Low Profile Regulated Piston System (L.P.R.)

Operators Manual

LOW PRO REGULATED PARTS NOMENCLATURE

2

Spring Guide

Return Spring

Op-Rod

Piston

Piston Cylinder

Gas Block

Regulator

KnobPosition

Indicator

Bolt Carrier Buffer

Bolt Carrier

Bolt Assembly

Cam Pin

Takedown

Pin

3

ADJUSTING THE LOW PRO REGULATOR

Figure 1 shows the position indicator on

the ejection port side indicating the

regulator is in the silencer setting. This

position reduces gas flow to compensate

for silencer back pressure.

Figure 1

The following instructions are to be referenced from the shooters perspective. To rotate the regulator knob between the various gas

settings requires the operator to grasp the knob firmly pressing it forward until it’s interlocking teeth are clear then rotating slightly,

release forward pressure and continue to rotate until the knob auto locks into the next gas setting. The knob may be rotated in either

direction a full 360 degrees with four settings at 90 degrees apart. See figures 1 thru 6 below for setting specifics.

Figure 2

Figure 2 shows how an operator pulls forward

on the regulator knob to clear the locking

teeth allowing rotation of the regulator knob

between gas settings.

ALWAYS USE THE LOWEST GAS SETTING THAT WILL OPERATE RELIABLY WITH WHATEVER AMMUNITION IS

BEING FIRED, THIS WILL OPTIMIZE THE SYSTEMS PERFORMANCE AND MINIMIZE WEAR.

The regulator knob has a small hole and a large hole at its forward end. The large hole is the position indicator.

4

ADJUSTING THE LOW PRO REGULATOR CONTINUED

Figure 3 shows the position indicator at the 12

o’clock position indicating the regulator is in the

normal gas setting. This is the setting for US

COMMERCIAL and US MILITARY ammunition

under normal shooting conditions.

Figure 4

Figure 4 shows the position indicator at the

shooter’s left or the 9 o’clock position indicating the

high gas setting. This setting is for adverse

conditions or light powered ammunition.

Figure 3

5

ADJUSTING THE LOW PRO REGULATOR CONTINUED

Figure 5 shows the regulator in the off

position shutting the gas off stopping the

action from cycling and effectively

making the firearm a bolt action. Note

the position indicator is at the 6 o’clock

while the small hole is at the 12 o’clock.

Figure 6 shows how the regulator knob was

design so a bullet could be used to adjust the

regulator if heat or fouling makes rotating the

knob more difficult.

Figure 6Figure 5

Figure 5

6

LOW PRO REGULATED PISTON SYSTEM DISASSEMBLY

Always confirm that the firearm is unloaded before beginning disassembly. Start by removing the upper

receiver from the lower receiver. Remove the bolt carrier group and charging handle from the upper. Fig. 1

Figure 2

Figure 1

Remove the hand guard retaining screws and remove hand guard by pulling it forwards straight off the end

of the barrel. Fig. 2

7

LOW PRO REGULATED PISTON SYSTEM DISASSEMBLY

Figure 1) Push takedown pin thru

the gas block. A bullet, firing pin or

similar tool may be use for this job.

Figure 2) With the takedown pin fully

extended out of the gas block remove the

regulator by pulling it out thru the front of

the gas block.

Figure 2Figure 1

8

LOW PRO REGULATED PISTON SYSTEM DISASSEMBLY CONTINUED

With the bolt carrier and hand guard removed pull rearward on the op-rod freeing the connecting link from the piston. Fig. 1

NOTE: IF YOU HAVE A TWO PIECE OP-ROD REFER TO FIG. 1 THRU 4. If YOU HAVE A ONE PIECE OP-

ROD SKIP TO PAGE 10. FIG. 5 THRU 7.

Figure 1

Grasp the connecting link and pull it free from the op-rod. Fig 2

Figure 2

Op-rod Connecting Link Piston

9

LOW PRO REGULATED PISTON SYSTEM DISASSEMBLY CONTINUED

Pull the piston rearward removing it from the piston cylinder. Fig. 3

Pull op-rod forward and up removing it from the upper receiver and barrel nut. Fig. 4

Figure 3

Figure 4

10

LOW PRO REGULATED PISTON SYSTEM DISASSEMBLY CONTINUED

With the bolt carrier and hand guard removed pull rearward on the op-rod freeing it from the piston. Fig. 5

Pull op-rod forward and up removing it from the upper receiver and barrel nut. Fig. 6

