UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 11-K

x ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934.

For the fiscal year ended September 30, 2012

OR

¨ TRANSITION REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934.

For the transition period from                  to                 

Commission file number 001-8137

A. Full title of the plan and the address of the plan, if

different from that of the issuer named below:

Ampac Fine Chemicals LLC

Bargaining Unit 401(k) Plan

B. Name of the issuer of the securities held pursuant to

the plan and the address of its principal executive office:

American Pacific Corporation

3883 Howard Hughes Parkway

Suite 700

Las Vegas, NV 89169

Contents

Report of Independent Registered Public Accounting Firm	1
Financial Statements
Statements of net assets available for benefits	2
Statement of changes in net assets available for benefits	3
Notes to the financial statements	4 - 10
Supplemental Schedule
Form 5500, Schedule H, Part IV, Line 4i - Schedule of Assets Held at End of Year	11
Signatures	12
Exhibit Index	13

Report of Independent Registered Public Accounting Firm

To the Plan Administrator and Participants

Ampac Fine Chemicals LLC Bargaining Unit 401(k) Plan

Las Vegas, Nevada

We have audited the accompanying statements of net assets available for benefits of the Ampac Fine Chemicals LLC Bargaining Unit 401(k) Plan as of September 30, 2012 and 2011, and the related statement of changes in net assets available for benefits for the year ended September 30, 2012. These financial statements are the responsibility of the Plan’s management. Our responsibility is to express an opinion on these financial statements based on our audits.

We conducted our audits in accordance with auditing standards of the Public Company Accounting Oversight Board (United States). Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements are free of material misstatement. An audit includes examining, on a test basis, evidence supporting the amounts and disclosures in the financial statements. An audit also includes assessing the accounting principles used and significant estimates made by management, as well as evaluating the overall financial statement presentation. We believe that our audits provide a reasonable basis for our opinion.

In our opinion, the financial statements referred to above present fairly, in all material respects, the net assets available for benefits of the Ampac Fine Chemicals LLC Bargaining Unit 401(k) Plan as of September 30, 2012 and 2011, and the changes in net assets available for benefits for the year ended September 30, 2012, in conformity with U.S. generally accepted accounting principles.

Our audits were performed for the purpose of forming an opinion on the basic financial statements taken as a whole. The supplemental schedule of assets held at end of year as of September 30, 2012 is presented for the purpose of additional analysis and is not a required part of the basic financial statements, but is supplementary information required by the United States Department of Labor’s Rules and Regulations for Reporting and Disclosure under the Employee Retirement Income Security Act of 1974. This supplemental schedule is the responsibility of the Ampac Fine Chemicals LLC Bargaining Unit 401(K) Plan’s management. The supplemental schedule has been subjected to the auditing procedures applied in the audits of the basic financial statements and, in our opinion, is fairly stated in all material respects in relation to the basic financial statements taken as a whole.

/s/ McGladrey LLP

Vienna, Virginia

March 27, 2013

1

Ampac Fine Chemicals LLC Bargaining Unit 401(k) Plan

Statements of Net Assets Available for Benefits

September 30, 2012 and 2011

		2012		2011
Assets
Investments, participant directed, at fair value (Notes 3 and 4):
Fixed annuity	$	13	$	19
Shares of registered investment companies		6,661,090		4,944,535
American Pacific Corporation common stock (Note 7)		1,170,537		674,753
Total assets		7,831,640		5,619,307
Notes receivable from participants		604,312		443,687
Liabilities		—		—
Net assets available for benefits	$	8,435,952	$	6,062,994

See Notes to the Financial Statements.

