INTRODUCTION

The “ATCHISSON” Mark III .22LR Caliber Conversion is a .22LR caliber rim fire device which replaces the standard bolt/bolt carrier assembly in the AR15/M16 family of firearms. It allows the use of inexpensive .22LR ammunition where the 5.56mm (.223 Rem.) cartridge is not required. It is a blow-back operated sub-caliber conversion device that allows semiautomatic firing of the .22LR high velocity cartridge in the AR15, A1 & A2. The same unit with the addition of the automatic trip and anti-bounce weight (M16 unit only) allows selective fire (semi and auto) firing of the .22LR high velocity cartridge in the M16, A1 & A2. It will not change the mode of fire capabilities of the firearm it is installed in.

OPERATION AND MAINTENANCE INFORMATION

Use premium grade .22 Long Rifle high velocity round nose ammunition. The unit was successfully test fired with Remington High Velocity 40 grain solid nose ammunition. The use of other brands, standard velocity, hyper velocity, or bullet design may adversely affect the operation of this unit. Never attempt to insert the .22 caliber magazine in the firearm while the standard slide is installed. Damage to the magazine will result. When chambering a new cartridge manually, pull the charging handle fully to the rear and release. DO NOT hold (ride) the handle as the bolt closes. This will cause a slow feed situation that can jam the device. The conversion bolt will activate the dust cover as the OEM bolt does. All components of the unit and your rifle should be thoroughly cleaned and lubricated after every use. To clean the unit you need only hold the bolt rearward while using a brush to clean the bolt and chamber adapter faces and a bore brush on the chamber and bore of the chamber adapter. Rinse the exterior in solvent and blow dry. Disassembly of the unit is not recommended as damage to the precise alignment of the receiver rails may result.       

The unit should be removed from the firearm before no more than 500 rounds and the chamber and bolt locking lug area of the barrel cleaned and decarboned using the standard chamber/locking lug cleaning brush and the bore with a bore brush. Firing the 5.56mm (.223 Rem.) cartridge will fully clean any residual .22 rim fire fouling from the gas system.

INSTALLATION INSTRUCTIONS

1.   Remove the standard magazine. Clear the firearm of ammunition. Visually check the chamber to be sure no live rounds remain.

2.   Use a 5.56mm cartridge to press the take down pin through the receiver. Pull the pin so that the upper receiver swings free.

3.   Pull the charging handle approximately half way out. Grasp the OEM bolt/bolt carrier assembly and remove it. Check the barrel for obstructions.

4.   With the charging handle approximately half way out, insert the conversion unit into the upper receiver. NOTE: When inserting the M16 (select fire) unit, be sure the anti-bounce weight and automatic trip are in the correct position (Figs. 1 & 2).

5.   Push conversion unit in as far as possible. Close the firearm and push the take down pin into the closed position

CAUTION:  ASSURE THE FIREARM IS UNLOADED.

Remove the magazine first, THEN visually check the chamber.

CAUTION:  NEVER use excessive force to install the conversion. If forces seems necessary, STOP, go back and reread the instructions and try again.

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