Bullets
I scored more than a thousand Hornady 55 grain CX. I believe this type of bullet (monolithic copper expanding) is ideal for the 223 cartridge that tends to suffer from under-penetration with almost every other type of middle-weight bullet suitable for the 1:9 twist. Old-fashioned FMJ achieve good penetration but they suffer on barriers and from unpredictable yaw effects. The M855 addresses these issues, but seems to suffer from poor axial symmetry, perhaps even more so in the 1:7 twist barrels. Besides the CX, I have enough Barnes MPG for a 3-day class where lead-free frangible are required. Both the CX and the MPG are flat-base. The .224 version of the CX does not feature a polymer tip like most of the other CX. The MPG is considerably longer than the CX. It is a long bullet since most of the 55 grains is made up of powdered tin and copper. I selected it in lieu of Sinterfire because I believe the gilding metal jacket will be superior for feeding from the magazine.
No Compressed Powder Loads
My Redding Competition Seating die came with a warning not to use it to seat bullets over compressed loads (discussed in detail elsewhere). A lot of the powders that develop higher velocities in 223 depend on compressed loads inside the small case. Slower powders that use high charge weights like CFE223, A2520, StaBall Match, and even some loads for BL-C(2), 748, and 4895 are likely to be compressed. So would Varget. While I wouldn't be averse to experimenting with some of these, I'm not wanting to buy pounds of several and shoot them all to find out. In my experience, that is the best way to learn, but my goals for the Mini-14 are modest and I can probably find a powder where the first 8 pounds won't go to waste.
Powder Alternatives
I believe LT-32 would be an outstanding powder for 223, but I don't think I'm willing to give up the velocity for the half-MOA or whatever it might gain me. The effective range of my sights and the size of my targets limits the benefits of increased accuracy. I'm not putting a huge scope on a folding Mini, neither am I shooting tiny varmints or match targets. I passed over 8208 for the same reason, though I don't think it has the quality of LT-32, it would also likely suffer lower velocities.
I have two pounds left of 8# of H335. I'll see where it takes me. I was just going to buy another 8#, but I'm betting I can get more velocity at a lower pressure with something different and before I'm forced into compressed loads. Maybe I could do it with BL-C(2).
I think higher velocities are developed within a given maximum pressure by increasing the area under the pressure/time-travel curve. This is done by using a larger volume of a slower (deterred) powder, by using a progressive rate powder, or both. I think of a progressive rate powder as one that starts out with a slower burn rate but which converts to gas at a higher rate further into the combustion. Progressivity is achieved either by granule shape like a perforated cylinder the surface area of which increases as it burns and the perforation expands, or by burning through a deterrent coating on a spherical ball where the core has a higher energy density. Because these qualities aren't isolated from other powder characteristics, I could be mistaken in practice, but I developed a suspicion that slow, degressive powders are likely to fill my case and get compressed before they deliver the highest velocities. Given a higher case volume, like Valkyrie, Nosler, 22-250, etc., they may be the way to go, but with 223 Remington, my unleaded bullets would be pushing up against the rule I've been given not to compress. Therefore, I am favoring more progressive powders. I believe Hornady does the same with their factory loading for the 55 grain CX which they market in their "Superperformance" line where that line touts progressive powders like "Superperformance" powder -- though it is doubtful the powder by that particular name is featured in the 223 Remington or 5.56 NATO cartridges. I don't know what they do use. I don't even know if it is worth trying to duplicate since I've never used it. I could try what I believe are more progressive powders in an appropriate burn-rate range. Those would be A2230 or A2460. It should be noted that progressive powders are not a new thing. They go back at least as far as nitroglycerin. Red Dot and Ball-C are notably progressive.
I've dismissed the long-stick extruded powders since I want to meter by volume with my Harrel's measure. I don't want to weigh every charge for a Mini-14. There are some short-stick powders I have considered like the already mentioned LT-32 and 8208. H322, 2015 and Benchmark are others. Those first three are related at least by history, all wannabe T-32 or whatever someone thought was an improvement on it. 2015 is supposed to be a slower-rate version of LT-32 that shares its geometry, allowing them to be blended. Based on multiple data sources, it still falls short of the velocity I think would serve me best.
The slower single-base extruded powders (Varget, 4064, N140) are likely to have too low energy density to get the velocity I want in the confines of an uncompressed load. The 4895's are about right, but won't flow through my measure as well as ball.
So my current thinking is to try the H335 that I already have and then maybe gamble on A2460 to see if I can get any better result.
Die Bushing
I received the dies and other tools and tested the .243 SAC bushing I ordered on the fired LC brass. My loaded necks were .246 and I believe the LC brass averages around 11 or 12 thou (.246 minus .224 equals .022 divided by 2 neck walls is .011) hence why I ordered .243" because I wanted an ID 3 thou less than my loaded cartridge. That way the expander ball would pull the ID back out 1 thou, and I'd have 2 thou of neck tension. My necks were .255" OD after firing. I have had bushings size brass down smaller than the bushing diameter (opposite of spring-back) when sizing down very far, and I have had to size down using incrementally smaller bushings. Thankfully, the .243" SAC bushing sized the necks down to .243" with no expander in the die. I installed the carbide button, and the necks came out .244" -- perfect -- no collection of bushings for me.
Lee Deluxe APP
I reluctantly ordered a Lee ACP back in February. I suspected it would be unsatisfying. I had been considering it for more than a year. The video by F-Class John convinced me it could work -- with a few fixes like the carboard flap thing taped on -- you know, like you expect from Lee. My ACP was a colossal failure. I'm not even going to get into it because it's moot now. Lee discontinued it. They offered me the Deluxe APP at a discount. I did say that when I was buying the ACP that I would have gladly paid twice as much for the machine if it worked. So that's what I did. The Deluxe APP seems to be working. It's not fool-proof -- it'll double-feed primers if the cases stop flowing, and it can fail to eject cases if the handle stroke is not consistent. But I can deal with a little jiggling. Even though I got the APP, I didn't get the primer pocket swager for it. Instead, I bought the Lee die that does it on the regular press. I have a very sturdy press and stand I think I'll prefer for swaging.
I might pause this project for a while because I've probably got to get a gas bushing. I'm going to put together a sling for the rifle and do some other things. I'll get back to reloading when I have some brass piled up.