Using the Marlin Guide gun 45-70, what would be its effective range for black bears? I have often read that using the 405 bullet it is at best a 150 yard caliber. Thoughts from experience?

It's the rainbow trajectory that limits the 45/70 not power. I took my bear this last spring with mine at about 60 yards and it flatend her. Excellent bear gun! My max range 200 yards and i'm shooting handloaded 400 Speers at 1950fps.

As Ol Bull says, the limit is not the cartridge, it's your ability to judge ranges and knowledge of its' trajectory... The Army used the .45/70 for target competition to ranges out to 1,000 yards...

MacD37
Would you not agree with the idea that 99 and 44/100ths of all big game shots are taken within that 225 yard range?
The 45-70's trajectory would not be much of a handicap at this distance.
I try to shoot 50 or 60 rounds of 45-70 once a month at 200 and 300 yards at steel gongs, off hand. No, I don't hit them every time but I don't miss the 12 by 12 gong by much. I'm using a Winchester 1886 with a tang site.
Jim

Track of the Wolf has tang sights (if that is what you're looking for) for $59-125, I think. Go to this page for the sights.

arkypete : I think its closer to 99 46/100ths.

An entire generation has been raised with the notion that a bullet has to be going at least 2500fps to be usefull. The 45-70 is enjoying a revival of sorts as guys discover that a large, moderately-paced, chunk of lead makes an awesome hole in critters.

I think Garrett's website still has the pictures of Vince Lupros "Big 5" hunt in Africa with his Marlin 1895. He didn't seem to have any problem dropping the bitey/scratchy/stompy beasties with a big chunk of lead.