New Mold Developed a Gap at the Bottom

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PhilRich
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New Mold Developed a Gap at the Bottom

Post by PhilRich » Sun Apr 25, 2021 10:37 pm

I just received a new high quality mold and have discovered it has developed a gap at the bottom when held closed up to the light after the first use. When first received it was tight without any noticeable light leaks. After experiencing this problem I checked two other molds that also have the same problem. The new one is made by BACO as well as one of the older ones and a Steve Brooks mold.

The result with the new mold is that the bullet is out of round by about .001 inch. I assume that is not good for long range shooting. After an internet search I found that a mold gap can be eliminated by adjusting the pins. However this did not help.

I'm using an RCBS temperature controlled melting pot. It's temp control has been reliable according to a thermometer. I usually set the temp to 775 degrees. After seeing this problem I increased to 800F but not higher. I was very careful cut the sprue and open the mold gently as possible.

I'm relatively new to casting and have been relying on this forum as a source of information to improve technique.

I'm concerned as these molds were received in excellent condition and the included bullets sent with them are "spot on" dimensionally. How common is this problem, and, what could I have been doing wrong?

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desert deuce
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Re: New Mold Developed a Gap at the Bottom

Post by desert deuce » Sun Apr 25, 2021 10:57 pm

After you have cast a bullet in the mold, how do you open the sprue plate and then separate the mold blocks?
Sometimes you get the chicken, and sometimes you get the feathers!

bruce m
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Re: New Mold Developed a Gap at the Bottom

Post by bruce m » Mon Apr 26, 2021 12:48 am

foreign material on the face of block(s)?
these can be insidiously hard to detect, particularly when as small as 0.001.
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Don McDowell
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Re: New Mold Developed a Gap at the Bottom

Post by Don McDowell » Mon Apr 26, 2021 6:46 am

Assuming you're using mould handles built specifically for "saeco" mould blocks.
Have you checked the screws that hold the blocks to the handles are tight? Sometimes if one or both work loose that can deal you some problems.
AKA Donny Ray Rockslinger :?

DaveC
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Re: New Mold Developed a Gap at the Bottom

Post by DaveC » Mon Apr 26, 2021 7:08 am

Check the edges of the holes the locating pins go into for burrs. Hastily closing the mould can sometimes cause the pins to ding the edges of the holes before they go into them. This condition can get stickier or harder to close as the mould heats up. Don’t ask me how I know this.

I look for a number or fractional drill that just fits the hole and push it through the block half from the handle attachment side. If it stops or tightens or snags before coming out the cavity side of the block, there’s your burr. I put the drill in a pin vise or lathe drill chuck, insert as before and turn by hand until the obstruction is gone and the drill slides smoothly out of the hole. Pressing the other block half into the locating hole block will normally show no light gap any more.

Having the pins come loose is a lot less common, and they are more likely to push into the pin block half than come out. However, if this is the cause, a bench block, pin punch and a small hammer (and some patience) will reset the pin. I give the rounded end of the pin a couple light taps, push the mould halves together and rub them against each other to check for slop in the alignment. If I get some, the pin punch goes into the handle side, and give it half the number of taps I used on the rounded end and check again. Eventually the blocks fit together with no light gap or sideways motion and I’m ready to cast again.

These custom moulds are marvels of precision, but they can be real prima donnas, intolerant of careless handling, junk alloys, wrong temperature settings and other things a mass produced mould would shrug off without problems.

charlie young
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Re: New Mold Developed a Gap at the Bottom

Post by charlie young » Mon Apr 26, 2021 7:35 am

I have same issue with my latest mould from BACO, variance in weight is enough to be disconcerting, so I called them. Will give it one more shot and if it isn't better it can go back. I don't think I need to be adjusting, hammering etc. on a brand new mould. My other ones from them have been perfect.

DeadEye
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Re: New Mold Developed a Gap at the Bottom

Post by DeadEye » Mon Apr 26, 2021 8:11 am

I saw in another thread that one of us was told that he might have a six month wait for his mould as they are not able to get blanks. They might be trying different sources to keep production going. Damn virus.

