<PAGE>   1

                                                                        EX-10.31

                      SEVENTH AMENDMENT TO CREDIT AGREEMENT



                           SEVENTH AMENDMENT dated as of December 6, 1999 (the
                  "Seventh Amendment"), to the Amended and Restated Credit
                  Agreement dated as of October 15, 1997, (as amended by the
                  First Amendment dated as of June 26, 1998, the Second
                  Amendment dated as of November 13, 1998, the Third Amendment
                  dated as of March 31, 1999, the Fourth Amendment dated as of
                  April 30, 1999, the Fifth Amendment dated as of September 30,
                  1999, Sixth Amendment dated as of November 15, 1999 and the
                  Amended and Restated Credit Agreement as so amended being
                  referred to herein as the "Credit Agreement"), among Firearms
                  Training Systems, Inc., as Parent (the "Parent"), FATS, Inc.,
                  as Borrower (the "Borrower"), the lenders listed on the
                  signature pages thereto (the "Lenders"), Bank of America,
                  N.A., as Agent, (in such capacity, the "Agent"), Swingline
                  Lender and Issuing Bank.

         The Borrower has advised the Agent that it does not have sufficient
funds to pay interest on the Loans that is due and payable on December 3, 1999
and that the failure to pay such interest would constitute an Event of Default
under the Credit Agreement. The Parent and the Borrower have requested that the
payment of past due interest on the Loans be deferred. The parties hereto have
agreed, subject to the terms and conditions hereof, to further amend the Credit
Agreement as provided herein.

         Capitalized terms used and not otherwise defined herein shall have the
meanings assigned to such terms in the Credit Agreement (the Credit Agreement,
as amended by, and together with, this Seventh Amendment, and as hereinafter
amended, modified, extended or restated from time to time, being called the
"Amended Agreement").

         Accordingly, the parties hereto hereby agree as follows:

         SECTION 1.01. Amendment to Article V. Article V of the Credit Agreement
is hereby amended by the insertion of a new Section 5.15 as follows:

                  SECTION 5.15. Best Efforts to Obtain New Capital. The Parent
         and the Borrower shall use their best efforts to consider and evaluate
         all potential sources of obtaining substantial amounts of new capital
         (including, without limitation, current equity holders, private
         investors, merger partners and public markets) and to negotiate with
         all such sources in good faith.

         SECTION 1.02. Amendment to Article VII (c). Article VII (c) of the
Credit Agreement is deleted and the following inserted in lieu thereof:

                  (c) default shall be made in the due observance by the
         Borrower or any other Loan Party of any covenant, condition, or
         agreement contained in Section 5.04, 5.05, 5.08, 5.11 or 5.15 hereof or
         in Article VI;

         SECTION 1.03. Amendment to Article VII. Article VII of the Credit
Agreement is hereby amended by deleting the "or" at the end of sub-Article (p),
inserting new sub-Articles (r) and (s) as follows:

                  (r) the Parent shall fail to enter into a binding agreement
         with a third party on or before December 31, 1999, relating to the
         infusion of new capital from investors or merger partners containing
         terms and conditions acceptable to the Lenders in their sole and
         absolute discretion; or

                  (s) any agreement described in sub-Article (r) above is not
         consummated on or before March 15, 2000.

         SECTION 1.04. Deferral of Payment of Interest Due. Notwithstanding
anything contained in the Amended Agreement or any of the other Loan Documents
to the contrary, the Deferred Payments (hereinafter defined) shall be due and
payable in full on December 31, 1999. For purposes of this Section 1.04,
"Deferred Payments" shall mean all interest and other amounts due on the Loans
which became due and payable on or before December 6, 1999 (without regard to
any period of grace, if any) and which has not been paid to the Lenders as of
the date hereof.

         SECTION 1.05. Representations and Warranties. The Borrower hereby
represents and warrants to the Agents and the Lenders, as follows:


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                  (a) The representations and warranties set forth in Article
         III of the Amended Agreement, and in each other Loan Document,
         including any Schedules thereto, are true and correct in all material
         respects on and as of the date hereof and on and as of the Seventh
         Amendment Effective Date (as defined below) with the same effect as if
         made on and as of the date hereof or the Seventh Amendment Effective
         Date, as the case may be, except to the extent such representations and
         warranties expressly relate solely to an earlier date.

                  (b) Each of the Borrower and the other Loan Parties is in
         compliance with all the terms and conditions of the Amended Agreement
         and the other Loan Documents on its part to be observed or performed
         including, without limitation, the obligation to pay all principal and
         interest due on and prior to the date hereof and no Default or Event of
         Default has occurred or is continuing under the Amended Agreement,
         other than the Defaults or Events of Default described in Section 1.02
         of the Sixth Amendment.

                  (c) The execution, delivery and performance by the Borrower
         and the Parent of this Seventh Amendment have been duly authorized by
         the Borrower.

                  (d) This Seventh Amendment constitutes the legal, valid and
         binding obligation of the Borrower, enforceable against the Borrower in
         accordance with its terms, subject to the effect of bankruptcy,
         insolvency, reorganization, arrangement, moratorium, fraudulent
         conveyance, voidable preference or similar laws and the application of
         equitable principles generally.

