If you care about the following;
The "craft" of reloading.
The need to be at safe pressures, over a complete velocity range, for a given calibre.
The "need" to chase velocity.
The need to understand first hand the interrelationship of components and how they can materially affect pressure.
The need to match your last accurate load with a new one but with different brass or powder, without throwing too much lead down range.
The need to understand that not all bullets of the same weight act the same.
Then you need a chrony.
The two biggest improvements in my reloading has been a chrony and Quickload. As stated previously, and by way of example, measuring the velocity spread of a given batch of loads is diagnostic.
It allowed me to correlate poor reloading practice to velocity. My .375 I was getting an SD of 8.5fps, It came time for annealing so I decided to hand anneal my brass (my first time at annealing). On the next batch of identical loads the SD drifted out to 25fps and accuracy took a tumble. This made me remember how some bullets seated more readily than others and clearly that my annealing skills were dismal. A re-anneal on a mates machine fixed the problem.
Now many would argue that a velocity spread of some 50fps odd at 100yds does not display significant variations in vertical displacement so one would miss this effect when looking at the target and evaluating it at face value. That is why ladder tests are conducted at 500yds plus. However, if one is a believer in the OBT method for developing loads (and I can positively attest that this is a highly efficient means to an end) then one would know that 50fps off the node speed is enough to open the group up. QL needs a chrony.
On the same .375 I was soon to realise that trying to match the velocity of off the shelf ammo was dangerous. In so doing I found myself at a calculated 72 000psi without any signs of pressure on primer, bolt handle or case On checking the brass had an internal case volume of 5gr. H2O less than SAAMI, the powder was a hot batch and it was a compressed load in order to get to the commercial ammo speeds. These factors culminated in higher pressures as pressure is not linear.
A chrony also proved to me that IMHO there is no such thing a s a flyer, a flyer is simply a poor shot. I have pulled shots an inch up and an inch right and the recorded velocity was less than the average. Explain that if velocity determines vertical displacement?
So as a hand loader I would not be without my chrony during load development.
