303 brit and neck tension issues,

[mac1911]

Since you are using a .314" sizer this seems to point to the brass. Has it been annealed too soft? Is the sizer actually sizing the GC down to .314"? I have bought a couple of Lee sizers that were oversized.

I have found in my rifles that the 16grs of 2400 does not produce the best accuracy. Usually works out good at 18 or 19grs.

Brass is all 1x fired HXP and PPU I have done nothing but size and trim the brass.
I will double check the sized/gas checked dimensions but almost certain it came out to 314"

[mac1911]

Ok so I came back and revisited my 303 Lee die set.
Ok the set I bought has both full length and neck size die.
I went with the neck size die, well on my last effort I blew the aluminum cap out of my collect die when I cammed the press over, hornady 007 press.
I thouht I had set the die to not cam over easily ? Any how

I then set up the full length die until it just sized the neck about 80% down. This has been the best solution so far. I loaded up some of my best 314299s with trailboss to try out. After seating the bullets I can firmly press the bullet tip into the work bench and it will not budge.

Thanks for all the tips, I used the same amount of flare(just a touch the gas check will just balance there) I have been using and used the mosin 762x54r FCD to just kiss the flare.
Im not to happy with how the 762x54r FCD works but for now it removes the flare good enough until a better solution comes along.
Thanks all

[jonk]

I've had this very problem with Lee collet dies, which is my understanding of what he is using. Went away when I annealed the brass.

What's odd is that it is holding the smaller diameter jacketed bullet; so perhaps it isn't an annealing issue after all.

I'd look long and hard at those boolits with a micrometer, not a caliper, and make sure the mold isn't dropping skinny.

Assuming not, I agree, could be over-flaring.

Could also be that the boolits are starting in crooked on seating and distorting the necks.

[DIRT Farmer]

If the casting is mesuring less than 314 annd you are using a gas check it will be just 314 + because of spring back. It will expand the case neck and leave the boolit loose in the neck. The jacketed will go in a uniform size and hold.
Try sizing the complete neck and keep the GC in the neck, it should hold then.