For me? There is no wiggle room, I accept what I have, I measure first, size and or form the case to off set the effect the chamber will have on the case when fired. Others fire first, become fire formers? Size cases 6 times and then start over, and still I ask "How do they do that, start over??
November 22, 2010, 02:16 PM
"seating the bullet into/against the lands "....seated out so it engages the rifling and holds the case head firmly against the bolt face...." this does not happen because of advise already given. First there is the primer that accelerates to a sped equal to or greater than the speed of the firing pin strike, I use fire forming primers, my primers are crushed by the firing pin before the primer knows it was struck, that leaves the case, powder and bullet setting still until my primer ignites (time is a factor), when the primer fires up it drives the case forward and igniting the powder (time is a factor), when the powder ignites pressure expands the case against the chamber, but because time is a factor the bullet is in the barrel before pressure is at it's max. Then there is that part where the case locks onto the chamber, if the case is driven forward by the primer the case i8s head is not against the bolt face.
Then there is the measure before and after, necking up a 30/06 to 338 pr 35 will shorten the neck, if necking up the case requires effort, the case could shorten or compress between the head of the case and shoulder when fired the case could shorten even more, when the case body fills the chamber the neck of the case is pulled back to form the neck, sharp shoulder and larger case body, SO, you can expect the fire formed case to shorten as much as .040 thousands, my opinion, the 30 Gibbs neck is short enough at .217 without causing it to get shorter. As an alternate method, I use 280 Remington cases , the 280 Remington is 2.540 long with a shoulder .051 thousands ahead of the 30/06, I neck the 280 up to 338/06 then size the neck up case by forming the second shoulder, in doing so I determine the head space of the 30 Gibbs chamber.
Problem: I chamber the 30/06 to 30 Gibbs, this leaves the length of the chamber unchanged, 2.495 + a little, the 30 Gibbs chamber length is 2.460 + a little, and that is the reason I use 280 Remington cases, by the time I neck up the case, establish a second shoulder and before fire forming I have added .040 thousands to the length of the neck, not as long as a 300 Win Mag neck but if most consider the 300 Win mag neck short they should consider the 30 Gibbs neck too short.
I do not use cereal, wax and or t-paper, I form cases once, the last Gibbs I formed I use the maximum powder load for a 150 grain bullet, instead of a 150 grain bullet I used a 200 grain bullet(do not try this at home), as I said 'time is a factor' and I used the one 30 Gibbs barrel to road test three Mauser receivers, the max load of 4895 for 150 grain bullets worked for fire forming with a 200 grain bullet when fire forming, after the case was formed that load could be the maximum after the case is formed (because time is a factor).
The cylinder brass by R-P is 2.650 long, for those that know when to quit forming when the case fits the chamber cylinder brass is the best option, again, this brass came out too late for me, I will never need another piece of brass, for wildcats and case forming the R-P cylinder brass is a bargain at $37.00 for 20.
And my favorite case is the 280 Remington or cases fired in a trashy old chamber. Cases for the few that know what they are doing are not available, cases for reloading are only availabe for those that load, fire and then try determine what effect the chamber had on the case when fired.