Nailgun;
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I've found that the RCBS 300gr FNGC is my bullet of choice for my GG.
I have had good success with the Lee 340grFN as well as the Lee 405gr HBFN. If you will cast these from wheelweights and lube with SPG lube, you'll be able to load the 405gr up to 1,800fps over IMR4064, RL-15, H4895, or Varget with full case loads of powder (48-55gr depending on powder choice). These are sufficient for anything that walks the planet.
If you will size to .459" and use the SPG powder, you'll probably not have to remove any lead from your barrel. With the 300grFNGC (mine casts to 318gr ith Hornady GasCheck and lubed) I get 1,950fps over 47.0gr of H4198. This is NOT a hot load for the 1895G, but is about all I care to shoot. It shoots flat (about like the .22mag rim fire), and flattens deer with authority. It also groups as tight at 100yds as my Rem. M700 in .22-250.
A good "cheap" load avoiding the necessity to gas-check the bullet is to pan-lube ( or hand lube; you remember how to "color" with crayons in kindergarden?) the 405grHB and run through a Lee .459" sizer (special order from Lee, the .458" is the standard size, but the .459" gives me much better accuracy from 4 different rifles- one a microgroove Marlin, two Ballard rifled Marlins, and a Sharps Reproduction in .45/90). I've had good luck with BlueDot and Alliant#2400 (and when it was Hercules, too!) About 20gr of BlueDot or 25.0gr of #2400 and you won't need to use a filler. If you choose to use a filler, use dacron pillow stuffing and fill the airspace. (dacron is the inert binder used in manufacturing the powder and is consumed in the combustion process and won't cause "buldges" in your barrel like some non conbustable fillers can.) You may even be able to get by without sizing the bullets if you do a neat and clean job on the casting and don't have large flashings on the sides of the bullets. Go easy with you Lee dies and they'll last a long time. I'm still using a Lee .309-150grFNGC that I bought in the mid-70s when they first started making bullet moulds. It still casts MOA capable bullets 30+ yrs later.)
Good luck with your .45/70.
And btw, nah, they ain't enough for elk,
but it did wipe out the bison! And with black powder at that.