Two Issues

[B R Shooter]

Casting rifle bullets for GCs. New, modern mould. Bullets come out nice, consistent weight, but....
1) First is a small fin of lead around the base on some which makes seating the GC a bit tough. If the fin wasn't there, the checks would start onto the base and the rest is easy. The sprue plate is down tight on the pivot end and it locks under the stud on the other end.
2) This may be my technique, but on some bases, I'm getting a small piece of lead where the sprue plate cut that is not cut off flush. I stand the bullets up and they wobble and are obviously not flat. This can't be good to get the GC seated square with the base. It's random, I can't say it's one cavity (4 cavity mould) or that it happens to all 4 bullets at the given time. I have filed off the bump, but doing that by hand is not the best way to keep things square.

Any thoughts?

[Ozark mike]

Lee mould?
1sounds like its not closing all the way
2 maybe temp of mold is not right
Would be better if we could see it

[kevin c]

I've been told that base fins can come from over tightening the pivot bolt, not from it being too loose. Apparently too much tightening on the end can cause the plate to lever upwards over the holes. There might be a retaining stud on the other end, but the plate may bow in the middle. That might also explain the high base nubs after sprue cutting.

[Bazoo]

Mould being too hot will cause base fins sometimes. I have a mould that fins a bit from damage, I'm able to remove the fin with my thumbnail.

Sprue bumps is from cutting too cold, or a dull cutter in my experience. The cutter hole needs a sharp bottom edge and not a rounded edge. I've tuned the cutter hole by hitting the edge from the top with a punch to lower the edge, then filing and stoning the dimple.

[Conditor22]

kevin is right! don't overtighten the sprue nut. I was given a mold that someone did that and cut a groove into the top of the mold making the sprue kick up at even a worse angle
https://i.imgur.com/K2u3KRO.jpg

the wave washers are what keep the sprue flat (if the mold doesn't have a wave washer I put one on). I have several sprues that just flip back in place and still show no light between the mold and sprue plate.

It would help if you mentioned the mold make style, Pictures are an even better help---

I don't/wouldn't use a file on a mold top. use wet/dry sandpaper on a piece of glass or large tile. touch up the mold top and the sprue plate.

make sure you keep everything flat and square when you sand.

often I have run across sprue plates where the holes need to be sharpened [don't forget to flatten/smooth the bottom when your done]

[tomme boy]

If the sprue plate opens when you turn the mold on its side then that is tight enough.
if you have to push it open when empty then it it too tight.

[charlie b]

Even on well fitted sprue plates I get that sometimes too. A fingernail takes care of it. NOE makes a tool for this

https://noebulletmolds.com/site/shop/tools/bullet-base-chamfer-tool-manual.

[dtknowles]

Lower your temperature and use less tin in your alloy. Your lead is flowing too much.

Tim

[B R Shooter]

It is not a Lee mold, but I didn't want to post the maker for fear of spreading false info, it is a very well respected maker. The plate does have a wavy washer that holds pressure on the top of the plate, I have it where it doesn't have much play but is free to swing open. There is a screw on the closed end that the plate stops against and again it keeps it flush but free to swing open. I will check the sharpness of the sprue holes, I understand it should be sharp edge with no rounding, and no burs. I casting linotype with some added lead and holding the temp to 700 as best I can.

[Rich/WIS]

Check the top of the mold and bottom of the sprue plate for any build up of lead. A small build up will raise the plate enough for hot alloy with a good percentage of tin to flow into the gap.

[dtknowles]

It is not a Lee mold, but I didn't want to post the maker for fear of spreading false info, it is a very well respected maker. The plate does have a wavy washer that holds pressure on the top of the plate, I have it where it doesn't have much play but is free to swing open. There is a screw on the closed end that the plate stops against and again it keeps it flush but free to swing open. I will check the sharpness of the sprue holes, I understand it should be sharp edge with no rounding, and no burs. I casting linotype with some added lead and holding the temp to 700 as best I can.

