Heat treating temp vs. resulting BHN question

[Marlin Junky]

My 50/50 alloy heat treats to BHN 23 after about 75 minutes in a 500F convection oven. What temp would I need to set the oven at in order to end up with boolits that are 19-20 BHN (assuming I do everything else the same)? I'm pretty sure the oven temp vs. resulting BHN is not a linear function 'cause I seem to remember that the same alloy reaches 21-22 BHN after 75 minutes at 450F.

Thanks,
MJ

P.S. I suppose I could try a batch at 440F and a batch at 430F.

[Bass Ackward]

Leave oven temp the same and mold larger diameter bullets. :grin:

[BABore]

I heat treat my 50/50 alloy at 435 F (tested) for 60 minutes. The resulting boolits come out at 22 Bhn. If you want lower, it's something that you are just going to have to test out. A better solution would be to adjust the Pb level slightly. Maybe try 45/55 WW-Pb. The difference, between yours and mine, may have more to do with your WW's vs mine. 357Max has takin the Pb level to over 60% and had them WD at around 16 Bhn.

[Marlin Junky]

Leave oven temp the same and mold larger diameter bullets. :grin:

Bass,

I just stared doing .44s for my 444P under those same conditions, so we'll see if they come out a bit softer.

BTW, my M77 .358 shot pretty well yesterday at over 2100 fps 'cause I loaded up some lighter boolits (RCBS 35-200FN at 214 grains checked). With the aid of QuickLOAD, I'm going to try to match the BHN to the boolit hardness and go for 2200 fps. The .350 may get a new barrel but I first want to see want happens to my .358 shooting now that I have a way to estimate pressure. The .350 could also be converted to a .375-350 but I can't find any decent info on that wildcat any more.

MJ

[Marlin Junky]

I heat treat my 50/50 alloy at 435 F (tested) for 60 minutes. The resulting boolits come out at 22 Bhn. If you want lower, it's something that you are just going to have to test out. A better solution would be to adjust the Pb level slightly. Maybe try 45/55 WW-Pb. The difference, between yours and mine, may have more to do with your WW's vs mine. 357Max has takin the Pb level to over 60% and had them WD at around 16 Bhn.

Bruce,

Yeah, I realize I'm in the fine tuning neighborhood now and I really need to play with the variables. Sounds like your alloy may have a bit more Sb than mine. It'll take some effort, but over the next couple weeks I'll need to break in my RCBS 35-200FN, (mold opens hard w/ sticking boolits) cast a bunch in 50/50 and HT at 430, 440 and 450F.

MJ

[Marlin Junky]

Leave oven temp the same and mold larger diameter bullets. :grin:

Bass,

I'm not sure what happened to the RCBS 44-240SWCs that I HT'd the other night but they came out BHN 27 to 28. I guess the couple pounds of reject boolits cast from range scrap that I threw in the half full MasterPot must have added enough Sb to give the HT'd results a 5 BHN bump (normally my 50/50 HT's to 22-23 BHN under the same conditions). I was going to draw the batch back to something softer, but first I'm going to shoot a few beyond 2200 fps to see what happens. I'm not expecting much because these 44-240s didn't come out very round because I needed to shim the mold to get .431" (max). I figure the best chance of getting them to group is by launching them with a healthy dose of 2400. According to QuickLoad, 35 grains of 2400 will launch a 249 grain RCBS 44-240-SWC at 2193 from an 18.5" barrel while generating about 42.8K PSI. Because of the hardness of the alloy, I'm anticipating a little more velocity ,(and probably a bit more pressure too) which is what I've been experiencing with my .35s shooting BHN 22-23 boolits (compared to QuickLoad's estimates).

MJ

[GabbyM]

Interesting to hear your RCBS 35-200-FN drops 214gr bullets. I cast my first ones yesterday and they were 215gr with lube and gas check. Using 50/50 with 1% tin.

I use 430 degrees for 40 minutes and end up with a strong 10 on the Saeco scale. That's in my gas oven with a loose fitting door from a broken hinge. Kind of like a convection oven with the extra air moving through.

Mj if you don't mind me butting in with a question. What O.L. Do you need to reach the rifling in your 358? I goofed up when I drew up this 230gr MM bullet design. When I deleted the crimp grove from the drawing it's area turned into grease grove instead of bearing surface. So I've a .100” front band with a .120” bore ride. Of .352” diameter. Attached photo of my 230gr next to a RCBS 35-200-FN. I've seen you write you wanted a bullet with more grease. Well this one has it.
Have wondered if this .100 band will reach to within .03 of rifling before exposing the grease.
http://castboolits.gunloads.com/picture.php?albumid=32&pictureid=149

[Marlin Junky]

Interesting to hear your RCBS 35-200-FN drops 214gr bullets. I cast my first ones yesterday and they were 215gr with lube and gas check. Using 50/50 with 1% tin.

No, I said 214 grains checked, meaning with the gascheck installed.


Mj if you don't mind me butting in with a question. What O.L. Do you need to reach the rifling in your 358?Heck, I'm pleased to impart some knowledge: 2.6"


I goofed up when I drew up this 230gr MM bullet design. When I deleted the crimp grove from the drawing it's area turned into grease grove instead of bearing surface. So I've a .100” front band with a .120” bore ride. Of .352” diameter. Attached photo of my 230gr next to a RCBS 35-200-FN. I've seen you write you wanted a bullet with more grease. Well this one has it.
Have wondered if this .100 band will reach to within .03 of rifling before exposing the grease.The M77s (both the .358 and .350) have a bit of throat. I'm sure the lube will be exposed forward of the case mouth on the .358. The .358 case mouth (on a 2.01" case) lands just about midway on the second driving band from the nose when the COL is 2.6".

MJ

[rhead]

MJ: If you gota dozen small containers about the size to hold a dozen bullets (tuna can sized?) Heat them to 380 and hold for 30 min, pull and quinch one can and increase the heat to 390, give the oven 10 or 15 min. to stabilize and pull another one. Save the bullets and check the hardness after they have stabilized and chart the hardness vs treating temp. 12 samples will take you to 490 degrees. You already know what 500 degrees will do. Your resulting chart will of course be good only for that one batch of alloy but should be close or other similar batches.