OK guys, once again I amnot near the experienced handloader that many in this forum are. But I have to ask some questions about using velocity as your primary indicator of pressure.
1) How do you know how accurate your chrony velocities are?
Chronies are a guide and NOT the final authority. They may or may not be accurate but in most cases they are very close.
2) If you are going to go by "published" data/velocites then what affect does using different primers, brass and/or seating depth have on the velocity?
All these things have a large effect. Even more is different "lots" of powder can cause HUGE differences. This is why we follow the "start low" and work up rule.
3) How different is the chanber, throat and bore of your rifle compared to the manufacturer's test rifle? Chamber, throat and bore dimensions can affect pressure which can and often are different from rifle to rifle.
You are spot on here. Again, this is where the rule "start low" and work up applies.
4) Different rifles will shoot the exact same ammo out of the same box or handload batch at different velocities.
Spot on again.
4) What about the case where two members here have reported getting 100-150 less fps while being at or over the "book" max in grains?
This is simple. It is usually a number of things. Chamber specs, bore specs, powder lots, seating depth, primer choice and lot, case capacity, freebore and more. Another case of start low and work up.
5) Not all data matches. If you visit the Nosler and Hodgdon sites and check the data for 300 RUM/200 gr AB using IMR 7828, you will find a huge difference in their data.
Hodgdon max -82.0gr/2857 fps
Nosler max - 87.5 gr/3102 fps
Now that is a huge difference. The Hodgdom max is lower than the Nosler starting load. Which is right?
Both are right. That is, with each set of indavidual components used, and a given companies "conservative" factor.
Also, if you check the Hodgdon site for the 300 RUM/Retumbo/200 AB you will see that they list 95.5 gr as max with a velocity of 3048, and I have read numerous posts in here with members getting 3200 or more with that load.
Finally, there are many cartridge/bullet/powder combinations for which there is no data - how do you determine max for those combinations?
Start low, work up. When the bolt gets sticky and there are ejector marks and craters on the primer, this is IMHO just over max. Once you back off a bit, this is the "max load".
IMO, if you are going to go by the "book" data then you need to go by ALL of it. Same primers, same brass, same brass dimenssions, same barrel chambering, same seating depth (COAL), etc. Once you change any of that you throw your book off because it all has an effect on pressure and velocity and then you start guesssing.
Not trying to pick a fight here with anyone, but I just dont see how any of these factors can be ignored. IMHO, the chrony can be a valuble tool but to say that it is the final or primary word on pressure I believe is a stretch.
Exactly. Even though I use a chrony as a guide, I still dont rely on it for the end result. For example the other day I was developing loads with a new powder and the 178 AMAX. The velocities were so high and the recoil so light I though I had accidentaly loaded 155 AMAX's. This is a case where max loads far exceeded "book" max. However, with totally easy bolt lift, normal primers and NO ejector marks, the velocity isnt a real issue. It wasnt until later that I learned that the powder I was using was made for higher than normal velocities.
OK, I stand braced
-MR