Heat treating question

[Marlin Junky]

I've got some range scrap alloy that obviously has more Sb than clip-on WW metal that hardened to BHN 24 after less than 4 full days. The boolits were HT'd at 450F for near 75 minutes and quenched in ice water.

My question is: If I want to HT at a lower temp to reduce the BHN, do I first need to bake at 450F and allow to air cool? I was shooting for BHN 20 the first time I HT'd these boolits and I baked them at 420F for 75 min. but the results after 2 days was about BHN 14 so I HT'd them again (without first annealing) at 450F which brought them to BHN 24 rather quickly. The as cast boolits measured about BHN 12 when air cooled.

Now for the practical question: Am I really going to notice a difference in accuracy in my fast twist .350 if my boolits are BHN 24 vs. BHN 20? I was shooting .002" over groove at BHN 24 and got the usual signs of too much diameter; e.g., alloy on the outside of the case necks, vertical stringing, and just bad accuracy; however, I don't know if I should be concerned about lack of obturation with a plain base BHN 24 boolit (Lyman 358430) that's only .001" over groove (I have already sized them down). I'm using fast pistol powders and trying to stay just over 1500 fps. Even at BHN 24 my barrel started to foul where the lands meet the wide grooves so I'm thinking that I may be getting some gas leakage even at .002" over groove (maybe due to the fast twist).

But here's the rub: My loads are producing a bit less than 20K PSI and for obturation to take place it is generally accepted that I need a boolit approximately BHN 13. The problem with boolits that soft is they are sized down to .356-.357 during the seating operation. I can imagine my 12" twist would carve 'em up pretty bad too. Sooo... what does it matter, BHN 18, 20, 24... would there be a difference in obturation under these conditions? Or, am I OK shooting them as hard as possible? I've tried to eliminate the lube as a variable by going with LBT Soft blue which is generally known to be a quality lube.

MJ

[BABore]

It's actually easier to anneal, or draw back fully hard bullets than trying to find that perfect OHT temp. Try annealing your hardened boolits at 325 F, for an hour, then turn the heat off. Remove them when cool. Hopefully your doing this in a conventional oven and not a toaster oven. They don't hold the heat well. May work though. Marshall Stanton, from Beartooth, once told me that he boiled HT'd boolits for 10-15 minutes to anneal them. Never tried it myself as I couldn't see how it would work at only 212 F. It didn't work for me in an oven at 250 F for an hour.

As far as what your gun will like best is up to it. Gotta try them. If you got a fair # of boolits, anneal smaller batches in 25 F increments, from 300 to 400 F. Several here shoot freshly heat treated boolits each day with a proven load. Since they take up to a week or more to fully harden, you can test hardness and shoot a different hardness level each day.

This info is based on tests done with WW's. No telling how your range scrap alloy will react. I got some indoor range scrap that was mixed 50/50 with WW's. It WD'd at 30 Bhn immediately. Zero wait time. The general consensus was that my scrap likely contained some bismuth from foreign 22 lr target ammo.

[Marlin Junky]

Thanks Bruce,

My range scrap is the cowboy type, commerically cast stuff that's laying about... mostly pistol calibers and 45-70's. I'll anneal a few and shoot them against the fully hardened stuff (all .001" over groove) to see if I can notice a difference on target. Annealing at 325F for an hour will back the BHN down to what? I don't want to reduce the BHN all the way back to about 12 because that's so soft, the .350's case necks will reduce the diameter of the 358430s to .356-.357". I need the diameter to remain at .3585" through the handloading process.

I'd like to participate in the 358430 group buy so I can make mounds of these boolits but I'm afraid of Lee's ability to produce nice round cavities (not that Lyman is immune to making junk) that'll size to .001" over groove all the way around.

Thanks again,
MJ

P.S. Does annealing reduce diameter at all? I noticed that heat treating/hardening can increase the diameter up to .0005" but that may be as a result of the ice water quenching.

[cbrick]

Marlin Junky,

How fast your bullets harden depends a great deal on the antimony percentage. I have run tests with varying percentages of antimony and they both reached the same final BHN, the lowest percentage in 2+ weeks and the higher percentage antimony in 3 days.

It will be intersting to hear how your hardened bullets do when sized .001" vs the leading of the .002" over groove dia. Its very possible that your 20+ BHN is too hard for the pressures (velocity) you mentioned. As an example, I shoot my 308 at 1900 fps with a 180 gr bullet, air cooled WW at 11 BHN. Zero leading and great groups at 100 and 150 yards. As for the case neck sizing the bullets down a larger expander plug or neck die should give much better results than a harder bullet. Perhaps Mr Buckshot could help you out with this.

