FN SLP Mark I Semi-Auto 12 Gauge Shotgun


by Jeff Quinn

photography by Jeff Quinn & Boge Quinn

October 27th, 2008




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Over the course of the past several months, I have fired a few weapons from FNH-USA, and have been highly impressed with each. FN builds many of the weapons that are used by our soldiers and Marines in Iraq and Afghanistan, and they are battle-proven, well-crafted arms.

During the past couple of months, I have been playing around a bit with this SLP Mark I semi-automatic shotgun from FNH. The Mark I is built on the short stroke piston principle, and is in function very much like its cousins, the Browning Gold and Winchester Super X2, and owes its lineage to the older Winchester Super X. The design is a good one, and works very well. Upon firing, gas is bled from two ports in the barrel, which pushes upon the gas piston, which in turn pushes upon the sleeve which contains the operating rod. The rod impacts the bolt carrier, propelling it rearward along with the bolt, and a spring pushes the bolt/carrier forward, chambering a shell. The short stroke system works very smoothly, and is cleaner than some other semi-automatic systems. The Mark I comes with two gas pistons; one for lighter loads, and the other for heavy magnum loads, whether they be 2 ¾ or 3 inch shells. Changing pistons takes about a minute, and is easy to do without the use of any tools.

The Mark I wears a twenty-two inch barrel, and has a full length magazine tube which holds eight rounds, for a loaded ready-to-go capacity of nine. The barrel wears a set of good rifle sights, with the front being a fiber optic orange rod, which is very visible in most lighting conditions. The barrel also has a cantilevered scope base attached which hangs over the receiver for the mounting of a riflescope or other optic. The base is not Picatinny compatible, so I could not mount an ACOG or Reflex sight, but it will accept any Weaver style rings. Packed in a hard plastic case, the shotgun comes with two interchangeable choke tubes and a choke wrench. The tubes provided are of improved cylinder and modified constriction, and are also approved for steel shot. The Mark I uses standard Invector choke tubes, of which there are many available from Browning/Winchester, as well as the aftermarket. More on that later. While I prefer a top tang safety to a crossbolt type, the safety on the Mark I is large and easy to use, and best of all, it is easily reversible for left-handed shooters such as myself.

The SLP Mark I is built to be a fighting shotgun. Many call this type of weapon a “defensive” shotgun, and the Mark I can certainly fill that roll. However, it is also well-suited for offense, as well as defense. A twelve gauge, properly loaded, is a formidable weapon at close range, and is also very effective out to 150 yards and beyond when stoked with good quality slugs. Up close, nothing available to the common man equals a shotgun. I have often heard it stated, by people who should know better, that with a shotgun you just point in the general direction and fire. That is not true at all. Across the distance of a bedroom or even down most hallways in a home, a load of shot will open up no bigger than a man’s fist. However, at that distance, that load of bird or buckshot will blast a rat-hole clean through an opponent in a gunfight. You still have to aim the weapon, but across a room, a twelve gauge delivers like nothing else, except maybe a ten gauge. That huge wad of shot is devastating at close range. I prefer bird shot myself at close range, like number 5 or 6, but many others prefer buckshot. Doesn’t matter much a twenty feet. Out farther, like forty yards or so, the buckshot is a better choice, and beyond that, the slug is the load of choice.

It used to be that shotgun slugs were pretty inaccurate at distances exceeding 75 yards or so, but with today’s modern slugs and rifled barrels, a shotgun can be as accurate as a good bolt-action rifle. The key to this is shooting the right slug. One of my favorites is the Winchester Rackmaster. Another is one which I have just started using is the Extreme Shock saboted frangible slug. Made of compressed tungsten, it is built to fragment in soft tissue.

While the Mark I would make a dandy offensive shotgun for police or military, it is also available to the rest of us, and would fill the role perfectly as a bedside shotgun. While pump guns are very good, I prefer a good semi-auto for a fighting shotgun. I do not know why, but many “experts” claim that a pump is more reliable. I do not agree. A good pump gun is more reliable than a bad auto, but a good auto like the Mark I or a Benelli M4 is just as reliable as a pump. I often hear the phrase that “the sound of racking the slide on a pump gun will scare the intruder so badly that he will……..whatever.” I don’t agree with that either. First of all, the sound of racking the slide will do nothing more than give away your position. If you hear someone breaking into your home at two in the morning, it ain’t the local Girl Scouts selling cookies, and the sound of the slide on a pump gun will probably not impress them. The intruder should not know where you are, and he should hear nothing. Maybe he will see a brief flash of light from your muzzle, but the load of shot should arrive before the sound, and he won’t ever hear a thing. I also like the semi-auto for its ability to be fired one-handed if needed. Sure, you can hold a pump gun between your legs and work the slide if necessary, but why? A good semi-auto shotgun is just as reliable as a good semi-auto pistol or rifle. I never hear proponents of the pump shotgun promoting the use of pump action rifles and pistols. I have nothing at all against a good pump shotgun, and they are cheap and reliable, but I like the advantages that a good semi-auto offers for a fighting shotgun, and the SLP Mark I is one of the best.

