Brass vs steel vs aluminium

[andym79]

Hi guys, I am looking at getting a couple more moulds. I have some brass, some steel and some aluminium.

I find the these to be the characteristics of my moulds when casting:

Steel, takes a lot of pours to produce anything worth keeping, I have taken to dipping the corner of the mould into the molten lead for 30 seconds and then its good to go on pour one. It sometimes stays too hot. however I find my steel moulds drop the bullets the easiest, sometimes without even a tap. They also seem to drop the best looking bullets! However they are a pain in terms of having to oil and clean of between each session, if they will be on the shelf for a while (they rust).

Aluminium, gets up to heat lovely and fast, sometimes the first pour is acceptable and always the second. They loose heat quickly which is often a good thing for fast casting. A couple of taps and they let go, not as well as the steel moulds, but well enough. I do however thing the steel moulds drop better bullets. The light weight ali allows for longer sessions or more cavities (which means more bullets in a session as opposed to either brass or steel).

Brass, takes a few pours to get up to a good heat (and I can't dip it like steel, as brass doesn't take much to warp), then holds it well (sometimes too well). It drops very nice bullets as good or better than the aluminium. However I find that often I really need to give it a hard knock to get it to drop the bullets. Sometimes to the extent that I am literally bashing the **** out of it. Would this be caused by a tin reaction with the brass, like soldering?


Are these the typical characteristics you guys find when casting with these materials?

Any way back to the point, my preferred mould maker (local) only makes his moulds in brass, and I am sick of hitting the mould so, it makes for frustrating casting and a sore hand.

Is there any way to avoid this sticking effect? Should I reduce the tin content?

My current alloy is about 4% tin, 2.5% antimony for the bullets I cast from my brass mould!
I also use a 3% tin 2% antimony but in my other moulds.

I am not deliberately using a harder alloy in the brass moulds, rather the I need a harder alloy for my 6.5x55 than for my lever guns! It may be worth trying a 2% tin 4% antimony alloy instead.

[Tatume]

Hi Andy,

Yes, you probably should reduce the proportion of tin in your alloy. It should be less than the antimony. My favorite alloy is 2/3/95.

Although I also use all three metals, my favorite molds are aluminum. They have the characteristics you describe.

Take care, Tom

[Dan Cash]

I have one brass and several iron (Lyman, Hoch) and several aluminum (Accurate and LBT) moulds and of the lot, the aluminum ones are the most trouble free. I am getting ready to order two new moulds which will be aluminum. They will retire two iron moulds.

Can't answer your question regarding tin and the brass mould. I use same alloy as with other moulds with no incident. The brass mould I have is an Accurate and drops bullets with ease but does seem harder to get up to temp.

[stubert]

I just purchased a new RCBS 45-300fn mold. The first time I used it I preheated it on a hotplate and had my lead up to temp. Every single bullet I cast, starting with the first one was perfect. Tip: Take an old circular saw blade and grind off the teeth, put it on the heating coil on the hotplate, it evens out the heat and you don't get hot spots.

[cbrick]

Doubtful bullets sticking in the brass mold is the alloy but the tin percentage should not be more than the antimony percentage to prevent pockets of free tin.

Releasing bullets, could be alloy temp in the pot, you didn't say what your casting at. The reason bullets fall out of the mold at all is because as they cool they shrink and no longer fit the cavity that made them. If your alloy is too hot it takes longer for the bullet temp to come down enough for this shrinking to happen. Add to this that the brass holds heat fairly well increasing the problem.

Also regarding pot temp, Sn both looses it's ability to reduce surface tension in the molten alloy and begins oxidizing much faster at about 750 degrees F. All of your molds, brass included should cast perfectly with the alloy temp no more than 700-725 degrees.

Rick

[geargnasher]

Brass, depending on exact composition, loses heat faster than aluminum. The coefficient of heat for free-machining brass alloy is about three times higher than 6061 T6 extruded aluminum. Want a challenge? Cast .22-caliber bullets out of a set of brass blocks. No way to keep the blocks up to temperature, just preheat in a mould oven and cast as fast as humanly possible until the mould gets to cold, then back in the oven again. One reason that brass moulds have a reputation for holding heat is that some of the manufacturers make them extremely large and heavy, partly to hold more heat, and partly to prevent warpage. The relief cuts on Mihec and Accurate brass moulds are important.

