03Tuning the contact patch

The Kraken arms and protrusions

The Kraken has a modular arm section, and this is the part most people miss. The arm is what presses the nub into the bucking, so changing it changes the shape and the length of the contact patch on the BB — and the contact patch is what sets the character of the flight, not just how much lift you get. Same chamber, swap one part, different rifle.

Both S2 and S3 want a large hop window to work in — Stalker Morpheus barrels, or other GBB/unbridged barrels with big square windows. That is not a coincidence: it is the same reason the Dual Bore Hybrid is the barrel we point you at two sections down. Changing a protrusion on the Kraken takes under a minute.

Protrusions for the S3

Only relevant if you run the S3. The Tigra and Prowler are CNC aluminium; the 60° and 75° Prowler rubbers are the softer knots. Harder protrusions hold their shape under heavy hop pressure and heavy BBs; softer ones conform more and are kinder to the bucking. Cold weather stiffens rubber, which is why having two on hand is worth more than picking the perfect one.

Which combination suits you comes down to BB weight and how far you actually shoot, so ask the assistant at the end of this section with your setup rather than guessing.

04The rubber that touches the BB

Buckings

The bucking is the only part of the rifle that actually touches the BB, and it has to match the chamber you picked above.

The Kraken buckings are the VSR-type side: the Gen 2 concave is the current one, the Gen 1 is still stocked for builds already set up around it, and the SR hop bucking covers SRS and TAC-41. Concave means the contact patch wraps the BB instead of pressing on a single line, which is what keeps a heavy BB stable at range.

Silverback flat hop, by hardness

These are the AEG-side rubbers for the FAST and the stock chamber, sold by durometer: 50, 60, 70 and 80. Lower number = softer = more grip and more hop for the same adjustment, but it deforms sooner under a heavy spring. Higher number = harder = holds up to hot setups and heavy BBs, but needs more pressure to bite. On a 2.8 J rifle with 0.40 g, the 60–70 range is the usual starting point.

06Air system

Pistons

The piston is half of the noise your opponent hears. It is not only about how much energy it moves, it is about how it stops at the end of the stroke.

The Stalker Scorpion lets you tune piston mass, cup and airbrake, which is the way to soften the mechanical slam without giving up energy — an airbrake traps a cushion of air ahead of the piston so it decelerates instead of hammering the cylinder head. The Silverback Variable Mass is the factory part and plays the same mass-tuning game. Both are shown here, side by side, so you can compare them properly.

08Energy

Springs, joules and the legal limit

Every spring in this section is 13 mm outer diameter, the SRS / TAC-41 / SSG / VSR size. Rapax are hand-made in Europe and their pitch is not only power but running quieter, which matters on a rifle built around being silent.

To play in Spain: 2.8 J

This is the one most people buy. It ships with a spacer, because no two builds are sealed identically — the spacer is how you dial in just under the limit instead of going over it.

The Rapax scale, by power

We quote the colour grades rather than exact joule figures on purpose: the real energy depends on your cylinder, your air seal, your barrel and your BB weight. Two rifles on the same spring do not chrono the same.

Silverback, rated in newtons

Silverback labels by spring force in newtons instead of joules: 90 N, 100 N, 120 N, 150 N, plus the M130 and M150. More newtons means more compression force and more energy, but also a harder bolt pull, more piston slam and more mechanical noise. There is a point where a stronger spring costs you more in stealth than it gains you in range.

10Mounting

Top rails

Three of these are A2/M2 top rails and one is not. Read your receiver before you order — Silverback is explicit that the A2/M2 rails fit the M2 variant only, and are not compatible with the SRS A1 or the plain SRS A2.

Flat A2/M2 rails: short or long

The difference is how much they cover. The short one spans the receiver plus the short handguards (HDG-06 aluminium or HDG-07 polymer) and ships with 7 screws and 2 M-LOK nuts; the long one covers the receiver plus the long HDG-05 handguard, 8 screws and 3 nuts, so the optic and anything mounted up front share one continuous rail with no step between them. 6000-series anodised aluminium, licensed Desert Tech.

The canted rail, and when you actually need one

There is a canted option: the long A2/M2 rail also comes in a 30 MOA canted version, sloped down at the front towards the barrel. What that buys you is usable elevation adjustment. A scope has a finite amount of internal travel, and the further out you zero, the more of it you burn just holding the crosshair up. Tilting the whole rail down at the muzzle gives the scope back that travel, so you are not sitting at the end of the turret at distance.

The trade-off: on a flat rail your mechanical zero sits in the middle of the range, which is where you want it for close and mid work. At the 2.8 J the law allows in Spain you will not run out of elevation, so for most players here the flat rail is the right answer and the canted one is for export builds and open-limit fields.

For the A1

One rail here is not an A2/M2 part at all: the SRS Long Handguard Rail (SRS105) is nylon-reinforced fibre and fits the SRS-A1. Note it does not fit the Covert handguard (SBA-HDG-02).

12Bolt handle

Bolt knobs

The bolt knob is pure ergonomics, and on a bolt-action that is not a small thing: it is the part you work between every single shot, usually with a glove on, usually without taking your eye off the scope.

By weight, since that is the real difference: the Light knob is the minimum at 20 g, the Vauban is 21 g in fibreglass-reinforced nylon with a steel nut, the Bakelite is 23 g and the original SRS shape, and the Carbon and Grip knobs are the heavy end at 38 g. The Grip one is the interesting one: it carries NBR80 O-rings for grip and is threaded on both sides, so you can extend or shorten the bolt handle to suit your reach.

The Match, Tactical, Operator and Twisted knobs are the CNC 6061-T6 shapes for the SRS bolt head, all generations — despite what some of the product URLs suggest, these are knobs, not trigger units.

14Ergonomics

Stock

The A2 nylon stock, as a spare or a replacement.