Retro Score

The XM177 series has a unique stock.  It's similar to today's carbine stock, but it's made from aluminum instead of plastic.

Despite being the carbine stock from 1964 through 1985, they're quite rare today.

On the left is the one I found today.  On the right is the one I've been using on Sabrina since 2009.

I paid $200 for that stock back in 2009 because I wanted an authentic vinyl-acetate stock.  Today I paid $100 for one in better shape!

There's two companies making reproduction aluminum stocks.  One place wants $100 and it's not very accurate at all (they're also dicks so no link!).  Essential Arms (Item C2) reputably wants $150, and these are both complete sets with receiver extensions, buffers, nuts and springs.

Originals like those pictured above run $250 to $500 (depending on condition) on gunbroker for just the stock body.

How can you tell it's Colt?

The teeny, tiny markings on the right side; hidden by the latch.

Here are the markings on my original stock:

That's a "1".

An 'NN' inside a cartouche.

The new stock is marked:

Essential Arms marks their reproduction with a large 'B' on the other side nearer the butt end.