I always swear by the Lee data whenever anyone trys to tell me they know best. If they say it, Lee, it's safe. Their entire charge table is one sheet of paper.
I've seen some recipes in books top 13,000psi, but I shoot a lot of older guns so I keep my loads right around the 3 dram level. 1oz at 1190-1250fps or so. Most are right around 10,000psi. I've just never seen that much HS6 in a load before.
How are you loading your buck pellets, bud? I think I tried every wad I could find and none that I know of would stack 3-3-3. When I load factory shells (dumped lead and replaced with buck) I go 4-2. Four layers of two pellets. That's why I always slice off the wad petals when I load my own. Only way I can get nine to stack right. I experiment a lot, too. I tried those plastic shot tubes they sell for skeet shooters on top of the trimmed wads, but they patterned no better than my factory loaded stuff. I just slice off the petals now.
My latest fun load is a Lee 7/8oz key duplex loaded with 3 00buck pellets. Those duplex loads, buck and ball, started showing up a couple of years back and they still run in the neighborhood of $3 a pop. I can load them for approx 40 cents a piece. Supposed to be a highly desireable HD round. They make a mess with over ripe melons, anyway.
Grab yourself some 7/8oz Lee slugs if you can and a bag of 00buck pellets. Buy a few boxes of Win 1 1/4oz heavy game loads. Your choice. Shot size makes no diff. You'll empty that out anyway. Open the shells and dump the shot, pull the wad and slice the petals off the wad. Reload that wad, count out three 00buck pellets and add just enough Cream of Wheat buffer to fill between the pellets but not cover their tops. Next, take a second wad and slice the entire bottom off it leaving just the shotcup. I know, I wish they still sold separate shotcups, too. I haven't seen any in ages 'cept in loaded ammo. Load the slug into that shotcup and load it into the hull on top of the buckshot. Here, I have to trim some of the top shotcup petals to get a good crimp. I use RXP's....no idea on yours. Crimp it and have fun.
They come in at the 1300-1330fps range, factory pressure, depends on what ammo you used to make them. The keyed slug isn't going to fly really slug-like, but they're only used as improvised balls anyway. Devastating round close up!
Damn, I can get long-winded. Sorry.
rich