Varying hardness in same bullet?

[Canuck Bob]

A greenhorn question to help understand rifle casting. Do bullets generally shoot to the same POA if hardness varies? Like aircooled versus quenched WW bullets?

[lwknight]

IMO , the biggest contributers to changes in POI are bullet weight and powder charge.
Bullet hardness would most like affect accuracy ( group size ) to one way or the other.

[Bret4207]

It depends. If the varying Bhn alters the burn rate and pressure curve or if the load is a little hot for AC but fine for WQ or if the WQ is too hard for the powder to do it's thing with obturation then it can make a difference.

[dverna]

An interesting question.

Bret raised some good points. Depending on the load, and bullet sized diameter I can envision situations it would make no difference or possibly some difference.

It would be an easy test but the results may only apply to that particular gun/load/bullet and may not be generic or universal.

Don

[btroj]

Bret is right. Too many variables for a simple answer.
I don't worry about it as I am not usually shooting balls to the walls loads. And I tends to shoot bullets that haveroven themselves to be a good fit in the gun they are being used in. Other than that, I just treat them all the same. Are some harder and some softer? Absolutely. O just don't care about that and so far, my guns dont either.

[Von Gruff]

The following all relates to my 7x57 with the 160gn Lyman 287641

I did a test yesterday with boolits cast from the same mould and with the same powder charge. There were two seperate tests with one being at 1900fps over Blue Dot and the other at 2400fps over H4350. I tried 50/50 ww/Pb and 70/30 ww/lino and straight lino. I had al GC and Cu, both Hornady and my own made. I have two sizing dies that are .285 and .2855. Groups were all shot with the same POI and were withing usuable differences within the velocity groups.
What I found was that the slower loads prefered the softer alloy and GC and best result was with the 50/50 alloy with an AL GC and sized larger at .2855 but the faster loads prefered the harder lino alloy with a Cu GC (both mine and Hornadies seemed to work equally well ) but sized in the smaller .285 die. From what I found the 70/30 alloy had no niche where it worked best although I have another plinking load at 1500fps over Red Dot that I use all my reject boolits in so will use up the 50 lb of ingots I have for plinking.
My exceptance of best was in the 1 1/2" @ 100yds with all trial loads being inside 3-4" except one at 6" and this is all for 5 shots. A bit more refining is in order but the differences in alloy and velocities were compounded by GC trials as well with about 100 rounds involved. No leading with any of the test loads was evident.
Not sure its relevant as the bases on all are the same ..... but..... my hunting loads with a 50/50 soft nose on a lino shank over the same load and shoot to the same poi and at the same velocity as the straight lino loads so that I can use the quicker to cast, straight lino loads for all practice, and know that the same results would occur with the hunting loads.

Von Gruff.

[243winxb]

Do bullets generally shoot to the same POA if hardness varies? Like aircooled versus quenched WW bullets? No. Accuracy will be worse if dropping from mold to water. Oven heat treating/water drop is better. If you want top accuracy, air cool with the proper alloy, diameter,lube, with a Gas Check, if needed.

[truckmsl]

243 - Please explain why you think water dropped are inherently less accurate.

[onesonek]

I haven't experimented enough to prove or disprove one way or the other as of yet,,,,but I can understand where heat treating is more consistent than water quenching. And generally, where more consistency is maintained, better accuracy is achieved. I guess for me, it would depend on what level of accuracy is desired.

[waksupi]

243 - Please explain why you think water dropped are inherently less accurate.

The time between drops can vary, so the temperature of the bullets as they quench will vary.
I did some testing with oven treating wheel weight boolits, and found by varying the temperature of the oven, you can get pretty much any level of hardness you need.

[243winxb]

When dropping from mold to water-
The time between drops can vary, so the temperature of the bullets as they quench will vary.
Waksupi said it well. :smile:

[kelbro]

Agree with the above. Casting your own boolits is quite a bit of work and I want my finished product to be as consistent as I can make it.

I tried water dropping a couple of times. How much temp did the sticky boolits lose before they hit the water? Don't know. Measured a good size sample from that batch and saw a spread of 8-10 BHN difference between them. I'm not 100% certain but I can't help but think that would create some inconsistencies.

[303Guy]

Well, I've got (or had) some alloy which age hardened with or without any heat treatment or water quenching. Only the time to reach max hardness changed and that was hours or days. Then they softened again! Another alloy in a 'special' mold would produce a harder base shank and softter nose shank. That was with a very hot mold which took a while to freeze. Varying bands of hardness? - Done that too. It's caused by the alloy freezing in 'shuts' or bands.

http://i388.photobucket.com/albums/oo327/303Guy/pictures001-1.jpg

Clearly visible here. I can actually measure the hardness differences - using my technique (which gives a comparison only).