Figure 5

Figure 6

11

LOW PRO REGULATED PISTON SYSTEM DISASSEMBLY CONTINUED

With the op-rod removed pull the piston rearward removing it from the piston cylinder. Fig. 7

SMALL PARTS DISASSEMBLY

Spring Guide 1 Return Spring 2 Op-Rod 3

Spring Guide 1 Return Spring 2 Op-Rod 3 Connecting Link 4

Figure 7

12

LOW PRO REGULATED PISTON SYSTEM DISASSEMBLY

CONTINUED

SMALL PARTS DISASSEMBLY

Spring Guide 1 Return Spring 2 Op-Rod 3

Spring Guide 1 Return Spring 2 Op-Rod 3 Connecting Link 4

Refer to Figure 1. Small parts disassembly starts by pulling the return spring (2) free from the

op-rod (3), next insert a dowel thru the return spring (2) and pressing out the spring guide (1). For

those with a two piece op-rod first remove the connecting link (4) from the op-rod head (5) and

complete disassemble as describe above.

Op-rod Head 5

Figure 1

13

Low Pro Regulated Piston System

Cleaning and Maintenance

• For quick field cleaning simply wipe out the upper receiver and wipe off the bolt carrier with a rag, add

a few drops of lubricant to the carrier and reassemble.

• For a thorough cleaning disassemble the piston assembly in to its individual parts and with a gun

cleaner of your choice follow the brands cleaning instructions. For detailed cleaning instruction for your

AR-15 type rifle we recommend consulting a US military technical manual such as ARMY TM 9-1005-

319-23&P

• Most owners will clean and maintain their system well above what is required. For others who use the

system daily they may only do a thorough cleaning when reliability suffers. Although the system in

daily use is nearly maintenance free, we do recommend routine inspection and cleaning as needed to

prevent corrosion. The system should be thoroughly cleaned and lubricated before lengthy storage to

prevent corrosion.

• We recommend wiping off any excess lubricant from the piston and piston cylinder before placing the

system in service because excess lubricant accelerates fouling buildup by providing a base for fouling to

adhere to then it burns off leaving only burnt on carbon / fouling behind.

• The use of corrosive ammunition is not recommended and if ever used will require an immediate and

extensive cleaning process to prevent corrosion. The corrosive ammunition cleaning process is beyond

the scope of this manual and customers are advised not to use corrosive ammunition.

• Do NOT use Ammonia base products on Nickel Boron Carrier.

14

Low Pro Regulated Piston System Reassembly

Figure 1

Figure 1) Insert the regulator thru the front of

the gas block. Be sure the locking teeth of the

gas block and regulator knob are seated flush.

Figure 2) Use your finger or an appropriate

tool and press the takedown pin in flush with

gas block. This completes reassembly.

Figure 2

15

LOW PRO REGULATED PISTON SYSTEM REASSEMBLY CONTINUED

SMALL PARTS ORDER OF ASSEMBLY

Spring Guide 1 Return Spring 2 Op-Rod 3

Spring Guide 1 Return Spring 2 Op-Rod 3 Connecting Link 4

Figure 1 illustrates how the individual parts go together to makeup the small parts

assembly. First press the spring guide (1) into the return spring (2), next slip the return

spring (2) and spring guide (1) over the op-rod (3). For those with a two piece op-rod insert

the connecting link (4) into op-rod head (5). That completes reassembly of the small parts.

Op-rod Head 5

Once you have the spring guide, return spring, and op-rod reassembled follow the instruction in

reverse order that are illustrated on pages 11 thru 6 to complete reassembly.

Figure 1

16

Low Pro Regulated Piston System (L.P.R.) Features:

– 4 Position Regulated Gas System

– Pull Free Regulator

– Multi Regulator Design

– Ambi-Regulator Knob

– 360° Continual Rotation

– Easily Adjustable with One Hand

– Easily Adjustable with Gloves On

– Easily Adjustable from Firing Position

– Audible and Palpable Setting Confirmation

– No Detent Pin to Push In to Adjust Gas Regulator

– Regulator Knob Allows for Zero Visibility Adjustment

– Interlocking Mechanism Prevents Accidental Rotation of Knob

– Knob Configured for Rapid Adjustment with No Loss of Target Engagement

For more information on Black Rifle Arms products please visit us at:

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Black Rifle Arms

New Smyrna Beach, FL 32168

386.428.7960