What is the ballistic coefficient and trajectory table for m855 62-grain projectile?
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Executive summary
Ballistic-coefficient (BC) values reported for the 62‑grain M855 “green‑tip” 5.56×45mm round vary widely in public sources — published calculators and vendors give BCs from about 0.243 to ~0.371 (G1/G7 definitions vary by source) and typical muzzle velocities cited range roughly 2,850–3,113 ft/s depending on barrel length and load [1] [2] [3]. Independent aerodynamic testing and military transition to M855A1 add complexity: researchers measured detailed aerodynamic coefficients for the M855 [4], and Ballistics authorities list different BCs for the M855A1 specifically [5].
1. Conflicting BC numbers: different players, different figures
There is no single authoritative BC for “M855” in the open web results. Commercial product pages and calculators list BCs anywhere from about 0.243 (one vendor listing for PMC X‑Tac) to 0.349–0.371 on other vendor/calculator pages [3] [6] [1]. Forum threads and informal discussions report an even wider spread (0.27–0.37) and emphasize that users get best results by tuning BC to match their chronographed velocities and observed drop [7] [8].
2. Why BC numbers diverge: models, reference standards, and barrel effects
BC depends on the drag model (G1 vs G7) and on how a vendor or laboratory fits data to that model. ShootersCalculator entries show BC and initial velocity are the two critical inputs and that trajectory charts change with barrel length and chosen BC [9] [1]. Empirical testing demonstrates M855 muzzle velocity varies with barrel length (charts and articles show velocities near 3,113 ft/s cited for some loads while other published product specs give ~2,850–3,060 ft/s), so using a BC pulled from a different barrel/velocity will mispredict real‑world drop [2] [6] [1].
3. Aerodynamic research gives the best physics — but not a single “BC”
Defense and research reports performed free‑flight and wind‑tunnel style tests on the M855 to derive aerodynamic coefficients and trajectory behavior; these studies produced tables and Mach‑dependent drag data rather than a single catch‑all BC, and that data was used to validate trajectory models [4] [10]. In short, rigorous aerodynamics work produces drag curves and trajectory predictions; single BC numbers in product listings are simplifications [4].
4. Trajectory tables you can realistically use
Public ballistics calculators (ShootersCalculator, Ammo.com charts) provide ready‑made trajectory tables for M855 when you enter a BC and muzzle velocity. ShootersCalculator hosts presets for “LC M855” using BC≈0.304 and vi≈2850 ft/s and for M855A1 using BC≈0.371 with higher velocity — these give drop/energy/velocity versus range tables that shooters commonly use as baselines [1] [11] [9]. Vendors and ammo‑listing pages also publish manufacturer‑specific trajectory charts tied to their stated BC and muzzle velocity [6] [12].
5. Practical advice shooters and analysts should follow
Do not rely on a single, uncited BC: chronograph your ammo from your barrel, pick a drag model (G1/G7) consistent with your ballistic app, and tune the BC to observed drop. Forum and field reporting consistently recommend “field calibration” to reconcile listed BCs with reality [7] [4]. For a quick starting point, the public presets and vendor specs above (BC ≈0.243–0.371 and muzzle velocities ≈2850–3113 ft/s depending on load/barrel) bracket the common values seen in open sources [3] [1] [2].
6. M855A1 matters — it’s a different projectile
Be aware the Army’s M855A1 is a different, lead‑free projectile with distinct geometry and published BC/velocity figures; Bryan Litz and forum posts cite different BCs for the A1 projectile (e.g., a G1 BC cited for M855A1 in one source) and official testing focused on that variant’s aerodynamics [5] [4]. If you need precision or long‑range work, check whether your data target is legacy M855 or the M855A1.
Limitations and note on sources
Open sources here are a mix of vendor specs, shooter calculators, forum threads and a technical aerodynamics report. Vendor pages and calculators provide convenient trajectory tables but use different drag models and input assumptions [6] [1] [9]. The technical report gives measured aerodynamic coefficients for the M855 [4] but does not provide one‑line “use this BC” guidance suitable for every rifle. Available sources do not mention a single universally accepted BC or a single definitive trajectory table for every barrel and environmental condition; field calibration remains necessary [4] [7].