UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

(Rule 13d-102)

INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT

TO RULE 13d-1(a) AND AMENDMENTS THERETO FILED PURSUANT TO

RULE 13d-2(a)

(Amendment No. 1)*

(Name of Issuer)

(Title of Class of Securities)

(CUSIP Number)

(Name, Address and Telephone Number of Person

Authorized to Receive Notices and Communications)

(Date of Event which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box. ¨

Note: Schedules filed in paper format shall include a signed original and five copies of this schedule, including all exhibits. See §§240.13d-7 for other parties to whom copies are to be sent.

(continued on following pages)

(Page 1 of 7 Pages)

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*The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

This Amendment No. 1 to Schedule 13D is being filed to amend certain Item 4 information previously filed in connection with the original Schedule 13D filed November 13, 2012 and a Schedule 13G filed February 12, 2013, and to make other updating changes to the cover pages and to Item 5 in light of the amendment of Item 4.

Item 1. Security and Issuer.

This Schedule 13D relates to the beneficial ownership of Common Stock, $.01 par value per share (the “Common Stock”) of A. M. Castle & Co., a Maryland corporation (the “Issuer”), whose principal place of business is located at 1420 Kensington Road, Suite 220, Oak Brook, Illinois 60523.

Item 2. Identity and Background.

The foregoing persons are hereinafter collectively referred to as the “Reporting Persons.”

Item 3. Source and Amount of Funds or Other Consideration.

HCM caused HCM’s clients to acquire the Common Stock held in such client’s accounts using client funds.

Item 4. Purpose of Transaction.

The Common Stock was acquired for investment purposes. The Reporting Persons may cause further acquisitions of additional shares of Common Stock or sales of Common Stock through (i) purchases or sales from time to time in the open market at prices prevailing in the market at the time of such purchases or sales, (ii) privately negotiated transactions at prices which may or may not be related to prices prevailing in the open market at the time of such purchases or sales, or (iii) a combination of open market and privately negotiated transactions.

Such acquisition or sale of additional shares of Common Stock on behalf of the Reporting Persons clients will be, in all cases, subject to the availability of shares at prices deemed by such Reporting Persons to be reasonable and consistent with prudent investment criteria and to general economic circumstances. As prices and economic factors are not expected to be static, there can be no assurances that the Reporting Persons will cause the purchase or sale of any additional shares of Common Stock or that the Reporting Persons will be causing the purchase or sale of additional shares of Common Stock at any given time, nor can there be any prediction regarding the number of shares of Common Stock over which the Reporting Persons will have voting or dispositive power at any given time or from time to time. The Reporting Persons reserve the right to cause the sale or other disposition of any or all of these shares of Common Stock at any time or from time to time.

The Reporting Persons may also engage in any hedging or similar transactions with respect to the Common Stock.

On August 31, 2012, the Issuer announced the adoption of a shareholder rights plan (poison pill) with a trigger at 10% of shares outstanding and a “grandfather” exception for any person or group owning 10% or more of the company’s outstanding shares immediately prior to the adoption of the plan, subject to some ownership restrictions.

HCM has previously communicated our belief that the poison pill serves to entrench existing management and the Board, and fails to treat all shareholders equally; specifically, there is no reason why those who crossed the 10% threshold prior to the poison pill’s enactment should be able to maintain their holdings at a level denied the rest of the shareholders.

On March 12, 2013, the Issuer filed a definitive proxy statement on Form 14A putting certain issues to a vote of the shareholders. HCM is disappointed that the Issuer chose not to put the poison pill to a shareholder vote. HCM continues to believe that the poison pill is not in the best interests of shareholders, is an impediment to the realization of the full and fair value of the Issuer, and serves primarily to entrench the interests of management and the Board, and perpetuate a culture of a lack of transparency and accountability.

In light of the information above, the Reporting Persons reserve the right to formulate other plans and/or make other proposals, and take such actions with respect to the investment in the Issuer, including any or all of the actions set forth in paragraphs (a) through (j) of item 4 of Schedule 13D. The Reporting Persons may also at any time reconsider and change their plans or proposals relating to the foregoing matters. 

ITEM 5. INTEREST IN SECURITIES OF THE ISSUER.

On behalf of its clients, HCM holds 1,695,397 shares of the Issuer’s Common Stock, equivalent to 7.3% of shares outstanding based on 23,209,389 shares issued and outstanding as reported in the Issuer’s Form 10-K for the period ended December 31, 2012.

Item 6. Contracts, Arrangements, Understandings or Relationships with Respect to Securities of the Issuer.

The Reporting Persons do not have any contracts, arrangements, understandings or relationships (legal or otherwise) with any person with respect to any securities of the Issuer, including, but not limited to transfer or voting of any of the securities, finder’s fees, joint ventures, loan or option agreements, puts or calls, guarantees of profits, division of profits or loss, or the giving or withholding of proxies.

Item 7. Material to Be Filed as Exhibits.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Dated: May 3, 2013

/s/ Joseph R. Huber

Joseph R. Huber

HUBER CAPITAL MANAGEMENT, LLC

By: /s/ Joseph R. Huber

Joseph R. Huber

Managing Member