2

Ampac Fine Chemicals LLC Bargaining Unit 401(k) Plan

Statement of Changes in Net Assets Available for Benefits

For the Year Ended September 30, 2012

Additions to net assets attributed to:
Investment income:
Dividend and interest income	$	191,118
Net appreciation in fair value of investments (Note 3)		1,246,514
		1,437,632
Interest income on notes receivable from participants		20,704
Contributions:
Participant		788,448
Employer match		405,788
Total contributions		1,194,236
Total additions		2,652,572
Deductions from net assets attributed to:
Benefits paid		237,156
Plan expenses (Note 7)		10,642
Total deductions		247,798
Net increase prior to transfer out		2,404,774
Transfer of assets to American Pacific Corporation 401(k) Plan		(31,816)
Net increase		2,372,958
Net assets available for benefits:
Beginning of year		6,062,994
End of year	$	8,435,952

See Notes to the Financial Statements.

3

Ampac Fine Chemicals LLC Bargaining Unit 401(k) Plan

Notes to the Financial Statements

Note 1.    Plan Description

The following description of the Ampac Fine Chemicals LLC Bargaining Unit 401(k) Plan (the “Plan”) provides only general information. Participants should refer to the Plan document, as restated, for a complete description of the Plan’s provisions.

General:    The Plan is a defined contribution plan open to domestic employees of Ampac Fine Chemicals LLC, a wholly owned subsidiary of American Pacific Corporation (the “Company”), who are members of a collective bargaining unit. Employees are eligible to participate after completing at least 3 months of service and are allowed to enter the Plan on the first day of each fiscal quarter. The Plan is subject to the provisions of the Employee Retirement Income Security Act of 1974, as amended (“ERISA”).

Contributions:    Each year, participants may contribute up to the maximum allowed by the Internal Revenue Code (“IRC”). In addition, the Plan allows for catch-up contributions by participants 50 years and older before the end of the Plan year. Participants may also contribute amounts representing distributions from other qualified plans, as defined in the Plan’s provisions.

The Company, at its discretion, may contribute to the Plan. For the year ended September 30, 2012, the Company elected to match contributions equal to 100% of participant contributions, up to the first 3% of participant compensation, and 50% of participant contributions, up to the next 3% of participant compensation. For the year ended September 30, 2012, the Company made matching contributions of $405,788.

In addition, the Company may make profit sharing contributions at the Company’s discretion. There were no profit sharing contributions made for the Plan year ended September 30, 2012. Contributions are subject to certain limitations.

Participants direct the investment of their contributions, Company discretionary matching contributions and profit sharing contributions into various investment options offered by the Plan. The Plan currently offers various mutual funds and employer stock as investment options for participants.

Participant accounts:    Each participant’s account is credited with the participant’s contributions; including amounts rolled over from other qualified plans, allocations of the Company’s discretionary matching contribution, the Company’s discretionary profit sharing contribution, Plan earnings, and is charged with benefit payments and an allocation of administrative expenses (loan and withdrawal fees). The allocations above are based on participant earning or account balances, as defined. The benefit to which a participant is entitled is the benefit that can be provided from the participant’s vested account.

Vesting:    Participants are immediately vested in their contributions, rollover contributions and employer matching contributions, plus actual earnings thereon. Vesting in the Company’s discretionary profit sharing contribution is based on years of continuous service. A participant vests 20% per year from years two through six of credited service. A participant’s interest in the Plan becomes fully vested if employment terminates due to death, total and permanent disability or retirement at age 65.

Notes receivable from participants:    In accordance with the provisions of the Plan, participants may borrow from their fund accounts a minimum of $1,000 up to a maximum amount equal to the lesser of $50,000 or 50% of their vested account balance. Loan transactions are treated as transfers between participant-directed investments and notes receivable from participants. Loan terms range from one to five years or up to twenty years for the purchase of a primary residence. The loans are collateralized by the participant’s vested balance in the Plan and bear interest at the prime rate plus 1%. Principal and interest is paid ratably through payroll deductions. Outstanding notes receivable from participants totaled $604,312 and $443,687 at September 30, 2012 and 2011, respectively. Interest rates on participant loans vary, ranging from 4.25% to 6.00%. Maturities range from July 2013 through August 2032.

