RCBS 38-150-KT

TomSp8

Active Member
Okay guys. Trying out the estate sale RCBS 38-150-KT 2 cavity this morning. Previously soaked in evaporust overnight (very light rust mostly on the outside) then washed with hot water and dawn, then dried and set aside til now. Alloy is mostly coww and some soww added, from my previously made ingots. Thoroughly fluxed with sawdust prior to casting. Ladle pouring. Temps from 715 to 775, with better bullets coming from the higher temps. Took about 10 or 15 pours to get my first keeper. Now the questions: the far cavity cast pretty good, but the near cavity was consistently giving me bases rounded and not filled. Tried pressure pouring that cavity, and it helped, but not consistently. When it did fill, it had a frosted look on the base band. They weigh about 156 +/- 1. I ran a couple thru the sizer (.3575) and noticed the front band was not being sized like the rest of the bullet. These will be powder coated, then sized, so I think that will make up for that?. Any advise good or bad?2022-7-30 9-21-0.jpg20220730_084419.jpg
 

Dusty Bannister

Well-Known Member
Look at the mold from the side and notice that the mold handles are leaving one end of the blocks open to the air, and the mold closest to the handles are acting like a heat sink. More temp and longer run. to see if you can get the blocks and sprue plate up to temp. Both bases look a little rounded, but the one closest to the hinge bolt might need to have the venting checked.

Pressure filling with a bottom pour pot also means you leave a little space to let the air escape from the mold. You are not trying to shove a cork in the bottle. Wear a glove, the lead will spurt around the nozzle.
 

Jeff H

NW Ohio
Probably the most common problems I've had with bases being rounded were HEAT (not enough), as stated, and just plain poor venting.

How tight is your sprue plate? I try to run mine so they will swing open and closed under their own weight. I BELIEVE that this allows for the best venting on the bases. It has cured a number of base issues for me in the past.

If the vent lines didn't clean up like the rest of the mould, that could be an issue. I've had to clean out vent lines, CAREFULLY by using a straight-edge and a very sharp scribe. Put the mould half in a small vise - if you try to hold the mould half, straight edge and do the scribing while holding it all in your hands, you'll get errant, ugly scribe lines going every which way. If that doesn't work, I will drag the top, inside corner of each half across a sheet of 400 grit (or so) abrasive paper, backed by the table-saw top or a sheet of glass - some similar, hard, flat surface - ONCE. Look for a THIN, shiny line. Try it before taking more off. If you look at how small the vent lines are, a new on at the top corner of the blocks need not be any larger. If that doesn't work, and you didn't make that vent too big, you'll never notice and no harm done.

That said, heat is more likely the issue and can be tested without permanent changes to the mould halves.

The rest of the bullet looks good. You may or may not want or need the front band to be full-diameter, but if you do, PC might make up the difference, or you could carefully lap the front band in the mould cavities. NOt a huge deal in a one or two-C, but on a mould with more cavities, I'll learn to work around it or move the mould. That'd be a lot of lapping and I only have so much patience.
 

Winelover

North Central Arkansas
Mold isn't hot enough. Even the first cavity looks to have slightly rounded base..........photo isn't that focused. Front band not being sized could be because RCBS molds are known to drop undersized bullets or your in and out sizer (Lyman or RCBS type) isn't sizing concentrically.
 

CZ93X62

Official forum enigma
This (I believe) is a Lachmiller/RCBS clone of Lyman's #358477. My first #358477 (1982-made) the front drive band as cast was about .350". My NOE version of #358477 has full-diameter front drive band. The Lyman bullet's meplat is radiused; the NOE version has unradiused meplat. Both shoot very well in 38 Specials. PoTAYto/PoTAHto.

Design poetry--say it ain't so!
 

Rick

Moderator
Staff member
If the bullets are mostly well filled out but with rounded base bands the sprue plate is too cool. You'll need to pour a far larger sprue puddle. Don't look at it as pouring lead, your pouring heat. You cannot get a good base fill-out with a cool sprue plate any more than you can get a good hollow point fill-out with a cool spud.

RCBS molds do tend to cast a bit small so the driving bands not being uniformly sized could be due to that depending on as cast size and the sizer your using.
 

TomSp8

Active Member
I've been trying to be very generous with the pour, even keeping it pouring and running back into the pot after the cavity is filled, especially at first, to get it hot. Not too concerned about the front band being a bit smaller really. Man, this casting thing is not as easy as it looks! But like everything, the failures are how you learn. I will inspect the venting, and the sprue plate is a tad tight, so will try loosening it up a touch too. Thanks guys.
 

