K2’s new 4mm, built to your 27.5″ and put on Jesse’s scale at 502.6 gr. Every number below is that arrow on the AX-90 — same engine as The Forge, no rounding in your favour.
Why this one flies flatter
The Teton runs 9.2 gpi against the Sawtooth’s 10.6 — 38 grains of shaft gone. K2 gives most of it back as a heavier 75 gr titanium front end, so you keep the mass where it does work and lose it where it doesn’t. That is the whole trick, and on this bow it costs you nothing: 8 fps faster, 2.4 points more FOC, 1.8 ft·lb more energy, and momentum dead level with what you already shoot. Lighter arrow, harder hit — the speed it buys more than covers the mass it gives up.
Spine — read this once
250 is the stiffest Teton K2 makes, and at 90 lb with 200 gr up front you are at the stiff end of the chart with no headroom. On the real-world speed basis The Forge runs by default, your effective draw weight lands at 97 lb and 250 is in range. Push the same numbers onto the bench-IBO basis and it reads one class weak. Both of your existing K2 arrows sit further inside the window because their front ends are lighter. Paper- and bareshaft-tune these before you hunt them — the chart says go, the target says stay.
What’s provisional
The Teton is pre-release. Its 9.2 gpi / .165 ID / .239 OD came from K2 direct, not a published spec sheet, and K2 has not given a straightness tolerance yet — so this page does not print one. The 502.6 gr is the one number that is not a model: that is Jesse’s scale, and the build sheet independently lands at 502.7. Everything gets re-checked against K2’s sheet at launch.
Also in your quiver — K2
the two you already shoot, same bow, same 250 spine, same 27.5″ and fletching — so the only thing changing is the shaft and its front end
Both of these still tune and both still kill — nothing above says otherwise. Keep them. The difference is that all three land within 1.8 ft·lb of each other on energy and dead level on momentum, so the Teton is not buying its speed out of your penetration budget. That is why it goes to the front of the quiver.
Numbers computed by the same engine behind The Forge — the recommendation, the dynamic-spine model, and the FOC math are the ones every Sparrow build runs on. First tap unlocks Sparrow Pro on your device and keeps it on.