Paul
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Don McDowell
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Re: New Mold Developed a Gap at the Bottom

Post by Don McDowell » Mon Apr 26, 2021 8:19 am

Some moulds get really picky about how tight the sprue plate is, if it's to tight weight variation can run all over the place as not filling out well, or to well.
AKA Donny Ray Rockslinger :?

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kenny sd
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Re: New Mold Developed a Gap at the Bottom

Post by kenny sd » Mon Apr 26, 2021 8:25 am

in the past, I have used my shell edge tool that cleans up the inside of the shell after sizing, to VERY slightly do the same to the pin holes.
this worked. It allows the pin to slide into the hole, rather than bump the edge. worked for me, and the mold is years old and still working.

go SLOWLY, you don't need much. Ken

DeadEye
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Re: New Mold Developed a Gap at the Bottom

Post by DeadEye » Mon Apr 26, 2021 8:50 am

Many years ago I was told to 'tap' the mould with my mallet as I opened it. 'WRONG' What I wound up with was four holes that looked like miniature craters and of course the mould would not close. If I remember the raised material was corrected with with my wet-stone and then I drove the pins out just a little bit more so they would engage fresh material.

Paul
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Gussy
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Re: New Mold Developed a Gap at the Bottom

Post by Gussy » Mon Apr 26, 2021 9:11 am

I have on a couple of old moulds, reversed the pins. Just like a new mould!

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kenny sd
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Re: New Mold Developed a Gap at the Bottom

Post by kenny sd » Mon Apr 26, 2021 10:21 am

dead eye is right, never hit the mold. hit the end of the handle, or the handle pivot.

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desert deuce
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Re: New Mold Developed a Gap at the Bottom

Post by desert deuce » Mon Apr 26, 2021 1:01 pm

Still waiting for the OP to describe his technique.

Correct, don't hit the mould anywhere.

Using a BACO, Saeco or Jones Mould with Saeco handles, I do open the sprue by gloved hand, with my second and third fingers of my left hand very lightly push the handles apart, if that does not open the blocks I "VERY LIGHTLY" tap the hinge pin of the handles while pushing the handles apart and the bullet usually falls free onto the padded surface. EXTREME caution is used when reclosing the mould blocks by holding the assembly straight up and visually ensure the two block surfaces mate without interference especially from the sprue plate.

Any tapping to release a sticking bullet is with the handles fully open and the mallet striking only the hinge pin of the handles.

If I see a part line on the bullet, usually only on one side, when I close the blocks and reposition the sprue plate I squeeze the handles together lightly and "tap" the hinge of the handles. If this does not cure the part line again on the bullet I look for detritus on the block faces or a burr on the edge of the cavity.
Sometimes you get the chicken, and sometimes you get the feathers!

semtav
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Re: New Mold Developed a Gap at the Bottom

Post by semtav » Mon Apr 26, 2021 4:25 pm

When I put mine together I noticed a faint light at the end of the tunnel too before ever using it.
I'll double check it again when i get back to it. it might be one of the holes need deburred.


I see kenny sd mentioned that too.

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PhilRich
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Re: New Mold Developed a Gap at the Bottom

Post by PhilRich » Mon Apr 26, 2021 11:01 pm

I spent some time making sure the surfaces were free of lead and checking for potential problems this morning. It didn't make any difference in the gap at the bottom - its more than a fine line. I've reduced casting temperature to 750F. I've been following the instructions for lubing the mold and for handling that came with it. I'm not slamming the mold shut. I use a soft plastic headed hammer to cut the sprue - gently. Most of the bullets have been falling from the mold without tapping the mold handles on the hinge.

This mold casts a 50 caliber ddpp bullet. I'm using the Seth Cole 55w paper, patching wet. I shot 12 rounds at 100 yds this afternoon. Accuracy was excellent without any leading. The club's max range is 200 yds

I'm going to cast a batch of bullets to last a while and then send the mold back to BACO. Thanks for your replies and advice. It helps to see how others handle and use their molds.

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