By the way, since I just realized not everyone here will understand why it's important for factory angles to be maintained on the M1 bolt and for both lugs to bear evenly, here is a little education. Because someone will get snickety about it, these images are NOT of a Marstar-sold rifle that I know of. They were off the CMP forum in the USA, but are illustrative ONLY.
USGI specs, for a field rifle, call for 80% contact on BOTH lugs to pass grade. If they gauge under that, they are returned for rework.
Here is an example of a gun where the lugs bore unevenly and the bolt failed. In this case, according to the CMP folks who examined the rifle afterward, only the right lug made contact and the left lug had been out by a gap of only .0035".
You can see the bearing lug sheared off and luckily the second lug held.
Another view:
A 1961 Watertown Arsenal study of the M14 bolt, which is built from the same steel and treated the same way as an M1 bolt, found its tensile strength to vary, as expected, from 275,000 psi at the case hardened surface to 200,000 psi at the inner edge of the case depth to 138,000 psi in the core. This shows that the bolts rely on surface hardness for wear characteristics and a lower core tensile strength (ductility characteristics) for "toughness".
Once a bolt lug is welded on, the whole welded area will only be as hard as the fully annealed strength of the welding rod used - which generally will be similar to untreated mild steel for the vast majority of welding rod alloys, and definitely less tough than even an un-welded bolt core which was heat treated at manufacture. Alas, we have no idea what Hauck (or is it Hack?) used for this operation. (PS: Funny he denies doing the work when the photos on his site show his MIG welder out on the bench, clearly "in use" next to a pile of M1 parts)
Now add in the fact that the bolts were ground, and we do not know if a fixture was used, how hot the lugs got, whether they became annealed from grinding heat (in case they weren't already annealed from welding), or anything really. I do know the photos show welds that would not pass magna flux or even dye penetrant testing. In my line of work they would be called what we refer to as a "visual fail" with "observable indications". A polite way of saying very poor welding. Like drunken worker poor.
Some bolts show the lugs undercut, for those engineers and physicists in the crowd, undercutting a lug creates a fatigue-prone stress concentration corner and increases the bending moment about the base of the lug, in line with the bore axis, that is likely to increase the shear stress impulse upon firing.
Translation: grinding a bolt and under-cutting the geometry into the edge of the bolt body magnifies the likelihood it will fail, above and beyond just welding on a lug, because of the laws of physics.
For those keeping a welded bolt lug M1, I felt it was important to explain the physics behind the risk you are choosing to undertake. Cheers.