In Part 1, I laid out the essential tools you’ll want to gather to make your build experience as easy as possible. In this 2nd and final part, I’ll take you through the build step by step. Your build may take you 45 minutes to an hour or more depending on your experience. This guide assumes you are using our mil-spec lower parts kit as well as our upper and lower receivers and build kit parts.

Lower Receiver Assembly

The lower receiver is where most of the build time will be spent. Assembling the lower for a .22lr blaster is exactly the same as for any standard AR-15 build. There are lots of videos out there taking you through it step by step, however, you may want to look through our steps below if you are using one of our lower receivers since ours have some very nice time and labor saving features not found on most other lowers.

To begin, tighten your lower receiver magazine vise block into your vise and place your lower onto it. Now you’re ready to begin assembly.

 

Step 1: Install the magazine catch

 

The mag catch assembly consists of the mag catch bar, the mag release button, and a tension spring. Place the stud of the mag catch bar through the hole on the left side of the receiver, then push the tension spring into the button hole over the stud on the right side. Then, while holding the catch bar in place, push the release button down on the spring until it makes contact with the stud. Now rotate the mag catch bar clockwise, threading the button onto the stud. Use a nylon punch to push and hold the button in the hole while turning the catch bar. On a mil-spec button, the end of the stud should be threaded until flush with the indent of the button.

 

Step 2: Install the forward pivot pin

Use a pivot pin install tool! Any other attempt to install that little detent and spring will end up with you on your hands and knees wishing you had used the tool.
 

 

Step 3: Install the bolt catch/stop

Here is where using our lower receiver becomes so much easier than the alternatives. Instead of using a roll pin, you’ll use the special dog set screw that came with your Canto Arms receiver. First, insert the bolt catch tension spring followed by the plunger into the recess. Then set the bolt stop into place. Now take your dog set screw and insert it into the hole, passing through the hole in the bolt stop. Tighten the set screw with an hex wrench. A ball-end hex wrench makes this job much easier and less prone to scratching your receiver while tightening.

 

 

Step 4: Install the fire control system

The fire control system consists of two sub-assemblies: the trigger group and the hammer group.

Trigger group assembly

First, insert the large end of the disconnector spring into the blind hole on the top-rear of the trigger. Then place the disconnector on top of the trigger with the hook facing forward. Install a temporary slave pin into the hole to hold the parts together. You can make a slave pin from a spare trigger pin by cutting it down to the width of the trigger body.

Orient the trigger spring with the legs at the bottom facing front. Slip the spring’s crossbar under the front of the trigger and loop the spring over the studs on the side.

Drop the trigger assembly into the lower, lining up the holes in the receiver with the trigger holes. Now insert a trigger pin from the left side of the receiver, ungrooved end first. This will push out the slave pin.

Hammer group assembly

Identify the front of the hammer – the flat side. The loops on the hammer spring slip over the studs on the side of the hammer with the open end of the spring to the front and the closed end to the rear.

Now insert the hammer into the receiver with the legs of the spring resting on the pin holding in the trigger. If necessary, gently drive the pin in place with a nylon hammer.

Fire control testing and break-in

This step is important – skipping it will commonly result in misfires, double strikes, or other firing malfunctions. 

Cock back the hammer and install your trigger test block (aka hammer block) using the pivot pin. Never dry fire a partially assembled AR without this block. Function test the fire control assembly by cocking back the hammer and pulling the trigger.

Next, break-in the trigger and hammer reset by cocking the hammer, and pulling the trigger but keep the trigger fully pulled after the hammer drops. Cock the hammer, then release the trigger. You should hear a click as the disconnector catches the hammer. Often times with a new mil-spec fire control group the click will be delayed or not happen at all because the parts are not yet broken in.

To break-in, dry fire then keep the trigger pulled back. With the trigger still pulled, cock the hammer then put moderate upward pressure on the hammer using your thumb. Maintain that pressure while releasing your pull on the trigger. This will force the hammer into the disconnector catch. Repeat this 5-10 times, then test the hammer reset again. Repeat the break-in steps until the hammer reset click happens instantly every time.

After testing and break-in, remove the trigger test block and continue with assembly.

 

Step 5: Install the trigger guard

Another must-have tool is the Wheeler trigger guard install tool. It removes all the headache of this step eliminates the possibility of screwing up a perfectly good receiver.

1. Install the end of the trigger guard that uses the spring loaded detent. That’s the end with the blind hole – the roll pin goes in the end where a hole goes all the way through.
   