4

Ampac Fine Chemicals LLC Bargaining Unit 401(k) Plan

Notes to the Financial Statements

Note 1.    Plan Description (Continued)

Payment of benefits:    Upon termination of service, if the vested value of a participant’s account is less than $1,000, his or her account will be distributed in a lump-sum payment. If the vested value of a participant’s account exceeds $1,000, he or she may elect to receive either a lump-sum amount, substantially equal payments over a specified term, or elect to have all the distribution paid in a direct rollover to another qualified employer plan, or a combination of the above.

Transfer of assets:    During the year ended September 30, 2012, assets of $31,816 were transferred to the American Pacific Corporation 401(k) Plan for former union employees who became non-union employees.

Forfeited accounts:    At September 30, 2012 and 2011, forfeited accounts totaled $0 and $5,810, respectively. Forfeited accounts are utilized first to reduce Plan expenses. Any remaining forfeitures are used to reduce employer contributions. Forfeitures of $5,810 were used to reduce Plan expenses or to reduce employer contributions during the year ended September 30, 2012.

Note 2.    Summary of Significant Accounting Policies

Basis of accounting:    The Plan’s financial statements are prepared on the accrual basis of accounting.

Use of estimates in the preparation of financial statements:    The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amount of assets, liabilities, and changes therein, disclosure of contingent assets and liabilities. Actual results could differ from those estimates.

Investment valuation and income recognition:    Investments are reported at fair value. Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. See Note 4 for discussion of fair value measurements.

Purchases and sales of securities are recorded on a trade-date basis. Interest income is recorded on the accrual basis. Dividends are recorded on the ex-dividend date. Net appreciation or depreciation includes the Plan’s gains and losses on investments bought and sold as well as held during the year.

Notes receivable from participants:    Notes receivable from participants are measured at their unpaid principal balance plus any accrued but unpaid interest. Delinquent participant loans are classified as distributions based upon the terms of the Plan document.

Payment of benefits:    Benefits are recorded when paid.

Expenses:    Administrative expenses of the Plan are paid by either the Plan or the Company, as provided in the Plan document.

Income taxes:    Management evaluated the Plan’s tax positions and concluded that the Plan had maintained its tax exempt status and had taken no uncertain tax positions that require adjustment to the financial statements. Therefore, no provision or liability for income taxes has been included in the financial statements. With few exceptions, the Plan is no longer subject to income tax examinations by the U.S. federal, state, or local tax authorities for years before 2008.

5

Ampac Fine Chemicals LLC Bargaining Unit 401(k) Plan

Notes to the Financial Statements

Note 2.     Summary of Significant Accounting Policies (Continued)

New accounting pronouncements:    In May 2011, the FASB issued ASU 2011-04, Amendments to Achieve Common Fair Value Measurement and Disclosure Requirements in U.S. GAAP and IFRSs, which changes certain fair value measurement principles and enhances the disclosure requirements, particularly for Level 3 fair value measurements. This update is effective for reporting periods beginning on or after December 15, 2011, and requires prospective application. Plan management has not yet determined the impact this guidance will have on the Plan.

Note 3.    Investments

The Plan’s investments that represented 5% or more of the Plan’s net assets available for benefits as of September 30, 2012 and 2011 are as follows:

	2012		2011
Shares of registered investment companies:
BlackRock Global Allocation Fund	$	551,885	$	396,445
Federated Prime Cash Obligations Fund		**		389,324
BlackRock Equity Dividend Fund		**		327,342
Common stock:
American Pacific Corporation common stock	$	1,170,537	$	674,753

** These investments are below 5% of the Plan’s net assets at September 30, 2012.

6

Ampac Fine Chemicals LLC Bargaining Unit 401(k) Plan

Notes to the Financial Statements

Note 3.     Investments (Continued)

The Plan’s investments, including gains and losses on investments bought and sold, as well as held during the year, appreciated (depreciated) in value during the year ended September 30, 2012 as follows:

