JT brass moulds conundrum

[Hubertus]

I just wanted relay today's experience to you and wanted to see if any of you had some feedback. This was the first time I had used a JT brass mould. I cast 162 pure lead ball of the .490"...my heaviest ball was 177grains. I weigh the balls and keep everything within 1 grain of the heaviest...and here is my conundrum... I was left with about a dozen balls. All the others were light!... so, the only thing that can be going on here is that I have air bubbles in what look to be good ball. My pure lead casting temp was 840 degrees F. I had no wrinkled ball, so I thought they were filling out nicely. What do you suppose went on? Obviously I need to increase the number of "good" ball and this has never happened to me.

Any insight you could provide would be greatly appreciated!

 

[necchi]

Going with the heaviest ball might be the trouble.
That one ball might not have had the mold closed completely or sumpthin and is just plain heavy.

I also keep my spread within 1grn, but I use an avarage of several ball then anything +/-0.5grn of the average is a keeper.
Anything not within that 1grn spread is tossed for re-cast.

 

[damron]

One of my 2 cavity .495 molds casts them about 2g apart and a bit over .001 bigger on the heavy one.Segregating the bullets and shooting separately gave no smaller groups.(under 2" at 50 yards with irons abut every group)Shoot them first before you draw a conclusion.Unless you just like to weigh and sort bullets.
I know i am probably the exception to this.

dont you have to nip the sprue on a tanner mold rather than being cut with a sprue plate?Is this the variation?

George

 

[Big John]

I take an average weight of 6 cast balls as my aim point weight, weight them to .5gr. generally I have 1-2 throw aways per hundred during a 1,000 casting session.

 

[Rifleman1776]

840 degrees seems way too hot.
I cast at about 700 degrees and balls fill out fine. Must qualify, I'm not using Tanner moulds but can't see where that would make a difference. Just stick with it. You might not be pouring at same rate each time. Are you using pure lead?

 

[Ken Rummer]

I bought a .590 JT mold and my first casting session did not go well. Rejects were 90%.

I noticed the mold was not filling out the ball at the top near the sprue. Since the Tanner design has a very long sprue I thought the sprue was cooling and plugging before the mold was full. I did not note my casting temperature but I will kick up the temperature for the next try.

Since other users have had success with the JT molds, I think a higher temp. will sovlve the problem.

 

[Rifleman1776]

These are the first (possible) non-favorable comments I have seen on JT moulds. Not having used them myself, I am inclined to think it is a matter of casting technique. Would welcome others who have used the JT moulds comment.
I'll probably have to get a JT (for an unusual size) before long and want this little mystery cleared up.

 

[Robby]

Are you using it with a bottom pour, or an enclosed ladle, mating it to the spru and pouring? If so you may be getting air in the ball or as Damron suggested there may be inconsistency in spru cutting. I use a couple Tanner moulds, once up to heat they work great, I pour the lead leaving the spru fairly open so air is displaced.
Robby

 

[Hubertus]

Rifleman1776: I am using pure lead.

Robby: I am using a bottom pour with the top of the mould about 1/4" from the lead spigot.

I cut open several of the ball and they all have a good sized air bubble usually below the sprue towards the middle of the ball...so lead is capping the bubble.

(Btw, JT does not make the moulds himself anymore, his son is now making all the small moulds .600 and under).

 

[Hubertus]

It might not have been crystal clear in my previous post(s)... I'm not knocking the mold at all... I'm trying to figure out what is going on and fix it. JT moulds (whoever actually makes them) have an excellent reputation, so at this point I'm going with "operator error".

 

[necchi]

Try holding it at an angle when you start the pour, bringing it upright to finish.
(twist of the wrist)

The idea is to get the molten lead to "swirl" as it's poured in the mold

 

[damron]

WOW I have never seen so many voids like that!That is a problem.I would try a ladle and let metal keep flowing into the sprue hole(and spill over the side of the mold) till the ladle is about 1/2 empty then top it off.its messy but it works.

