OK, my shooting buddy's brother has a 4in. Mountain Gun in .45LC. A black bear has been eyeballing his farm. He wants to know if Buffalo Boar hard cast bear loads would be OK in his Smith. Thanks!
The original .45 Colt black powder loads delivered in excess of 600 fpe from a 7.5" barrel way back in 1873. Just like today, the Army decided that was far too much power and kick and so specified a reduced load with a 230 grain slug delivering around 350 fpe - just like the .45 ACP half a century later. Factory .45 Colt ammo today is loaded to around 14,000 psi which is nothing with modern, solid-head brass in modern steel guns. The larger the bore, the more "power" can be generated due to the simple fact that a larger bullet has more base area to push against and so will go faster with lower "chamber pressure" than small bores. This is why .45 "magnum" level loads in the old load manuals were stipulated to be no more than 25,000 psi, which is far lower than modern 9mm, .357 magnum, .40 S&W, and 10mm, and only about 5-6 thousand psi more than garden variety .45 ACP loads which are intentionally loaded mildly.
So the question is, can his S&W Mountain Gun handle Buffalo Bore's top .45 LC ammo. Simply put, yes it can, but can HE handle it? Big bores with big, heavy slugs tend to KICK because you can't make real power going thataway, without paying for it going thisaway. Is 25K psi too much for the modern brass case? NO. Is it too much for modern steel, not even close. The problem is a Mountain gun only weighs about 38-39 ounces 'cause they're made to ride on the hip over busting off 1,000 rounds at the range. A standard 4" S&W M29 only weighs 44 ounces - maybe 6 ounces more than the Mountain gun, but that, plus the added weight of a 6th cartridge certainly attenuates kick better than a 5-shot M69, or a Mountain gun with tapered barrel.
If I may be so bold I suggest a serious look at the Colt Anaconda 4 inch which kicks it up to 47 ounce with a lot of mass forward. I'm sure your buddy's brother loves his .45 LC chambering, but when the rubber meets the road, the entire reason the .44 magnum came into existence is because it was a better path forward to magnum power - just ask Elmer Keith, and he tried 'em both!
These ultra light .44s and .45s are GREAT when sitting around yapping about 'em, but in real life, the old standards exist for a reason.
BUT, to reiterate about your question, the S&W Mountain gun can handle BB ammunition, but nobody will want to stand behind it for 6 shots.
