Quick Bullet Hardness Question

[Dimner]

Quick question for you guys. I need to get my CWW bullets harder using the heat treat process.

However, even if the question is quick, the background info necessary will take some explaining. So here is the process and my objectives to give a better picture of what is going on.

The objective is to get at least 2MOA accuracy at 100 yards with my 16" mid length AR-15. I have some specialized components so it will cycle at lower pressures than a normal mid-length system. Cycling isn't really an issue right now. I'm getting good cycling with powders with burn rates ranging from H4198 up to Varget. So far the most accurate has been Shooters World Match Rifle and H4895 (they are pretty much the same burn rate)

I am currently at around 3MOA with these loads, but they are leading the barrel to the point where around 30+ loads open up groups to 4-5MOA. Barrel slugs to 0.224. Currently I suspect my bullets are not hard enough for the ~2050-2150 fps I am shooting these at.

• I'm working with MP molds 75 grain heavy nato bullet gas checked. https://www.mp-molds.com/product/mp-227-75-gc-nato-6-cav/
• I am casting using straight clip on wheel weights. Air cooled from the mold
• Gas checked and sized to 0.226
• Powder coated using Smoke's Ford Blue and Bacon Grease (kind of a custard yellow) - Using a convection toaster @400 degrees for around 20-22 minutes. Air cooled after removal.
• No additional sizing after the powder coating process.
• Bullets pass the hammer test.
• After around 8 hours, or a day later (basically when I am confident the bullets are at room temperature)
  • Heat treating using the convection toaster at 425 degrees for 1 hour.
  • Toaster oven shows 425 degrees, but my TEL-TRU shows 415-420 degrees.
  • After an hour, immediate quench in ice cold water
  • Probably sits in the ice water around 5 minutes. I make sure the water remains ice cold.
• 7 days post heat treat, I file a flat portion of the bullet and check the hardness. I'm getting 11.8 - 14.3 BHN.
  • Oddly enough, bullets that I have not heat treated, but only PCed on 400 for 20 minutes and quenched in ice water measure at around 15.0 BHN.
  • This is using the Lee hardness tester. It's not perfect, but I did test a bunch of non-PC non-Heat treated bullets that I cast a year ago and let air cool from the mold, those are testing at around 11-12 BHN. So even if my #'s are not spot on, the difference in BHN should be much greater with my heat treated bullets.

So back to the quick question:

1. Why are my bullets not hardening to the point I'm expecting (18-22bhn). Since these are 22cal bullets, I thought I had the temp/time of heat treat adjusted correctly.
   • I dont have the time currently to do the full blown hardness testing array of different temps and days let set after heat treat.
2. So with that, given my current setup, what variable would you change to get a harder bullet? I'd rather not change the alloy as the only other thing I have on hand is a small amount of tin and pure lead. I do not have any lino, or hard type leads.

 

[358156 hp]

Have you tested to see how hard are the bullets after 30 days?

 

[Spindrift]

I can’t explain the difference in hardness, it’s weird.
If I understood you correctly, you size to .226 before applying the coat, and do no sizing after the coating. You are probably shooting .228-9 bullets, in that case?
I think this might be the souce of your leading problems. Your alloy is probably sufficient. But you coating is scraped off during the engraving process. I would simply try a batch of bullets sized to .226 after coating.

 

[Dusty Bannister]

I suspect that the low antimony of the COWW will have an affect on the speed of hardening. The range of hardness is curious and makes me wonder if you are using a wire basket or an enclosed container which does not allow a rapid flooding of the bullets when quenching. It is suggested that the basket not be stacked deep, so that all the bullets heat through evenly and then quickly plunged into the quench water.

If there is some of the coating scraped off during the loading process you should be finding a lot of debris in the action when you clean the firearm. If the bullet is all that oversized then you might encounter difficulty in the seating part of the reloading process or the round will fail to chamber at all.

 

[Dimner]

thanks for the quick replies.

