After reading these forums for a while, I started thinking about building an AMD 65 kit on a Tapco flat.
I think I've gotten most of the information I need, but I have a question I haven't seen addressed in any of the topics I've looked through.
Tapco's web site says their receiver flats need to be heat treated after bending.
How have you gentelman tackled this process?
What temperature did you use for the heat treatment and for how long?
How did you keep the receiver from warping during quench?
Thanks for any help you can provide.
I built two laser cut receivers made of 4130 steel and heat treated both of them. The first one I did the entire receiver and oil quenched. The specs for 4130 steel are as follows:
AISI 4130 Steel, water quenched 855°C (1570°F), 480°C (900°F) temper
As quenched hardness: 51 HRC surface, 50 HRC
After 900 deg. F temper :Hardness, Rockwell C 36
I did the entire receiver and I did not attain the hardness listed. I checked the receiver on a rockwell hardness tester and it was still soft or annealed. I then used my torch oxy/acy. and spot treated all the features I wanted and WATER quenched. The material hardened this time.
I did all of the fire control group holes,front trunnion rivet holes and receiver rails. I did the rails 1/2 at a time. After flame hardening and water quench I put it in the draw onev at 900 F.
When I checked some features this time they were in the Rc 35 range.
The oil quench was the problem. I think the metal cooled to slowly. If anything I normalized my welds from the first trip in the furnace. I did not get any warpage from the oil quench. I did get a little warpage from the water quench and torch treatment. Nothing on the rails but a small amount by the front trunnion rivets. This warpage is minimal and will not be seen after riveting the trunnion in place. Any future builds I will always use my torch and a bucket of clean water.