PC HV Rifle questions...

[NYBushBro]

I have a few questions that I've wondered about (and not sure how many others have) and would appreciate recommendations/observations regarding something that Dragonheart mentioned in a thread a while back concerning HV rifle PC coating thickness.

1) Dragonheart mentioned that his engineer/scientist friend recommended ~ 3 mil (.003") coating thickness for HV rifle (IIRC), consisting of 1 'partial cure' coat followed by a second coat (for proper integration/bonding between the two coats.) Has anyone observed any difficulty sizing the GC with a 'partially cured' PC coating? NOTE: I plan to use Smoke's CLEAR for the 'top coat' after applying the GC, but am concerned that the partially cured 'base coat' might be scraped, scratched off or otherwise be compromised when going through the sizer die.

2) Forum members have discussed ordering 'undersized' molds for PC, so that the finished, PC'd item approximates dimension 'specs' (ie: bore rider designs). I have observed that the various mold companies design their products to be used with a particular alloy (ie: H&G - linotype, RCBS - 10:1, Lyman - #2 alloy, NOE and Mihec - WW) and I have personally noticed that a 300 gr. H&G mold (for 35 Win) comes up a bit shy in diameter when using isotope core alloy.
Question: would having a GB for a mold spec'd for linotype (and using a more 'shrinky' alloy like iso-core or perhaps even 16:1 or 20:1) fulfill that purpose? (NOTE: see RCBS Cast Bullet Manual #1 for shrinkage chart for various alloys.) This could possibly provide that .001-.003" wiggle room to compensate for the added PC thickness.

3) A number of forum members have reported that softer alloys benefit from higher velocities upon application of PC. Has anyone considered using a hardness tester to compare BHN of the SURFACE of PC-coated samples versus uncoated ones (especially the 'partial-cure double-coated' PC technique), from the same casting session - to eliminate all ,other variables?

I don't have a hardness tester, but would be interested to see how much (if any) difference in hardness the PC 'jacket' adds to the equation, which would in part explain the higher velocities of softer alloys with PC (with its associated increase in RPM/centrifugal force in faster twist barrels - a la Larry Gibson). Might the PC coating act to some extent like a girdle, holding in the soft underbelly of Pb alloy as it is being spun in the rifling, and 'push the envelope' of the RPM limitations on Pb-Sn-Sb alloys?

Also, might there be ANY 'flavors' of PC which deonstrate the GREATEST 'hardness' increase after cooking? This might be a good question to ask Dragonheart's scientist friend (ie: polyester? vs. other PC composition).

(EDIT: Smoke's BACON GREASE comes to mind.)

The goal here is approaching (or attaining) jacketed velocities with PC-coated castings in fast twist HV rifle cartridges (ie: 1 in 10", common in 30-06, and faster, such as 8x57, AK/SKS, AR-15... and of course the notorious 6.5 Swede) with attendant accuracy for HUNTING purposes, without resorting to a barrel swap with a slower twist of rifling (ie: $$$$$$$$$$).

Empirical and/or anecdotal data would be appreciated, not only by me, but also by other members who may have asked themselves these same questions (or those that may have had professional/career/scientific experience with this technology, and therefore, answers).

Thanks in advance for your constructive comments/observations. I summon the 'collective intelligence' of this forum!

[popper]

1) partial cure for first coats are fully cured with 2nd coat. The idea is for best bonding of multiple coats. If you have to use multiple coats I'd do the GC after the last or before any coats.

2) The nose is usually the problem, you can not coat it, nose size or get a custom mould with undersized nose.

3) my 308W AR is 1:10 and I push to 2700 without problem but the alloy has to be ~ 4% Sb heat treated (adding 0.3-1% Cu really helps). HF red ESPC, one coat. Smoke's black is good, Bama has indicated a different color leaves less residue. Check his thread. I run my BO carbine (1:10) 2100 fps with a single coat of HF red, isocore with Cu added. I don't know of anyone who has done the 223 at jacketed fps with success. Don't plan on PC helping harness at all at HV rifle. Alloy has to be up to snuff.

[Bama]

The coating thickness will vary with the method of application. I use shake and bake and slightly preheat bullets to counter the effect of high humidity. I also size before and after powder coating including the neck as Popper noted and stand bullets up which although not required, it does help give a uniform coating thickness. There is no problem with 169 gr in 308W 1 in 10 at just over 2800 fps and 97 gr at 2800 fps in 6X45 with 1 in 8. It does require copper in alloy or the bullet will come apart ( read some of Poppers threads, I use copper sulfate). Smokes bacon grease has made cleaning no more than one or two at most more patches than jacketed bullets. Just try it and experiment and keep good notes and go back and read them. Have fun.