Heavy barrel No 1 rifles shoot really high, light barrels not quite as high, and No 3 virtually none at all.

It all depended on the cartridges getting wet, which will lead to more action bend.

The general rule of thumb back when 303 MK VII SAA was the norm was:

Heavy barrel SMLE: up to 10 to 12 minutes, depending on forend regulation method

regular SMLE: 4 to 5 minutes

No4 , 4 minutes with either central or front end barrel bearing.

No 3 rifle: virtually nothing.

Source :

Essentials of Marksmanship, Maj. Reynolds, 1964, page 93

I have seen something very similar in one of A.J Parkers write ups , circa 1958/9, where the main focus of his article was the heavy barrel SMLE did not solve all the issues with the SMLE and introduced some of its own.