Mr MO5 -
Welcome aboard !? Just for your comfort, first let me say that your OAL calculations match mine exactly as recorded in my reloading notebook on 4/12/2008.
So you have done your homework correctly. (This is one good reason to keep a reloading notebook.) So you are on the right track.
? Bullet feeding is a combination of MANY variables; length is just
one of many. So I would not jump to any conclusions about a certain OAL working or not, without trying it. Conversely, you could have a nice long OAL and find that a slightly shorter one worked more reliably after shooting thousands of rounds. You just never know.
On to your questions.....
1) Adding length to a round totally depends upon the tolerances YOUR press delivers. If 50 rounds of
your ammo has a total OAL spread of .020", then 'no' you cannot
lengthen. But if you measure 50 rounds and the total OAL spread is .003", then 'yes', you can subtract less than the .015" I recommended
and lengthen the OAL.
It's a tolerance study. The object of subtracting .015" is to make sure
ALL the ammo works; the short ones
and the long ones. Follow that ?
2) As our mutual friend
Mr. Painter pointed out, since the
starting load is way below the limit, you can proportionalize the load and start working up from the new calculated starting load numbers.
This is NOT a perfect answer!! You may find that the calculated starting now lands in the middle of the actual "new" load range, but I'd hardly expect to be so far off that you blow your self up.
It also stands to reason that if the new starting load for the shorter round is (say for instance) 0.8 grains lower, then the new max load will ALSO be 0.8 gr lower!! This since the load range is a "window". If you mounted a 30 inch high window up near the ceiling in your home, you don't necessarily get a better view or more light, you simply get the same 30 inches of window
at a different level. So the bullet and powder determine the
size of the window;
we're now going to adjust the position of that window. Follow?
So mathematically, your new load becomes...
(Book starting load) x (New OAL), all divided by (Book OAL). That will give you the new "starting load". Use reason. If you are shortening the OAL, then you would expect the load to go down. If your calculated number is higher, then something is wrong.
Working from the calculated numbers, you must work up slowly from there in 0.2gr increments until you find an appropriate load. A chrono helps a lot when doing this.
Hope this helps!
