Originally Posted by ronin.45
The chart tells me that I should go with "+1" sights for the 21 vs. "+0" for the 17.
What chart is that? Glock OEM fixed rear sights do not use such terminology. Glock's authoritative document of proper factory
rear sight elevation is found in the Glock Certified Armorer Parts List and Will-Fit Info
(see page 5).
Why is that? If they are very close in sight radius should there be much difference?
The exterior ballistics
of the cartridge being fired have great effect on determining the required rear sight elevation to achieve impact at or near point-of-aim. Those ballistics are quite different between 9x19mm and .45 ACP! A slower projectile will drop more in flight to cover the same distance to target
than will a high velocity projectile...thus the slower projectile must be fired with its barrel elevated more than the barrel of the higher velocity projectile.
The G17 is supplied with a 6.5mm elevation
fixed rear sight. This is indicated by a mark on the right-hand side of a Glock OEM rear sight of a single long dash
The G21 is supplied with a 6.9mm elevation
fixed rear sight. This is indicated by a mark on the right-hand side of a Glock OEM rear sight of a short dash above a long dash