FN 509 9mm vs Sig Sauer P320 Full Size 9mm

Both are 17+1 full-size 9mm strikers with polymer frames and stainless slides, and both ship with two magazines. The Sig Sauer P320 Full Size 9mm is the longer gun: a 4.7" barrel and 8.0" overall length against the FN 509 9mm's 4.0" and 7.4", with a 6.5" sight radius vs 5.79". It is 1.4 oz heavier (28.3 oz vs 26.9 oz) but 0.10" narrower (1.25" vs 1.35"). The 509's trigger is listed 1 lb lighter at 5.5 lb vs 6.5 lb. The P320 arrives optic-ready with SIGLITE night sights; the 509 in this configuration is not cut for an optic and wears 3-dot luminescent sights. MSRP is $515 for the P320 and $639 for the 509.

Pick the FN 509 if:

• You want the 1 lb lighter factory trigger pull (5.5 lb vs 6.5 lb)
• You want the shorter, lighter package: 7.4" and 26.9 oz vs 8.0" and 28.3 oz
• You size a grip with interchangeable backstraps rather than a fixed textured polymer grip

Pick the Sig Sauer P320 Full Size if:

• You want a factory optic cut and night sights included rather than added later
• You want the 0.71" longer sight radius (6.5" vs 5.79") and the 4.7" barrel
• MSRP is $124 lower ($515 vs $639) and the slide is 0.10" narrower

Capacity, caliber and materials are a wash. The decision is the 509's lighter trigger and smaller footprint against the P320's optic cut, night sights and lower MSRP.