Shares of registered investment companies:
BlackRock Equity Dividend Fund	$	76,251
BlackRock Small Cap Growth Equity Inv Fund		62,530
Invesco American Franchise		56,110
DWS Equity 500 Index Fund		49,281
Dreyfus Small Cap Stock Index Fund		46,931
BlackRock Global Allocation Fund		43,846
Lazard Emerging Markets Open Fund		43,672
Invesco Real Estate Fund		42,161
Ivy Science and Technology Fund		41,478
Franklin Naural Resources Fund		32,946
American Funds Europacific Growth Fund		30,261
Allianz NFJ Small Cap Value Fund		28,833
American Funds Fundamental Inv Fund		28,396
JP Morgan Smart Retirement 2040 Fund		24,652
MFS Utilities Fund		21,661
Artisian Mid Cap Value Fund		19,773
JP Morgan Smart Retirement 2030 Fund		19,207
Prudential Jennison Mid Cap Growth		18,457
Templeton Global Bond Fund		17,791
JP Morgan Smart Retirement 2035 Fund		17,309
Alger Health Sciences Fund		15,024
JP Morgan Smart Retirement 2045 Fund		13,589
JP Morgan Smart Retirement 2025 Fund		12,168
JP Morgan Smart Retirement 2050 Fund		9,132
JP Morgan Smart Retirement 2015 Fund		7,569
JP Morgan Smart Retirement 2010 Fund		7,165
JP Morgan High Yield Bond Fund		7,012
JP Morgan Smart Retirement 2020 Fund		6,345
BlackRock U.S. Opportunities Inv Fund		6,143
Artio Total Return Bond Fund		4,106
PIMCO GNMA Fund		(877)
		808,922
Common stock:
American Pacific Corporation Common Stock		437,592
Net appreciation in fair value of investments	$	1,246,514

7

Ampac Fine Chemicals LLC Bargaining Unit 401(k) Plan

Notes to the Financial Statements

Note 4.    Fair Value Measurements

FASB ASC 820, Fair Value Measurements and Disclosures, provides the framework for measuring fair value. That framework provides a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (level 1 measurement) and the lowest priority to unobservable inputs (level 3 measurement). The three levels of the fair value hierarchy under the new guidance are described below:

•    Level 1:	Inputs to the valuation methodology are unadjusted quoted prices for identical assets or liabilities in active markets that the Plan has the ability to access.
•    Level 2:	Inputs to the valuation methodology include:
Ÿ	Quoted prices for similar assets or liabilities in active markets;
Ÿ	Quoted prices for identical or similar assets or liabilities in inactive markets;
Ÿ	Inputs other than quoted prices that are observable for the asset or liability;
Ÿ	Inputs that are derived principally from or corroborated by observable market data by correlation or other means.
	If the asset or liability has a specified (contractual) term, the Level 2 input must be observable for substantially the full term of the asset or liability.
•    Level 3:	Inputs to the valuation methodology are unobservable and significant to the fair value measurement.

The asset’s or liability’s fair value measurement level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. Valuation techniques used need to maximize the use of observable inputs and minimize the use of unobservable inputs.

Following is a description of the valuation methodologies used for assets measured at fair value. There have been no changes in the methodologies used at September 30, 2012 and 2011.

Fixed annuity:    Valued based on method outlined in the annuity contract, as calculated by the annuity provider, based on observable inputs through the review of existing contracts and readily available financial information available on the websites of the issuing financial institutions.

Registered investment companies:    Valued at the net asset value (NAV) of shares held by the plan at year end.

American Pacific Corporation common stock:    Valued at trade prices that are determined by real trading executed for the Plan during market hours. The trade price may be derived from a single trade or may be an average of several trades executed for the Plan and is adjusted for commissions and applicable SEC fees.

The methods described above may produce a fair value calculation that may not be indicative of net realizable value or reflective of future fair values. Furthermore, while the Plan believes its valuation methods are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different fair value measurement at the reporting date.

