How I Mount a Chronograph and Bipod on the FX King and AEA Zeus with the Saber Tactical Bottle O-Clamp and King Chassis

Over my last couple of competitions, including the run that landed me first place at Extreme Benchrest 2025, one of the biggest changes to my bench routine has been parking a chronograph right next to the rifle and watching velocity shot to shot while the match is actually happening, because if something weird starts creeping into the string I want to see it in real time instead of finding out later when I'm staring at a group that opened up for no obvious reason. The catch is that a chronograph, a bipod, and a tripod all need somewhere solid to live on the gun, and on a bottle gun like the FX King that is not always as simple as it sounds, so this Field Notes is all about how I solved that with the Saber Tactical Bottle O-Clamp on a stock-configuration King, how the Saber Tactical chassis for the FX King handles it when you want the full chassis route, and why I am excited to put one of the smaller O-Clamps on the AEA Zeus for next deer season.

Hero photo: my FX King in the bronze Saber Tactical chassis at the woods range, with the FX Pocket Chronograph Pro on its tripod beside the bench. Photo: @upnorthairgunner on Instagram.

Why Run a Chronograph at the Bench During a Match?

When you are shooting a benchrest card at 100 yards, the score really comes down to precision, meaning how consistently the rifle can stack shots into a tiny group, and velocity consistency is one of the biggest pieces of that puzzle because every fps of swing turns into vertical at distance. I used to treat the chronograph as a tuning tool that lived on the workbench at home, but these days I want it at the match too, sitting there reading every shot so if the regulator starts doing something funny or I get a shot that drops off, I know right away whether it was me, the wind, or the gun. During a match you really don't need a big downrange radar reading the projectile out past 100 yards to spit back a ballistic coefficient, and for that kind of work I still go to the FX True Ballistics Chronograph, which is hands down the best chronograph in our sport right now. At the bench, all you are really after is muzzle velocity and those shot to shot fluctuations, and that is where the little FX Pocket Chronograph D1 earned its spot in my range bag.

The D1 gives you feet per second, foot pounds of energy once you enter your projectile weight, and different units of measurement right on the screen, and it stores every shot string in the FX Radar app on your phone so you can go back through your configurations later, plus firmware updates get pushed to the unit wirelessly from that same app. It takes up basically no room in a gun case, which is exactly what you want when you are already hauling a bag rider, a rest, pellets, slugs and a cooler to the line.

Where Do You Mount a Chronograph on an FX King Without Touching the Barrel?

The D1 comes with quite a few attachments in the box, and one of them is a barrel mount that just straps on with rubber bands, which works fine if you plan on always shooting with the chronograph on the gun. If you are really getting into tuning though, I highly recommend not having anything touching or hanging off your barrel, because you want the mechanical and structural harmonics of the rifle to stay as pure and repeatable as possible, and a chrono that is on for one session and off for the next is a variable you just don't need. What I do instead is use the 90 degree Picatinny attachment FX includes, which pushes into the side of the unit with a couple of little tabs and rotates to lock, and then that whole thing clamps onto a side Picatinny rail where it is completely off the barrel.

The problem a couple of years ago at the Northeast Airguns Classic was that I was running my FX King bone stock in a gorgeous wood laminate stock from my buddy at GRS Rifle Stocks, and as beautiful as that thing is, there was no easy way to put a bipod on it or drop it onto a tripod without adding rails or modifying the platform. Saber Tactical's original bottle clamp was absolutely usable right out of the box as a basic bipod mounting point, but loading into a bipod during competition is where I noticed I wanted a little more rigidity, and that is exactly the gap the O-Clamp fills.

The O-Clamp on my laminate-stocked FX King, with the FX Pocket Chronograph D1 on the side Picatinny using FX's 90 degree mount and the bipod underneath, so nothing is hanging off the barrel. Photo: @upnorthairgunner on Instagram.

How the Saber Tactical Bottle O-Clamp Locks Onto the Bottle

The O-Clamp wraps the full circumference of the bottle, and on the inside there are rubberized inserts that get tensioned by a couple of grub screws, so it does not mar up your bottle and you really don't need to crank on it, just give the screws a little bit of a snug up. Once it is on there it honestly feels like it is permanently attached to the bottle, completely locked in, and that is the rigidity I was missing when I was loading into a bipod at NAC. The body is 6061-T6 aluminum with a matte black anodize, and every version has Picatinny on the side, which is the spot the D1 lives on my setup, with either Picatinny or Arca on the bottom depending on which model you grab. The adjustable inserts also matter more than people think, because bottle diameters can vary a little even within the same model, so the clamp can take up that difference instead of you shimming it with tape.

