We are going to deal with an AR-15, M16 and M4 rifle and carbine platform problem known as “Front Sight Base Cant”, or FSB Canting, and how to correct it
Franco Palamaro
The FSB cant problem is obvious in this brand new upper, zero on the iron sights is impossible to achieve on the range
Franco Palamaro
A typical AR-15/M-4 Front Sight Base, mounted on the rifle barrel with tapered pins
Franco Palamaro
It may be easier to just replace the front sight base with a gas block. Blocks are available with or without Picatinny rail
Franco Palamaro
An alternative is to use a clamp-on FSB, in this case both standard and foldable styles are available
Franco Palamaro
The upper receiver's indexing pin slot is easily visible
Franco Palamaro
How the barrel, front and rear sight have to be aligned to achieve a "mechanical" zero
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