I think I answered my own question. I shot some 400 gr cast bullets today using 4198 and 5744 powder. I started at 19 grs with the 4198 and 20 grs with the 5744. I increased the powder charge 1 gr for 10 rounds each. Action stayed open on all of the powder charges. Velocity was around 900 fps on the low end and at the high charges the velocity around 1400 fps. Lots of unburned powder — especially with 5744.
I noticed on the upper end of the charges, with both powders, that the cases had shave marks on the base (bottom) from the extractor groove in the bolt face. Indicating to me that two things were happening — 1. Chamber pressure was now high enough to seal the case against the chamber walls — 2. Chamber pressure was still high when the bolt was trying to open, most likely because the bullet had not exited the barrel yet.
Primers showed no pressure signs and actually looked very mild. I had used CCI 450 Mags (Small Rifle Magnum).
Velocity maybe needs to be at least 1700 fps (lowest velocity in Hornadys load data) to provide proper timing for bullet exit prior to chamber opening.
Hornady doesn’t have it — it was what I loaded up. I used 27 grs of Lil’Gun with a 400 gr. 45-70 bullet sized to .452. Velocities ran around 1550 fps. I feel that is too slow for proper unlocking of the action.
On another note — my load that I use for the 275 gr. Barnes is 35 grs of Lil’Gun. Velocity was about 2050 fps. Accuracy was 1 1/2 inches.
I shot 5 rounds today over the chrony. I used the 400 grain Speer, sized from .458 to .452. Used Lil’Gun and WSR Primers.
Charges and velocities are as follows:
1 — 27 grs, 1576 fps
2 — 28 grs, 1614 fps
3 — 29 grs, 1689 fps
4 — 30 grs, 1736 fps
5 — 31 grs, 1768 fps
Shots 3,4 and 5 all grouped in to .75″. Shot #1 was 3 inches below cluster and Shot #2 was 2 inches below cluster. Sweet spot must be 30 grains.
Charges #1 and #2 show nil primer flattening. Charges #3 thru #5 showed progressive flattening. ALL CASES SHOWED WIPE MARKS FROM THE EXTRACTOR AREA ON THE BASE AND SHOT #5 SHOWED EJECTOR SWIPE.
I would consider this data the upper extreme and would be very, very cautious about its us.
WW296 and H110 are Ball-Powders and their data is interchangeable and not AA1680 (also a ball-powder), which is a much slower powder. As always in matters of reloading you are on your own and anything you read here should be taken with a grain of salt. Your caution is commendable but be very careful with reduced loads. I consider your load with 37grs of 296/110 to be just on the good side of low, you might see speeds in the 2000/2200fps area, but increase the OAL if you can (2.250”). Keep in mind Slash’s 45gr load, according to the picture record he provided for us, had no problem with pressure. 37gr of 1680 is definitely low and possibly dangerous. Watch for sooting down the sides of the case, if you see it the case is not sealing, because pressures are low in the chamber and of course at that moment increased bolt thrust could become a problem. I would definitely start with 45gr of 1680 with your 240gr bullet. Funny thing, RX7 is the next logical slower powder than 1680 and if used in the 450bthe speeds drop off 500fps, you just can’t get enough RX7 in the case. Good luck…t
Ok Slash, once again Randal is correct. Yule of thumb is one caliber for the depth, and he is also right about those numbers aren’t quite right for the larger calibers. It sounds like the xtp might be a little shorter than the FMJ’s. I normally seat my shorter .4515 bullets to a depth of .187” with no ill effects at all, your number of .166” is a little skinny, but hey, try’em, but get that OAL out there a bunch more, someone quoted a 2.017” OAL and that’s simply way too short, probably works great, but, the shorter the OAL the more the pressure. ; H110 is interchangeable with the data for WW296 and is a great powder for the 450b as is 4227, but AA1680 will keep the speeds up there and lower the pressures.