All said, with proper casting techniques, any good mould will cast excellent bullets, you just have to learn what those techniques are and how one needs to change from one mould to the next. I tend to gravitate toward aluminum moulds these days, though the thinner, lighter, iron or mehanite seem to be the easiest to cast really high-quality rifle bullets from, likely due to the slower cooling and lower heat transfer properties. Just don't get in a hurry with them.

Gear

[andym79]

I tend to gravitate toward aluminum moulds these days, though the thinner, lighter, iron or mehanite seem to be the easiest to cast really high-quality rifle bullets from, likely due to the slower cooling and lower heat transfer properties. Just don't get in a hurry with them.

Gear

Glad I am not the only one to find steel drops the best bullets!

[cbrick]

Brass, depending on exact composition, loses heat faster than aluminum. The coefficient of heat for free-machining brass alloy is about three times higher than 6061 T6 extruded aluminum. Gear

You could be right but that's not been my experience with any of my MP brass vs. any of my aluminum molds regardless of make. The aluminum heats up faster than the brass and cools faster than the brass via Al's temp probe. All of my brass molds once at proper casting temp are a joy to cast with. I don't have any 22 molds in brass but I would think it could be tough to get a brass 22 mold up to temp by casting with it because it heats slower. Because my brass molds hold a steadier heat than my aluminum molds I get less weight variation with brass.

I get much smoother bullets from the brass vs. iron also because it does machine so much better.

Rick

[dragon813gt]

I have the same observation as Rick. Brass holds heat better. Once up to temp it stays there. It does tend to have a very narrow operating range. If bullets are sticking the mold isn't at the right temp for that bullet/alloy. You should heat cycle the mold a few times before casting w/ it. It helps start the patina process and reduces your chance of tinning the mold. The more you use the mold the greater the patina and the easier it will be to cast w/. They really shine when the shine is gone, pun intended.

And get yourself a hot plate. All molds benefit from proper preheating. A coffee can cut in half makes a perfect, and cheap, mold oven.

[geargnasher]

You could be right but that's not been my experience with any of my MP brass vs. any of my aluminum molds regardless of make. The aluminum heats up faster than the brass and cools faster than the brass via Al's temp probe. All of my brass molds once at proper casting temp are a joy to cast with. I don't have any 22 molds in brass but I would think it could be tough to get a brass 22 mold up to temp by casting with it because it heats slower. Because my brass molds hold a steadier heat than my aluminum molds I get less weight variation with brass.

I get much smoother bullets from the brass vs. iron also because it does machine so much better.

Rick

Do you have any aluminum moulds that have blocks comparable to the size of Miha's? Apples to apples can be tough to do. I base my comparisons on the casting qualities of several identical mould block sizes from the same manufacturer, in both brass and aluminum. I can cast as fast as I want to with cooler alloy using the brass, but the aluminum overheats quickly and cools down more slowly. If I let up on the brass, even for a second, it takes a pour or two to get it back. This is NOT tested with a temp probe. My observation about thermal coefficients is probably not exactly 100% valid here because there is also a huge difference in MASS between equal-sized aluminum and brass moulds, and the more dense material has more molecules in it per gram to excite with the heat energy, therefore more BTUs per gram are capable of being absorbed by the brass.

Gear

[Tatume]

The thermal conductivity of aluminum is nearly twice that of brass. Pure aluminum has a thermal conductivity of about 205 Watts/meter/Kelvin. Brass with 70% copper has a conductivity of about 109 W/m/K, and brass of 63% copper has a conductivity of 125 W/m/K. Given two molds with the same dimensions, an aluminum mold will heat faster and cool faster than a brass mold.

[303Guy]

Gear is right about aluminum have a higher specific heat than brass. It has twice the specific heat capacity of brass. However, brass is three times denser so the molds are heavier making the volumetric heat capacity 30% greater than aluminum.

I have a one piece brass mold (smooth side) I made which used to cast easily. Then I changed the alloy and now it won't drop the boolits. Less shrinkage causing the boolit to lock in an irregularity in the mold.

