I have a Remington Super Magnum and a Mossberg 930 JM pro.
I am very familiar with the 930 as I use it in 3 gun but it does shoot slugs high. The Remington is poa for the most part. I guess my real question is which is more advantageous: a 3.5" camber or semi auto capability? I will be using buck shot which needs to be tested in both yet, but looking for some general opinions.

Thanks

Take what you shoot best at acceptable ranges.  

Don't nerd out about it.  Properly placed buckshot makes shit die.

I don't think either 3.5" chamber nor semi-auto capability are necessary or advantageous for deer hunting with a shotgun.

When WI was all shotgun(in the southern half of the state) I used a regular ol' 870 express magnum with 2.75" slugs.  Kilt them dead.

Whichever one you're more comfortable making good shots with is your winner.

When I hunt deer in buckshot only areas of Virginia, I use a 930 with 3" 00.  I like the extra pellets in the pattern from going up to 3".  I don't know if jumping up even further in recoil to 3.5" is worth it.  

My best advice is buy a couple brands of buckshot then try out your shotguns.  Is your 930 JM Pro ported?  My 930 is ported, and I believe the porting may be interfering with Flite Control wads, because my 930 groups regular buckshot and Federal Flite Control the same.

spend the money on a rifles slug barrel and buy sabots.

if your shots are under 75 yards 2 3/4- 3 inch shells are all you need.

Some areas of Virginia are buckshot only.

OP, are you hunting with dogs?

ohh..
its illegal here, but people use it when running dogs illegally.

My recommendation?  Don't use buckshot.  I know its tradtion in many places, but a great many people simply don't really know how poorly it performs.  If you insist on using the buckshot, pattern it.  Use whatever shoots tightest.  the problem is this:  Many people might try shooting a round or two at 15 or 20 yards, but few ever pattern the stuff at 40,45,50 yards.  at those ranges a lot of shotguns are miserable, and instead of a half a dozen pellets in the vital area, you've got one or two in the lungs, a third in a shoulder and another somewhere in the guts.  No one would advise hunting deer with a .32 ACP pistol but compare energy, velocity and bullet diameter.  The average 00 buck is basically a 32 ACP performance wise.  And 00 buck works when you can get 5 or 6 of them into the vitals.  Thats really difficult with many shotguns.  And most guys won't pass up a 50 yard shot on a 12 pointer if the shotgun is loaded with buck.  That usually means a poorly hit wounded deer.

Use a simple foster slug in whatever gun shoots it best.  call it good.  The slugs work soooo much better than buckshot

Really need to figure out what kind of range you will be shooting at to figure out what kind of load you are able to use for that range.

If using buckshot for some reason, get a Buckkicker choke tube and go with 3.5" Federal premium buckshot (18 00 pellets).  It is devastating in my 3.5" browning gold.  Slugs can be more accurate but if you want 100 yrds you need to try several brands of slugs to find the one you gun likes.