joeb33050
12-29-2008, 08:27 AM
This article with pictures is attached.
BULLET BASE BUMP DEFENSES
Sometimes cast bullet bases have bumps of alloy where the hole in the sprue plate was. Some shooters contend that these lumps cause inaccuracy.
With gas-checked bullets, the lump ends up as a bump on the gas check; that certainly looks like it should cause inaccuracy.
With plain base bullets the lump may be there on the bullet base.
I know of no test or experiment that shows inaccuracy caused by bumps with either gas checked or plain-based bullets. Doesn't mean that these bullets with bumps aren't inaccurate, just that we have no data showing that inaccuracy.
Nonetheless, I don't want the bumps.
If you're plagued by these bullet base bumps, here are some ways to fix the problem.
First, the mold.
Loring Hall told me years ago that molds frequently require adjustment, and I have found this to be true.
The top of the mold and the bottom of the sprue plate should be flat, without any burrs or bumps.
The sprue plate should be loose enough to almost/just barely swing of its own weight.
We're told by alleged experts that the sprue plate hole/s must be sharp. I've fiddled with some sprue plates, cutting or lapping the sprue hole to make it "sharper", but can't remember any notable success or seeing a sprue plate where the hole edge isn't sharp looking. An 82 degree countersink suggests itself as the tool. (Some claim that lapping the sprue hole/s aids in sprue release. I find that a tiny dab of NRA Alox in the hole just makes those sprues fall right out.
I lubricate the sprue plate screw-top of the mold at the screw-top of the sprue plate at the screw with the tiniest bit of NRA Alox formula bullet lube. I use the same tiny bit of lube on the alignment pin ends. All this lubing every now and then as I cast. This lubing ends up as a very slightly lubed top of the mold and bottom of the sprue plate, kind of baked on but still slightly greasy.
Here are four approaches to getting rid of the bumps.
First is the "file or grind or cut the bumps off the bullet bases" method. We've all filed bullet bases, and tried to cut the bump off the bullet base; by hand. This never worked for me, so I gave it up many years ago.
Sometimes this method employes fairly elaborate machinery. For an example, see "Making Flat Base Bullets" by Art Coover in "The Fouling Shot", No. 162, March-April 2003
Second is the "open-the-sprue-plate-with-the-gloved-hand" method. This is said to result in bumpless flat bullet bases. Dan Willems and Wallly Enga use this method. I have tried the gloved hand to open the sprue plate, gave it a good shot over a lot of bullets and molds; including a John Greene mold with a wooden handle on the sprue plate extension. This method didn't work well for me.
If I opened the sprue plate too soon, there were holes in bullet bases, see the examples in the picture.
.
If I waited too long, the alloy hardened and it was hard to cut the sprue.
I needed the yellow mallet to entice the sprue to fall off the sprue plate and the bullets to fall out of the mold. I must whack the handle hinge to get the bullets out of the mold, sometimes, and I've done all the cavity polishing tricks there are. And, I'm left handed-in a world where ladles are made for righties. Put it all together, keeping in mind that we have to pick up the mallet anyhow, and the hand opened sprue plate didn't work for me.
Third is the "cool the sprue plate briefly by touching the hot metal to a cooling sponge or rag, then cut it off conventionally. The hardened alloy will cut uniformly clean when the sprue is cut with the force of the mallet blow directed at a slightly downward angle"; advocated by Forrest Asmus. Others, including Pete Mink, use this method without the cooling.
Fourth is the "cut the sprue-move the sprue plate back so the hole is not over the bullet base but the sprue plate is over the bullet base-whack the sprue plate to flatten the lump" method, which I invented.
After casting and opening the sprue plate, close the sprue plate such that the plate and not the hole is over the bump, and give the top of the sprue plate a good whack with the yellow plastic mallet. This will mash the bump down and make it go away.
So here are four methods of getting rid of those annoying bumps. Try the last three and pick the one you like best.
BULLET BASE BUMP DEFENSES
Sometimes cast bullet bases have bumps of alloy where the hole in the sprue plate was. Some shooters contend that these lumps cause inaccuracy.
With gas-checked bullets, the lump ends up as a bump on the gas check; that certainly looks like it should cause inaccuracy.
With plain base bullets the lump may be there on the bullet base.
I know of no test or experiment that shows inaccuracy caused by bumps with either gas checked or plain-based bullets. Doesn't mean that these bullets with bumps aren't inaccurate, just that we have no data showing that inaccuracy.
Nonetheless, I don't want the bumps.
If you're plagued by these bullet base bumps, here are some ways to fix the problem.
First, the mold.
Loring Hall told me years ago that molds frequently require adjustment, and I have found this to be true.
The top of the mold and the bottom of the sprue plate should be flat, without any burrs or bumps.
The sprue plate should be loose enough to almost/just barely swing of its own weight.
We're told by alleged experts that the sprue plate hole/s must be sharp. I've fiddled with some sprue plates, cutting or lapping the sprue hole to make it "sharper", but can't remember any notable success or seeing a sprue plate where the hole edge isn't sharp looking. An 82 degree countersink suggests itself as the tool. (Some claim that lapping the sprue hole/s aids in sprue release. I find that a tiny dab of NRA Alox in the hole just makes those sprues fall right out.
I lubricate the sprue plate screw-top of the mold at the screw-top of the sprue plate at the screw with the tiniest bit of NRA Alox formula bullet lube. I use the same tiny bit of lube on the alignment pin ends. All this lubing every now and then as I cast. This lubing ends up as a very slightly lubed top of the mold and bottom of the sprue plate, kind of baked on but still slightly greasy.
Here are four approaches to getting rid of the bumps.
First is the "file or grind or cut the bumps off the bullet bases" method. We've all filed bullet bases, and tried to cut the bump off the bullet base; by hand. This never worked for me, so I gave it up many years ago.
Sometimes this method employes fairly elaborate machinery. For an example, see "Making Flat Base Bullets" by Art Coover in "The Fouling Shot", No. 162, March-April 2003
Second is the "open-the-sprue-plate-with-the-gloved-hand" method. This is said to result in bumpless flat bullet bases. Dan Willems and Wallly Enga use this method. I have tried the gloved hand to open the sprue plate, gave it a good shot over a lot of bullets and molds; including a John Greene mold with a wooden handle on the sprue plate extension. This method didn't work well for me.
If I opened the sprue plate too soon, there were holes in bullet bases, see the examples in the picture.
.
If I waited too long, the alloy hardened and it was hard to cut the sprue.
I needed the yellow mallet to entice the sprue to fall off the sprue plate and the bullets to fall out of the mold. I must whack the handle hinge to get the bullets out of the mold, sometimes, and I've done all the cavity polishing tricks there are. And, I'm left handed-in a world where ladles are made for righties. Put it all together, keeping in mind that we have to pick up the mallet anyhow, and the hand opened sprue plate didn't work for me.
Third is the "cool the sprue plate briefly by touching the hot metal to a cooling sponge or rag, then cut it off conventionally. The hardened alloy will cut uniformly clean when the sprue is cut with the force of the mallet blow directed at a slightly downward angle"; advocated by Forrest Asmus. Others, including Pete Mink, use this method without the cooling.
Fourth is the "cut the sprue-move the sprue plate back so the hole is not over the bullet base but the sprue plate is over the bullet base-whack the sprue plate to flatten the lump" method, which I invented.
After casting and opening the sprue plate, close the sprue plate such that the plate and not the hole is over the bump, and give the top of the sprue plate a good whack with the yellow plastic mallet. This will mash the bump down and make it go away.
So here are four methods of getting rid of those annoying bumps. Try the last three and pick the one you like best.