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.
Yesterday I had loaded up 6 cases with the Hornady 45 caliber sabots. These sabots held a .400 caliber 200 grains SST Bullet. I used 5744 powder, starting at 20.0 grs and ending at 25.0 grains. I shot them over a Chronograph and had velocities that started at 1,259 fps with the 20 gr. charge and 1611 fps with the 25 gr. charge. My goal was to get to 2500 fps with this bullet. With the powder charges used the action would not lock open.
Recovered sabots had a small 1/2 circle piece of the sabot base missing. This missing piece was about .10 inches. Each sabot had this piece missing at the same location based up visual appearance of the rifling impressions on the sabot. This is most likely the diameter of the gas hole in the barrel. I am assuming that when the base of the sabot passes over the gas hole, the pressure blows the skirt into the hole because it is unsupported. All other portions of the sabot look OK.
At this point I am not going to proceed any further with shooting sabots in a gas gun — unless a sabot is designed specially for this — as it does have potential.
Regarding the low charges — I started low and was working up until I hit a charge that would hold the bolt open — just didn’t get that far. With the sabot — the case holds about 32 grs.
I shot 6 loads today using the 45 caliber sabots (with 40 caliber sst bullets). Using 5744 powder — 26.0 grains to 30.0 grains. Top velocity was 1750 fps at 28 grains. Velocity decreased with higher charges and also was a lot of unburned powder. I was hoping for 2500 fps, but it appears that will not be possible with 5744. Also, the case would eject, but action would not stay open.
I did have to modify the sabots by removing some of the rear of the cup — about .05 inches. The skirt was too thin and was blown apart when passing over the gas hole. Trimming helped a little, but still there was a “divit”. I am out of sabots — so I will put this little experiment to rest (maybe).