Recovered PC bullets

[Brad]

Here is a 200 swc from the berm. Bullet was loaded over 4.5 gr of Promo and fired from my Gold Cup.
Near as I can tell the coating isn’t really cut by the rifling.
The coating sticks very well even after impact. This is some tough stuff.

 

[Wasalmonslayer]

Fantastic!
Is that the grey powder??

 

[Brad]

Fantastic!
Is that the grey powder??

Why yes it is. Works very well for me. I much appreciate you sending it to me.

 

[fiver]

well...
you know I been looking at this picture for 2 days now.

question.
does the lube groove look like that all the way around?
like someone placed a pretty decent weld around the center.

 

[462]

Not being a bullet forensic technician, what caused that base crater?

 

[popper]

Rifling looks even neater. Soft alloy. I hit an edge of steel with 308W (smoke's red) foud a sliver of the nose - wrinkled alloy on one side, red PC on the other. Yes, it does stick well.

 

[Wasalmonslayer]

Why yes it is. Works very well for me. I much appreciate you sending it to me.

Your welcome!
Let me know if you run low I have quite a bit stashed away.....

 

[fiver]

short answer.
pressure in a void.

longer answer.
the bullet was cooling, the sprue was cooling, there was no alloy transfer from one to the other to make up the take up of alloy.

 

[Ian]

The lube groove got squinched between the base going 800 fps and the front suddenly going to zero. I wonder how much of it happened when the opposite was occurring.

 

[462]

short answer.
pressure in a void.

longer answer.
the bullet was cooling, the sprue was cooling, there was no alloy transfer from one to the other to make up the take up of alloy.

So, the sprue puddle was not too big enough?

 

[Ian]

Or the sprue plate too cool and the sprue froze before the bullet had fully solidified. The bullet shrinks as it cools and needs the sprue to draw from as it hardens. If the sprue freezes first, it can't flow to supply the bullet base so the base pulls itself apart as it cools and shrinks. The fix is to continue to pour metal over the sprue hole for a few seconds after the cavity is filled, then form the sprue. I call this "washing out the sprue".

 

[fiver]

it could easily have been.
it might have occurred before the sprue puddle was totally poured.

if you watch your puddles closely they don't always suck down.
sometimes it's because they don't need to, and well,, some times they can't even though they want to.
if you are seeing a little dimple form on the sprue right before it flashes over then you know the bullet is pulling extra alloy in as it cools.

 

[Ian]

It's not always a bad thing to have a crater in the back of a pb bullet, usually it hurts nothing and might in work in some caoacity to improve obturation by distributing pressure to the barrel walls.

 

[462]

My sprue puddles get sucked down noticeably enough, but have seen them not do so, too.

When weight sorting, I figure the occasional lighter weight bullet is due to a void, but what causes one to weigh two to three grains more than the other 49?

 

[Ian]

Losing focus on handle pressure or a little speck of alloy getting between the block faces are the usual suspects. If you get a heavy one, measure it and compare to bullets in the normal range, I bet you find it to be larger in the dimension 90⁰ from the parting line.

 

[Brad]

Not being a bullet forensic technician, what caused that base crater?

If I hit you in the base with 15 K PSI your base would pucker too!

I would imagine some base porosity from shrinkage with insufficient sprue. May need to work on that. Pouring longer into each cavity or going back across the cavities after all are filled may help.

 

[Ian]

But...it only matters if it does.

This is an instance of it mattering (50K psi 2450+fps):



The base looked fine but it obviously had a soft/porous spot under the sprue hole. The sin was revealed after firing and not concealed in the least by the thin copper gas check.

 

[Brad]

And 50 K PSI will make it an issue long before 15 K PSI will.
Just another example of why bullet quality, and I don’t mean weight segregation, is so critical at HV.

 

[Rick]

I would imagine some base porosity from shrinkage with insufficient sprue. May need to work on that. Pouring longer into each cavity or going back across the cavities after all are filled may help.

I have heard that before. A time or two actually.

 

[Brad]

I have heard that before. A time or two actually.

Me too. And always in the same voice. Imagine that?