First successful casts and a question about sprue shearing

[Wadestep]

I got to cast my first boolits over the past week, with fairly good success (for a beginner). I cast some .38 SWC from a steel Lyman mold, a .45 colt at over 300 grains from a Mihec brass mold, and a .308 from an aluminum Lee Mold.
http://i639.photobucket.com/albums/uu118/wadestep/misc%202/IMG_20130331_191042_943_zps90e4a3a7.jpg
http://i639.photobucket.com/albums/uu118/wadestep/misc%202/IMG_20130331_190958_783_zps66221d5b.jpg

Now here's the question: The 300+ grain from the brass mold keep shearing off the center of teh sprue - as shown here:
http://i639.photobucket.com/albums/uu118/wadestep/misc%202/IMG_20130331_191023_783_zps8f3c2d3c.jpg
I couldn't get it figured out no matter how fast I casted, how hot the mold/melt was, or how fast/slow I cut the sprue. I know the answer lies in there somewhere, any pointers?

BTW, I didn't have teh same problem at all with either the Lee .308 or the Lyman, as pictured:
http://i639.photobucket.com/albums/uu118/wadestep/misc%202/IMG_20130331_191052_944_zpsd2168d9d.jpg

Thanks for any ideas of what to try next round. I figure they'll still shoot. I had about a 50-60% cull rate for now, but I didn't cull them until after casting, to keep the molds up to temp.

[Jon]

Try letting them cool longer. Check for burs on the sprue plate. Mine look like that for my 45 mold when I'm cranking them out.

Take a look at this thread as well.
http://castboolits.gunloads.com/showthread.php?132775-Sprue-Plate-Mod

[Huntducks]

Agree try letting it cool a few sec longer also if the sprue hole has a burr or is not at the right angle to cut it will just tear the lead.

How do they shoot I have had a few that look that bad and they shoot just fine.

[cbrick]

Those are outstanding boolits for a first time caster.

Couple of tips, brass molds hold heat and that outstanding sprue plate that Miha makes is quite thick and will hold heat also. Pour a very generous sprue puddle to help with your somewhat rounded bases and then watch the sprue puddle freeze, after it freezes give it a 3 or 4 count before opening. The bases are torn because the alloy didn't freeze before opening the sprue plate. It's a timing thing that a bit more practice will cure.

Rick

[44man]

Those are outstanding boolits for a first time caster.

Couple of tips, brass molds hold heat and that outstanding sprue plate that Miha makes is quite thick and will hold heat also. Pour a very generous sprue puddle to help with your somewhat rounded bases and then watch the sprue puddle freeze, after it freezes give it a 3 or 4 count before opening. The bases are torn because the alloy didn't freeze before opening the sprue plate. It's a timing thing that a bit more practice will cure.

Rick
YES, OUTSTANDING boolits. Timing is the key.
In the end, the tear's will not make the boolits shoot bad and you might not see a single difference at the target.
I am just so happy to see a new guy cast so good, he belongs here for sure!

[Wadestep]

Thanks for the replies. I'm understanding that the sprue needs to sit for an extra couple seconds before cutting it. I will try that next time. While casting I was trying to go faster when anything went wrong, so I was exacerbating this problem, I guess. I havent' yet shot any of them, as I have to travel a ways to get to a range. I'll hopefully give them a try this weekend. Thanks all.

[cs86]

I get the same problem and it seems to be the sprue plate is to hot. One thing I've tried to help get the sprue plate temp down but keeping the mold hot is after cutting a sprue I leave it open for a few seconds and leave the bullet in the mold. The bullets helps keep heat to the mold and the sprue plate is cooling. Then cast another. Once the sprue plate starts to drop to the right temp you will feel it cut a little harder and end up getting a nicer cut. I haven't perfected it just something I've tried and its helped. I've heard of others using a damp cloth to cool the plate.

[gray wolf]

Those are very nice looking boolets--very nice.
I have found that as long as all the bases were the same, all smooth, or all with the little blem
they all shot well. Even when some were mixed together.
However if I am shooting for extreme accuracy I want all the bases as nice as I can get them
so that part of the equation is removed. Then again I see nothing wrong with wanting perfection.
Your bullets look like they are on thee way to being perfect so why not go for a nice smooth base.

[pipehand]

Wadestep, what you may have done by cutting too soon, is cause a lead smear on the bottom of your sprue plate. You may have to clean it off because it will continue to drag and cause problems, possibly galling on the top of the mold block.

What has worked for me to remove the lead, is to dip the sprueplate in the molten lead, and let it get hot. Then use real natural fiber burlap and scrub the leaded area. The lead will be removed.

You may want to use a sprue plate lube like Bullplate. It will prevent a lead buildup on the sprue and block top.

What you are also seeing, is the longer time it takes for the more massive boolit to solidify actually gives the alloy time to "crystallize." Mainly due to the antimony in the alloy. Pure lead or a lead/tin alloy won't do what your bases are doing.

Dennis Marshal wrote a good primer on the metallurgy of cast alloys. You can find it here http://www.castpics.net/subsite2/ClassicWorks/CastBullets-s.pdf starting on page 118. It is from the NRA Cast Bullet publication- a collection of American Rifleman articles from back when they actually had technical articles. Lotsa good info.

You're off to a great start, and thanks for posting the pics.

[KinkBreaker]

shoot 'em. they will still go bang

[BubbaJon]

Wadestep, what you may have done by cutting too soon, is cause a lead smear on the bottom of your sprue plate. You may have to clean it off because it will continue to drag and cause problems, possibly galling on the top of the mold block.
Nice lookin boolits! The smear on mine was caused by this exactly - took off the sprue plate and the lead was smeared on it. I polished it up and no more problems - plus of course I now give it an additional 4 count after the puddle gets hard.