This document provides instructions for operating and maintaining a Low Profile Regulated Piston System (L.P.R.) for an AR-15 style rifle. It describes the parts of the L.P.R. including the spring guide, return spring, op-rod, piston, regulator and bolt carrier. It provides details on adjusting the four position regulator between settings for normal, adverse, and silenced conditions. Disassembly and reassembly of the small parts and the full piston system is illustrated in figures and text. Cleaning and lubrication recommendations are provided.

1. Low Profile Regulated Piston System (L.P.R.)
Operators Manual

2. LOW PRO REGULATED PARTS NOMENCLATURE
2
Spring Guide
Return Spring
Op-Rod
Piston
Piston Cylinder
Gas Block
Regulator
Knob Position
Indicator
Bolt Carrier Buffer
Bolt Carrier
Bolt Assembly
Cam Pin
Takedown
Pin

3. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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:
Online Store: www.blackriflearms.com
YouTube Channel: http://www.youtube.com/user/BlackRifleArms
Facebook Page: https://www.facebook.com/blackriflearms
Black Rifle Arms
New Smyrna Beach, FL 32168
386.428.7960