Ar15 Lower: Jumping In

[n3480h]

Thanks Ron. Yeah, I might have said a bad word or three.
Got back at it today. Set the little flycutter for Ø 1.125" and cut a shallow circle in position for the buffer tube threading, then drilled the center and plunge milled near the circle's perimeter.


Switched back to the flycutter to take the bore to its final diameter. Pretty pleased with the finish the little flycutter delivers. I used the same flycutter to cut the chamfer on the edge of the bore. Also used it to cut the straight chamfer at the top rear of the buffer tube ring (far left in the pic). Located and center drilled the buffer tube key, then finished with a .500" endmill.


New setup got the breakdown pin detent drilled, (without breaking the bit off this time!), and milled the slot through the pin lug. This was done with a Ø .375" endmill, then opened up to .500" width.


Finished up for the day by milling and drilling the pistol grip boss. Now if I could just find that 1/4" fine thread tap I set aside for the grip.

Tom

 

[Rick Leslie]

Got my 1/4-28 taps off ebay. Great looking work BTW.

 

[n3480h]

Got my 1/4-28 taps off ebay. Great looking work BTW.

Thanks Rick. I get lucky sometimes. I did find my 1/4-28 . . . right in the very secure place I had put it so I wouldn't lose it. I was amazed how hard forged 7075 aluminum can be. Even though I used the correct pilot drill, it felt like I was tapping cast iron. Slow, with a lot of withdrawal to clear chips won the day and the grip screw fits nicely. I've started on the mag well, with all the corners drilled with 1/8th inch and bulk material drilled out with a 1/2 inch drill. Peck drilling and lots of WD-40 seems to be the ticket with deep drilling. Tomorrow I begin milling the mag well to final dimension. Getting close, so I better order the Cerakote. The 300 HBAR barrel, slick sided upper receiver, M-16 bolt group, and tactical charging handle arrived Monday from MAS Defense (great prices and fast delivery!). Back to having fun with this project.

 

[cozmogeek]

How many hours total do you think you'll have in this by the time you're done? It is pretty awesome but a lot of work.

 

[n3480h]

How many hours total do you think you'll have in this by the time you're done? It is pretty awesome but a lot of work.

A LOT of hours. But I'm not doing this to save time or money, just to learn milling processes and to enjoy the challenge. I enjoy the mill even more that the lathe because milling requires more planning and forethought, especially so with a minimill. And I suppose there is some "cool" factor in knowing that I machined the lower receiver for my 300 Blackout build.

Made lot of chips today milling out the magwell. I was definitely challenged with this op, since it's much more complicated than just a few holes. The good news is that it worked out great. I had very little filing/fitting to do, and the mag drops out just as it should. More luck than skill.


I was interested in shaving out the intersecting edges of the 1/8" holes as Brandes suggests. Since I have no carbide inserts to make the tool, I tried using a long boring bar I had in a kit from LMS. It worked very well, taking about .005" per pass. Not fast, but better and more precise than filing. The pic shows the "slick side" upper receiver I am using. No forward assist (never needed one) and no door. I clean my firearms often, so the dust cover door is not really required for my use.

Tom

 

[dave2176]

I have a 308 lower that has a tension set screw under the takedown pin. What do you think about adding a feature like this? I've been told it really makes a solid setup.

 

[Karl_T]

I LIKE your project. Neat fix on the OOPS. We all make them.

 

[n3480h]

Thanks Karl, I've gotten pretty good at fixing oops.
Dave, I guess I don't understand the set screw under the pin. I understand that it will positively capture the pin, but if the sprung detent is positioned correctly it will also capture the pin. Maybe it reduces play between the upper and lower receivers? Maybe its an AR10 thing - I haven't built one of those yet, so I don't have much knowledge about them.

What I have thought about is a set screw behind the trigger to limit trigger over-travel. I usually hone engagement surfaces on triggers and sears to provide a very smooth break and reduce creep, but whether or not I can safely limit the rear travel of an AR trigger remains to be seen. Definitely do NOT want to wind up with an auto sear. Perhaps a member here might know if this can be done. I've done it on bolt action rifles and semi-auto pistols with good results, but those are completely different than the AR platform.

Thanks again guys, for the encouragement and interest.

Tom

 

[Rick Leslie]

The set screw doesn't tension the pin itself, rather it tensions the rear lug. Pressing up on the lug theoretically removes the slop between the upper and lower at that point. (If I'm understanding the procedure correctly.)
As for overtravel screws, I have seen s 1/4-28 set screw put in on top (before) the grip screw and adjusted in such a way as to limit the trigger take-up. No help on the overtravel though.

 

[ScrapMetal]

I like the idea of putting pressure on the rear lug to eliminate slop but I ended up taking the "easy" way out and bought a few accu-wedges to get the job done.



http://www.brownells.com/rifle-part...cu-wedges/ar-15-m16-accu-wedge-prod16662.aspx


I shopped around and found them much cheaper than this one, seems a bit much for a small piece of silicone/rubber IMO.

-Ron