I'd say you got it right Jim.
The golden rule is it must fit in the magazine, regardless of what caliber you're loading for.
In the case of this particular caliber, strong and consistent neck tension is incredibly important. The easiest way to get it is by the amount of bullet surface area in contact with case brass. Unfortunately, the deeper you seat your bullet to increase that surface area, the more powder capacity is lost and of equal concern, the further the bullet has to jump before engaging the lands.
Crimping enhances that tension. Crimping into a cannelure even more so. The rub is, most bullets with cannelures in them were not designed for this caliber and the cannelure is located appropriate for the caliber it was designed for. So, we compromise some times in order to take advantage of it and some times we ignore it due to it's inappropriate location for our caliber. As I previously mentioned, the 300 XTP Mag, while it has a cannelure, it is located poorly for our caliber and I got better results Sunday loading the bullet a lot longer and relying upon it's weight as much as the neck tension to resist starting in motion during ignition. With lighter bullets, we lose the benefit of Newtons first law and rely more upon exotic crimps and pre-tensioning (TiteNeck) to increase the resistance to movement. For my efforts, the big challenge is compromising the insertion depth, versus case capacity with slower powders. That's not even considering the issue of the bullet pulling a little from the inertia of chambering. A factor that has to be considered unless you hand cycle each round using the charging handle followed by a tap on the FA. I've never fessed up to this, but that's how I load every single round when I'm doing load workup. When I'm trying to assess a new load, adding the variable of bullet jump muddies the contributing factors.
I'm a firm believer that regardless of what bullet you choose to use, never use a seating depth that is less than 1/2 the caliber of the bullet and even that is an extreme compromise. IE in the 450b, never less than a quarter inch. Optimally, I like a full caliber insertion depth. With bottleneck calibers, that is much easier achieved and you can choose neck sizing bushings to set the neck ID and subsequent resulting tension to whatever you like, assuming you're using that style of sizing die. Since the 450b headspaces off of the mouth as opposed to the shoulder in a bottleneck or the rim in the case of rimmed calibers, or the belt in the case of belted magnums, we can only shrink the mouth of the 450b but so far.
Then there are the crimps. I dabbled in excessive taper crimp while not going so far as to distort the bullet too much or too far so that it won't catch the chamber lip. Recently I learned that despite brass being harder than copper, excessive taper crimping winds up imparting a permanent taper in the brass thickness at the mouth. Then, when you go to taper crimp the next time, the crimp diameter that worked the previous time proves insufficient the next time because the mouth wall is now thinner and you have to set the taper die even tighter to get the same tension. This is a vicious cycle that eventually leaves the case irreversibly thinned out at the mouth and susceptible to splitting. All this compromising catches up with you in one way or another. Then there's the factor of bullet overall diameter. I've now seen them fall anywhere between a true .452, down as small as .4497 out of the box. That winds up equating to a double whammy. First, you have to taper crimp the case down even more to achieve the same amount of tension and second, they offer less resistance going down the bore. The latter is as important to the pressure curve as the starting tension. The issues with a stab crimp are self evident. Despite the adjustability of the LeGendre Stab Crimp using shims, I've had a challenge reproducing the exact same result once Ive broken down the setup and reinstalled it at a later date. If you reload for different bullets, you're almost forced to make a dedicated stab crimp die for each bullet, custom fit to place the stab crimp in the same place and to the same intensity the next time you run a batch. Since uniformity of crimp is directly proportional to uniformity of neck tension from one batch to the next, you really need to get that worked out if you want the same results the next time out. The same applies to the TiteNeck method. I still like that approach as opposed to the stab crimp, but it an imprecise process and still in it's infancy. It also can not make up for insufficient insertion depth. With very short bullets, there's just not enough to get a good grab onto. I ran into that with my recent foray into the 160gr TAC-XP bullets. The worst is solid bullets, since they have to be shorter than their hollow point cousins of the same weight since copper and lead weigh more than air and a ballistic tip.
So IMHO, it all revolves around having sufficient neck tension, however achieved, that is repeatable, non-destructive and consistent in order to balance the bullet weight you choose as well as it's diameter, against the characteristics of the powder you choose, in order to obtain efficient combustion without detracting from accuracy. That's a tall order in this caliber. It's also an equation of IMHO, too many variables. If you stick to one or two favorite bullets, you can eventually figure it out. If like me, you like to play with a wide spectrum of bullet weights, lengths and diameters, it all adds up to a lot of headaches keeping everything straight.
It's late and my objectivity is starting to drift, so I'll bid you all good night.Hopefully, when I read this again tomorrow, it won't sound like the ramblings of a tired, OCD plagued, old guy.
Hoot
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