winman1550 wrote:First let me say I'm not a reloader. I do read with a learning interest most of the posts about guys trying this bullet and that bullet, this powder and that powder and how much of each. As an observer, some I understand and some not so much. My question is, if with my 18" Tromix barrel I'm getting groups like the second picture in the above post at 200 yards with factory ammo as I'm sure others are, why all the experimentation? I know I'm pretty happy with my results and know I'm not going to get 5 shots all in the same hole at that distance no matter what I do. Using the chronographs and checking to see if I'm gaining or losing 100 fps between bullets, powders, primers etc... Don't seem like much difference? Is it for the fun? Cost savings? Or just something to do. Just curios.
Greg
the issue is greg, when it comes to reloading - EVERY firearm, or at least every barrel - is a little bit different.
no two barrels, even produced from the same production run , are going to have identical rifle twists. there's always some minor variation. additionally relatively minute differences in profile thickness, or metal consistency, can cause harmonic changes, etc.
this also applies to chamber cuts. Every chamber is a little bit different - even SAMMI standards have a +/- tolerance built into them.
so when you get down to reloading information re: charge weights and whatnot, the published information is a
guide. that data is only concrete for the test barrel the publisher used to acquire the data and with the specific powder lot used for testing. ANytime you change a single component, the recipe is going to change. Commercial ammo manufacturer's test powder every time they get a new lot and adjust each batch of ammo produced with it to the proper
pressure and then verify that the rest of the data holds true (velocity, consistency, etc) before they load it in bulk. This is why sometimes you'll find that even your favorite factory load sometimes shoots wonky if you get a bad lot.
so for us reloaders - doing load development with varying charge weights from min-max published data is a way to not only safety check that published data is good for OUR rifle, but also for accuracy. Every powder/bullet/brass/primer combination has a (or several) sweet spots where ignition produces a very consistent velocity. We call these sweet spots "nodes" - and then pray that these nodes match into our barrels harmonic timing too. By doing tests with small changes in powder charge, but keeping everything else consistent it allows us to identify these ES/SD nodes as well as searching out the magic velocity needed for our harmonics. It also allows us to watch for signs of pressure getting too high by reading our primers (more like reading tea leaves in some respects compared to the pressure test barrels commercial ammo mfgs use) to know if a load is still safe to shoot in our guns.
so while it may seem a bit of voodoo and waste of good projectiles, and time, its a way for us to fine tune a bullet's performance in our individual firearm. We as reloaders can often produce a significantly more consistent load than commercial manufacturers produce, as well as being able to match to the specific harmonic profile of our individual barrels.
because of the 450's short stubby bullets, we're likely not often going to find a 200 yd magic 1 hole group like you can with many other calibers, but this is one aspect of shooting that once you adopt the hobby of reloading, you're often going to get stuck on tinkering until you get things as good as they can be
as far as chrono's go - knowing your velocity and your consistency (ES & SD) is always a good piece of information to have - even with factory ammo. You need accurate velocity information to do trajectory calculations easier and save ammo from getting out in the field and figuring out your drops by clicking away. Not that we should trust that data to be 100% without verification, but just like bore sighting - it'll usually get you in the ballpark.
HTH