2. Lightly oil the trigger guard roll pin. With no pin in the tool, place the trigger guard roll pin into the drive hole of the tool. Straddle the tool across the receiver’s trigger guard ears and drive the pin into the hole just enough to keep it there. Back out and remove the tool.
3. Move the trigger guard into place and push the long pin into the hole opposite of the roll pin. This will keep the trigger guard aligned as you drive the roll pin into place.
4. Insert the short drive pin into the tool. Open the tool enough so that it fits over the width of the trigger guard and protruding roll pin. Turn the knob until the dog end of the drive pin seats inside the roll pin. Keeping the tool squared, start turning the knob to drive the pin into place.

 

Step 6: Install the rear takedown pin

Again, our lower receiver makes this step a bit easier since our receiver has a set screw for the detent spring. You’ll need to cut 2-3 mm of the detent spring off to adjust for the set screw. Insert the takedown pin into its hole on the right side of the receiver with the detent slot oriented toward the rear of the receiver. Now insert the brass detent into the rear hole followed by the detent spring, flat (uncut) side first. Place the set screw onto your hex wrench and carefully push straight in until the threads meet the receiver. Screw into the receiver until the set screw is flush with the receiver back, do not tighten beyond flush.

Finally, take your receiver end plate and slip it over and past the threads of the receiver end cap. Hand thread the end cap into the receiver while guiding the end plate into place. Tighten with a hex wrench, do not over tighten.

 

Step 7: Install the receiver tensioning screw

A unique feature of our receivers is a receiver tensioning screw. This screw is optional to install as our receivers fit together fairly snug and do not rattle. Some receivers may fit more loosely and you will then notice a slight rattling which this screw resolves.

To install it, insert the tensioning screw green side up into the bottom of the receiver. Using a hex wrench, screw it into place until the green tip is flush with the inside of the receiver. If you think you may want to tension the receivers to keep them from rattling, install the empty upper receiver right now for fit, then turn the tensioning screw inward until it meets with the upper receiver and there is slight tension. Too much tension and you will have a very difficult time taking down the upper from the lower and an impossible time getting it back together.

 

Step 8: Install the safety selector and grip

Cock the hammer back and insert the safety selector into the left side of the receiver. Hold the hammer and pull the trigger, gently allowing the hammer to drop. Remove the lower receiver from the vise block. Insert the safety detent into the hole beneath the safety selector. Insert the detent spring into the hole at the top of the grip. Ensuring that the safety selector is in the “Fire” position, bring the grip together with the receiver, keeping the spring aligned with the detent. Take care that the spring compresses and does not bend during assembly. Place the star washer onto the grip bolt and insert the bolt into the bottom of the grip and tighten. 

 

That’s it for the lower receiver! You have some extra parts – the .22lr blaster pistol does not have a buffer tube so the buffer tube detent and spring are unused.

 

 

 

Upper Receiver Assembly

Upper receiver assembly is a quick process so we’re almost done! Prep by placing your upper receiver into an upper receiver vise block and securely clamping that into your vise.

 

Preparation

 

Upper vise block modifications

If your upper vise block is the type that utilizes and internal component like this one, you’ll need to drill out the forward end of your vise block’s internal component so the barrel’s internal portion can fit.

 

Step 1: Barrel installation

Note: Do not apply lubricant to the threads of the receiver or barrel nut.

Insert the barrel into the receiver then slip the barrel nut over the barrel. Hand tighten the barrel nut onto the receiver. Using a torque wrench and a 32mm slim crowfoot, tighten the barrel nut to 35 lb-ft.

 

Step 2: Muzzle device installation

Slip the crush washer onto the end of the barrel, cone facing rearward. Hand tighten the muzzle device onto the barrel. If you have a non-marring wrench, you may use that as well. However, do not overtighten with a wrench as the aluminum threads may strip.

Once the shroud and muzzle device are installed, remove the upper assembly from the vise block to continue.

 

Step 3: Bolt group assembly

Partially insert the charging handle into the upper receiver. Slide the bolt assembly into the receiver. Push both the handle and the bolt assembly into the fully inserted position. The rear of the bolt assembly should be flush with the upper receiver when fully inserted. This may require the gentle persuasion of a rubber mallet.

Note: We have noticed that some of the CMMG bolts have not been fully seated into their rails during assembly at the factory. If you have trouble inserting your bolt assembly into the upper receiver, inspect the bolt assembly to see if it is correctly seated into its rails. You can easily test this by sliding the bolt back against the spring. If it will not slide, pull the frame apart gently and move the bolt into place in its rails. It will then be able to insert properly into the upper receiver.

 

Finally Assembly

To finish your build, tighten your lower receiver magazine vise block into your vise and place your lower onto it. Open both the takedown and the pivot pins. Set the upper receiver onto the lower and push in the front pivot pin. Then push in the rear takedown pin. Note that the RTB slick side upper receivers run on the tight side and a nylon hammer may be needed to drive the rear pin into place. This is normal and will loosen up a bit over time. Using lubrication on the pins when assembling is recommended.