pwoller wrote:So if you were going out for the first time with lil gun, 450 primers and the 250 trex at .5 increments what would you load up to and how many rounds of each load would you take? My first rounds are always over a chrono.
Assuming your brass prep and reloading technique is consistent, 100 yd, 3 shot groups will give you all the data you need to determine the best load for your platform. For a 250gr bullet, albeit a monolithic copper one, I would start at 36gr Lil Gun and work up from there carefully in .5gr increments seat the bullets to the COL that fits your magazine. Again, I have not seen the Trex bullets. If like the Barnes XPB/TSX bullets, the Trex have driving band grooves around them, there is a benefit to driving a taper crimp down into one of the the grooves, close to maximum COL. Some times that involves loading to a COL slightly less than mag capacity and limiting your maximum powder charge appropriately but the benefit is cartridges where the bullets don't pull out or push in from cycling them. The groove gives the taper crimp something to hold onto as opposed to just the friction between the brass case and the copper bullet. With the Barnes bullets I worked with, I gladly sacrificed a tenth or two of COL for the benefit of a firm hold onto the bullet. Many AR platform users can attest to the tendency of the bullet, even when properly taper crimped, to move a little from the inertia imparted when chambering. Think of an inertial bullet puller. If you have a caliper or better yet a micrometer, measure the diameter of your cases after sizing right where the case walls begin above the web and write them down. Take your measuring device to the range with you. After each shot, measure the same diameter to see how much growth occurred. Repeat with every increase in charge weight step. Some growth is normal but once you see growth greater than .001, that's a pressure sign that's the stop right there point. Also, pay attention to the case heads. If they start backing out of the chamber upon ignition and causing the bolt face to imprint into them, that's a watch your step indicator. Primer flattening is also a go slow sign. I've taken 250gr ftx bullets, which generate less pressure, up to where that occurs and they still don't cause case diameter growth of .001. The imprinting, swipes and primers beginning to lose their rounded edges are not a stop right there indicator. More of a warning of that point not being too far ahead.
Trident barrels are well made but they tend to have fairly tight chambers like match grade barrels have. Of greater concern is that your rifle does not have a rifle length gas system. That can be a booger to get to cycle reliably across a wide range of bullet weights and velocities. I know because once upon a time, I had a 20" Trident barrel that had a rifle length gas system. I ordered it that way so I had no one to blame but myself. I had to open up the gas port size to get it to run but the amount of work and loads it took, ruined my impression of it and I sold it out of spite. Hopefully yours has a carbine length gas system or mid-length one though IMHO, for a 16" barrel, a carbine length gas system is more forgiving. Just my opinion. Bushmaster knew what they were doing when they spec'd their original 450 16" with a carbine length gas system.
Don't hesitate to call it a day if you encounter the aforementioned pressure signs. I hate pulling down risky loads as much as the next guy but as I said, this caliber is just as lethal at 2200fps as it is at 2300. Certainly not worth pushing your luck for the bragging rights of a few more fps.
Hoot