Casting problem

[hickfu]

Hey guys, I have a brand new mold from Accurate Mold a new Lee 4 20# bottom pour pot and I am trying to make some good boolits. Most come out looking nice but I like to weight them after to make sure that they are around the same weight. Yesterday they ranged from 416gr to 427gr. Tonight I was getting some at 401gr.... I know I am getting air bubbles in them because I can see the holes in the base of some. My question is how do you guys that use the bottom pour pots get them to pour consistently without getting air bubbles in there? Are the sprue plates with the trough easier to use when pouring a 4 cavity 425gr mold? or am I just needing to practice more pouring with this thing?


Doc

[geargnasher]

Tom's mould blocks and sprue plates lock together like Fort Knox, and don't vent the air out very well compared to some other designs that have sloppy sprue plate fit and other things that let the air vent better.

My solution to the trapped bubbles hidden in the bases has been to adjust my pour technique. First, I tilt the mould downward slightly on the handle end, about 20 degrees or so depending on how long the boolit design is (more tilt for short, fat boolits, less for long, skinny boolits). Then, I place the mould on the pot's support bracket so that the alloy stream falls through the left side of the sprue plate hole without touching the edge and splashing. What tilting the mould and dropping the stream off-center does is set up a sprial, or vortex motion of the alloy inside the cavity, which tends to pull the air to the center of the cavity and up, out of the hole as the mould fills, effectively purging the cavity of air. No lead splashing around and trapping air that way.

You can also "break" the sharp edges where the blocks meet together at the top to make a slight "trough" for air to vent out from under the sprue plate, which will help prevent rounded base edges assuming your sprue plate is hot enough not to be the cause.

Gear

[Larry Gibson]

You must open the adjustment all the way up on the spout if you intend to get any kind of consistent cast with that big a bullet. The weight varience is because the alloy begins to cool and solidify to soon. I quit using a bottom pour on bullets over 325 gr many years ago. A dipper is the best way to cast those larger bullets with any consistency.

Larry Gibson

[D Crockett]

Doc you might want to take your mould to a michine shop and have them put a vent line in the top of the mould this way you can vent the air off the top of the mould also you might try to hold the mould up to the poure spout I haad a mould once that I had to do that with D Crockett

[462]

Excellent advise already given, but . . .

. . . or am I just needing to practice more pouring with this thing?

The more you cast the more proficient you will become. Nothing replaces good old OJT.

[Dale53]

Over the years I have cast with a dipper (early years), a Lyman 11 lb pot bottom pour (for many, many years) and now a couple of RCBS 22# bottom pour pots. I have case every thing from 90 gr .32's to 530 gr 45/70. All have been done at match level with all weights.

For the large, long bullets, my standard was plus or minus .6 (six tenths of a grain). That, together with my loads, gave me truly competitive equipment (no one had better shooting equipment).

Just like shooting, it takes "trigger time" or as 462 states, On the Job Training...

My RCBS pots have an adjustable mould rest. I adjust it to allow the metal to fall about 3/4" before entering the mould. That DOES make a difference. I used to pressure cast some moulds and that's something I don't do anymore - the drop seems to do the same thing (enhance fill out).

If you do not hold the mould handles with the same tension the mould can spread when casting and THAT can cause variable bullet weights also. In fact, it is so common, that Cabine Tree offers a mould handle that locks kind of like a vise grip. I use one for my precision rifle bullets. Yes, it Did/Does make a difference. Those are cast at +or- .2 of a grain.

FWIW
Dale53

Dale53

[Old Caster]

If using a bottom pour furnace I do exactly as Gear does and I don't pour the lead in too fast because I think that can trap dirt in the bullet because of the force of the liquid racing in. If it is slow the dirt has a chance to float to the top and go out into the sprue. It does require a high temperature so it won't freeze prematurly in the mold. I would however much prefer to ladle cast bullets that are that big and hit the empty ladle on metal between every pour so nothing can accumulate in the spout tunnel. I don't know of any of the BPCR competitors that used bottom pour for their bullets even though most of them had the option. -- Bill --

[chboats]

All good advice above. Another thing that may help is to make sure you leave a large poodle of lead on the sprue plate at the end of the pour so that there is plenty of lead to pull from as the boolit shrinks during cooling

Carl

[462]

". . . a large poodle . . ."

Man, its yelping would tear at my heart.

[Le Loup Solitaire]

A factor often overlooked that can cause air bubbles and poor fill-out is that of a sprue cutter being too tight. The sprue plate should be adjusted so that when it sits on top of the blocks and the mold is tilted then the cutter should swing freely on its own weight. Not sloppy loose-up and down, but just right. This will enable air to escape between the plate and the top of the blocks. A pool of melt left over the plate's pouring hole will allow additional melt to be drawn into the bullet and help prevent voids in the base. A slight tilt to the old will set up the "swirl" and that will definitely discourage the formation of bubbles in the pour. Another little trick that also helps (if needed) is to let the mold (when full) drop slightly and "bump" it with a bit of gravity. Some casters believe that the little jolt helps with fill-out. LLS