[andym79]

So my experience of bullets sticking in a brass mould is not unique. I will try it with less tin!

[cbrick]

So my experience of bullets sticking in a brass mould is not unique. I will try it with less tin!

Tin? Antimony shrinks less creating a slightly larger bullet. Shrinking is why they fall out of the mold. How much antimony is in your alloy?

Rick

[andym79]

My current alloy is about 4% tin, 2.5% antimony

[C. Latch]

I have exactly one brass mold, it is a fine example of the mold maker's handiwork, I am proud to own it, and when the temperature is right it drops beautiful bullets, but I must admit: I do not enjoy casting with it, and one day will ask one of the custom makers to recreate it in aluminum blocks. I am waiting for an invoice from another group buy from that maker, and while I look forward to having the bullets, I dread having another brass mold.

I enjoy casting with molds that are as small as the 2-cavity Lee molds and as large as a 4-cavity NOE aluminum mold. If cost was no object, everything else I ever bought would be in 4-cavity aluminum blocks. YMMV.

[cbrick]

Oh yeah huh? Says that right there in post #1. I don't know if reducing the tin would aid in bullet release but tin should equal antimony so it wouldn't hurt to reduce it to about 2% to 2,5%.

Rick

[Tatume]

Hi Andy,

Yes, you probably should reduce the proportion of tin in your alloy. It should be less than the antimony. My favorite alloy is 2/3/95.

Although I also use all three metals, my favorite molds are aluminum. They have the characteristics you describe.

Take care, Tom

We've come full circle.

[W.R.Buchanan]

I have found that certain types of boolits run better in certain types of moulds. Short Fat boolits run easily in any material but brass moulds seem to work best. Long skinny ones seem to run best in Aluminum or steel.

That said virtually all of my RCBS, SAECO or Lyman Steel moulds hardly ever make bad boolits All work beautifully however some produce boolits that are smaller than I want hence the need for custom Brass and Alunium moulds. I have a Magma .44-190 SWC Steel mould that has never dropped even one bad boolit.

I have had great luck with Lee Alunimum moulds and everyone I have ever used has made good bullets. The first mould I ever bought was a Lee 429-240GC. I have made a zillion boolits with that mould and virtually every pour results in two good boolits. I have a Lee 309-190GC single cavity mould and every single boolit that has ever come out of it has been good! I have about 5 or so Lee moulds and I doubt I have $50 in the lot. Hard to bitch about that level of success.

My life in boolit casting really began in earnest when I purchased a hot plate and started preheating my moulds on it.

It has made casting so much easier it is scary. I actually went to my local Hardware store and bought a new one for $15. Single best investment I've made.

My Brass Mihec Moulds are the best ones I've ever used but both of them are .44 Revolver boolits not long skinny ones.

I have one Lyman 173gr .38 cal mould that has never dropped even one good boolit, and I have no idea why.

My whole take on this subject is that all of the common materials work about the same overall. It is up to you to figure out what combination works best for each one. This can be frustrating sometimes, but when you get it right it becomes very rewarding.

I tend to write down what works for each individual mould in a log book. That way I don't have to search each time I want to make boolits of a certain type for a certain mould. Surprisingly some factors tend to overlap from mould to mould.

There is no "Universal Truth" in Boolit Casting, that's part of the reason why it is fun.

Randy

[dkf]

You could be right but that's not been my experience with any of my MP brass vs. any of my aluminum molds regardless of make. The aluminum heats up faster than the brass and cools faster than the brass via Al's temp probe. All of my brass molds once at proper casting temp are a joy to cast with.

I don't have any 22 molds in brass but I would think it could be tough to get a brass 22 mold up to temp by casting with it because it heats slower.

Because my brass molds hold a steadier heat than my aluminum molds I get less weight variation with brass.

I get much smoother bullets from the brass vs. iron also because it does machine so much better.

Rick

I have an MP 75gr 4cav in brass and an ACE 75gr 4cav in alum both .22cal. The MP has lot smaller blocks than the ACE with cavities close together. Both molds cast really well and it is not hard to keep them up to temp. I will say though the ACE alum molds drops the boolits easier, seems like the jump out. The MP needs a little tap to release all the boolits.