                  (e) The execution, delivery and performance by the Borrower of
         this Seventh Amendment (i) does not conflict with or violate (A) any
         provision of law, statute, rule or regulation, or of the articles of
         incorporation or by-laws of the Borrower, (B) any order of any
         Governmental Authority or (C) any provision of any indenture, agreement
         or other instrument to which the Borrower is a party or by which it or
         any of its property may be bound and (ii) does not require any consents
         under, result in a breach of or constitute (alone or with notice or
         lapse of time or both) a default or give rise to increased, additional,
         accelerated or guaranteed rights of any person under any such
         indenture, agreement or instrument.

         SECTION 1.06. Effectiveness. This Seventh Amendment shall become
effective as of December 6, 1999 (the "Seventh Amendment Effective Date") upon
satisfaction of the following conditions precedent:

                  (a) The Agent shall have received duly executed counterparts
         of this Seventh Amendment which, when taken together, bear the
         authorized signatures of the Parent, the Borrower and all the Lenders.

                  (b) The Lenders shall be satisfied that the representations
         and warranties set forth in Section 1.05 hereof are true and correct on
         and as of the Seventh Amendment Effective Date.

                  (c) There shall not be any action pending or any judgment,
         order or decree in effect which, in the judgment of the Lenders or
         their counsel, is likely to restrain, prevent or impose materially
         adverse conditions upon performance by the Borrower or any other Loan
         Party of its obligations under the Loan Documents.

                  (d) The Lenders shall have received such other documents,
         legal opinions, instruments and certificates as they shall reasonably
         request and such other documents, legal opinions, instruments and
         certificates shall be satisfactory in form and substance to the Lenders
         and their counsel. All corporate and other proceedings taken or to be
         taken in connection with this Seventh Amendment and all documents
         incidental thereto, whether or not referred to herein, shall be
         satisfactory in form and substance to the Lenders and their counsel.

                  (e) The Agent shall have received payment of and all fees and
         expenses set forth in Section 1.08.

         SECTION 1.07. APPLICABLE LAW. THIS SEVENTH AMENDMENT SHALL BE GOVERNED
BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK, EXCEPT
TO THE EXTENT THAT THE FEDERAL LAWS OF THE UNITED STATES OF AMERICA MAY APPLY.

         SECTION 1.08. Fees and Expenses. The Borrower shall pay all reasonable
out-of-pocket expenses incurred by the Agent and the Lenders in connection with
the preparation, negotiation, execution, delivery and enforcement of this
Seventh Amendment, including, but not limited to, the reasonable fees and
disbursements of counsel.


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         SECTION 1.09. Counterparts. This Seventh Amendment may be executed in
any number of counterparts, each of which shall constitute an original but all
of which when taken together shall constitute but one agreement. Delivery by
facsimile by any of the parties hereto of an executed counterpart of this
Seventh Amendment shall be as effective as an original executed counterpart
hereof and shall be deemed a representation that an original executed
counterpart hereof will be delivered, but the failure to deliver a manually
executed counterpart shall not affect the validity, enforceability or binding
effect of this Seventh Amendment.

         SECTION 1.10. Credit Agreement. Except as expressly set forth herein,
the amendments provided herein shall not by implication or otherwise limit,
constitute a waiver of, or otherwise affect the rights and remedies of the
Lenders, the Agent or the other Secured Parties under the Amended Agreement or
any other Loan Document, nor shall they constitute a waiver of any Default or
Event of Default, nor shall they alter, modify, amend or in any way affect any
of the terms, conditions, obligations, covenants or agreements contained in the
Amended Agreement or any other Loan Document. Each of the amendments provided
herein shall apply and be effective only with respect to the provisions of the
Amended Agreement specifically referred to by such amendment. Except as
expressly amended herein, the Amended Agreement shall continue in full force and
effect in accordance with the provisions thereof. As used in the Amended
Agreement, the terms "Agreement", "herein", "hereinafter", "hereunder", "hereto"
and words of similar import shall mean, from and after the date hereof, the
Amended Agreement.

         IN WITNESS WHEREOF, the parties hereto have caused this Seventh
Amendment to be duly executed by their duly authorized officers, all as of the
date first above written.

                                  FIREARMS TRAINING SYSTEMS, INC.
                                  as Parent


                                  By:
                                     ------------------------------------------
                                     Name:
                                     Title:


                                  FATS, INC.
                                  as Borrower


                                  By:
                                     ------------------------------------------
                                     Name:
                                     Title:


                                  BANK OF AMERICA, N.A., as Agent, Swingline
                                  Lender and Issuing Bank and individually as
                                  a Lender


                                  By:
                                     ------------------------------------------
                                     Name:
                                     Title:


                                  U.S. BANK NATIONAL ASSOCIATION


                                  By:
                                     ------------------------------------------
                                     Name:
                                     Title:



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<PAGE>   4

                                  FIRST SOURCE FINANCIAL LLP, by First Source
                                  Financial, Inc., as Agent/Manager


                                  By:
                                     ------------------------------------------
                                     Name:
                                     Title:


                                  BHF (USA) CAPITAL CORPORATION


                                  By:
                                     ------------------------------------------
                                     Name:
                                     Title


                                  BANK AUSTRIA CREDITANSTALT CORPORATE
                                  FINANCE, INC. (FKA CREDITANSTALT CORPORATE
                                  FINANCE, INC.)


                                  By:
                                     ------------------------------------------
                                     Name:
                                     Title:


                                  By:
                                     ------------------------------------------
                                     Name:
                                     Title:


AGREED and CONSENTED,
as of the date first above written:


DART INTERNATIONAL, INC.

By:
   ---------------------------------
   Name:
   Title:


FIREARMS TRAINING SYSTEMS, INC.

By:
   ---------------------------------
   Name:
   Title:


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