Now I would like to get into the versatility of this shotgun with the addition of a couple of accessories. FNH-USA markets the Mark I, and all of their shotguns, as fighting guns. With their matte black finish and composite stocks, they fill that role well and really look the part. However, the Mark I can be much more than that, and the key is the interchangeable choke tubes. Many manufacturers of fighting shotguns fit them with a fixed cylinder bore or maybe a fixed improved cylinder choke, but FN has, thankfully, fitted the Mark I with choke tubes. Seeing this shotgun as much more than just a gun for resolving social conflicts, I called George Trulock at Trulock Chokes and ordered one of his legendary turkey choke tubes, and also one of his rifled choke tubes. Filling its role as a bedside gun every night, the Mark I is very well suited to make an excellent turkey gun. It can easily handle the heavy three inch magnum turkey loads, the twenty-two inch barrel and rifle sights make for a handy woods gun, and the sling swivels are also an excellent feature on a hunting gun. Screwing in the Trulock turkey choke, I tested the Mark I with number 5 shot three-inch magnum loads out to sixty yards, and the gun patterned perfectly for bagging a turkey. The matte black finish and plastic stock makes for a good, rugged shotgun that can withstand being banged around in the woods without fear of damaging the finish, and the non-reflective finish will not spook the birds.

I have wondered for a while now if a rifled choke could stabilize a modern slug for good accuracy as well as could a fully rifled barrel, and that is why I ordered the Trulock Slug Mate extended tube. I mounted a Mueller illuminated 2 to 7 power scope atop the cantilevered mount with Warne Quick Detach rings. Having a scope that can be added or removed without tools adds greatly to the versatility of this shotgun. I tried three different Winchester slug loads that exhibited good, but not excellent accuracy from the Slug Mate in the Mark I, grouping into about one and one-half to two inches at fifty yards, which is acceptable for deer hunting at those ranges. However, the Extreme Shock BD-50 round was really impressive, grouping into one ragged hole at 100 yards! I was expecting pretty good accuracy, but nothing like that good! These loads have a saboted compressed tungsten bullet loaded into the 2 ¾ inch shell, at an advertised velocity of 2000 feet per second. I tried repeatedly to get a reading over my chronograph with these loads, but could not, perhaps due to the muzzle blast or the sabot separating from the bullet as designed. I will just have to take Extreme Shock’s word for it, which I have no reason to doubt, as I have found their advertised velocities of their other products to be accurate. With a bullet weight of 325 grains, these loads should be devastating on flesh. I hope to try these out on a Russian boar hog very soon.

I fired the Mark I with a variety of loads from light one ounce target loads to heavy turkey loads and the aforementioned high performance slugs. The shotgun cycled perfectly with every load tested. The gas pistons are marked for loads below one and one-half and above one and one-half ounces, but I found that the gun would cycle just fine with the heavier gas piston in place, and recommend its use for all of the slug loads, regardless of weight. I tried the lighter piston with some of the slugs that were below one and one-half ounces, but the heavier piston is highly recommended for the Extreme Shock slug load. Even during extended bench testing sessions with the Mark I, recoil was not bothersome. The gun is very soft on the shoulder, and that is another reason that this gas-operated auto is a good choice for a fighting shotgun.

A good semi-auto shotgun of the quality of this Mark I is not inexpensive, but it is a good value. Selling for about the same price as a quality handgun, the Mark I offers much more power for home defense or as a police shotgun, but the versatility of the Mark I to easily fill the role of a turkey gun in the Spring and a deer gun in the Fall, while protecting the homestead all year long makes the SLP Mark I a really good buy.

Check out the entire line of quality FN products at www.fnhusa.com.

To order a wide variety of high performance shotgun chokes for almost any shotgun made, go to www.trulockchokes.com.

To order Extreme Shock ammunition, go to www.extremeshockusa.net.

To find an FNH dealer near you, click on the DEALER FINDER at www.lipseys.com.

To order FNH products online, go to www.galleryofguns.com.

Jeff Quinn


For a list of dealers where you can buy this gun, go to: To buy this gun online, go to:


Trulock Slug mate rifled slug choke tube.



Trulock turkey choke.



Winchester's slug loads.



Extreme Shock slugs.



Winchester's Extended Range turkey load.



A load of number 8 bird shot at 20 feet, typical across-the-room distance.


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- Boge Quinn



Click pictures for a larger version.


FNH-USA's SLP Mark I shotgun (right) is the same length as a 26-inch 20 gauge double gun.



Safety button is large and reversible for left-handed shooters.





The SLP Mark I comes with a good set of rifle-type sights...



...and a cantilever scope mount for optical sight use.



Mueller illuminated scope.



Synthetic black checkered stock features sling studs, black plastic grip cap, and an excellent recoil pad.





Gun easily strips for cleaning & maintenance without tools.



Comes with two interchangeable gas pistons for light and heavy loads...



...as well as sling swivels, extra choke tube, and choke tube wrench.





Gas ports in barrel.