When I worked for the B & M---I quit in 1986--- I had a chance to see the rail welding operation. The B & M bought the Monon's rail welding plant from the L & N. A very long straight track was used in the yard at Billerica. A open sided shed was constructed with electrical hook-ups. A string of about 25-30 gondolas with ends knocked out and rollers mounted on the floors was backed up to the shed. A 39 ft. rail was placed in position; 18 inches at each end where the joint holes were punched was cut-off. A second rail was then positioned and likewise sawn. Then some kind of compound was placed on the two freshly sawn pieces to be joined, they were clamped together and welded. Then the rough edges were sanded or buffed. The weld was tested for quality and then the rail gang got together and with muscle power pushed the 72 ft. section onto the rollers in the first and second gons. After a time I suspect the ever lengthening string was pretty heavy and I suspect a front end loader/swing loader or some other type of machinery gave the push.