FX KING 600 FAC - Air Power!

The FX King gives the immediate impression that it is following in the footsteps of the Crown II, and with a full walk-around inspection, it certainly shares the GRS stock option that was available on certain Crown models. Where the King differs, is the location of the Wika bottle and regulator pressure gauges, now mounted at a 45º angle on the left side of the action. Slightly less obvious is the over-barrel plenum rather than a secondary shroud.

Inside
The new over-barrel plenum on this 600mm barrel is 34mm in diameter and separated into two sections. The muzzle sports a removable collar wrapping a ½” thread that can be used for an additional moderator, and the forward 205mm section can be unscrewed to see the inner barrel. However, unlike previous Crown models, the King, like the Dynamic and Panthera, requires more detailed disassembly to change barrels if that is a desired function. Quite simply though, a very small number of shooters are regularly swapping barrels in the UK and the great benefit is that the barrel liner/shroud/plenum structure is significantly more rigid. When you remove it, you can see the mounting structure and the tighter fitting O-rings that maintain position more securely around a physically heavier inner core.
This rifle has the Superior Heavy STX barrel liner within the 156cc Plenum, and it’s fair to say it’s an FAC-only variant with the capacity to drive very heavy pellets and slugs into the 950-1000fps sweet spot that seems to get the best from FX rifles.

First looks
The King is supplied in a spacious polymer carry case with a new design that will fit the rifle with a scope attached. A single 18-shot magazine was supplied with the .22 rifle on test, but .177, .25, .30, and .35 calibre are also available, although if you are chasing the big energy benefits, then I’d ignore the .177. The new magazines are 13mm deep allowing longer, heavier projectiles, and this improvement has been coupled with a wider slot for the mag’s central position in the receiver.
The main Picatinny rail is now inclined 30 MOA for longer ranges, and just forward of the receiver, on the left and right side, there is more Picatinny rail for accessories. If you flip the gun over, you can see the Foster connector, which is used to fill the carbon fibre 480cc air bottle to the suggested 250 bar. The cap is magnetic, and an adaptor is supplied.

Reliable adjustments
A 23-stage macro power adjuster is sited on the left/rear of the action, with the corresponding micro adjuster in front. These adjust the Mk II AMP regulator within and meant I could adjust the power from approximately 17 to 52 ft/lbs with the pellets and slugs I was using. However, individual tuning styles will affect this. Importantly, you must only alter these when the rifle is uncocked, and they have tactile clicks on all settings, so once you have learned your preferences, you can change and return to your desired values accurately and with confidence.
The right-side cocking lever operates smoothly, and the rotary magazine automatically feeds projectiles until the last one, which activates the automatic hold open. The underside trigger is adjustable and offers a crisp and consistent 2-stage pull weight of 300-grams/11oz. Finally, the right side shows a 2-position safety catch lever.

Stock options
This King was in the Green Mountain version of the GRS stock but it’s also available in brown or grey/black Nordic wolf colours. The vertical pistol grip is asymmetric, with no left-handed option, and although it’s possible to shoot left-handed if needed out in the field, it’s not particularly comfortable. The cheekpiece has 22mm of vertical adjustment to ensure good scope alignment and the comb has been kept relatively narrow so it fits your cheekbone without lateral displacement. The length of pull is adjustable from 13 3/8”-15” (346-380mm). Both adjustments are controlled by push buttons, so no tools are needed. The LimbSaver recoil pad grips well in your shoulder, and on the underside, there’s a hand stop and bag rider, giving excellent control in the prone or bench-rested position.

Housekeeping
For testing, I took a 7-litre air bottle in the truck to the range and set about zeroing and tuning the rifle with a variety of pellets and slugs. For ultimate power, you need to stick with projectiles weighing at least 22-grains, and you get the best performance around the 25-grains+ mark. For long-range shooters, the slugs will offer better ballistics, yet the ultra-heavy JSB Exact Jumbo Monster Diabolos, weighing 25.39-grains, were a firm favourite, and for ground-level vermin within 50m, they would be my choice around farm buildings with ricochet-prone surfaces. The 18.13-grain JSBs were over-stabilised at full power but on setting 13 or below, offering 38 ft/lbs, they were usable for close-in work. I liked them the most on setting 1 with 17 ft/lbs (661fps), but the rifle is a bit excessive to be used at these relatively low power levels.

Results on paper
Up at setting 23, the rifle really hit its mark, and during testing, I shot out beyond 80m. There was a lot of wind about at the time, but it was more about measuring ballistic variables than going for supergroups. The performance advantages of the slugs became immediately apparent in the gusty winds, where you just can’t be on top of all the breeze when you are shooting a very light, low BC projectile. FX’s 22-grain slugs shot nice groups, although the heavier 25.5-grain Zan slugs seemed to show the best balance of performance (912 fps, 47.1 ft/lbs, and a G1 BC of 0.082). Shot-count-wise, the 250-bar fill was giving me three magazines/54 shots while on full power, before it needed topping up. However, the shout count is very dependent on the exact tune and calibre.

Paper chase
The performance on target was consistently dependable, yet this is where a slight quandary arises. The gun is no doubt a precision performer, with some superb ballistics and incredible shot-to-shot consistency from the AMP II regulator and plenum system. So consistent in fact, that when I shot a 20-round string using the 28-grain Zan slugs, the rifle managed a very impressive variation of 4 fps. This was using an overall setting while trying different projectile weights on full power. I never tuned each individually, which is what an owner could do over a longer period.
I used a bottle clamp to shoot with a bipod from most positions yet did shoot from a tripod and with some soft bag rests as well. The tripod clamp locked securely onto the GRS stock without any inconsistency, although there was not much space for it. The bottle-mounted bipod was stable, but you do have to be sure that the bottle stays tight, as the leverage of the bipod is directed through it.
Shot from a bag resting on a fence post, the gun is centrally balanced, and a moderator added virtually zero to what had become a 5kg package that included a scope too. The moderator significantly cut noise, making it quieter than an unmoderated Panthera, which I shot while wearing ear defenders. Once a SAK moderator was added to the King, it became more refined and a pleasure to shoot.

Is it the stock for you?
The GRS stock allows great positional control and head alignment for the right-hander. The bag rider/hand stop is comfortable and stabilises the gun well, with reassuring retention in your shoulder when operating the cocking lever. It’s a shame that there are no sling mounts if you do intend to hunt though.
If this rifle was a centrefire, you would probably term it a ‘varminter’, also known as something precision to shoot from a fixed location at live quarry. The bulk is hard to ignore in more dynamic scenarios, but you are getting the precision in return. The Panthera is rightly a better target-specific tool, thanks to the versatility of the stock systems, as here you are restricted compared to modern chassis systems.

Conclusion
The King 600 is doubtless a very capable high-power FAC airgun, but you must be really sure it is what you need in terms of the overall ergonomic facilities. All of the controls, and especially the deeper 13mm magazine, are significant benefits, but look at the whole FX range and see which one really suits your needs. I will end by saying that the over-barrel plenum is not just about efficiency, as it stiffens and stabilises the barrel for more consistent performance and far less chance of the slightest bump shifting your zero, as I found the Crowns susceptible to this.