NOOriginally Posted by thesmi
The point of full length re-sizing is to return the case as near as dam it to SAAMI spec.
Fold do this for many reasons.
Often folk using semi autos or even straight pulls where quick hassle free loading si important will do it to ensure a smooth chambering.
Sometimes you might find that FL re-sizing produces better groups
You may also want to do it with once fired brass from another rifle as you may not be able to chamber it in its new owner.
Brass also has a property called spring back, whereby it will literally spring back slightly from where it was re-sized to. This along with slight tapers is what allows you to remove a round from the chamber after firing. It si also why some folk load their cases last minute (before the neck springs back and increases the neck tension) or even on the range.
Sometimes of course if you really over do something it wont spring back, so things get awkward.
With a neck sizing die all you are doing is re-sizing the neck. It may bump the shoulders back a bit I guess depending on how you have it set up and how your chamber is cut, but its purpose is to re-size the neck only and leave the rest alone, fire formed to your rifle.
Bush or bush bump dies are designed to allow a choice (by way of different sized bushes where the neck is sized) as to how much tension you have on your neck. this can be handy if you have to neck turn, if you use lapua brass (as it can be quite thick necked) or if you want to experiment with neck tensions (as Richness showed in an article in target shooter, this can be quite important for group sizes/super consistent velocity if you are into precision disciplines).
Often these only squeeze the outside of the neck(as there would be no point getting to a certain size only to drag a bloody great ball through it again), you can also control how much of the neck you re-size if needs be. Brass from a precision bolt action rifle tends not even to be ejected so should not pick up the nicks and dents that easily.
Thats the bush bit, the bump bit allows you to bump the shoulders back a thou or two. Some high power rifles fireform the cases quite well. Someone commented that if the case came out, it should go back in again, but there are always exceptions, and the last place you want to find out is on the point in a comp.
The difference between a hot chamber/case and cold chamber/case may not help.
It does not take much with some of the actions to stop you being able to close the bolt, and as far as I am concerned, if the only thing between me and the hell and corruption going on in a case on firing is the case...I want it to obturate..right, so a good fit helps.
Mine seem to move a thou or so, I know one world class shot who used to FL resize every 5 firings or so to avoid this, but now does it on every firing.
You might also want to use a die to bump back without touching the neck (for forming cases etc), I tend to use mine with the bush out to de-cap dirty cases, it saves cleaning the necks before sizing, I then chuck em in the US cleaner. Then put the bush back in for sizing when clean.
I am told you can also get full length bush bump dies, and again Russel Simmonds tends to FL his comp brass with a FL Forster die with teh ball removed, he then uses a Wilson neck expander to just ease the neck enough to get the tension that suits him, its down to what works.
I started out with a pair of dies and have ended up with (for .308) Bush/bump, Neck, and FL as well as the usuall seaters etc.
The bottom line is the less you need to work yoru brass the better, and if you can anneal well, its worth a look.
Reply With Quote