So I normally hunt in northern Michigan where it's alright to use centirefire rifles, so I normally take out my 30-30 or 300 Win Mag depending on the distances I'll be shooting.  I've never hunted lower MI where it's a limited firearm zone meaning shotguns or rifles that can shoot a pistol caliber with a straight wall case 1.8" or less.  I have an S&W 500 which is legal to use, and I can shoot it good out to 25 yards but have never shot beyond that and don't know that I'd be comfortable doing so.  I got invited to start hunting with a guy who hunts on private property in southern Michigan, so now I need a gun I can use.  I have two semi auto shotguns: a Benelli Super Black Eagle 3 and a Beretta A400, but neither of them shoot rifled slugs worth a damn.

I need to get a new gun that I can use in the limited firearm zone, so my options right now are a 450 Bushmaster or a shotgun with a rifled barrel.  I'm curious what everyone thinks the best choice is?  For the 450 BM my options are either build an AR, or buy a Ruger American Ranch or Savage 110 Wolverine.  For the shotgun my only option I am considering is the Browning BPS Cantilever Buck.  I used to have a BPS that I sold and I miss it, so that's really the only shotgun I will consider.

I've never shot a rifled shotgun with sabot slugs, so I am curious what the range is on them and how it compares to the 450 BM.

The hot “new” trend in slugs is 20ga because MV is significantly higher than 12ga, providing a flatter trajectory and so greater useful range.

However, I’ve hunted for years with a pump 12ga with cantilever barrel and have no complaints. I use Lightfield slugs and useful range is about 110yds, limited by the rainbow trajectory. The Lightfields are accurate enough to use all of the range, but the vast majority of deer I’ve killed have been inside of 50yds.

I suspect your regs would also permit the use of a muzzle loader, and there may be a separate muzzle loader season. I set up my muzzle loader for about 125yd point blank range using 2/3 of the max powder or pellet load. I dropped charge from the max because most opportunities were within the 125yd range, like with my shotgun. So selecting a muzzle loader rather than a shotgun or 450 Bushmaster is perhaps an idea that makes sense.

Get a Bushmaster AR upper in 450 or a Ruger American in 450.  Top it with the LPVO of your choice or this one by Leupold:

VX Freedom 450

You are generally limited to 125-150 yds. with a rifled barrel shotgun if you can find sabot slugs that it likes extremely well.

The 450 Bushmasters are easily 250 yard guns and generally very accurate.

Both should work fine.

Though rifled slugs guns with sabot slugs can be legitimate 200 yard guns in my experience and from talking to a lot of guys over at Shotgunworld.com forums, getting a 12 or 20 gauge rifled slug gun to do 200 yards with good accuracy though possible is not easy.

450 Bushmaster on the other hand is pretty easy to setup to do 2.0-2.5 MOA or better out to 200 yards especially if you're a reloader.  I am using Barnes 275gr TSX in my 450 Bushmaster AR and the accuracy has been very good.  If I can just get a deer in my sights.  So far I have bagged one Trash Panda and one Tactical Opossum this season.  450 BM and that Barnes bullet does really unpleasant things to varmints, far more damage than I thought that bullet would do to a small critter.

If you already have a shotgun that would be the only reason not to buy a 450 for Mi deer. The ruger go wild is the most popular factory gun.
Shotgun rifled slugs cost at least twice as much and are less accurate . One inch groups at 200 yards are the norm with custom guns and we zero at that distance.
Last year I shot a doe in late does season at 309 yards with a custom Remington 450 . She took one step and went down . We've been practicing at 400 yards and getting groups around four inches.
Wind is the biggest challenge 10 mph full value will drift about eighteen inches at four hundred.

Thanks for that.  I just bought a Spikes lower receiver so it looks like I'll be going with the Bushmaster.  I was considering 50 Beowulf for a minute, but I want to buy all my own parts and saw that nobody sells them separately.  You have to either buy a full rifle or an upper from Alexander Arms.

We had a couple upper come thru on consignment not sure how they shoot. Are you in the CWD area you  can hunt with your 450 in muzzleloader season this year ?

I'm not sure what area my buddy hunts in.  I don't remember where he said it was.  Where I hunt up north for rifle season is DMU 487 and I believe they are a CWD area.  I'll still be going up to 487 for regular firearm, and then I'll go with my buddy for late firearm doe season to his spot on private land.  I won't be able to go this year though as I am saving up for a vacation so I can't build the 450 BM outright just yet.  Gotta order parts and do it piece mail so it probably won't be ready until Summer.

Similar in Iowa. I struggled for years with different 12 ga and 20 ga shotguns with slugs the conclusion is Slug Guns Suck, Totally Suck, not just a little.  But I have high expectations having grown up in Texas hunting with 30-06. Because you are limited to straight wall cartridges the pick of the litter are 45-70, 44 mag and 357 mag.  Yes you could do 450 Bushmaster and they have been selling lots of them in the Ruger American bolt action. LINK  Henry has started making some single shot rifles in these calibers. LINK The Ruger American has been a popular choice here. LINK  Marlin 45-70 lever guns also worth consideration.  
Or you could probably use a musket and that is what I have killed most of my deer with here.  Actually if you use a scope for a musket on a 45-70 or 450 Bushmaster it should be very close on the ballistic reticle.

In MI we are limited to 1.8" cartridge length so 45-70 is a no go.

I switched this year from an 870 Express Magnum to a custom 450 AR.  I am chasing the longer range and I think I’m onto something.  I killed a doe at 125yds, and it really didn’t feel like a difficult shot.  With my 12ga, I didn’t use a optic, it would have been pushing it.

Agreed, slug guns suck. Every time I found an accurate slug for my gun, they would discontinue or change it. At 3-5$ per slug, screw that. A box of 450 is 28$ or less on sale. More shooting means more practice and more dead deer.
Plus a 450 in an AR or Ruger bolt gun is lighter, shorter, and more trim than a shotgun.
I got so sick of the slug thing I hunted with a handgun for 4 years before Ohio allowed straight wall cartridges.

Definitely go to the 450 I went from a rifled SBE2 to a 450 bushmaster ar last year when the law changed here in Iowa way more accurate and a lot cheaper to shoot not to mention in the AR platform you have a very handy much more customizable weapon.

The ruger(and I think savage) bolt actions  would also be great options.

Ended up getting a Ruger American Rifle in Go Wild camo in .450 Bushmaster.  My LGS got one in for $530.