Sliding the O-Clamp for Bipod vs Tripod Balance

The other thing I love is that the clamp slides forward and backward on the bottle before you snug it, so you can dial in the balance point for whatever support you are running that day. For me on a bipod, I like kicking it out as far forward as I possibly can, because that gives me more stability in the rear and the rifle settles into the bag rider a lot more naturally. If you want to run the same gun on a tripod though, you want that balance point a bit further back closer to the center of mass, so being able to loosen two screws, slide the clamp back, and lock it in again is actually really critical when you go from a bench day to a field day.

Up close on the FX bottle, the O-Clamp wraps all the way around and the bipod rides underneath, and the whole thing slides fore and aft to set balance. Photo: @upnorthairgunner on Instagram.

Picatinny Bottle O-Clamp
Picatinny bottom and side, 52mm, 60mm and 63mm.
Shop the Picatinny O-Clamp

Arca Bottle O-Clamp
Arca bottom with side Picatinny, 52mm and 60mm.
Shop the Arca O-Clamp

Going the Full Chassis Route: Saber Tactical Chassis for the FX King

If you would rather stop working around the factory stock altogether, the Saber Tactical chassis for the FX King is the other way to solve all of this, and it is the setup in the hero photo at the top of this post. The chassis already has an Arca and Picatinny front rail plus M-LOK on the sides, so the bipod, the tripod clamp, and the chronograph all have a dedicated home without adding anything to the bottle, and you get tool-free adjustment on the cheek riser, butt pad and length of pull, a QD sling swivel, and a castle nut mount on an AR buffer diameter tube. It comes in grey or bronze and runs about 6 pounds, and mine is the bronze one you see in these photos.

For this test I had the King in the Saber Tactical chassis at the woods range with the FX Pocket Chronograph Pro set to the medium projectile trigger sensitivity on the 200 to 1,800 fps setting, ringing steel from shootingtargets7.com. I started with FX 44.8 grain slugs just for demonstration, and the first shot read 974 fps, and the 10 shot string came back with a 7.1 fps extreme spread and a 2.2 fps standard deviation, with that last shot dropping off a little bit. That gun is tuned for the 50 grain though, so I hit new string, loaded the 50s, and it was right where I left her with an extreme spread of 5.7 fps and a standard deviation of 1.8 fps, and the last shot of that string read 934.1. What I love about the Pro is that it did not seem finicky at all about where it sat on the table relative to the barrel, even as I moved angles and backed it off a bit, and it also gives you a BC range over the string when you pair it with the app.

Just for fun I ran the same chronograph on the rimfire side with a Bergara B-14R and an 18 inch barrel wearing a Dead Air Mask in our Saber Tactical Menace chassis, and CCI Quiet pistol ammo averaged 902 fps with a 34.2 extreme spread and a 12.2 standard deviation, while CCI Standard Velocity ran about 1,091 fps with a 47.4 extreme spread. I love my rimfires, but that is exactly why a well-tuned PCP absolutely dominates on extreme spread, and why I keep a chronograph on the bench to make sure it stays that way. If you want the rest of that Menace story, the Menace deer build Field Notes covers the 6.5 Creedmoor side.

Running 10 shot strings on the King in the Saber Tactical chassis, with the chrono reading every shot from its tripod beside the rifle. Photo: @upnorthairgunner on Instagram.

FX King Chassis Fitment: Bottles, Extension Rail and Conversion Kit

The King chassis fits the FX 480cc and 580cc bottles as it comes, and if you are running the 700cc bottle you will want the Saber Tactical Extension Rail so the front end covers the longer bottle. If you are on an FX Panthera or FX Dynamic instead of a King, the Panthera and Dynamic Conversion Kit (ST0093) is what lets that action drop into the same chassis, so you can get the same rail layout for your chronograph and bipod on those platforms too.