Annealing was in Veral's book and I can attest that it does work. It's far easier and faster to arrive at a desired BHN range by using a convection oven and a pre-determined temp setting. Here's an article that will give you some starting temps. Heat Treating Lead Alloys (http://www.lasc.us/HeatTreat.htm)

Hope the article helps.

Rick

[runfiverun]

i think that the drawback hardness is about 22.
your ht'ing is also based on the amount of tin in your alloy, the ability of your oven to maintain it's level of heat [ fluctuations in temp]
the size [ mass ] of your boolit, composition [ alloy]. and time.
all will play a factor here, consistency is gonna be your friend here m.j.

[Marlin Junky]

Tonight I annealed two batches of the range scrap 358430s that were HT'd to BHN 24 last week.

The first batch was baked at 350F for a little over an hour and the final hardness was just about that of the as-cast air cooled alloy.

The second batch was baked for an hour at 300F and ended up at BHN 13 which is just about 1-1.5 BHN points above the as-cast air cooled alloy.

Obviously, my range scrap responds to heat treatment a lot differently than clip-on WW metal... probably because of higher Sb levels and lower Sn levels. After all, Sb is a cheap/effective hardener and the cost of Sn will eat into the commercial caster's profit. Perhaps the fast twist M77s may benefit from an alloy of commercial caster scrap (for additonal Sb), clip-on WW metal and soft (near pure) Pb.

Monday I'll shoot the BHN 24 358430s against the BHN 13 358430s using 14 grains of 453 (Scot 453 can be described as a fine grained WW-231). I'm not going to be surprised if things go haywire. I don't know if the 13 BHN 358430s were squeezed down any upon seating into their cases but at least the leading band is still .3580-.3585" in diameter. I suppose if the boolits are soft enough to be sized down during the seatng operation, they'll obturate with 14 grains of Scot 453 behind them. Problem is, the M77 doesn't like soft boolits.

Attached are two targets from last week. The vertical string was shot with 19 grains of H2400 (1532 fps) and the 4-o'clock group was shot with 14 grains of 453 (1541 fps). Boolits were .002" over groove and HT'd to BHN 24. This is becomming too much like work... I may move on to something less challenging, such as SAECO 356 and RCBS 35-200FN. Maybe I need a 38-55 with an 18" twist or a 45-70.

(targets are both 7" in diameter)

MJ

[runfiverun]

the 2400 loads look like some velocity variations.
maybe a primer change. W L Pistol or fed 210.

[HeavyMetal]

You haven't said what caliber your shooting other than .350.

This isn't important, just curious. Sounds to me like you need to treat this rifle round like a pistol case.

Most rifle dies are set up with an expander button designed for J- bullets. If you have a 38 special die set you might pirate the expander die and, if it's .357 diameter, run 10 or 20 case's through it and then load as usual.

If the case's were sizing your boolits this should stop it! Continue to use boolits in the 14 to 15 bhn range for this experiment and see what it gets you.

[Marlin Junky]

My experience using a Lee Pacesetter sizer for the .350 and a Lyman M-die are as follows:

.3585" gas checked boolits at BHN 15 (I just seated some SAECO 352 cast of Lyman#2 last night) slide into the .350 case necks with little more than the weight of the loading press ram handle, while .3585" 358430s at BHN 13 create a lot more friction in the sturdy .350 necks during seating (feels like at the trailing band). When I seated a couple .3585" 358430s at BHN 12, I pulled them from the case to measure the trailing band diameter which ended up at .356-.357" around their circumference.

I'll see if I can find a load to shoot a BHN 15+ plain base boolit from the .350 accurately. After which, if I want to go with a softer boolit/lighter load, I'll order a Lee Collet Sizer for the .350. With a Lee Collet sizer one can vary the inside neck diameter by .001" or a little more and definitely loosen things up a bit. Too bad Lee doesn't offer a Collet Sizer for the .350 and .358 as a regular production items.

MJ

[Marlin Junky]

the 2400 loads look like some velocity variations.
maybe a primer change. W L Pistol or fed 210.

Here's the stats on both loads... (I never do any load testing w/o my chronograph).

2400 load:
high=1554
low=1511
range=43
mean=1532
std.dev.=15.2
% dev.=0.99%

453 load:
high=1550
low=1529
range=21
mean=1541
std.dev.=6.17
% dev.=0.40%

While the 453 load produced better stats, both loads have 2MOA potential or better if all the essential variables are compatible.

MJ

[runfiverun]

the 2400 loads look like a ladder test where the wind intervened.
if you can figure it out....it should be solid 1"
your neck tension sqeeezing boolits could be a likely culprit....
especially if they are not equal from case to case, it could cause it to look like poor ignition
simply by releasing the boolit at a different pressure point.
if you want accuracy, top accuracy, you are gonna have to build ammo better than the rifle is capable of shooting.
unless you have an awesomely built b.r. rail gun.