If so, did tapping the buffer tube hole trash your tap and also how did it go drilling those small detent holes?  I was thinking cobalt drills might do ok for the drilling... but those hss taps could dull quickly.  Perhaps it would be good to drill the buffer hole a little oversize for shallow threads and utilize a little JB weld to help hold the tube in place with weak threads.

What in the world was the lower made out of that would trash a tap?????? The buffer tube hole has to be the proper size before the tapping process is started. If you tried to tap the original casting hole then you might trash your tap. The hole is too small to tap so a drill is to be used first.If the casting is made of aluminum it is easy to drill. Make sure the small drill bit is turning real fast when you drill small holes. If the hole is deep you need to clean out the hole several times before you get to the desired depth. Hope this helps you.

Thanks, but I'm asking if anyone has any experience tapping those SS castings, which are quite hard.  I burn thru taps very quickly tapping the trunions on AK47 builds.

If the SS dulls the taps I may just build all the 7075 aluminum lowers I want before trying a SS one.

Howdy,

You have either one of two problems,

A cheap tap or a SS forging that is "poor".
If you are using a Sossner/Greenfield/other brand name tap and the they are turning to junk then the forging is poor. It has too many hard spots or it is "work" hardened.
Are you sure it is a casting ? No matter, even castings can have hard spots in them.

Make sure the hole is the correct size before you try to tap it. If you are trashing taps, stop, you are just wasting money.

Those AK47 trunions are hardened.  I did go to TiN coated taps and those lasted much longer than HSS for the AK builds.

I know the AR15 stainless castings are very hard also... not as hard as the AK trunions.  The only AR buffer tube taps out there seem to be HSS.... and at $45 a pop you hate to even dull one of them.