Rifle-Weird accuracy with PC

[30CalTy]

I tumble PC'd some bullets and shot them today using a load that has delivered great accuracy with a non-PC bullet (frequently well under 1MOA w/ fliers occasionally).

257 Roberts AI, 257312 GC, sized, 15grs 2400
3 5-shot groups at 100yds
#1 - 7/8" - very satisfying group all inside a 1" black circle.
#2 and #3 were baseball sized groups (~3") with no rhyme or reason to them--just big and scattered here and there, up and down
Velocity was 1950fps--essentially the same that I get with non-PC.
No leading

I used 2:1 COWW to soft lead. The non-PC bullets were water quenched and culled (maybe 20% of the outliers). PC bullets were NOT water quenched and ruthlessly culled and also sorted by weight--should be better in my mind.

I used HF red PC, tumbled on and baked on their sides in a wire rack.

I'm puzzled why group #1 would be gorgeous and the other two would be completely different. No elevation or windage diff in them either.

[RedlegEd]

I used HF red PC, tumbled on and baked on their sides in a wire rack.

Hi. If I were to hazard a guess, I think the above is your clue. I suspect that the weight of the curing PC migrated to the side that was downward, creating an imbalance in your bullets. Isn't that mould supposed to throw around an 85 gr bullet? If so, I'd guess that it wouldn't take much to throw it out of balance and create a wobble. That's my $0.02. Ed

[popper]

PC bullets were NOT water quenched You have to WD them out of the oven for equivalent.

[wizofwas]

I have a hunch that RedlegEd is right. But that is just a guess.

[BK7saum]

Yous have two possibilities to cause the inaccuracy. I'd say both are potentially the culprit.

1. Differences in hardness with the PC coated being softer.

2. Imbalance due to tumbled and baked on side.

My bet is on the hardness difference.

[RedlegEd]

Yous have two possibilities to cause the inaccuracy. I'd say both are potentially the culprit.

1. Differences in hardness with the PC coated being softer.

2. Imbalance due to tumbled and baked on side.

My bet is on the hardness difference.

Hi. It's easy enough to check.
1. Water quench and powder coat on side so you get the same hardness, but duplicate the possible imbalance of PC.
2. Don't water quench, but stand the PC bullets up on their bases so you get a more uniform coating.

I also didn't think to ask. Did you size all the bullets the same? In other words, did you size the PC's bullets after coating so they were the same as the non-PC'd bullets?

Ed

[GhostHawk]

What did you shoot in that gun prior to the first group?
Any chance you had traces of lube left?

Go back and work it out, step by step what you did right in #1 and what was different for the rest.

You should find some change someplace.

[Oily]

Stand those boolits up when curing! I have just started PC and have done both stand up and lay down baking. The lay down method on mesh almost always gives thicker coverage on one side ie the bottom. even after sizing I feel that the boolit is out of round with the coating being thicker on the laying side and even sizing does not correct this problem. My limited testing with 30 cal boolits has shown 3 to 4 inch groups at 50 yds with lay down boolits and 1 to 2 inch groups with stand up curing with the same load and same rifle. The powder coat flows when it is curing in the oven as you can observe while baking. If you have patience and watch through the baking process you can actually see the coating flow down on stand up boolits. If you have doubts use a micrometer and measure your lay down cured boolits and you will see a 2 to even 6 thousandth out of roundness by the lay down method. When you size these boolits you are movind the lead not the coating and you have a unbalanced boolit IMHO. I am in the infancy of PC but I have read and absorbed all the info on this site and had great results using the knowledge everyone has imparted to me. lay down is fine for handgun loads at 25 ft but if you are looking for accuracy with rifle boolits at extended ranges you must have consistency in alloy, coating/ lube, and sizing to fit bore. Different lubes can effect accuracy with conventionally lubed boolits, so I believe you have to have to have a uniform layer of PC on the boolit and the only way to get that result is to stand the boolits. Silicone hot pads or as they are distributed trivets work great for 30 to 32 cal boolits 7"X7" size square holes 20 holes per side or 3 per inch. The honey comb trivets at 29 to 30 holes per side work for 22 to 243 size boolits and help you keep boolits standing on the way to the oven if you shake like me

[30CalTy]

Thanks for the ideas. Last thing I shot with the rifle was a doe back in December. I know I at least patched the bore after that. Maybe not though.

Bullets were all sized in the same manner.


In the interest of getting a little more data (being as how I have a decent pile of coated, cherry-picked bullets dropped from a single-hole mold), I'm going to take a handful and pop them back in the oven for a while and see if I can't heat treat them.

May ditch PC (at least here) if I can't find a reasonable way to keep a tall 25 caliber bullet upright.

[res45]

I always stand my bullets rifle or pistol, I also size and gas check after coating.

1. If you air cool your bullets when cast then PC them an allow them to air cool again the second time there is no change in the as cast BHN of the bullet.

2. If you air cool your bullets when cast then PC them and quench them right out of the toaster oven they will gain a hardness of about 75% over the as cast BHN.

3. If you quench your bullets out of the mold to begin with then PC them and allow them to air cool they will soften around 50% from the original first quenching BHN.

4. If you quench your bullets out of the mold to begin with then PC them and quench them right out of the toaster over a second time you only loose around 15% hardness from the first quenching.

Powder coat is just another tool, if traditional lube with a given load and bullet works better that's what I will use.

[30CalTy]

That's excellent info! Thanks! I've got my PC bullets in the oven at 455-460F. I'll drop them in water after a half hour or so and see how they shoot. My Lyman Cast Bullet HB says HT is done at 456F (per Am Society for Metals).

These are sized w/ GC's on them already.

[Bama]

I always stand my bullets rifle or pistol, I also size and gas check after coating.

1. If you air cool your bullets when cast then PC them an allow them to air cool again the second time there is no change in the as cast BHN of the bullet.

2. If you air cool your bullets when cast then PC them and quench them right out of the toaster oven they will gain a hardness of about 75% over the as cast BHN.

3. If you quench your bullets out of the mold to begin with then PC them and allow them to air cool they will soften around 50% from the original first quenching BHN.

4. If you quench your bullets out of the mold to begin with then PC them and quench them right out of the toaster over a second time you only loose around 15% hardness from the first quenching.

Powder coat is just another tool, if traditional lube with a given load and bullet works better that's what I will use.

Having a problem standing bullets up? If you are, gas checks may not be fully seated or not 90 degrees ti the bullet axis. This would cause groups to be all over. Also is you are running the same powder charge, you may want to check with chronograph. Mine usually runs. From 150 to 350 FPS faster with pc with the same powder load. This can get you out of the sweet spot especially at the higher velocities.
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