8

Ampac Fine Chemicals LLC Bargaining Unit 401(k) Plan

Notes to the Financial Statements

Note 4.     Fair Value Measurements (Continued)

The following table sets forth by level, within the fair value hierarchy, the Plan’s investments at fair value as of September 30, 2012.

	Investments at Fair Value as of September 30, 2012
	Level 1		Level 2		Level 3		Total
Fixed annuity	$	-	$	13	$	-	$	13
Shares of registered investment companies:
International funds		1,141,390		-		-		1,141,390
Large cap funds		1,150,703		-		-		1,150,703
Mid cap funds		517,425		-		-		517,425
Small cap funds		741,208		-		-		741,208
Asset allocation funds		838,544		-		-		838,544
Bond funds		914,773		-		-		914,773
Specialty funds		1,051,737		-		-		1,051,737
Money market funds		305,310		-		-		305,310
American Pacific Corporation common stock		1,170,537		-		-		1,170,537
Total investments at fair value	$	7,831,627	$	13	$	-	$	7,831,640
	Investments at Fair Value as of September 30, 2011
	Level 1		Level 2		Level 3		Total
Fixed annuity	$	-	$	19	$	-	$	19
Shares of registered investment companies:
International funds		527,824		-		-		527,824
Large cap funds		819,689		-		-		819,689
Mid cap funds		418,661		-		-		418,661
Small cap funds		672,773		-		-		672,773
Asset allocation funds		752,470		-		-		752,470
Bond funds		463,635		-		-		463,635
Specialty funds		900,159		-		-		900,159
Money market funds		389,324		-		-		389,324
American Pacific Corporation common stock		674,753		-		-		674,753
Total investments at fair value	$	5,619,288	$	19	$	-	$	5,619,307

Note 5.     Plan Termination

Although it has not expressed any intention to do so, the Company has the right under the Plan to discontinue contributions at any time and to terminate the Plan subject to the provisions of ERISA. In the event of Plan termination, participants would become 100% vested in their accounts.

9

Ampac Fine Chemicals LLC Bargaining Unit 401(k) Plan

Notes to the Financial Statements

Note 6.     Income Tax Status

The Plan was adopted from a non-standardized prototype plan document offered by Orchard Trust Company (“Orchard”). The Internal Revenue Service (“IRS”) has determined and informed the prototype sponsor by a letter dated November 27, 2001 that the prototype plan is designed in accordance with applicable sections of the IRC.

The Plan has received a determination letter from the IRS dated June 23, 2011 indicating that the Plan as adopted is designed in accordance with the IRC. The Plan administrator and the Plan’s management believe that the Plan is designed and is currently being operated in compliance with the applicable requirements of the Internal Revenue Code (“IRC”) and the related trust was exempt from taxation as of the financial statement date.

Note 7.     Exempt Party-In-Interest Transactions

Certain Plan investments are shares of registered investment companies managed by Orchard or its affiliates. Orchard is the trustee as defined by the Plan and, therefore, these transactions qualify as party-in-interest transactions. Fees paid by the Plan to Orchard totaled $4,831 for the year ended September 30, 2012.

At September 30, 2012 and 2011, the Plan held 98,282 and 92,053 shares of common stock of American Pacific Corporation, respectively, with a fair value of $1,170,537 and $674,753, respectively. At September 30, 2012 and 2011, the Plan held 13 and 19 units in the Employer Stock Awaiting Purchase Fund, respectively, with a fair value of $13 and $19, respectively.

Note 8.     Risk and Uncertainties

The Plan invests in various investment securities. Investment securities are exposed to various risks such as interest rate, market, and credit risks. Due to the level of risk associated with certain investment securities, it is at least reasonably possible that changes in the values of investment securities will occur in the near term and that such changes could materially affect participants’ account balances and the amounts reported in the Statement of Net Assets Available for Benefits.