The trick is to get those bands even and concentric. It's from a nose pour mold. Do they shoot straight? Seem too. I paper patch them but I see no reason why they shouldn't work as is with dip lubing. (Assuming the size is right). It's hidden voids and uneven shrinkage that will cause inaccuracy.

The nose with sprue remnant.

http://i388.photobucket.com/albums/oo327/303Guy/pictures003-1.jpg

[rhead]

243 - Please explain why you think water dropped are inherently less accurate.

An addition to Waksupi's post: If the dropped boolit hits the water SIDEWAYS one side of the boolit will be harder than the other. This will sometimes cause larger group sizes. My hornet is particularly picky about this when loading to full power. It wants me to oven heat treat with the boolits standing on their bases with at least a quarter inch between the boolits. Other rifles may be more forgiving.

Any variable that can be controlled should be controlled.

[Bret4207]

Some pretty darn good observations here. Von Gruffs post shows that little variations can male a difference. Rheads seen the same thing. IMO the tricky part is figuring out just what it is your gun wants. In my case the learning continues. Every time I think I've almost got "it" figured out, something out of the blue smacks me with a giant dose of reality!

[44man]

A greenhorn question to help understand rifle casting. Do bullets generally shoot to the same POA if hardness varies? Like aircooled versus quenched WW bullets?
Yes. The only difference will be group sizes if your gun does not like the hardness of the alloy. If loads are all the same, they should hit around the same POA.
Some guns will see a change from boolit damage, skidding or slumping but if there is no boolit damage, then they should impact the same areas.
If you shoot BR or very tiny boolits, then it could make a difference but on the average, a few points in BHN means nothing at all.
I find my guns prefer water dropped and even oven hardened boolits are no better. Too much hoopla over such small things that are not important.
I just checked a pile of WD'ed WW boolits that have aged and every one is 27 to 28 BHN. I assure you that a few seconds difference in contact with the water is meaningless.
Your brass and how you work it will ruin groups faster then anything else you do.
Once a boolit holds it's shape and takes the rifling, I defy anyone to tell me that a few points in BHN makes any difference.

[truckmsl]

Well 44man - looks like we're in the minority here, but for the shooting I do the water dropped boolits perform very well.

[44man]

Well 44man - looks like we're in the minority here, but for the shooting I do the water dropped boolits perform very well.
Yes, kind of blew me away to find my WW boolits are so hard, they are usually 22 BHN but darn it, they shoot so good, who cares? I sure can't tell the difference. All I know is too soft creates too many problems I don't want to fool with.
Until you need expansion at certain velocities for hunting, of what use is a soft boolit? Shoot paper or steel or close range, what does soft do for a guy? Plain old WW's are as good as it gets.
It will be a cold day when I use air cooled for one gun, water dropped for another or a different hardness for each powder charge increase.

[runfiverun]

the thing i find strange is how i can drop a 7mm boolit then switch to a 375 boolit and when i take the 7's from the water how hard and clinky they are right off.
and how the 375's are still soft, same pot of alloy same temp and same tempo.
what gives there?
i know the surface area is different, but the alloy temp didn't change, and they have the same grey appearance of mold/alloy temp combination.
the only real big difference in hardness should be from the initial start [i usually just dump to the side the first 10 or so pours] once you get into rythmn
of pour ,cut, return sprue,dump,pour,cut,return sprue,dump.
you should have a pretty consistent bhn.
when i weight sort for target use i usually find a whole run will be well within 1% weight variance.
so if you have a big swing in hardness it's gotta be from start-up,and inconsistent cast speed.

if you are gonna heat treat i'd just air cool then weight sort then heat treat in the oven, it will get the whole batch the same hardness.
but for most shooting water dropping will suffice if you take care of the details.

[44man]

The inside of larger boolits just can't cool fast enough. What counts is what comes in contact with the rifling and the insides just do not need to be as hard. They will, however age harden more just like air cooled will over time.
Some air cool all the time, then don't load the boolits for a few months. They will have hardened. water dropping just speeds up the process and adds a little more surface hardness.
If you air cool, size and load right away, is there a difference from the boolits stored in a box for months? Of course there is so why not just water drop to start with? Air cooled makes more variables over time. I laugh at the guy that says he shoots nothing but air cooled but casts 3000 boolits at a time, then loads all year. I see no posts saying as the boolits get harder, they shoot different. My guess is that the old boolits shoot better yet the answer is always air cooled.
The most important thing is that I hate casting and I am lazy. Water dropping keeps me from rolling boolits around on rags or towels with the small space I cast in. I even water drop pure round balls but I don't WD the huge BPCR boolits because they can be damaged when they hit other boolits. They double the casting work. No, they don't harden either way but it is so much easier to dump into a bucket.
If I reach under the bench and take out two year old boolits that have been water dropped, load and shoot them, there is no difference from the ones I cast last week. Most have not been lubed or run through a sizer either.
Since water dropping shortens the time needed to load and they work the very best in every one of my revolvers, I will never change what I do. I refuse to air cool, then oven harden and will only oven harden boolits I did not cast. Softer alloys like 50-50 need the oven or you will wait forever before they shoot best. These also need a GC.
I do not weigh boolits or sort by hardness, it is nothing but "make work." If one boolit is 22 BHN and the next is 25 BHN and I shoot them from a good revolver, I bet I can make them touch at 100 yards.

