Success!!!
I made it out to shoot my Gahendra just now and am very happy with the results!!! I slugged the bore 3 times and it came up .457 +/- every time. Long time loaders of this caliber said the 577/450 is typically not that tight & I very much believe that.
For some reason, this one is that tight. I used .458 hollow base bullets @ 400 - 405 grains made from straight wheel weights over 30.0/AA 5744. I still don't have any real black. Using the Lee dies, the bullets were loose in the neck after FL sizing, so I used a 45 Colt FL die to correct that just like I do for 43 Dutch Beaumont. Used a firm crimp.
Keep in mind that normal bore diameter for Brit Martini-Henrys is around .468, give or take. The Gahendras and Martini-Henry copies made in Nepal have tighter bores. As with any other cast bullet application, be sure to slug your bore and select a bullet .001/.002" over that diameter for a good gas seal. This will help accuracy more than I can describe.
I was out of targets & it was too late in the day to buy more @ wally, so I just grabbed a small box from the pharmacy dumpster & marked it with a sharpie. No measured yardage where I shot so I paced off a distance between 50 & 60 yards. ( it was rough ground)
Shooting with only my elbows as a rest from a picnic table, I got the group shown which was about 4" high @ the distance specified. I wasn't so concerned with group as I was with keyholing. That would have shown the bullet was too small for the bore, but happily, that was not the case.
Cases dropped from the chamber - hardly any soot on them - almost no granular powder residue which I believe shows the powder is buring efficiently in the barrel. Recoil was not a bit painful - the rifle is heavy enough to help. The Gahendra fits me really well, too. I'm 6-3 & had it in my mind soldiers from Nepal might be shorter... I dunno. A 577/450 cartridge is shown beside the group for size perspective.
Velocity for 3 shots went: 1297 - 1236 & 1300 on the money.
I don't mean that this report is the final word - far from it. It's a place to start. For other experimenters, the 1st order of biz is to slug the bore and select a bullet just slightly wider than that. - Just like any other cast bullet application. Make of the data what you will.
In addition to the target, I"ve shown how I reduced the neck diameter of the case with a 45 Colt FL die to hold the smaller bullet - a standard FL sized 577/450 is shown for comparison. I did this operation very carefully. Jamison cases cost $3.63 EACH, and I didn't want to ruin any.
If you are careful, cases can be made from the cheeper 24 gauge brass shotgun cases, but I was afraid I'd ruin so many there would be no savings.
I am happy with the results and feel I need look no farther for a standard load for this particular rifle.
SW
*** all the standard caveats and disclaimers apply here.. don't run with scissors... etc & so forth!
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Edit to add: given the odd design of the hammer, I do not recommend dry firing a Gahendra.