Going from an AR to an M4

Well back last year I was in one hell of wreck, along with me was my AR15. While it was in the trunk of the car, it didn't survive undamaged. After the wreck the weapon would still drive tacks but I could not get the sight back on target. The bolt would not stay in place and the slightest bump would allow it to override the bolt stop.

So I decided to rebuild it and show a picture journal of what was done and give the specs of the build not so much the parts but the build itself.

So lets get started, shall we.

The base gun, a full length AR15 with 20 inch upper.


The first thing that we do is clear the weapon and make it safe. Duh but you never know.

Then the take down pins are released and the weapon is separated in to the two halves. Since in this case we are completely replacing the upper since the barrel is bent and I want a flat top upper and a shorted barrel.

We are going to deal with the lower mainly on this build and on the next build will focus on the upper receiver, so stay tuned for that build later.

You will need a few tools for this build.

1. A phillips head screw driver
2. A fillister head screw driver
3. A small hammer
4. a few punches
5. A stock wrench.

We begin with an inspection of the lower receiver and found that the bolt stop was bent.



We continue the inspection of the outside and find nothing else out of whack. So the next thing that we do is to remove the butt stock from the weapon. Using the phillips head screw driver and remove the screw at the back of the of the stock and remove it.

Now be careful here there is a hidden spring that launch itself.


From here you will have to remove the buffer tube. Be warned that it is holding a pin and spring in place. Using the stock wrench we loosen the buffer tube and twist it out, going slowly till the tube clears the buffer retaining pin and spring.

Ok, from here we will remove the bolt catch by using a small punch and hammer and drive the pin out of the latch but not all the way out.



Now be warned, just about everything that you move or remove in an AR will have a spring. This is no different.

With the bolt stop removed you can see the pin and and spring.


I went ahead and replaced the bolt stop here instead of later after stripping the receiver.

Here is the installed part, note that it is straight.

Ok before we can take the insides out we need to remove the safety. It is not 100% necessary but I want to examine the safety to make sure that there are no cracks or anything else that might cause the safety to fail.

We start with the fillister screw driver and remove the screw that is hiding in the pistol grip and remove it, again there is a spring hiding out in there. Hold the grip and remove slowly. When the grip is pulled away, you will find a spring and a pin holding the safety in place.

Now for the trigger, disconnecter and hammer. Here is rule that I always follow, Out from left to right, in from right to left. Take a punch just under the pin size and push, be careful because they are under spring pressure.

Pay real close attention to the springs that are there. If you remove them they will have to be put back in place correctly. Here there are just for you.

Hammer:


Trigger:


I will tell you now, you will never, never, never ever use a hammer to remove or install the trigger and hammer pins. They will go in and come out without any problem when they are lined up correctly. Use a punch or blind pin but not a hammer!

From here I took an emery board and too some scratches off of the trigger and hammer, making it noticeably smoother and reinstalled the trigger and disconnector at the same time.

Pay close attention to the way the springs are in the lower receiver.

Here is the trigger is in place. The trigger spring legs go forward.


The hammer spring goes to the rear and sits on the shelf that is cut into the trigger. You can see these cuts in several of the pictures that are already posted.


Notice how the springs ride along the side of the receiver and fit into the recess that are. It helps keep the trigger from shifting on you. Now test it, thoroughly.

Time to reinstall the safety by pushing it in from the side and make sure that it is flush, hold it sideways and install the safety pin. Push the spring into the grip and push the grip onto the receiver but hold it sideways to keep things from falling out.



It keeps this from a 3 handed job. When you tighten it down be careful not to bind the spring. Once installed, test! Test, test, test.

Ok now it is time to get busy, we will have to install the rear take down pin, retainer pin and spring, buffer tube and buffer pin and spring all at the same time without kinking or binding any springs or lose them.

Don't let it over whelm you. It is easy.

Assemble the parts.
Buffer retaining pin and spring


take down pin and springs


don't lose this pin it goes in the gun


The buffer tube, lock nut and back plate ready to be installed


Hold the weapon as usual and slide the take down pin with the slot facing you, now slide the pin in the hole at the back and put a spring on of it.

The back of the gun as you will be looking at it.

Install the take down pin, retaining pin and spring, the groove facing the rear.


Begin installing the buffer tube by screwing it into the lower receiver. When you get close to the hole for the buffer tube retaining pin, out it in and hold it down with your thumb, continue to screw the tube until it covers a portion of the pin and line up the back plate over the retaining pin spring.

tighten the lock nut down



Torque it down, I will get you the exact setting a little later but if you snug it down nice and tight you will be ok.

Time for the butt stock. This one just didn't quite fit right. I don't know but it might be me.




Now it time to install the prebuilt upper and test.

The finished product!

John, looking good, I hope the Department is paying for all these upgrades

I got 2 lowers sitting in the safe I need to complete, if you and Brad keep posting topics like this I might actually get off my butt and finish em.

very nice tutorial I swear i am gonna buy an AR platform gun... but i keep talking myself out of the expense, and awesome posts like this are not helping me to kick the bug, hehehe.... but I am wanting an AR 308 platform....

Great Job John

Looks good!

Nice rifle! What optic is that?

Very good instructions! Thanks for the walk through.

RemMan700 wrote:Nice rifle! What optic is that?

It is a BSA red dot from walmart. I am waiting on the the CQB scope to arrive as well as the back up irons.

I needed something to shoot it with now didn't I