George

 

[Rifleman1776]

Very interesting revelation.
How big is the hole? I have heard of having to enlarge the hole sometimes on other brands. You may not be able to pour fast enough with a small hole. Just conjecturing. :hmm:

 

[Robby]

Try holding it at an angle when you start the pour, bringing it upright to finish.
(twist of the wrist)

The idea is to get the molten lead to "swirl" as it's poured in the mold

What Necchi said! :thumbsup:
Rifleman, I found the same problem with my bottom pour and started using a ladle and pouring like nicchi advises, leaving just enough room between ladle and mould for air displacement.
Robby

 

[Hubertus]

Thanks for all the suggestions! I'll certainly try Necci's "swirl" suggestion...technique is the easiest fix.
I've been in contact with JT also and he suggested, as did Rifleman1776, to open up the pour hole by half a millimeter. I've done that now and will see what my weekend casting session will produce.

 

[Grizzled Roberts]

I have many JT moulds for all of my calibers. First off I use a ladle not bottom pour. I use a lead thermometer.
Step one I crank my furnace all the way up to 900.
When the temp gets to 700 I start pouring.
Tanner moulds are brass, brass heats up faster than steel so here is my way past this.
after you start getting good looking ball run around 20 more then turn down the pot to 850 and run 50 or so ball. Turn it down to 800 and finish the pot.

I have enlarged the pour holes in all of my moulds over 54 caliber.

When the pot starts heating up I prop the brass mould on the rim of the pot so the brass will start heating up.

When I start pouring I hold the mould over the pot I always pour in more lead than is needed the excess lead falls back in the pot.

When I heat the mould up I sometimes get useable ball between 5 - 10 balls from the start.
This process has served me well for some time now.

If you run the pot wide open the brass will get to hot and you will not be happy with your results.
I hope this helps.

 

[mooman76]

Great picture for the post. I have always heard of air bubbles as a possibility but I never envisioned them being that large.

 

[Hubertus]

Just wanted to give an update on trying to eliminate the air bubbles: enlarged the pour hole to 3/16" (.6mm larger) and swirl method...still had bubbles in almost all ball cast. Then tried the dipper method...and voila, only had 14 out of 163 ball being light. Problem solved, I'm thoroughly sold on not using a bottom pour anymore.

 

[Dphar]

I just wanted relay today's experience to you and wanted to see if any of you had some feedback. This was the first time I had used a JT brass mould. I cast 162 pure lead ball of the .490"...my heaviest ball was 177grains. I weigh the balls and keep everything within 1 grain of the heaviest...and here is my conundrum... I was left with about a dozen balls. All the others were light!... so, the only thing that can be going on here is that I have air bubbles in what look to be good ball. My pure lead casting temp was 840 degrees F. I had no wrinkled ball, so I thought they were filling out nicely. What do you suppose went on? Obviously I need to increase the number of "good" ball and this has never happened to me.

Any insight you could provide would be greatly appreciated!

Are you using a commercial ladle?
If so hold it on the blocks longer to fill the void caused by shrinkage.
Don't have a commercial ladle? Using a bottom pour pot? Either of these could be the problem.
Bottom pour pot are only good as door stops or boat anchors if trying to cast really good bullets.
Make SURE metal is hot and the pots temp has stabilized. Make sure the mould is hot. Cast about 10-20 bullets and scrap them until the mould is hot enough the sprue takes a few seconds to set.
Be very consistent in your casting and DO NOT stop once started. If you stop and the mould cools chances are the ball will weigh different.
Tanner makes a good mould but I use a Lyman if they make the size I need over all others. If you get a bad one sell it and buy another. I have a 2 cavity .495 that casts a very uniform ball of the same weight from both cavities.

Dan

 

[Hubertus]

When I originally posted this I was using a bottom pour pot but have switched to a ladle and dipper pot...that seemed to have done the trick. I haven't heard of the "commercial ladles"...how is it better? I used a Lyman ladle (you know, the spherical-looking one).