Product Description
"SM125 Armourer's plug gauge .307" - Bore reject - Rifles No 4 & 5, inserted at muzzle end. Must not enter muzzle more than 0.25 inch. SM125 has an engraved line at the end showing this measurement. For Vickers M.G. SM125 must not enter muzzle!"
(Source: https://forums.gunboards.com/archive/index.php/t-588729.html)