I'm using silicone mini ice cube trays for the heat treat, and dumping from that tray directly into ice water. I just tip the tray to 90 degrees and use a pencil to knock off any bullets that are sticking to the tray. So, I don't think the rapid flooding is the issue. The tray has .5" squares if i remember correctly. The 11.8 to 14.3 range in hardness with my current technique is really a result of my ability to use the lee hardness tester. That range represents a 0.006" different in the indentation with the tool. Add to this is the fact that I have to keep the bullet perfectly still, line up the 20x microscope with it's scale, and do all of this backwards due to the optical flip, I'm okay with a 0.006 difference. I'll 3d print a jig in the future to help me get better, more repeatable readings.



The bullets do chamber with no engraving, but they are seated deep almost to the end of what I would call the 'seating band' that is located past the final lube groove when moving towards the nose. They are coming out to an average of 0.2275 after the PC. And yes, I do see some PC debris when cleaning. But I am finding it in the barrel and not the action. Maybe I size to 0.225 and then PC? I was of the understanding that sizing after the heat treatment is something that should be avoided.

 

[Dimner]

Have you tested to see how hard are the bullets after 30 days?

Have not had the chance yet, (i am on day 7) but all the sources I have read it's not going to get 10BHN harder by day 30 if I am in the 11-14 range now.

Which is why I do not want to wait the whole 30 days before I start again. I figure if I cannot get something around ~18bhn after the heat treat (8hrs to1day after), there is little hope of getting to the range I am looking for.

 

[CWLONGSHOT]

This is what Im trying to tell folks.

Just cause ya have COWW, dosnet guaranty it WILL BE X HARDNESS!! There aint no governing body overseeing all WW are X Y or Z!!!!

So what ever your batch is its light of hardness! Its frustrating I understand. Its like alchemy. Iffin ya really want bullets that hard why not cast from harder alloy like say Linotype alloy?

CW

 

[Rockydoc]

thanks for the quick replies.

Maybe I size to 0.225 and then PC? I was of the understanding that sizing after the heat treatment is something that should be avoided.

Size after PCing and before heat treating. I am not sure what happens to powder coating that is heated to 400+ degrees for a whole hour. The PC may be damaged by the heat treatment?

 

[Dimner]

Size after PCing and before heat treating. I am not sure what happens to powder coating that is heated to 400+ degrees for a whole hour. The PC may be damaged by the heat treatment?

okay, I can try sizing after PC but before heat treating. I'll see what happens both ways. With a 0.225 before PC and 0.226 before PC and sizing afterwards. The bullets do pass the hammer test just fine.

This is what Im trying to tell folks.

Just cause ya have COWW, dosnet guaranty it WILL BE X HARDNESS!! There aint no governing body overseeing all WW are X Y or Z!!!!

So what ever your batch is its light of hardness! Its frustrating I understand. Its like alchemy. Iffin ya really want bullets that hard why not cast from harder alloy like say Linotype alloy?

CW

What i'm totally confused by is why my PC and ice quenched bullets are harder than my PC air cooled followed by the HT and ice quench process. That's insanity regardless of what alloy it is.



I think I may have overstated the leading. I used a bore scope, it there is only really a few specs of lead here and there. I'm lucky enough to have never experienced leading my my casting over the past 5 or so years. So being able to identify it is hard for me. The naked eye looked like leading, but the borescope shows the real deal.

Someday I do plan on going through a whole battery of hardness tests with my alloy with different process of casting temps, quenching and heat treat times/temps, but for now, I just want a harder bullet. Which should be doable with CWW.

 

[Joshua]

Try sizing .0005” over your slugged diameter.
It sounds like you might be scrapping off your PC.
Josh

 

[waco]

Are you expanding the case necks?

 

[Dimner]

yes, expanding case necks. maybe not enough though? I was using the lyman M die for 22 cal. but it was way too hard to get the bullet into the mouth.

I am going to try the NOE .226 x .222 Exp. Plug . or should I go with the .228 x .224 Exp. Plug ? I have both.

 

[Rockydoc]

You will find a very good article on heat treating here: http://www.lasc.us/HeatTreat.htm

 

[waco]

I’m not familiar with the NOE plugs. Maybe someone else will chime in.

 

[CWLONGSHOT]

The PC could be acting as a insulator changing the desired outcome.

