Much is written about what should arrest the barrel's downward movement at linkdown. Some say the VIS in conjunction with the link in compression with no contact with the receiver bed. Others say by the receiver bed alone with no compressive force on the link.
Based on Ordnance Dept. blueprint spec's it seems a vast majority of GI M1911A1's assembled with in-tolerance parts would have the barrel stopped by receiver bed contact.
This conclusion was based on determining what "size" link would be needed to halt the barrel's downward motion by contact with both the bed and the VIS, with the link just starting to get compressed. A slightly longer link would prevent barrel/bed contact and thus stop the barrel by link compression/VIS contact. A slightly shorter link could never be in compression and thus rely on bed contact to do the stopping.
Note: "Size", as used here, refers to the distance between the edges of the link holes [ O<size>O ] - not their centers.
The only assumptions made were: barrel bore axis was parallel to the receiver top at linkdown; barrel link pin diameter equalled the feet hole diameters for a press fit.
Calculations (lots of 'em!) led to 0.1056 +/- 0.0102 inch as the "size" needed to stop barrel downward movement by both the VIS and the bed. With no specification available for the link, a new, unused Colt standard "0.278" link was measured and its "size" was 0.097 inch. In a mid-spec GI M1911A1, this link is almost 0.009 inch short of allowing stoppage by both the VIS and bed, could therefore never be in compression, and would thus cause the barrel's fall to be halted by the bed.
Don't know what JMB's intention was for this, but it seems (to me at least) that most GI M1911A1's assembled with in-spec barrels, barrel link pins, links, slide stop pins and receivers would stop the fall of their barrels by contact with the receiver bed - and their links would be loose at linkdown.
If all this is close to being correct, why all the fuss about avoiding barrel/bed contact? Was JMB wrong? Or, does it really make any difference how the barrel's fall is stopped?
Bookmarks