bullet seating/some seat hard and base to ogive measures long...the problem

[lpreddick]

we have all had this happen, esp new brass or unannealed brass. bullet seating is smooth and without resistence, then one resist seating and we measure base to ogive and it is .005-.008 longer! the next one seats perfect... in days past, i would screw the die down the .005 or.008 and run the case back into the die. one of three things happens. (1) nothing, (2) bullet seats to the desired level, (3) bullet seats way too deep! i had no clue. i read on this site that what is probably happening is the neck resist bullet seating such that the bullet actually advances into the hollow seating stem until the neck give way and allows bullet to seat...the extra base to ogive measurement being the distance bullet advanced into seating stem. i followed everyone's advice and all is well . i took this pic last night to demonstrate the very slight mark on a bullet that seated nicely and the one that was long. i once tried adding stuff to the hollow stem so that the contact with the bullet was over the entire tip, this would prevent bullet into stem..could not get uniform material and runout was excessive. also each bullet has a different shape so one would need multiple stems unless only one bullet was to be used...may work on this more. one observation of importance: if a bullet seats long, put is aside and seat the others, culling any that seat long. wait a few and run back thru die w/o any adjustments. very often the bullet now seats to the desired depth. i surmise the brass just below the bullet's base has relaxed enough to let bullet seat deeper. new brass is the worst at this with me, so i usu add a tiney bit of case lube to the bullet and they seat with the same resistence. too much lube and i worry bullet may self seat if i go into the lands more than .010. once fired brass almost never acts up, so i seat .020 and none move.

 

[mikecr]

i surmise the brass just below the bullet's base has relaxed enough to let bullet seat deeper.

It's actually opposite. Relaxed for the neck is toward un-expanded dimension.

Good seating is provided by a consistent balance of static and dynamic friction.
It takes more force to get the neck around the base to begin, than further seating(until hitting donut). This extra force is where your stem is wedging over the nose.
So unless wedging damaged the nose, immediate reseating should suffice to finish seating to desired depth.
But, this is not so cut & dry.
Immediate reseating could actually lead to a bullet seated too deep. This, because on reseating the stem is not seeing that typical force peak(reseating is easier). And here the stem wedges even less over the nose than your normal seating causes.
This is the balance we deal with.

With new and/or squeaky clean necks, we should expect friction variances. Fortunately the carbon layer in fired necks is as perfect a seating lube as ever invented. If you don't mess with the carbon, you can focus purely on tension to provide consistent seating forces.
But I think we should still verify every CBTO,, every single round.