Keep in mind the original Winchester 1886 in 45-90 had a different twist then the same rifles in 45-70. The 45-70s could use bullets up to 500 grains. The 45-90 was limited to 300 grain bullets in the era they were made. I don't know how the newest Miroku rifles are twisted, but in 1986 when Browning re-introduced the M1886 they were chambered in the 45-70 but twisted slower like the 45-90s were which is why they shot 300 grain bullets very well, 350s OK and 400 poorly as a rule. 500 grain bullet would impact sideways at 25 yards I has 2 of them and they were definitely "light bullet rifles"
I have been told that Winchester addressed that problem (After the joining with Browning) and the the new Winchester 1886s are twisted 1-18 instead of 1-30, but I have not proven that to myself yet, so take it as hear-say for now,.
This is the first I’ve read that Browning 1886 rifles were fitted with a slow twist barrel. Admittedly that was something I had never checked but assumed the twist to be a 1 in 20” twist. The two Browning 1886 rifles I had shot superbly with heavy bullets. In fact I rarely use anything lighter than 400 gr. Anyhow I went and dug my Browning 1886 out of the safe and checked the twist using a tight patch. As near as I could determine it has a 1 in 20” twist.
I believe some of the barrels fitted to Miroku 1885 rifles in 45/70 and 45/90 (mainly heavy round barrel BPCR versions) were 1 in 18” Badger cut rifle barrels.
The tight barrel dimensions and the SAAMI throat (ie no throat) does make for difficult chambering of some jacketed and cast bullets in the Browning. For years prior to its introduction in the Browning, Marlin and Ruger had produced 45/70 rifles with a short throat, longer than what they do now. That’s what bullet producers were used to making their bullets fit. The 300gr pills generally weren’t a problem fitting the Browning 45/70 chamber. I suspect this is what made people come to the conclusion that the Browning won’t accept heavier bullets.
