Using Lyman #457671 mold, Gas checked, linotype metal. H4198 at 1858 FPS average. Approximately 50% of them "keyhole", balance group about 2.5" at 100 yds. What's wrong? Metal too hard? Didn't have a problem with a small test of wheel weight and added tin (9# to 4 oz)

Thanks for any advice

Might check your sizer out. Had that problem with mine, got to looking and the sizer was shaving just enough off one side to make them keyhole. I was getting keyholes at 50yds.! Course I wasn't using gas checks, so I don't know if that will help you any or not.

Patience. The quicker twist (1-14,16") makes them much more touchy to work with than the 1-20,24") of a 45-70. Lower velocities help a lot.

I'm guessing that your bullets are too light. I do not shoot less than a 450 gr bullet in an 18" twist .45-100. I would shoot at least 500 gr bullets in your rifle. Maybe 550s to get them to stabilize.

Brent

Prior to casting the bullets..Did you make the proper sacrifices? Of course having the local shaman read some chicken entrails is always good for confirming the alloy consistancy, not to mention the effectiveness of putting you bullet lube outside during a full moon, while you conduct a vigil and beat on a tom-tom.
Once you've taken care of the spiritual side of bullet casting check the diameter of the bullet compared to the diameter of the bore.
If that does not help go back to feathers, tom-toms, baying at moon and determine if your wife would miss one of the kids should a greater sacrifice be required. A word of caution sacrificing wives don't work! Of course the wife may be of the type that when rendered down could supply several years worth of bullet lube and fluxing material.
Jim

Caution!! If you use wife-tallow lube, you'll be constantly reminded of your inadequacies.

You guys crack me up. My usual spiritualism when cast boolits go sideways involves a number of Germanic and Anglo-Saxon coprological and copulatory references, some of which end in "hard K" sounds. These get delivered with considerable spirit indeed.

If the boolits fit the throat, dunno why a longer one would do these antics in the 1-14" or 1-16" twist the 458 usually features. My 45-70 has 1-20", and has not done good things with any boolit over 400 grains. I borrowed another long boolit mold recently, and I'm going to try again with the heavier castings--but I'm not expecting miracles.