I think you should lower your casting temperature. Lino flows very well for good fill-out without high temperatures. I found this on the LASC website.

http://www.lasc.us/CastBulletAlloy.htm#:~:text=If%20you%E2%80%99re%20 going%20to%20cast%20of%20straight%20linotype,cast% 20at%20a%20lower%20temperature%20than%20many%20all oys.

"Lino with its eutectic 464o melting point can and should be cast at a lower temperature than many alloys. The common practice of casting at 700o to 750o or hotter is at least 236o over its liquidus temperature. Dross formation and metal loss from oxidation can be reduced by casting a little cooler, about 550o-600o. An additional benefit of the reduced temperature is that the mould doesn’t get as hot and you won’t have to wait as long for the alloy in the mould to freeze, you can actually cast at a faster rate. When casting lino at 550o-600o be cautious of adding new alloy to the pot too quickly and lowering the pot temperature below the liquidus and causing dross to form or dropping the pot temp below liquidus temp.."

Tim

[B R Shooter]

Thanks Tim, I will lower the temp next time and see how it goes. I did notice taking a quick look at the sprue plate, the tapered hole bottom is not particularly sharp. I'll work on that too.

[gwpercle]

It is not a Lee mold, but I didn't want to post the maker for fear of spreading false info, it is a very well respected maker. The plate does have a wavy washer that holds pressure on the top of the plate, I have it where it doesn't have much play but is free to swing open. There is a screw on the closed end that the plate stops against and again it keeps it flush but free to swing open. I will check the sharpness of the sprue holes, I understand it should be sharp edge with no rounding, and no burs. I casting linotype with some added lead and holding the temp to 700 as best I can.

Be sure and use sprue plate lubricant .

There is a very fine line between too tight and too loose . A gap between the blocks and sprue plate can cause the base fin and/or the base nub.

Hold the closed blocks up to the light ... if you can see any daylight ...something is wrong .

The top of the blocks and the underside of the sprue plate must be clean , smooth and level and lubricated .

The photo in post #5 shows a severely damaged mould block top...looks like no lube was ever used and the person just kept casting causing more and more damage ...that block has been damaged badly by abuse .

After making sure underside of sprue and block top are smooth and lubricated , adjust cold mould so the sprue plate will just barely stay in place when turned sideways ...barely tight ,
As the mould heats up it will loosen so if you notice fins / base nubs starting to appear , grab driver and tighten the plate up...keep it lubed too .

The only way to learn when and how much to tighten sprue plate , clean underside and lube the plate is by doing ...
watch out for fins , nubs and streaks of metal on underside of sprue plate ...as soon as anything is noticed , stop and correct it ...things only get worse if you don't .

Sometimes block tops and sprue plate underside have to be removed and sanded dead level with each other ...any build up in these areas causes uneven contact and that is where the fins and base nubs come from.
Gary

[osteodoc08]

kevin is right! don't overtighten the sprue nut. I was given a mold that someone did that and cut a groove into the top of the mold making the sprue kick up at even a worse angle
https://i.imgur.com/K2u3KRO.jpg

the wave washers are what keep the sprue flat (if the mold doesn't have a wave washer I put one on). I have several sprues that just flip back in place and still show no light between the mold and sprue plate.

It would help if you mentioned the mold make style, Pictures are an even better help---

I don't/wouldn't use a file on a mold top. use wet/dry sandpaper on a piece of glass or large tile. touch up the mold top and the sprue plate.

make sure you keep everything flat and square when you sand.

often I have run across sprue plates where the holes need to be sharpened [don't forget to flatten/smooth the bottom when your done]

YIKES!!!

Talk about what NOT to do!

[Wayne Smith]

If you haven't solved it and our advice hasn't solved your problem contact the mold maker. Most of them are very responsive and instructive.

[B R Shooter]

Took the sprue plate off and looked at the edge with a magnifying glass, and it was not a sharp edge. I used a countersink bit and took the taper down just enough to get it sharp, then used a flat file to make sure there were no burs on the bottom. It ought to slice the lead off now.