so im getting ready to reprofile my first A2 lower. I bought 3 cheapo PSA A2 lowers to practice on and my main concern is how much of the reinforcement do i take off without compromising the buffer retaining spring hole (this may not be the correct name, but its the hole that can be found on the right side of the lower) And how much aluminum do i mill off towards the buffer end without taking all of it off (what is the measurement of the slight amount thats left on both sides in other words) Im using a CNC mill to do this on, but im using the manual control feature so i can get it very precise since i dont have a path drawn. Sorry if i am being unclear, i just am unable to find exact measurements of before and after reprofiling.
Thanks!

I suppose a simpler question is: what is the proper dimensions to reprofile the a2 lower to a1....... realized my last post may have been over complicated.

When I was going to do it I just looked at pictures over and over eyeballing it.

Then I chickened out.

It's worth noting that a reprofiled A2 will not have the exact demensions of a real A1, there is some material in the buffer tube area that is absent on an A2.

Good luck and post pics.

did you read this sticky that's located at the top of this page?


http://www.ar15.com/forums/t_3_123/294264_AR15_M16A1_Lower_Receiver__Model_Guide_Clone_Building_Guide_FAQ__redux.html

Brennon, about the "buffer retainer spring hole".....yeah, I think you are wanting to know about the "rear takedown retainer hole".  Buffer retainer is the one that you see right behind the fire control pocket, a vertical hole with the retainer that keeps the buffer from popping out when you seperate the upper/lower receiver. (it's at a 6 degree angle off vertical)
   The take down retainer hole,that runs alongside the right side of the receiver, that has a spring and retainer held in place by the stock or receiver plate on a carbine, is the one I think you are asking about. Here's the approx.dimensions off of an SP1 carbine I have.  The vertical rib, at the very rear of the receiver, is approx. .200 wide. It varies a little, as it flares very slightly at each end of the rib. The length of that rib, from the very bottom of the "rear takedown retainer hole rib" is approx. .700    
 As far as weakining the retainer hole......you shouldn't be changing the profile of that rib. If you look at that rib from the rear of the receiver (imagine holding the receiver so that you look at it as if looking down the buffer tube).  OK, so look at that rib from the rear.  The cross section of that rib won't change after reprofiling. You'll remove some material, but it will be to make the cross section/profile of the rib to continue on back to the .200 wide vertical reinforcing rib.
  If this is clear as mud to you, I can take a pic of one and place the dimensions on the pic.....or try to. Let us know.
I think the hardest part of the reprofile job is the reprofiling after the fence is removed from the mag button........if you do a slabside or partial fence.  The "S" radii, to match the S radii on the left side of the receiver, is pretty tough to do exactly.

i did but it gave no dimensions or anything of the sort. It is hard to tell how much of the rear portion is left extending from the back portion behind the retaining pin to the buffer tube area and how deep to remove the aluminum to give it the un reinforced look

Here is a crude MS paint of the areas im concerned about

OK........the rectangle block in red........it is approx. .200 wide....at top and bottom of rib (each end) it flares out to about .210 or so.  It is approx. .650 long on the left side rib, and approx .700 on the right side rib (on the rt side the length is longer, because I measured from the bottom of the horizontal rib that houses the rear take down pin/spring)
On the left side, the one you have pictured.......the bottom of the rib will start at the existing bottom edge of the reinforcement. (does that make sense?)

Just for clarity sake....are you taking this on because you just want to do it or are you taking this on because you couldn't find a lower with an A1 profile?

Nodak sells 80% lowers now with the A1 profile for example as well as complete lowers in the A1 profile.

Wes

Brennon.........you have an IM

Pics of my particular lower. After speaking to a forum member, we discovered that there are variations in manufacturers A2 forgings.

Pay someone else to do it!

Even if you don't buy Nodak...Their page has some useful photos:
http://www.nodakspud.com/AR%20Lowers.htm


Wes

I'd get a lower with distinct detention column under reinforcement spot. I've done two myself, paid to have one dobe. All mibe were 80 presenters that had standard a2 set up.  Build something else with that one.  