Chassis for the FX King
Grey or bronze, Arca and Picatinny front rail, M-LOK.
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Extension Rail
For 700cc bottles on the King chassis.
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Panthera and Dynamic Conversion Kit
Puts a Panthera or Dynamic into the King chassis.
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The O-Clamp on the AEA Zeus .72 for Deer Season

The reason the different O-Clamp sizes get me fired up is the AEA Mark II Zeus .72 caliber I was hunting with last deer season, which is an absolute monster and an air-belching beast of a big bore. AEA turned it into a bullpup, so all that weight that used to hang out front and made it really tough to carry in the woods moved to the rear, which makes it way more shoulderable when you are walking in. The flip side is that when I set it up on my BOG DeathGrip tripod, having all that weight to the rear made it pretty rear heavy, with the DeathGrip grabbing it right around the bottle. What I really wished I had was a Picatinny rail I could lock into the clamp on my tripod head and know that thing was not going anywhere.

That is exactly what one of the smaller O-Clamp sizes does for a bottle like the Zeus, because it just slides right over the top of the bottle and you can set it forward if you are running a bipod from a blind or a bench, or move it all the way back and lock it in as a perfect mounting point for a tripod. For anybody hunting with a heavy big bore bullpup, a rigid Picatinny or Arca point on the bottle opens up a lot better tripod options and makes these big guns far more practical in the field. Measure your bottle with a set of calipers before you order so you grab the right size, and if you want the full clamp lineup side by side, our bottle clamp fit guide walks through every size.

My AEA Zeus .72 Mark II on the BOG tripod in the snow last winter, the rear-heavy bullpup setup that made me want a rigid Picatinny mount on the bottle. Photo: @upnorthairgunner.

AEA Zeus on the bench with Saber Tactical gear, including a Saber Tactical bottle clamp ready for the bottle. Photo: @upnorthairgunner.

What About the Original 60mm Picatinny Bottle Clamp?

The original Saber Tactical 60mm Picatinny Bottle Clamp is still among the most adopted Saber Tactical gear within the precision airgun community because it is a simple, proven bipod point for FX carbon and steel bottles, the RAW HM1000X, Daystate Red Wolf and Air Wolf, and the Brocock Commander and Bantam. If you are mostly plinking or hunting off a bipod and you don't need a side rail for a chronograph, it is a great way to go, and if you are loading hard into a bipod at a match or want that side Picatinny, PJ and I recommend stepping up to the O-Clamp.

60mm Picatinny Bottle Clamp
The original Saber Tactical bipod clamp for 60mm bottles.
Shop the 60mm Bottle Clamp

FAQ: Saber Tactical Bottle O-Clamp, FX King Chassis and Chronograph Mounting

Can I mount an FX Pocket Chronograph to the Saber Tactical Bottle O-Clamp?

Yes, every version of the O-Clamp has a side Picatinny rail, and the FX D1 includes a 90 degree Picatinny attachment that pushes into the chronograph and rotates to lock, so it clamps onto that side rail and stays off the barrel.

Why shouldn't I mount a chronograph on the barrel?

If you are serious about tuning, anything hanging off the barrel changes its mechanical and structural harmonics, so unless the chronograph lives on the gun every single time you shoot, we recommend a side rail mount so the barrel stays clean and repeatable.

What is the difference between the Picatinny and Arca Bottle O-Clamp?

Both have Picatinny on the side, and the difference is the bottom surface, which is Picatinny on the Picatinny O-Clamp (52mm, 60mm and 63mm) and Arca on the Arca O-Clamp (52mm and 60mm), so pick the one that matches your bipod or tripod head.

Will the O-Clamp scratch my air bottle?

No, the inside uses rubberized inserts tensioned by grub screws, so it is non-marring and only needs to be snugged up, not cranked down.

Where should I position the O-Clamp for a bipod versus a tripod?

I run it as far forward as possible on a bipod for more stability in the rear, and further back toward the balance point when the rifle goes on a tripod, which is especially important on rear-heavy bullpups like the AEA Zeus.

Which bottles fit the Saber Tactical chassis for the FX King?

The King chassis fits FX 480cc and 580cc bottles, the 700cc bottle needs the Saber Tactical Extension Rail, and FX Panthera and Dynamic owners need the Panthera and Dynamic Conversion Kit (ST0093).

If you have questions about which O-Clamp size fits your bottle or how to set up a chronograph on your King, reach out to us at Saber Tactical and PJ and I will help you get it dialed, and if you want to see more of my bench and hunting setups, come hang out with me on Instagram at @upnorthairgunner or on YouTube at UpNorth AirGunner, where the full O-Clamp and D1 video and the FX Pocket Chronograph Pro video are up.