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                                                                     EXHIBIT 5.1

                        [MAYER, BROWN & PLATT LETTERHEAD]



                                                                 August 10, 1999


Metal Management, Inc.
500 North Dearborn Street, Suite 405
Chicago, Illinois 60610

Ladies and Gentlemen:

         We have acted as your counsel in connection with the registration of
certain 12 3/4% Senior Secured Notes due 2004 (the "Notes") of Metal Management,
Inc., a Delaware corporation (the "Company"), and the guarantees thereof (the
"Guarantees") by certain subsidiaries of the Company listed on Annex A hereto
(the "Guarantors"), pursuant to a registration statement on Form S-4,
registration no. 333-83547 (the "Registration Statement").

         In rendering the opinions expressed herein, we have examined and relied
upon such documents, corporate records, certificates of public officials and
certificates as to factual matters executed by officers of the Company and the
Guarantors as we have deemed necessary or appropriate. We have assumed the
authenticity, accuracy and completeness of all documents, records and
certificates submitted to us as originals, the conformity to the originals of
all documents, records and certificates submitted to us as copies and the
authenticity, accuracy and completeness of the originals of all documents,
records and certificates submitted to us as copies. We have also assumed the
legal capacity and genuineness of the signatures of persons signing all
documents in connection with which the opinions expressed herein are rendered.

         Based upon the foregoing, we are of the opinion that:

         (i) the Notes have been duly authorized for issuance by the Company
         and, when the Notes are duly executed, authenticated, issued and
         delivered in accordance with the indenture governing the Notes, the
         Notes will be legally issued and will constitute a valid and legally
         binding obligations of the Company, except as may be limited by
         bankruptcy, insolvency, reorganization, moratorium or similar laws
         affecting creditors' rights generally or by the effect of general
         principles of equity, including, without limitation, concepts of
         materiality, reasonableness, good faith and fair dealing (regardless of
         whether considered in a proceeding at law or equity); and

         (ii) the Guarantees have been duly authorized for issuance by the
         Guarantors and, when the Guarantees are duly executed, authenticated,
         issued and delivered in accordance with



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Metal Management, Inc.
August 10, 1999
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         the indenture governing the Notes, the Guarantees will be legally
         issued and will constitute valid and legally binding obligations of the
         Guarantors, except as may be limited by bankruptcy, insolvency,
         reorganization, moratorium or similar laws affecting creditors' rights
         generally or by the effect of general principles of equity, including,
         without limitation, concepts of materiality, reasonableness, good faith
         and fair dealing (regardless of whether considered in a proceeding at
         law or equity).

         We are admitted to practice law in the States of Illinois and New York
and we express no opinions as to matters under or involving any laws other than
the laws of the States of Illinois and New York, the federal laws of the United
States of America and the corporate laws of the State of Delaware.

         We hereby consent to the filing of this opinion letter as an exhibit to
the Registration Statement and to the reference to this firm under the caption
"Legal Matters."

                                   Very truly yours,

                                   MAYER, BROWN & PLATT




                                   By /s/ Paul W. Theiss
                                      -----------------------------------------
                                          Paul W. Theiss, a Partner of the Firm



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                                     ANNEX A


Aerospace Metals, Inc., a Delaware corporation
American Scrap Processing, Inc., an Illinois corporation
California Metals Recycling, Inc., a California corporation
CIM Trucking, Inc., an Illinois corporation
Cometco Corp., an Illinois corporation
Cozzi Building Corporation, an Illinois corporation
Cozzi Iron & Metal, Inc., an Illinois corporation
C Shredding Corp., an Illinois corporation
EMCO Trading, Inc., an Arizona corporation
Ferrex Trading Corporation, a Delaware corporation
Firma, Inc., a California corporation
Firma Plastic Co., Inc., a California corporation
FPX, Inc., a Tennessee corporation
Houston Compressed Steel Corp., a Texas corporation
HouTex Metals Company, Inc., a Texas corporation
The Isaac Corporation, an Ohio corporation
Kankakee Scrap Corporation, an Illinois corporation
Kimerling Acquisition Corp., a Delaware corporation
Mac Leod Metals Co., a California corporation
Metal Management Arizona, Inc., an Arizona corporation
Metal Management Gulf Coast, Inc., a Delaware corporation
Metal Management Pittsburgh, Inc., a Delaware corporation
Metal Management Realty, Inc., an Arizona corporation
Michael Schiavone & Sons, Inc., a Delaware corporation
Naporano Iron & Metal Co., a New Jersey corporation
Newell Recycling West, Inc., a Colorado corporation
NIMCO Shredding Co., a New Jersey corporation
138 Scrap, Inc., an Illinois corporation
PerlCo, L.L.C., a Tennessee limited liability company
P. Joseph Iron & Metal, Inc., an Ohio corporation
Proler Southwest Inc., a Texas corporation
Proler Steelworks L.L.C., a Delaware limited liability company
R&P Holdings, Inc., a Delaware corporation
Reserve Iron & Metal Limited Partnership, a Delaware limited partnership
Salt River Recycling, L.L.C., an Arizona limited liability company
Scrap Processing, Inc., an Illinois corporation
Torrington Scrap Company, a Delaware corporation
Trojan Trading Co., a California corporation
USA Southwestern Carrier, Inc., an Arizona corporation