hello , i give you my feedback, because i had a near issue.
more taht the cratering on my reload ammo my RFB succes to drill the primer ( and this without overpressure)
this weapon is manly build for military usage , and primers on military ammo are very strong ( i dont speak about fire powerfull but about the strength/solidity)
first of all you must verify that the head of the striking pin. This one must be very clean, smooth and little bit spheric.
if it's not the case, polish this one.
second step, verify the hole of the firing pin on the bolt , it not do have burrs, if not you must burr-free with drill bit by example, but very soft , not elarge the hole.
because if you have some burrs, this do like a die cut when the presure puch the primer on it.
and when the striking pin isn't have a good surface state this weakens the primer.
you must know you have differents solidity of primer, by example, wichester primer are very soft and have a hole easyer, while the CCI primer it's more strong that wichester and Federal match more stronger that CCi.
other things , on a half-auto the striking pin isn't launched like bolt action but it's a hammered stiker and you have lot of free-space between the striking pin and the bolts who allowe to the primer to expend in this space and increase the possibility to produce a hole.
by experience with the same ammo , in the RFB have a hole or cratering and not in a bolt action.
evidently more hight is your load , more hight is your chance to have a hole even without have an overpressure.
in last step you may change the two hammer springs to decrease the load by 50 %.
I did on my RFB and i always shoot with not fault event with strong primer like CCI or FEDERAL.
on the other side, i din't try with winchester to know if my RFB drill the primer again
but i will try , because winchester give me good result , it's more easyer to buy and it's very not expensive.
also , the change of the two hammer spring reduce the weigth of the trigger ( and that's so cool ) and need less gaz system to reload and reduce the mechanical constraints.
but the cratering spoken up above is due to the space between the striking pin and bolt and this effect is more important like you have more space , hight load and soft primers ( also verify the state of your usure state of your pin)
By the way, for my reload the best powder it's initially use for .223. Why, because the barrel is short and with powder for .308 i need to up the load to have the same velocity and i had a big flame at the muzzle break that i have not with 223 powder.
because we have a short barrel the powder must be more fast for not burn outside the barrel.
My powder it's "ReloadSwiss RS40" and i use Lapua senar Bullet 167gr or nosler 168gr HPBT.