.50-110 PC'd bullets were not accurate?

[Rapidrob]

I'm a little disappointed in the accuracy the PC'd bullets gave me at 200 yards out of my .50-110-750 ( .50 Alaskan) Rolling Bock rifle. The rifles shoots .50 BMG 750 grain FMJ's very accurately out to 500 yards ( furthest tested so far)
I cast up some SAECO 650 grain flat nose and powder coated them with HF Red for 30 minutes.
The load was 31 grains of IMR4198 and a magnum primer. Velocity was estimated between 1,100 and 1,200 fps at our ranges altitude.
The rifle grouped OK but I was hoping it would shoot as well as the FMJ's which were 10" smaller group.
I fired two rounds into the berm and after digging a foot into the hard pack sand found the bullets.
Powder coating stayed on the base of both bullets. There is still some PC on the walls of the bullets even after the bullets expanded.
I ran a dry patch through the bore and hit a "Rough Spot" about 10" in front of the chamber. The patch was forced through to the muzzle and has a silvery flaky substance that turns to dust as soon as you touch a "flake" ( it is NOT lead)
This stuff is either powder fouling or the powder coating is leaving residue? I'm not sure what it is.
What are your ideas as to increase the accuracy of these bullets?
Thanks.
http://i31.photobucket.com/albums/c374/Rapidrob/50110B_zpsf3cohk9j.jpg
Through the spotting scope

http://i31.photobucket.com/albums/c374/Rapidrob/50110A_zpsg27mejzl.jpg
At the 200 yard target. Smaller hits are another shooters hits.


http://i31.photobucket.com/albums/c374/Rapidrob/50110E_zps5fxt7pb1.jpg

http://i31.photobucket.com/albums/c374/Rapidrob/50110D_zpslg478itu.jpg
Photo bucket flipped the images,no idea why.

[Echd]

You mention the flaking and residue. What temperature are you curing them at and do you have a reasonable certainty that your oven is operating at the temperature you think it is?

I do not think that is a problem, though, just out of interest. I get flaking in some guns with some powder types but it is not consistent.

[noisewaterphd]

I'd have to agree with both previous posts. Your pics look like you have some skidding, and it never hurts to double check the oven temp.

I have yet to get my best PC loads shooting as accurate as my best lubed or FMJ loads.

They aren't horrible, I definitely have useable loads, especially in pistols. Still, you might want to temper your expectations a bit.

Do I think you can get your PC load performing better? Absolutely. I think you will end up finding acceptable accuracy.

Are you going to match the accuracy of your FMJ load? I don't know the details of your bullet or load, but probably not. You should be able to get close though.

[Rapidrob]

I bought a oven and calibrated the thermostat using a digital calibrator. I used 425 degrees for 30 minutes and let the bullets cure for several days. The coating is tough but flexible.
popper, you say skidding in the bore. Do you see signs of this? Smeared rifling?
The barrel was made from a M2 Browning .50 BMG. Bore is .510, my bullets are .513.
Thanks for your ideas.

[noisewaterphd]

If you do have skidding going on, as it looks like, then that is the first problem to address. And maybe the only thing to address.

Additionally:

So you size to .513 after PC? What do they measure before?

Also, do you have the means to try .512 and .511?

[noisewaterphd]

popper, you say skidding in the bore. Do you see signs of this? Smeared rifling?


Yes, your engravings don't look uniform. What was your alloy hardness?

[Rapidrob]

Here is the patch and the residue. It is not lead. If you pick up one of the "flakes" it turns to dust instantly. The flakes are black and shiny.
I'm thinking powder fouling,not 100% sure though.
http://i31.photobucket.com/albums/c374/Rapidrob/50110F_zpsvbbhwhht.jpg

[Rapidrob]

I may be pushing the bullet too fast. Since the PC is a lube, the bullet may very well be skidding in the bore as the rifle has a very long throat.
Seating the bullet further out may help as well. I will have to try a diff powder as well as the gap between the powder charge and the base of the bullet will be excessive and will cause problems as well.
I did not check the hardness of the bullet after PC was applied. I read that folks drop them into water right out of the oven.
The bullets fired were not sized. They dropped out of my mold as .511 and after powder coating read .513. I do have dies to size to .510 and .511
Thank you for your replies so far.

[Smoke4320]

there is skidding as seen in the bullets pics .. This has to be fixed first ..

I may have missed it but did not see what alloy you are using

If you are not sizing after coating you do not have a uniform size bullet .. hard to be accurate at 200 yds

keep asking we will get you thru this

Thanks

[Rapidrob]

The bullets read a BNH of 9. Not the hardest,but harder than wheel weights. I think I'm pushing them too fast. I will try a diff powder that will fill the case. The bullets were deep seated into the case to reduce the empty space above the powder charge. The rifle has a very long throat to allow the .50 BMG 750 grain bullets to be shot. The bullets may be jumping into the rifling causing the skidding.
Thank you for your replies so far.

[Rapidrob]

I'm going to do a casting of the chamber. The more I think about it,the more the bullet jump seems to be a problem as I'm sure it is excessive,perhaps an inch or more.

[Echd]

Wow! You would make Roy Weatherby proud with free bore like that!

[Smoke4320]

yes with that much free bore the bullets are likely not square to bore causing a unstable/unbalanced bullet

[Rapidrob]

I cast the bore. There is a full 1/2 inch of free bore in front of the mouth of the chamber. There is no shoulder in the throat.
Seating the bullet to prevent an air gap over the powder gives a full inch for the bullet to jump to the rifling. I think Roy would say this is a little too much.
My options are shoot the 750 grain .50 BMG projectiles only or come up with an idea for the PC bullet. Breech seating could be done but is not the best solution.
Any ideas?

[Echd]

Maybe call up Accurate molds and get a one off mold done that mirrors the 50 BMG profile (or slightly shorter)? Could be an interesting experiment if you aren't squeamish.

[Smoke4320]

or lop off the threads and rechamber

You are asking a lot for a cast bullet to make it undamaged and centered in the bore with a 1" jump

there are others on here with way more experience than me at cast bullet shooting. Hope they chime in and give you some real good help

[Rapidrob]

Due to the shape of the .510 cast bullets being offered, there really is not a choice to fit my rifle. But, the rifle was designed to do one thing very well, shoot the .50 BMG bullets, which it does very well. I was getting into PC'ing bullets and wanted to see it they would work out of this rifle. It's not a big deal as I have other rifles to shoot PC bullets.
Thanks for all your ideas. I've PM'd jpl to ask some questions on the loads he used in his rifle back in '09.

[greenhornet-1]

http://noebulletmolds.com/NV/product_info.php?products_id=371

Check out this mold! 850 grn!