sydandpaigesdad said:
1st What is meant by OAL, if overall length is it a measure of max. or min.
They have the sieera mk as 2.775" OAL
sydandpaigesdad , we're all here to learn so I hope you reconsider your position of "leaving this forum". Anyway, OAL can be confusing particularly for someone starting out in reloading. As an example, let's say you want to reload for a .308 and you made the smart decision to load 168 grain Sierra MatchKing HPBT bullets. If you refer to Sierra's manual (50th Anniversary Edition) it lists the following specifications.
Maximum OAL: 2.810"
Cartridge OAL for 168gr SMK HPBT: 2.800"
The manual lists 20 different powders for the 168 grain bullet but simply states
cartridge OAL of 2.800"
Now let's say you want to get a second opinion and you refer to "Modern Reloading Second Edition by Richard Lee". You look up the .308 Winchester cartridge and the schematic shows the length of a loaded round to be 2.810". The figure doesn't explicitly say
"Maximum OAL" though. So now you look up the loads for a 168 grain jacketed bullet and you notice that there's a
"Minimum OAL" length listed for each of the 16 different powders but no absolute
OAL as in the Sierra manual. Reloder 15 has the
Minimum OAL listed as 2.700" and a bunch of others show 2.800". So now you look at another manual, Speer Number 11, and find that they don't list any
OAL dimensions either
Minimum or
Maximum. Confused yet?
If so, then welcome to the world of reloading. How can one manual give the
Max. OAL and the same
cartridge OAL for 20 different powders, another manual list the same value simply as
OAL and then list
Min. OAL values for 16 different powders and another manual give no information at all about Min, Max or cartridge OAL?
So what's going on? The
Max. OAL is selected so that the loaded round will chamber in "standard" chambers and possibly magazines (if there's a standard for those). If you exceed that length, the bullet might contact the lands of the barrel before the action is closed. This most likely won't happen on a Remington .308 since the throat is excessively long. Sierra probably developed the loads listed at the given cartridge OAL so that's how they report their data. If a manual lists
Min. OAL for a specific powder (as Lee does), you can bet that they developed and tested the load at that OAL and are concerned about a possible pressure increase in the case if you seat the bullet deeper. In the case of Lee, you have the "safe" option to seat the bullet so that the OAL is somewhere between the
Min. OAL given and the
Max. OAL given. You might ask why Lee changed the OAL for the same bullet but with different powders. It's possible that they were trying to keep the loads within a certain CUP, PSI or velocity range. I have no idea why Speer doesn't list ANY cartridge dimensions. Perhaps their attitude was "if you're smart enough to reload, you're smart enough to figure it out". Like most aspects of human life, reloading has developed over the years in a random, disorganized, non-standardized sort of way. If a group had got together (such as SAAMI) 200 years ago and come up with a set of standards BEFORE we began reloading, maybe every manufacturer and manual would be on the same page (no pun intended). That didn't happen so we're left with the task of making sense of the nonsense.
From Wikipedia ...
BC = SD/i = M/(i *d^2)
where:
*
BC = ballistic coefficient
*
SD = sectional density, SD = mass of bullet in pounds or kilograms divided by its caliber squared in inches or meters; units are lb/in2 or kg/m2.
*
i = form factor, i = drag coefficient of the bullet/drag coefficient of G1 model bullet (G1 drag coefficient = 0.5190793992194678)
*
M = Mass of object, lb or kg
*
d = diameter of the object, in or m
From me ...
A good "rule of thumb" for BC values for a bullet is ...
Muzzle Engergy *0.5 = BC * 1000 (yards)
... in other words, your bullet with a BC of 0.462 will have half of its initial muzzle energy at approximately 460 yards.
I hope some of this is helpful.