Barbell vs Bullet Portfolios

Two bond portfolios can carry the exact same average duration and still behave completely differently when the yield curve moves. A bullet portfolio holds bonds clustered around a single maturity — say, mostly 7-year notes — so its duration comes from one concentrated point on the curve. A barbell portfolio instead splits the same money between very short bonds (2-year) and very long bonds (30-year), with nothing in between, engineered so the weighted-average duration matches the bullet exactly. The two portfolios have identical sensitivity to a parallel shift in rates, but diverge sharply when the curve twists: a barbell has more convexity, meaning it gains slightly more when rates fall and loses slightly less when rates rise than a bullet with the same duration, because convexity is a curved (not straight-line) benefit that grows with the spread of maturities held. The bullet, in exchange, tends to outperform when the curve flattens toward the bullet's concentrated maturity, since a flattening pulls the barbell's long end down in yield relative to its short end in a way that hurts the barbell's mix specifically.

A manager expecting range-bound rates but worried about a sharp shock in either direction often prefers the barbell's convexity cushion, paying for it by giving up some yield if the market simply grinds toward the bullet's maturity instead.