KeithB

Resident Half Fast Machinist
I have a couple Lyman SWC molds that have the same diameter front band as the rest of the bands. This is from measurng the mold. The bullets that come from the mold have a smaller diameter band that sometimes doesn't size completely. I attribute this to having the extended nose of a SWC drawing some material from that area as the bullet solidifies and shrinks on coooling. I could be wrong on the reason but I'll trust my measuring tools enough to say its not the mold.

I also have several Lyman molds where the front band IS smaller in the mold itself and of course the bullet has a definite diameter difference between the bands.
 

Petrol & Powder

Well-Known Member
My first thought is the mold is cold or the sprue plate is cold (more likely the sprue plate)

I get those same rejects with my RCBS molds for a few cycles, but they go away as soon as everything is up to temp. My casting cadence is quick! I think a lot of folks believe that you have to go slow to get quality. Speed can be your friend when dealing with variable heating.

When everything is up to temp, the process runs fine. I run that quick cadence until the bullets start to come out frosted. That high heat is usually a combination of the lead in the pot getting low (more heat, less mass) AND the mold getting too hot from the rapid cadence. After a while you get a feel for the balance between the level of lead remaining (I try to keep it between ½ and ¾ full) and the speed of casting that keeps the mold at an acceptable temperature.

There are a LOT of variables such as ambient temperature, mold material, cavities in the mold, amount of lead you are adding to the pot, etc.

Bottom line – it’s more instinct than hard science.

I will say that I tend to err on the side of hotter is better in terms of reducing the number of reject bullets I produce in a given amount of time.

Edit:
I have a lead thermometer and I can’t remember the last time I even bothered to put it in the pot. The exact temperature is not important. Results are important. Sometimes more information just serves to bog you down in minor details.
 
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Bret4207

At the casting bench in the sky. RIP Bret.
There were designers who had the front band smaller with the idea that they would ride the lands sort of and align the full sized body bands better. That may explain that issue.

Agree, the mould isn't hot enough. Looks like part of the mould is getting there, but it takes time to get it all nice and hot. With a ladle, pour a very generous sprue puddle and cast FAST until you start getting keepers. It's just a matter of practice. I would also avoid the Evaporust unless you have a really rusty interior. The outside doesn't matter, it's the inside is what matters and I find that the nice heat blue on an iron mould gives me better results.
 
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fiver

Well-Known Member
i get rounded ones like that when i simply stop filling the mold then go again, or i don't make enough of a sprue puddle.
don't be afraid to over shoot a little, the worst that happens is you have to scrape up a little lead from the pan.
 

TomSp8

Active Member
After some great advise, I went back at it this morning and afternoon. Much better results, getting things hotter. I also loosened the sprue plate screw a touch as suggested so I don't have to hammer it opened and closed....Had a really good rythem going until the pot got low. Doesn't take long to lower a 10 lb pot!! I have enough keepers today to powder coat, size, and load now. Thanks everyone for all the great advise in starting this journey.20220731_094015.jpg
 

Brad

Benevolent Overlord and site owner
Staff member
Stopping the pout too soon gives rounded bases every time for me. Last cavity poured is the worst.

I am with Rick, keeping adding heat by pouring a large sprue puddle
 

Bret4207

At the casting bench in the sky. RIP Bret.
Ya know, this brings up the question of surface finish and what the individual will accept. I have a few moulds that apparently walked on the wild side in their lives with previous owners. The interior cavity finish is not factory, it's what you get when rust attacks metal! I cleaned them up and I think all of them shoot acceptably. But they all have that freckled surface, they don't look like Bens Bullet Porn pics. Some folks might be bothered by that, but I'm not. Fill out is the thing for me, square and complete. I like frosty bullets anyway so the freckles don't matter. Someone else may hate the appearance.

I suppose powder coating would hide it all anyway!
 

TomSp8

Active Member
Well.....as a newbie, I'm just happy to get em to come out looking like bullets! I've got 3 molds for .38, two old Ideal/Lymans, and this RCBS, and I am not educated enough yet to know what, if anything, has been done to them by the prior owner(s). Im just glad I can make this one work after screwing around with the first one I tried. The third one is a 358156 double that I will be asking a lot of questions about in the near future....wish I had a "master caster" neighbor!