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A lot of the Mark VI rifles were converted to Sniper Rifles when WWII broke out. ...snip...
This is not true. None of the No1MkVI rifles were converted to snipers.
The No1MkVI does not have enough height on the left receiver side rail for the front pad, and the lightening hole on the rear of the action interferes with the location of the rear pad....ie) there is nothing to screw to.
The initial sniping No4 conversions were based on the remaining No4MkI trials rifles dated from 1931 thru 1933 (some may be dated as late as 1936, but earlier dates are overstamped).
Having said that, part of the confusion may be linked to 2 facts:
1. The initial 1931 No4 trials rifles were originally designated as "No1MkVI" (there were at least 3 main MkVI varients) until someone recognized that there were too many changes from the MkVI and redesignated them as No4MkI rifles.
2. Existing MkVI rifles and actions were rebuilt to as close to No4MkI status as possible so that they could be utilized. MkVI rifles will be found with No4 wood, barrels, bolts, sights and other parts fitted as necessary.
NOTE** I understand that on some of the early receivers, you
may be able to see part of the overstamped original MkVI designation markings on 1931 dated No4MkI trials rifles.