[BABore]

the thing i find strange is how i can drop a 7mm boolit then switch to a 375 boolit and when i take the 7's from the water how hard and clinky they are right off.
and how the 375's are still soft, same pot of alloy same temp and same tempo.
what gives there?
i know the surface area is different, but the alloy temp didn't change, and they have the same grey appearance of mold/alloy temp combination.
the only real big difference in hardness should be from the initial start [i usually just dump to the side the first 10 or so pours] once you get into rythmn
of pour ,cut, return sprue,dump,pour,cut,return sprue,dump.
you should have a pretty consistent bhn.
when i weight sort for target use i usually find a whole run will be well within 1% weight variance.
so if you have a big swing in hardness it's gotta be from start-up,and inconsistent cast speed.

if you are gonna heat treat i'd just air cool then weight sort then heat treat in the oven, it will get the whole batch the same hardness.
but for most shooting water dropping will suffice if you take care of the details.

It's the diameter difference and temperature the boolits are at when they hit the water. What happens if your alloy requires a minimum HT temp. of 425 F to harden at all? If you below that temp., they don't show much if any hardness change over air cooled? Now take that line of thought to a water dropped boolit whereas it temp. is say 435 F. Upon hitting the water the quench acts from the outside inward. Cold attracts heat and vis versa. While the exterior is rapidly quenched while it is above the minimum HT temp, the inner core is getting the heat sucked out of it before the full effect of the rapid quench gets to it. The core is below the min. HT temp. threshhold and doesn't get hardened. Small diameter boolits will typically HT fully or closer to the core than larger dia. ones.

To get a more thorough HT on larger diameter boolits you have to run the temps hotter. That does not necessarily mean running the pot temp. higher, but rather the mold. Myself, I don't fret at pulling some sprue from the boolit base. Not alot mind you, but a small, consistent chunk out of the center of the base. I found it doesn't affect accuracy to any extent. Allowing the sprue to cool til you get that "text book" clean cut causes more problems than it solves. Your boolits are cooler cause you waited and the mold temp is fluctuating more as well. Weight variation as well as the increased chance of air pockets in the base can occur.

Being able to consistently control the temp of the WD boolits just above the minimum HT temp, also has other benefits. Hard right down to the bone is not always the best route. Having a hard shell and a progressively soft core makes for a tough boolit. They give more instead of being brittle. This technique is normal practice in the automation field. Precision ball screws are typically very hard on the exterior and soft in the core. It allows a high wear factor with springback when torques are high. It one of the reasons myself and several others like a 50/50 WW-Pb alloy. When WD'd at a specifc temp, you can make a boolit with a hard shell and soft core for good exanpsion at higher velocities.

[44man]

It's the diameter difference and temperature the boolits are at when they hit the water. What happens if your alloy requires a minimum HT temp. of 425 F to harden at all? If you below that temp., they don't show much if any hardness change over air cooled? Now take that line of thought to a water dropped boolit whereas it temp. is say 435 F. Upon hitting the water the quench acts from the outside inward. Cold attracts heat and vis versa. While the exterior is rapidly quenched while it is above the minimum HT temp, the inner core is getting the heat sucked out of it before the full effect of the rapid quench gets to it. The core is below the min. HT temp. threshhold and doesn't get hardened. Small diameter boolits will typically HT fully or closer to the core than larger dia. ones.

To get a more thorough HT on larger diameter boolits you have to run the temps hotter. That does not necessarily mean running the pot temp. higher, but rather the mold. Myself, I don't fret at pulling some sprue from the boolit base. Not alot mind you, but a small, consistent chunk out of the center of the base. I found it doesn't affect accuracy to any extent. Allowing the sprue to cool til you get that "text book" clean cut causes more problems than it solves. Your boolits are cooler cause you waited and the mold temp is fluctuating more as well. Weight variation as well as the increased chance of air pockets in the base can occur.

Being able to consistently control the temp of the WD boolits just above the minimum HT temp, also has other benefits. Hard right down to the bone is not always the best route. Having a hard shell and a progressively soft core makes for a tough boolit. They give more instead of being brittle. This technique is normal practice in the automation field. Precision ball screws are typically very hard on the exterior and soft in the core. It allows a high wear factor with springback when torques are high. It one of the reasons myself and several others like a 50/50 WW-Pb alloy. When WD'd at a specifc temp, you can make a boolit with a hard shell and soft core for good exanpsion at higher velocities.
Thank you Bruce! You explain it very well.