

Yodogsandman:
No stoning, filing, etc. was done to the sprue cutter, nor was any adjustment needed.

Ben:
I had tried all the other techniques and tricks, but the problem persisted.

 

[Ben]

462

Question,..........You have or have not done what you see in my photos above ? ?

 

[Brad]

I have a 9 mm mould from HM2 that was horrendous at first. I got close to 1/3 with rounded bases, possibly closer to 1/2.
Took me a few sessions of file and cast. File and cast. After the third session of fiing I got it right. No more rounded bases.
Like Ben said, go ssssllllllllooooooooowwwwwww

More can be removed but no metal can be added back.

 

[Ben]

Like my Barber says......." I can take it off with no problem, putting it back on, ....well that is another story ! "

 

[Rick]

Like my Barber says......." I can take it off with no problem, putting it back on, ....well that is another story ! "

Rogane . . . A barbers best friend.

 

[Brad]

Rogaine. Active ingredient minoxidil.

I know how Rick loves to be corrected!

 

[Rick]

eh . . . How would I know? I have more hair now than when I was 20.

 

[Ian]

I have the same amount as I did when I was 20. It's just not concentrated as much in the same places as it used to be.

I'm still stuck on this think about using a cricket to chamfer the base of the cavities, that's not what I do at all....but it works?. I leave the edges of the holes razor sharp and break the edges of the blocks with a file as per Ben's photo, that way the air can escape from around the bases. This is something I learned to do with Accurate moulds because the top of the blocks and sprue plate close together literally air tight and it seemed that I was always chasing a bubble right around the edge of the bullet base, or would have one just under the surface.

 

[Rick]

I have the same amount as I did when I was 20. It's just not concentrated as much in the same places as it used to be.

Nose and ears don't count.

 

[Ian]

Well that's no fair.

 

[Ben]

because the top of the blocks and sprue plate close together literally air tight and it seemed that I was always chasing a bubble right around the edge of the bullet base, or would have one just under the surface.

Been there, done that.
I not certain I've ever seen a mould that was filling out poorly on the bullet's base that didn't respond 100% to the treatment, we've discussed here.

Ben

 

[Ben]

Using an RCBS deburr/chamfering tool and lightly applied pressure, I gave the tool a half turn. Instant success.

Not certain If I'm clear on this ?

Are you spinning a deburring tool in the base of the mould cavities ?

 

[fiver]

that's what I make of it.

I use a sharpening stone on the edge of my molds.
that's what HM-2 was using too, at least they were when JT was still there.
I gave him the stone and showed him how to use it, and he would run it down the edge of every mold as it come off the CNC machine.
which reminds me the casting pot is heating up, and I'm making more of those 9mm boolits again today.
it seems like I never have enough of them.

 

[462]

Ben:
With the mould in the closed position, I inserted the tool into the tops of the cavities and gave it a slight twist, letting the tool’s weight do almost all the work. Visually (non-magnified), there doesn’t appear to be any change, but running a finger over the opening tells that the sharp edge is gone.

Ian:
Perhaps an unorthodox method, but, yes, it did work.

 

[Ian]

Ok, I was imagining you took off more metal than that.

One reason for rounded bases and even poorly defined lube groove bottoms is those sharp edges of the mould cool off quickly when the mould is open, so you get "cold mould syndrome" in just those spots. If your casting routine involves the blocks being open for any amount of time beyond the minimum to shuck the bullets and get it closed again rapidly, this can happen. It's worse with brass than anything IME. I can see how just barely touching up those sharp base edges would reduce the cooling fin effect slightly, just enough to make a difference. I was thinking this was a venting thing, but maybe not. The vee-grooving of the blocks is definitely a venting modification to improve the base fillout and reduce base voids.

 

[5shot]

Somewhat related question - How much do those super square edges matter on a GC Bullet? If the weight variation is within reason, and the base is going to be uniform due to the GC, I can't imagine it makes a huge difference.

I always strive for sharp bases, but have been curious about this.

 

[KHornet]

A very good and informative thread, particularly for relatively new casters and loaders.