X0206 3 2021-10-27 0 0001863428 Seaport Calibre Materials Acquisition Corp. SCMA 0001258998 MCMASTER ROBERT R 360 MADISON AVENUE, 20TH FLOOR NEW YORK, NY 10017 1 0 0 0 Class B Common Stock Class A Common Stock 115494 D Shares of Class B Common Stock will automatically convert into shares of the Issuer's Class A Common Stock at the time of the Issuer's initial business combination on a one-for-one basis, subject to adjustment, as described under the heading "Description of Securities" in the Issuer's registration statement on form S-1 (File No. 333-258024) (the "Registration Statement") and have no expiration date. The shares of Class B common stock beneficially owned by the reporting person includes up to 15,065 shares subject to forfeiture to the extent the underwriters of the initial public offering of the Issuer's securities do not exercise in full their over-allotment option as described in the Registration Statement. /s/ Robert McMaster 2021-10-27