Changing out A1 Upper housing for A4 Flattop

AR/M4 AR Technical Discussion
1

Okay…I finally found A4 Flatop reciever and want to change it out with the original A1. I have been reading how its done for a while but I cannot find the upper housing vice block anywhere and none of my local gunsmiths have one. Is there any other safe way to hold the upper reciever housing steady while loosening and re-tightening the barrel nut, and not damage the housing??? One thing I was thinking of was using 6" lengths of 1 1/2" angle iron. I have some 1/16" neoprene sheeting so I was going to wrap the housing with it and place the angle iron on both sides lengthwise. The upper leg would ride against the base of the picatinny rail and the lower against the mounting lugs, using brass to fill in the difference. My vise has angled jaws that the angle would fit the angle iron perfectly. Have any of you done it differently and if so how??

Here’s a crude drawing of how I would do it…would this work for a one time installation???

2

I wouldn’t trust it. Brownells has the DPMS block for $50: DPMS Block

It’s a worthwhile investment. I use mine all the time. Don’t forget to get a good barrel wrench, as well.

3

If you look around Brownell’s site, they may even have a video that shows you how to make the change and show you the tools needed.

John

4

I would be willing to loan you my DPMS block if you are interested.

Buckaroo

5

I agree with everyone else - either invest in the proper tools yourself, or borrow them from someone. I’m afraid that if you did it the way you proposed you’d end up with an interesting paper weight.

6

If interested, mail the upper and new receiver to me and I’ll swap your parts and mail it back as part of a trade deal for the old A1 (been looking for a used one and I have all the tools).
We can work the details via email, if it sounds at all appealing.

Cheers,
Otto

(same “otto_esq” from AR15.com, add a “@hotmail.com” to contact me)

Any time, and the finished prodect looks great! - too bad you want to keep the old upper – if you change your mind… :wink:

7

otto,

Thank you for the offer!!! I went by a buddies to talk to him about his newest AR, he finally found a Colt 6920, and he had a vise block and lent it to me to use. I already have a DPMS combination wrench and all the punches, torque wrench and large bench vise I will need. I am planning to make the change today.

tex

8

Well using the block was the way to go and it took all of about one hour to make the switch. Everything went into place perfectly and I was just amazed. Now I have a more versitle gun gor home defense and just fun shooting. I think I will keep the A1 upper for a future retro build I am thinking of…who knows??? Here is the finished product and everything I want to do to this little Bushmaster except finding a rear folding sight.