Just run into a friend with a Jonathan browning mountain 45cal browned precision Mz today and what's to sale and its mint what's the value of this gun. and any info thinks

I did some searching and I can't find a value on them. However the 45s likely were not as popular as the 50s or the 54s. Nothing wrong with a .45 though IMO. The Browning Mountain Rifle is a fine looking piece and $300 would be a pretty cheap price for one. I wouldn't go over $500.
Maybe someone else has more info they can share with you.

300 would be way to cheap imo. $500 for starters,they are not a cheap muzzy. The big votes sell for as much as 750 on the auction sites.

would you not what the twist is on this gun

I have an old copy of Fjestad's "Blue Book of Modern Black Powder Values" from 2002 and it states that there were two models offered...

Jonathan Browning Mountain Rifle - .50 perc., 30 inch octagon barrel, single set trigger, select walnut stock, cased with medallion and powder horn. 1000 mfg. in 1978. The value listed in 2002 for 100% condition was $750

Mountain Rifle - .45 or .54 caliber perc., similar to the Jonathan Browning model without Centennial embellishments, not cased.
The value listed in 2002 for 100% condition was $595

There is no mention of what the twist rate was for these rifles. I'd say offer $300... if he takes that, grab it and run!

BPS

the reason I said $300 was because of it being a .45. The 50s and 54 (especially the 50) are far more popular after the Jerimiah Johnson movie came out.