I'm using my mp 4 cavity brass mold to cast some bullets,everything is up to temp but I have one cavity that doesn't seem to want to produce a sharp edge on the band. What might be causing this? Contamination of some sort? I believe it to be in the cavity closest to the mold handles. I've tried pouring in both directions with no big change.
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Wipe the mold down with a 100% cotton rag that is wetted with synthetic two-stroke engine oil. If the mold is hot enough it will steam profusely and any contamination will wipe off. If it does not Steam then the mold is not hot enough. Once the correct temperature has been established then use a cotton Q-tip dipped into the oil to wipe the mold cavities with the two cycle oil then repeat the casting and see if the defect continues. I like to use a swirling twisting motion with the Q-tip while I squeeze the handles shut with my other hand. Then I like to open the mold and wipe down all available surfaces with the cotton rag this will remove tinning carbon lead smears or any other type of trash . Any residual oil will be completely burned away in two or three casts if the mold is hot enough.
While waiting for an answer I decided to add just a touch more pewter and things improved dramatically however I will try your method of wiping things down.
Damn... I used a heavy duty paper towel to apply a little two stroke to the top of the mold before I read your post and it stuck like a glue mixture on top. Now I have to stop and let it cool and clean the whole mold from scratch!
The two-cycle cotton rag will remove nasty burnt on plasticy mess too!!!
I tried that but it seemed to make it worst. I'll clean it from scratch with some brake cleaner and start all over again.
Sorry that didn't work I had the recombinated paper towel get me once as well
No worries...the mold needed a cleaning anyway. Took it apart and cleaned it as if it were new. Ready to give it another go. Hope it works better now.Originally Posted by Recycled bullet
When I have had that type of defect/lack of fill, I have found that it is insufficient sprue size or sprue cooling too quickly. The boolit cools without being able to draw in extra alloy and has rounded bands. At least that fixes my rounded band issues.
One of those boolits shows a divot from what appears to be burrs near the vent lines. Check for burrs that may prevent proper venting.
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Also, if you have a burr that makes the boolit stick, then your mold can cool off too much before you get a chance to pour in more hot lead.
The sprue size is large but I did heat the mold up on the hot plate and also speeded up my cadence and that did improve things some.
I never noticed any divot.
Look at the parting line of the boolit at the very top of your image. I can see small divots on the driving bands, and maybe one inside the lube groove. These are caused by burrs in the mold. Place that boolit in the cavity of your mold and look at the vent lines that contact those divots - you’ll find a burr there. Burrs are easily formed at the intersection of the vent line and boolit cavity, and these burrs are the most difficult to remove without damaging anything.
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If your mold is freely raining boolits by just opening the handles, then I’m wrong.
Well the boolits are not falling free by opening the handles but they do with just a single tap on the handle bolt. I'll take a closer look tomorrow.
This happens to me on occasion. Play around with how you fill the cavs. I have one 4cav mold that like 1st & last cav filled before filling 2&3. Weird I know but it works.
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What are you using to pour lead?
What's the tin content of your pour? I've OCCASIONALLY been able to pour decent bullets with 1.6-1.8% tin mix, but I've never NOT been able to pour melts with 2% tin content, or more. Melts with 2.1 or 2.2% would fill out all exclusions on the lube grooves, but would also make the "sharp shoulders" reappear with good result. It could be the way that your mould was cut, but I would try melts with tin content up to 2.5% before I gave up on the way that the one cavity casts. Even at 2.5%, a cast bullet alloy is soft enough to do what it is supposed to do, inside and outside the barrel.
If, at 2.5-3.0% tin, you do not get sharp shoulders in every cavity, inquire of the vendor. At that point, I believe it is reasonable that they did not get it right.
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Yeah the 2 stroke oil works really well to lube the Sprue Plate Pivot, I wouldn't coat the whole mould with it as that is just making a mess. Clean the whole thing with Brake Cleaner and Alcohol and put a drop on the pivot and pre-heat the mould until the boolits come out frosted. Then back off a little on the mould temp.
As far as getting a perfectly sharp edge on the trailing edge of every boolit I wouldn't worry too much about that. You need to understand that these will be primarily used as Practice Ammo and a few not totally perfect boolits aren't going to affect your shooting one Iota. Nothing wrong with going for 100% perfection, I do it every day. Only problem,,, 100% Perfection isn't obtainable, so you've got to figure out what is good enough for your intended use.
Hope this helps
Randy
"It's not how well you do what you know how to do,,,It's how well you do what you DON'T know how to do!"
www.buchananprecisionmachine.com
Check the vent lines in that area, that may be the problem.
Every time I've had one cav not fill out, venting has been the cause
Calamity Jake
NRA Life Member
SASS 15704
Shoot straight, keepem in the ten ring.
Using a Lee 4-20 pot.
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