Big bullet or projectile

[foamcupman]

Hello all,
A friend of mine found this in his backyard, about 6 inches deep. He lives in downtown Mason, MI. It looks like a big bullet or projectile. It's made of very hard lead, I can't ding it with a fingernail so it's harder than a normal shotgun slug. It looks a lot like a typical Foster slug for a smoothbore barrel.

It's 1-15/32 of an inch in diameter and 1-17/32 of an inch long. It weighs 331grams, which is 11.68oz.

For a sense of scale, it's sitting next to a 20 gauge Foster slug.

Any ideas what it is?

Thanks!

 

[Jim West Pa]

Definately not from a smooth bore.
There's rifling grooves in it.
Possibly a Hughes.
How many grooves on it?

http://civilwarwiki.net/wiki/1.5_inch_Hughes_Breechloading_Cannon

 

[foamcupman]

I counted 16 grooves on it. I found a utube video of a Hughes being fired and they showed the projectile but it was about 2x longer than the one I've got.