Fixing Out of Round Molds

[frnkeore]

I was asked to describe how I fixed my out of round mold. Here goes............

I bought this mold off Ebay for my 33 caliber rifle. When I received it and cast some bullets, I found that they where 4 to 5 thousands out of round, way to much! I took them to the range a fired a 100 yard group to see if they might have promise and got a 3/4 group so, I thought it would be worth working on.

First I examined it and found that it was done in a 4 jaw chuck but, the blocks weren't parallel to each other by about the same amount (.005), shown exagrated in picture four. So, when the jaws were tighten it pushed the pins over, even though it was clamped together.

I made a brass button to fit in the base band of the mold and placed the block on top of each other and clamped them in my Kirk vise. Here you need to be sure that the block are the same distance, top to bottom, or one block will be loose and able to wobble when worked on. A little machinist trick you can use if one is .0005 shorter, is to put a piece of paper at the bottom to take up the difference and hold both block fairly evenly.

The top of the block must go against the solid jaw, to keep the bullet base parallel, the button must be no more than .0002 smaller or larger than what the base band was machined to. What I do to determine that is, with the mold pins out, I use gage pins in the base band, until one fits tight, w/o clearance between the blocks.

These were Lyman blocks with 5/32 pins and with the two blocks in the vise, tapped gently together, I indicated the pin hole and drill through both blocks, .010 (#16) undersize for a 3/16 undersize (.001) dowel pin reamer and move over to the other pin hole and do the same.

At this point, take them out of the vise and ream the off side with a 3/16 or 1/4" reamer. You might want to reamer at least 1/2 of the dowel pin side the same, from the back side so, the pin isn't to hard to press in.



I bought some 3/16 SS dowel pins, rounded one end and pushed the pins in until they just fit w/o clearance in the opposing side.
The bullets out of this mold now mic round

Part II

I did that over 3 years ago and over the next two years, those pins loosen, because the one was on the edge, as you can see. So, last year, I pushed the 3/16 pins out and put the same brass plug in the base band and made three more pin holes, this time 1/4" dowel pins have been used and I don't expect any more shifting, EVER!

Before I did this mold, I fixed a DC 320366 but, this time, I had another SC 323366 mold. Fortunately they cast with in .001 of each other. I filled both cavity's and putting it in a vise, I also used a finger clamp to hold it down. I then open the 5/32 holes, as above but, I put a third 3/16 pin in between the cavity's. I could have fixed it just like the 33 mold, using two but, I hadn't thought of the brass plugs yet.

Frank

 

[Ian]

Good tutorial, thanks for taking the time to write it up. It's better than what I have been doing which is to just file and peen, which isn't a lifetime solution like re-drilling the holes as you've shown.

Another thing I see a lot of, with Lyman moulds in particular, is the cavities not having been cut deep enough in the blocks, as if the vise/mill operator was lazy and didn't clear the chips frequently enough near the end when milling the cavities. For that, I dimple the block faces with an obtuse-ground center punch in about four or five places to raise metal and then carefully dress the rims of the craters until the cavity is round. I call it "permanent Beagling" and it works really well unless you pressure-cast.

 

[KHornet]

An old method of rounding up round balls, was to make a fairly shallow wooden box of X dimension, with a piece of glass that fit in the bottom. I used glass from a picture frame many years ago to test this. Put the cast round balls which are always in my opinion at least somewhat out of round counting or not counting sprew. Put the box on the floor in the trunk of your car, put the round balls in the box on the glass with enough room to allow them to roll around fairly freely, and drive around with it in the trunk of the car for a couple of week. I only did it a couple of times back when I was shooting front stuffers, but after a couple of weeks, the balls (36/40/45/50) all miked out completely round, no sprew at all, and no effort on my part. That said, they shot no better than those with the sprew up on the patch when shooting round ball.

 

[fiver]

I just throw mine In the tumbler with some graphite and give e'm an hour or two of spinning them around.
a little bit of #F through #2 sized steel shot seems to help.

 

[frnkeore]

Any bullet can be sized round on the outside by a few different methods but, what you have to understand is that, a grease groove bullet has two diameters. I'll call the outside diameter the major dia. and the minor dia will be the bottom of the grease grooves. As long as you size the bullet and still leave any of the grease groove, the bullet will still be eccentric and there for, will still be out of balance. This also extends to any part of the bullet nose, it can't ever be brought in to concentricity with the bottom of the grease grooves.

The bottom of the grease grooves, is where a lot of a bullets weight is on most designs. That's why I consider as cast round bullets important.

Frank

 

[Ben]

Frank,

Thanks for taking your time to share with us.
I enjoyed reading and looking at your photos.
You're a pretty good machinist.

Best,
Ben

 

[frnkeore]

Thank you, Ben. I'm happy to share.

Frank

 

[minmax]

Yes, thanks for your post. I wish I had the ability to do such modifications.