Why are my bullets growing?

[btroj]

I wonder if some of the growth could also be diameter related?
Do bullets under say 40 cal not grow while those over 40 do? Could the difference in rate of cooling have anything to do with it?
I have not had a situation where I KNOW a bullet grew but that certainly doesn't mean I think it can't happen.

Looks to me like more testing needs to be done. Bad thing is it is probably very alloy related and who knows what the "magic" mix is?

[Blackwater]

I ran into a similar situation with my 1885 Brng BPCR when I first started shooting it. I was compressing the powder with the bullet when I seated it. The pressure of compressing the powder squished the bullet out a bit, and some ctgs. just wouldn't seat in the chamber no matter how hard I tried. I got a compression die to compress the powder charge with, and no more problems.

[462]

My instance of boolits growing fatter involved Lyman 429421's. They were cast in the winter of 2010 of 100% wheel weights, dropped at .433+" and air-cooled. After setting for a day, they were sized and lubed in a Lyman .433" sizer die, then stored.

Earlier this month, I went to load some and they wouldn't fit in the case mouth, which had been expanded to .433", by a custom M-die expander plug (first step .431", second step .433"). I removed the lube from a couple boolits, cleaned and measured them. They measured .434". I re-ran the boolits through the .433" sizer and was able to load them.

I'm neither a chemist nor a metallurgist, so I don't know, nor can I explain, the how's and why's. All I know is that it happened.

[Stick_man]

Stop watering them. Soon they will wither up and die. Also, maybe cut back a little on the fertilizer. That should stunt the growth some.

Mine tend to grow quite a bit on one end, but that is usually after firing them and hitting something pretty solid.

[leftiye]

Thay's yung yet. Thay'll stop growin' when thay mature.

[fatelvis]

I know this is a very old thread, but I just found that my previously .311" sized 311299 boolits now mic @ .3116" after finding them after 8 years. They contain tin and Antimony, and maybe a bit of copper (used plumber's solder to alloy). Would the Copper, or some other foriegn additive make it grow? Thanks for your input!

[JSnover]

I know this is a very old thread, but I just found that my previously .311" sized 311299 boolits now mic @ .3116" after finding them after 8 years. They contain tin and Antimony, and maybe a bit of copper (used plumber's solder to alloy). Would the Copper, or some other foriegn additive make it grow? Thanks for your input!

Yeah, after 14 years I assume the OP has it sorted out. I had the same thing happen when I started experimenting with neck tension a long time ago. Loaded twenty rounds and I noticed the first ones were visibly longer than the last. As they sat in the loading block (un-crimped) pressure in the case pushed the boolits back out. Can't remember if it was black or smokeless, new brass or used. Double-checked my dies, polished the expander plug and sizing die, and the problem went away.

[Taterhead]

Since we're back into an old thread, I'll add this. My alloy is about 3% sb 1% sn. I observe growth so consistently and reliably that I count on it. E.g., I cast and powder coat 10mm bullets then size to .401. The NOE sizer gets them to .401 on the dot. After a couple of weeks they will be .402 and that is what my Glocks prefer. 9mm, same thing.

No clue about the metallurgy or science, but just what I see with repeatability. It's like a slow motion springback from the sizer.

[fatelvis]

Since we're back into an old thread, I'll add this. My alloy is about 3% sb 1% sn. I observe growth so consistently and reliably that I count on it. E.g., I cast and powder coat 10mm bullets then size to .401. The NOE sizer gets them to .401 on the dot. After a couple of weeks they will be .402 and that is what my Glocks prefer. 9mm, same thing.

No clue about the metallurgy or science, but just what I see with repeatability. It's like a slow motion springback from the sizer.

That is very interesting! I do like the fact that the growth is expected and is so predictable. Once again, I’ve learned something on this website. Glad I found this place years ago!

[JonB_in_Glencoe]

I know this is a very old thread, but I just found that my previously .311" sized 311299 boolits now mic @ .3116" after finding them after 8 years. They contain tin and Antimony, and maybe a bit of copper (used plumber's solder to alloy). Would the Copper, or some other foriegn additive make it grow? Thanks for your input!

As I understand it, bullet alloys with Antimony can, or will, grow as they age harden (grow crystalline structure), depending on the amount of Tin content. Also, if the alloy contains Calcium and/or Copper, those can act like a catalyst for more growth. In several months (6 to 24), bullets can grow as much as .0005" diameter, to an excess of .0015" ...depending partly on the caliber diameter, the larger, the more growth is possible.
I have also theorized that Heat treated or cold water dropped bullets have that crystalline structure growth happen much faster and diameter growth over extended amounts of time is lessened or eliminated.

[popper]

"When you loaded it, you smushed the nose a bit to make it fatter." yup. My alloy is Pb & Sb maybe a tad of Cu sometimes. There is NO alloy of Pb & Sb. SbSn is an intermediary molecule that is NOT stable. In precipitation cooling, it is the mechanism to make layers of Sb/Sn 'heavy' MIX. it degrades into Sb & Sn with air cooled, some may stay with WD. Tin tends to glob together, (atoms move at room temp) and can cause larger diameter.
I recently had some 300 BO that wouldn't chamber. Soft alloy GCd. Suspect some un-annealed cases with tight neck clearance (same expander and cast batch) caused the front band outside the neck to be a thou. larger from SEATING. GCs were not annealed and were Sages (IIRC).