CW

 

[popper]

Your COWW may not have as much Sb as you think. Might get a little superhard to increase Sb. Add some chilled shot for arsenic that speeds up heat treat hardness. Bake @ 400 + a little for an hour then into ice water (as you are doing). Note - as you get to slump temp the lower melt temp metal of the alloy will beging to sweat out and loosen the PC coating. It will NOT hurt the PC. Your AR15 is 1:7 twist? If so check out the adding Cu by CuS04 method (add Cu to exceeed the RPM threshhold and no I'm not going there). You will get some accumulation on the land edge - possibly a LIGHT coat of 50/50 Jwax/LLA will keep the bore shiny. Any solvent will degrade the PC.

 

[Ian]

Welcome aboard, Dimner, I think many of your questions have been answered but I think at the same time that you may be focusing on the wrong thing.

First of all, I have been able to produce stacks of 10-shot targets all 1.3-1.7 MOA using powder-coated .22 bullets about 68 grains cast of straight clip-on wheelweight alloy, air cooled from the coating oven, and fired at 2700 to 3000 fps (24" barrel). My final bhn is 12-13. I have heat treated from the coating oven to a maximum of about 18 (430⁰F for 45-50 minutes is required, I do it during the powder cure to save time). I didn't find in my limited testing and with my particular rifle/components/methods that the tougher bullets grouped significantly better. Maybe a little, but not significantly more so in a small sample. So I think you may be barking up the wrong tree there, at least until some other things are refined.

Here's what I HAD to do to eliminate leading, jacket fouling, and to get reasonable accuracy:

• Get ALL the copper fouling out of the barrel.
• Size the bullets to a half-thousandth smaller than throat entrance diameter.
• Use a seating tool to apply and partially crimp gas checks before sizing the bullets.
• Hone the neck of the resizing die so that neck ID was no more than .220" (expanding ball barely even drags in the way out).
• Expand the case necks with an RCBS cast bullet expanding die (or suitable facsimile which has NO, repeat NO abrupt diameter change) so that the necks are NO MORE than .002" smaller than the actual bullet body diameter as determined by the throat entrance.
• Use a Forster Benchrest in-line bullet seating die and apply a very light crimp in a separate operation (crimp moth only to assist feeding).

.223/5.56 has short, hard necks and a two-step expanding die like Lyman and NOE sell is too little/too much unless modified. Neck tension is important and you need the whole neck to give it, so don't use a tool that ruins the tension at the top and crushes the bullet at the bottom. A .224" RCBS spud and die body should be about right for most purposes. Adjust it so the tapered part bells the mouth just enough to take most of the gas check easily when a bullet is placed on top.

Age your COWW bullets a minimum of TWO FULL WEEKS after coating before testing or shooting. Numbers will be all over the map and drive you nuts until the alloy settles down. They will also shoot patterns until the dendrities get through precipitating and stabilize.

You can size your bullets after coating, but do it immediately after they cool, and try to minimize the reduction after coating. Do the lion's share of sizing before, then only clean up a thousandth or two after coating. Use a push-through die for final sizing after coating to help keep bases square.

The single biggest problem I had with 5.56 was the resizing die crunching down the necks to a ridiculous .212". When expanding back up for cast bullets, the necks would invariably stretch off-center by as much as .005". Best practice is don't size the necks too much in the first place. Use a bushing full-length die to bump the shoulder/body and size your necks the minimum actually needed, or hone the neck out carefully with a split rod and oiled wet/dry sandpaper.

After you get your ammunition sorted so the necks are true to the bodies, have uniform and correct tension on the bullets, and are holding the bullets straight in line with the bore (minimal runout....check this, don't guess!), then play with seating depth and powder charges a little to tune your groups.

I'm probably forgetting a few things but that's a start.

 

[Tomme boy]

Definitely get the RCBS neck expanding die. Or if money does not matter then "21st century" neck expander set up

 

[fiver]

I'm with Spindrift.
Ian has good instructions, but I think the size is what's killing you.
try for 225-6 final.

 

[Ian]

Yep. Remember I was getting some leading and bigger groups at .225-ish in my 5.56 but it cleared up going to .2265"? Throat entrance was .2272". The bigger bullets corked up the throat better, sooner, and stopped the coating getting washed off. Any bigger than .227 and things went south again. Gotta get the fit just right with PC when you're slamming soft bullets with 50,000 PSI.