I have a Remington 870 slug gun for deer / pig hunting in a shotgun only section of Fort Hunter Liggett. Looking to see if upgrading to a better barrel will a difference.

Depends on what you have now and what difference you want it to make. For the 870 Rem, a fully rifled barrel with a cantilever scope mount is about as good as it gets. Experimenting with different slug loads to find what it likes best is a key to any of them.

Current barrel is a Remington rifled barrel with cantilever mount. Looking for opinions on Hastings, etc...

Ted,
You may get better performance but maybe not.
I trust you've tried a bevy of sabots?

If you use the gun solely as a a slug gun to hunt deer, go to your gun smith and get the barrel permanently mated to the frame. I did this with mine and it made a world of difference. Another thing you could do is get the trigger smoothed up a bit or replaced. As others have said, you've tried many different slugs through it, right? Different guns shoot better with different loads. With quality slugs starting about about $2.00 a piece, I'd want the most accurate I could find without breaking the bank. My gun likes Hornandy SST's, but who knows what flavor yours will lean towards.

Tried the 5 lead free loads I could get my hands on so far, plan to drop it off at a gunsmith later this month to be pinned since this is only used for pig hunting.

This. I have/had a Hastings, a Remington, and Mossbergs. All shot more than acceptable with the slugs they liked, but they didn't all like the same slugs. My current two both shoot the Lighfield EXP well enough. The one also like the Federal Barnes slugs and I still have two boxes, but I still just use the Lifghtfields. Easier to just have to keep one brand around.

As an aside, I've had better luck, accuracy wise, with 2.75" slugs than the longer versions.

Slugs that shot ok one day are less accurate the next, hopefully pinning the barrel and going to a solid scope mount will correct that issue.

I sure like my Savage 220.

++1 on the savage 220

Ted,
I used to have an 870 (cantilevered rifled barrel).
It shot very well but I must say, with 3" slugs, some days I was less than enthusiastic in testing/sighting slugs from the bench.

Don't discount that part of the equation. And, rather than a new barrel, you might consider an 11-87 with the cantilevered barrel.
They can be had all over in WI (due to a recent rule change allowing rifle hunting statewide).

Just a thunk.

i bought the hastings cantilever barrel then my county went to rifle.But in testing mine liked lightfields and wasn't enough better for me the smooth bore with fosters would put 3 touching at 75yards.The sabots cost twice as much

I've only used full-diameter slugs in smoothbores, but I've read, and been told by sabot users, that plastic residue from the sabots affects accuracy, often after just a few rounds.

I second the comment on Hastings cantilever mount scope barrels and Lightfield 2.75" slugs as being the most accurate for my 870. Much better accuracy than smooth bore and Foster style slugs for me.

I didn't see a difference. Lightfield, Federal/Barnes and Remington Accutips have been very accurate for me in a variety of slug guns but each is different. If you are serious about accuracy, I'd save a few more bucks and get a Savage 220. And if your currently shooting a 12 gauge your shoulder will thank you .

You won't gain anything much with buying a Hastings. I did it because I wanted one for an LT20 and Remington didn't make one. Pinning the barrel to the action makes the biggest difference. TarHunt will pin it for you or semi-permanantly install an ER Shaw barrel. I pinned mine myself. It's not too hard. My suggestion would be to buy a Savage 220 and be done...

Savage 220 will out shoot most of my rifles.

For about the price of a new barrel you could get an H&R ultra slug. The 20 ga. that I have is unbelievably accurate. The down side is that they are ugly and very heavy. If I was starting over as others have said the Savage is hard to beat.

Shooting a slug gun is unlike a rifle, I had a father son in up state NY build me a custom 11-87 with a badger barrel, pinned, and these guys REALLY knew slug guns. I also gleaned much info from the guys at Lightfield slugs.

Its important to hold the forend with your hand between the front bag and not just let it rest and wrap what would be the front hand around the rear bag. If you dont the gun will appear to shoot high, WAY high, than if you hold the forend.

Anyway my point is form is huge with a slug gun, more important than with a rifle by a long way. call the guys at Lightfield slugs and have a chat with them, they were a big help to me. That and shoot it a LOT!

http://www.litfld.com/news-resources/shooters-toolbox/slug-gun-sighting-technique/

instead of messing with barrels, I would try more slugs. I have a couple slug guns and they take a while to find what they like. It seems like a long time after taking 3 inch slugs beat you on the bench.

I've have seen slightly better accuracy overall from Hastings barrels over the Remingtons over the years; dunno if twist rate or finish.

Never cleaned a rifled slug barrel(just kept gas ports clean/functioning if they were part of the barrel), unless some dolt fired Brennekes or Fosters through them....

+1
Nothing like cleaning a rifled barrel with a few boxes of Brenneke's down it