Having an A1 profile lower in hand to compare it to is a BIG aid in getting the profile(s) modified correctly. I would start with radiusing the heavy reinforcing from the top to the sides of the extension (buffer tube) mating area. As you approach the sides and the area in question, STOP and examine the transition into the area in question and pics provided by others.

Go Slow.

That is my rifle, and lower is a Braceman 80% reprofile FWIW.

Brennon, here are 5 different lowers. an 80% TM, a  Dalphon A2 lower, a DPMS lower,  SP1 carbine , and my 607 that I reprofiled from a TM 80%er
Your lower already has the correct profile existing. If you look at it from the very rear, that is the correct shape. If you were to "blue up" the narrow area in front of, and behind the reinforcement material that gets machined off, then you would have a guide of where to machine to. For example...........if you had the receiver laying on its' side on the milling table, and the narrow areas oneither side of the reinforcement were blued up, as you passed the endmill back and forth, dropping a little each pass, you would not want to touch the blue/dykem. Make sense?  After you removed all you could with that setup, then you would have the pocket/recessed area to mill out, leaving the .200 X .650-.700 rib left. (the rib at the very rear of the receiver)  Make sense? (if not, say so, and we'll try another explanation)

Brennon....alright, here's YOUR lower that you posted. I put it in "Paint" and we'll start with this. I blued up the areas in frt/behind the A2 reinforcement. Imagine that being dykem/High Spot Blue. The yellow is retaiiner/spring rib (the very rear of the rib already exists on your lower)  If you/your machinist has the lower on the millig machine table, laying on its' side, then you will pass the endmill "left to right" and "right to left", removing the A2 material. You DO NOT want to remove any of the blue or yellow. After the A2 material is removed down to the blue, the yellow will be left also. (there will be more material to remove after this machining operation)


OK.......so you are going to remove the red  material down to the level of the blue material, without removing any of the yellow. (since the A1 profile ALREADY exists at the very rear of your receiver now, you just remove red material down to the blue level. DON'T let the endmill touch the blue. You'll have to finish sand/polish everything to get it all to the same plane.


After that machining you should look like this.


In this last pic we'll remove the material that is green, down to the plane of the receiver side. Imagine drawing a line along the top edge of the receiver and continuing on back to the little vertical rib that you are going to leave, then down to the point where the rear take down pin rib would intersect the plane of the receiver side.........IF you continued the radius of the take down pin rib on around to the receiver side plane.  I know that sounds confusing, but you can see where the yellow gets wider IN FRONT of the vertical rib that you want to leave.
After that green material is removed, you'll work on removing the white material. You'll match the curvature of the front of the "ear" (the part of the receiver that holds the buffer tube)


Hope all this mumbo jumbo helps. If not, we'll try something else.
Stoner25mkiv

what/why does the green material need to be removed?

OK.......I might have made that confusing.    There will be material adjacent to/above the YELLOW. You'll remove that material just above the yellow, down to the level/plane, of the receiver side.  I represented that material by the GREEN, meaning that after that material is removed, it will be on a plane represented by GREEN........and all the green area will be at the same plane as the rest of the side of the receiver.   I could have painted the whole side of the receiver green. It would not mean that you remove material from the side of the whole receiver. It represents that anything green will be at the plane of the receiver side. (make sense?)  If not, say so and I'll try another explanation.

HMMMM......maybe this pic will clarify.   The outlined green rectangle in the pic above........it will have material that needs to be removed, down to the plane of the receiver side. (represented by all the green circles) Does that help explain it?  If not, say so and we'll try something else.
Stoner

Makes perfect sense! What is the radius of the yellow portion?

I'm at home at the moment and do not have radius gauges here. I can get that info for you later, but for now would it suffice to say that you will continue the existing radius that is at the very rear of your receiver.....that radius will continue on forward to the rear take down pin spotface.