Variation in diameter

Hello,

I recently started to use a lee 6 cavity mould.
I use it with the advised handles.

The thing is...
When i cast, the boolits come all nicely out the mould every time again. But several times the diameter is a few thousands of an inch bigger then it should be.
This is causing chamberingissues in my k31.

Im fairly new to casting and i havent observed a "reason" for this. I give very good attention to the closing of the mould. The alloy temperature is very stabile (pid).

Who can tell me possible reasons for this?

Many thanks in advance!

You say that you "give good attention to the closing of the mould". Nothing wrong there, but could you be using to much hand pressure on the mould handles? All that's needed is a gentle hold, no need to squeeze the handles tightly.

On another note, what Lee 6 cavity mould are you using with your K31, just curious.

Hey WouterNL
When using a gang mould, you need to alternate the casting front to back and back to front. Casting in the same direction repetitively will cause hot and cold sections in the mould. It also seems you are shooting as cast slugs. A sizer of some sort will probably be in order for you. Keep going, you'll get it.
Roy

Shooting Cast in the K-31 slower than 1400 fps? If faster than that they should have gas checks and a trip through the sizer to crimp them on.

Are your chambering issues because the bullets are too big? Or because they are a set a bit long?

Did you do a pound cast of the K-31 throat?

How much difference in diameter are you getting? If just a thou or so it could be casting technique.

Are the "good" boolits well filled out or do they have rounded edges on driving bands and base?

I suspect the mould is not closing properly sometimes. This can happen if the alignment pins are a bit tight or not lubed. Have you applied any sprue plate lube to the alignment pins?

Also, the Lee 6 cavity moulds have the cam operated sprue plate and if you squeeze that handle when you close the mould it can cause the blocks to open a little bit so watch for that. This will produce oval boolits. As Czech too said, you do not need to squeeze hard and with the cam handle there is a tendency to include that in the squeeze which can lead to problems.

Since this seems to be an intermittent problem it isn't likely lead spatters between mould faces but check to make sure the mating faces of the mould blocks don't have any spatters stuck to them.

Longbow

From my experience with six cavity Lee molds, it sounds like you are holding the sprue handle while casting.

What I found worked best for me was to close the mold, move the sprue plate to the fill position, let go of the sprue handle while holding the two mold handles gently, then fill the mold.

Robert

Is the sprue plate closing easy with no catch or no pressure?I sometimes have problem whit that a dab of synthetic 2 cycle oil helps and keep firm grip on the handles when closing the sprue plate.i went thru it step by step with a lee 6 holer.you can do it with the mold cold.all you need is a bright light to look and see if the mold is still closed all the way.fist open the mold and close it look at the light for a gap.next close the sprue plate look at the light again.do this several times and you will see where things are going wrong.i would bet it is when you close the sprue plate.like said above do not touch the sprue plate handle after you close it.

If the above is not the problem you may have cavities of different sizes.eay way to tell that drop the boolits and watch what cavity they came from mic them.do this several times and you will know what size each cavity is.

the lee 6 holers are great molds for the price,It just takes a bit of practice with them to get going.Practic opening and closeing the mold You will be casting bunches of boolits in no time

Quote:

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Originally Posted by Mk42gunner

From my experience with six cavity Lee molds, it sounds like you are holding the sprue handle while casting.

What I found worked best for me was to close the mold, move the sprue plate to the fill position, let go of the sprue handle while holding the two mold handles gently, then fill the mold.

Robert

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Yes, I have had the same experience.

Another if only a couple thousandths is mould expansion from almost to cold to almost to hot. It only takes .001 expansion to make .002 difference in dia. Light hand grip and not holding the sprue handle will help also. On my brass and Iron moulds I also close on a flat rail then give a tap or 2 ( very light and on the right side mould mount of the handle to make sure blocks are seated together. Another interesting check would be to cut the last sprue and leave the bullets in the mould till cool. Then measure each bullet one at a time to see if a cavity or 2 might be slightly oversize. If your ratio of oversized bullets to good bullets is consistant this may be the reason.

Lee does that intentionally so you can try diff. diameters.

"Lee does that intentionally so you can try diff. diameters."

That's the funniest post I've read in a long time. I was laughing for like 5 minutes.

This is the reason that we size them. Lee makes a little tool you can use on your press to size them to the diameter needed.
Diameters will vary with any mould, the mould temperature , alloy temperature , which cavity you are filling all conspire to cause this. Sizing the boolit is the easiest fix.
Gary

Hello,

Im positively surprized by the number of posts and good ideas...

In reply to several questions:
Im using the lee c312-155 mould.
During operating it i handle the handles with care. I give not mega hard force on the handles.
I size them allways with a gascheck.
I got chamberingissues due to the variation in nosediameter. Varying from ca .309 to .315
Its measured with good calipers with the measuring elements paralel to the cast-rim. (I dont have a namenfpr it. I mean the line on the boolit at thenplace where the mould.halves connect.
So. I conclude that everything has to do with properly closing the mould.

With the same 2cavity mould i dont have this problem (and not the castingspeed..)

Shortning the col is not an option.

The diameters of all six cavitys is ok (one cast)
The problem is the variation between the different casts.

I learned that during closing the mould several forces working against each other. This is causing the issue.

What works is:
-closing the mould
-closing the sprueplate.
-get good grip on the mould handles and i give a few a little -taps with a plastic hammer on the side of the mould while giving gentle pressure to the spruehandle preventing get opened a bit while tapping
-during casting i dont touch the spruehandle

This is giving way less variation (casts moslty .309 with some at .310 or .311 measured on the nose.

But...
Also the good boolits do not fit very well in my k31. The nose is sligtly to big for the throat..

I have to figure out if i can solve this with shortning the col a very little.

I keep you informed.


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Quote:

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Its measured with good calipers with the measuring elements paralel to the cast-rim. (I dont have a namenfpr it. I mean the line on the boolit at thenplace where the mould.halves connect.

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The name you are looking for is parting line. From where the mold parts.

From reading your last post; it seems like the alignment pins may be binding when you close your mold, causing the variations in diameter.

"But...
Also the good boolits do not fit very well in my k31. The nose is sligtly to big for the throat.."

Then you are using the wrong mould.

Quote:

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Originally Posted by Mk42gunner

The name you are looking for is parting line. From where the mold parts.

From reading your last post; it seems like the alignment pins may be binding when you close your mold, causing the variations in diameter.

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Yep, and a tiny bit of sprue plate lube on those alignment pins should make all the difference in the world.