10

Ampac Fine Chemicals LLC Bargaining Unit 401(k) Plan

Form 5500, Schedule H, Part IV, Line 4i - Schedule of Assets Held at End of Year

September 30, 2012

	Identity of issuer, borrower, lessor, or similar party	Description of investment, including maturity date, collateral and maturity value	Cost		Current Value
	Fixed annuity:
*	Employer Stock Awaiting Purchase Fund		**	$	13
	Shares of registered investment companies:
*	BlackRock Global Allocation Fund	Mutual fund	**		551,885
*	BlackRock Equity Dividend Fund	Mutual fund	**		414,577
*	Lazard Emerging Markets Open Fund	Mutual fund	**		370,709
*	Templeton Global Bond Fund	Mutual fund	**		353,842
*	Franklin Natural Resources Fund	Mutual fund	**		332,568
*	Prudential Jennison Mid Cap Growth	Mutual fund	**		330,952
*	Federated Prime Cash Obligations Fund	Mutual fund	**		305,310
*	DWS Equity 500 Index Fund	Mutual fund	**		302,146
*	Invesco American Franchise	Mutual fund	**		292,482
*	Artio Total Return Bond Fund	Mutual fund	**		283,302
*	BlackRock Small Cap Growth Equity Inv Fund	Mutual fund	**		275,845
*	Dreyfus Small Cap Stock Index Fund	Mutual fund	**		251,463
*	Ivy Science and Technology Fund	Mutual fund	**		240,490
*	American Funds Europacific Growth Fund	Mutual fund	**		218,796
*	Invesco Real Estate Fund	Mutual fund	**		217,722
*	Allianz NFJ Small Cap Value Fund	Mutual fund	**		213,900
*	Artisian Mid Cap Value Fund	Mutual fund	**		186,474
*	PIMCO GNMA Fund	Mutual fund	**		167,168
*	MFS Utilities Fund	Mutual fund	**		162,226
*	JP Morgan Smart Retirement 2040 Fund	Mutual fund	**		151,022
*	American Funds Fundamental Inv Fund	Mutual fund	**		141,498
*	JP Morgan Smart Retirement 2030 Fund	Mutual fund	**		130,783
*	JP Morgan Smart Retirement 2035 Fund	Mutual fund	**		115,627
*	JP Morgan High Yield Bond Fund	Mutual fund	**		110,460
*	Alger Health Sciences Fund	Mutual fund	**		98,732
*	JP Morgan Smart Retirement 2010 Fund	Mutual fund	**		92,741
*	JP Morgan Smart Retirement 2045 Fund	Mutual fund	**		90,062
*	JP Morgan Smart Retirement 2025 Fund	Mutual fund	**		87,461
*	JP Morgan Smart Retirement 2015 Fund	Mutual fund	**		71,861
*	JP Morgan Smart Retirement 2050 Fund	Mutual fund	**		64,778
*	JP Morgan Smart Retirement 2020 Fund	Mutual fund	**		34,208
					6,661,090
*     American Pacific Corporation Common Stock		Common stock (98,282 shares)	**		1,170,537
*     Participant Loans		Interest rates ranging from 4.25% - 6.00%,
		maturing through August 2032	**		604,312
Total investments				$	8,435,952

  * Represents a party-in-interest to the Plan.

  ** Cost information is not required for participant-directed investments and, therefore, is not included.

See accompanying report of independent registered public accounting firm.

11

SIGNATURES

The Plan. Pursuant to the requirements of the Securities and Exchange Act of 1934, the trustees have duly caused this annual report to be signed on its behalf by the undersigned hereunto duly authorized.

	Ampac LLC Fine Chemicals Bargaining Unit 401(k) Plan
	By:	American Pacific Corporation, as Plan Administrator
Date: March 27, 2013	By:	/s/ JOSEPH CARLEONE
		Joseph Carleone President & Chief Executive Officer

12

EXHIBIT INDEX

Exhibit     Index	Description
23.1	Consent of Independent Registered Public Accounting Firm

13