A 12-gauge shotgun is arguably the most versatile firearm you can own. Feed it light loads of bird shot and you’re ready for anything from quail to pheasants. Step up to heavy steel shot and you can take on waterfowl from teal to giant Canada geese. Push big charges of BB to T shot and you’re armed up for coyotes and bobcats. Load nearly any shotshell and you’re set to defend the home from marauders.

Then there’s the big-game slug option. It’s not a long-range option, but with the right barrel and load, it can be effective to 200 yards. With today’s best loads and barrels, it’s a slam dunk at 100 yards. That’s more than double the distance from 40 years ago — if you get the right setup. That’s what this article is about.

Slug Guns of Yesteryear

Back in the bad old days, slug guns were notoriously inaccurate because they spit full-bore lead slugs down smooth barrels with chokes near the muzzle. That’s a recipe for inaccuracy. For one thing, you can’t make a bullet accurate until you give it gyroscopic spin via barrel rifling. Adding injury to insult, smoothbore slugs had to be built undersized because ammo makers never knew what choke constriction shooters would use. Squeezing a lead slug from a nominal bore diameter of .729 inch down to the .709-inch diameter of a modified choke, the .699 inch of a full choke or even the .684 inch of a turkey choke could be disastrous  — even with soft, malleable lead. So everyone made slugs undersized.

The Foster-style slug with spiral grooves in it came along in the 1930s. The spirals don’t really spin the bullet, but they make it easier for the slug to squeeze through various chokes. The hollow in the back of a Foster slug creates thin walls that flare under pressure for a good gas seal — increasing velocity and accuracy.

Improved Accuracy

Today, with a multitude of sabot slug shells available to shoot through rifled slug barrels, slug gun accuracy has dramatically improved. The ideal slug gun is built stiff like a rifle. Heavy barrels are screwed to heavy actions. Think Savage 220 Slug Gun, Browning A-Bolt Shotgun and the discontinued H&R Slug Hunter single-shot. But such shotguns are not conveniently general-use shotguns. You aren’t swinging one of these at fast-rising quail or decoying mallards. If you want to optimize the versatility of your bird gun, you need to upgrade yours like I did mine.

Like so many American outdoorsmen, I already own a 12-gauge autoloader for waterfowling, turkey hunting, coyote calling in thick brush and some upland bird hunting. It’s a Mossberg 930. It shoots up to 3-inch shells, which is all the recoil I want to handle. I’ve not seen the need for anything bigger.

But how am I going to make this smoothbore into a deer rifle? By giving it a rifled barrel. This is the key to making any shotgun accurate enough for deer way beyond the traditional 50-yard slug range. Modern sabot slugs have the velocity and ballistic efficiency for adequate terminal performance at 150 to perhaps 200 yards. Combine them with a rifled barrel and you can get accuracy to match.

Mossberg sells a 24-inch rifled slug barrel with an integral cantilevered scope mount base. Replacing my smoothbore barrel was as simple as screwing off the end cap and swapping barrels. Follow directions that come with the new barrel so you don’t forget any of the gas piston rings involved. Mounting a scope was dead simple. I got a versatile 2.5-8x36mm Leupold VX-3i and Leupold rings to fit the Weaver-style bases, set the scope in them, secured it loosely so I could adjust level and eye relief, then tightened everything down.

Zeroing a slug gun can be painful and expensive. My technique for saving time, ammo and my shoulder is this: I bore sight it with a Wheeler Professional Laser Bore Sighter, which sticks to the muzzle via a magnet to project a laser dot downrange. I aimed mine on the side of a barn, then turned the scope turrets until the reticle slid over the laser dot.

At the range I set a paper target at 25 yards and the gun in a Caldwell Lead Sled. My first shots were with Hornady’s Custom Lite 2¾-inch loads, which proved so mild I needn’t have bothered with the Lead Sled. The first hole wasn’t too far off my aim point, but to perfect it, I positioned the gun in the Sled with the Leupold reticle right over my original aiming point, the center bull. Then, without disturbing the gun’s position, I carefully turned the scope’s windage and elevation knobs until the reticle was centered over the bullet hole. Barrel and scope were then pointing to the same spot.

At this point I began accuracy testing at 50 yards by shooting three-shot groups, keeping the gun in the Lead Sled to minimize human induced errors. I worked with 2¾-inch loads only because in my experience those have more than enough punch for good and effective penetration on deer and black bears, but mostly because lighter loads often group better in pump and autoloading bird rifles fitted with slug barrels.

Here’s why: The light shotgun frame and barrel alluded to earlier do a poor job of dampening the violent vibrations of an exploding load pushing a heavy bullet. In pump actions and autoloaders, barrels are secured to the actions merely with a press fit and the tension of the magazine tube cap. This means they are additionally subject to strong, variable and accuracy-robbing vibrations. The heavier the loads fired, the more likely these vibrations are to reduce accuracy. This isn’t absolute, but it’s a safe starting place.

So I began by shooting three-shot groups at 50 yards with the lightest load and worked my way up, chronographing velocities at the same time. Here are the results:

As I’d guessed, the slower, lower pressure, lighter loads proved more accurate than the fastest, with the sweet spot seeming to fall near the middle. Both the Whitetail and SST loads deserved second-stage testing, so I moved the target to 100 yards and shot again. Here are those results:

In the world of precision rifle shooting, groups measuring more than 2 inches are dismissed out of hand. But not so fast — we’re talking about projectiles expected to strike whitetails and black bears at a potential maximum range of 200 yards (not that this is set in stone for every hunter and every rifle). At 200 yards both of these groups would cluster inside of a 6-inch circle. Draw that circle on the center of a deer’s chest and you’ve hit the vitals every time. Put another way, each slug would strike no farther than 3 inches from point of aim. That’s dead-deer accuracy.

Frankly, I was impressed with this degree of accuracy out of an autoloading shotgun with a press-fit barrel. I could hunt with this rig any day, every day in slug-only hunting units. If I felt a crazy need for additional accuracy, I would visit with an accomplished gunsmith to discuss pinning or epoxying the barrel to the action. Both techniques are designed to stiffen the fit for consistency, which leads to better and more consistent accuracy. However, epoxying a barrel into the action means you aren’t removing it and replacing it with a waterfowling smoothbore barrel, so there goes your Most Versatile Gun.

While I credit the 2¾-inch Hornady loads with much of this Mossberg 930’s accuracy, it wouldn’t happen without that rifled barrel. That is the real key. This one features barrel ports that direct escaping gases upward just before the muzzle. This both reduces recoil slightly and muzzle jump appreciably. That’s nice for getting back on target for follow-up shots.

I’m more than satisfied with my versatile Mossberg 930. The Leupold scope means I’m more accurate and can aim more precisely in low light than I ever could with any open sight, and the magnification gives me added confidence.

This really is the most useful, versatile firearm I own.

— Firearms expert Ron Spomer is one of North America’s most seasoned deer hunters. He has worked as an outdoors communicator for more than 45 years and is a longtime D&DH contributor.