GC or flat bottom??

[nekshot]

I love PC! Now that is established but I still can not decide if a GC is "really" needed for accuracy or a nice flat bottom? Any pearls of wisdom on that side of the boolit? I am referring to 1700 to 2200 fps delivery.

[Reddirt62]

Well, call me paranoid, but I still gc my coated 454 Casull boolits.

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[popper]

I use a 145gr PB in BO @ >2K fps. I barely can control the base flatness without adding an unlevel PC to the base. I cast some, changed my sprue cut timing and got non-flat bases. Target with those shows an almost perfect circle @ 100. PCd base can have same effect. GC or not is up to you, haven't tried PB in 308W yet but 30/30 & 308MX give same results PB & PC. PC is not a GC.

[bluejay75]

Popper,

Mind sharing your BO load?

JB

[Dragonheart]

As far as protecting the base of the bullet from the short duration of extreme heat and gas cutting at high velocity the PC will do that. However, to achieve the best accuracy I believe a gas check is the best alternative if it is set absolutely flat and completely uniform. PC will improve the imperfections in the base of a cast bullet, but the bullet's base will never be as perfect as that can be made using a GC.

[Lloyd Smale]

if your looking for the absolute best accuracy a bullet will deliver if its a gas check use gas checks. If you don't want to use gas checks buy plain base molds. If leading is your only concern then you can probably coat and not check.

[blikseme300]

Flat bases with and without GC's are always needed for accuracy. GC designs PC'd but with no GC have always done poorly for me.

If care is not taken a GC can be flat but off-square and this will degrade accuracy. Goodsteel did an interesting experiment some time ago that went into this in depth. I need to find his post and link it here.

As for the need of GC's at higher velocities in my limited experience it depends. My experience has been that with 30cal no matter the alloy with and without PC that GC's are needed for accuracy above around 1,600fps. Others probably do better than this but I have not experimented more but simply use GC's for higher velocity.

With 500gn PB and GC'd CB's PC'd through a Ruger M77 458WM I had very little difference in accuracy at between 1,800 & 2,000fps. The CB's where PC'd using shake&bake and set on their bases before baking. The CB's used were cast from the same mold but one cavity was modified to remove the GC step to become a PB.

My guess is that there is a relationship between the base area and the pressure that allows the larger calibers of CB's to work fine without GC'c at higher velocities than compared to smaller calibers.

I am still learning so this hobby stays fun.

[popper]

Bluejay - 31-142C, isocore(96/3/1) with Sn replaced with Cu, ESPC. PC wiped from base, WD after 1/2 hr bake on hot plate. 16.5gr. H110, 18" 1:10 McGowan SS barrel/carbine gas. Avg 2112 ES 47 RCBS powder dropper/ not trickled - Lee die and FCD. Sized 3085. On a rare day I get < MOA @100.