AccuShot MonoPod for AI AX

The rear of the AX chassis has two keyslots on the underside so that you can attach one of the rail sections that come with the stock for using a monopod. You'd have to use something like a BT12-QK.

Amen on this.
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I have an accu-shot monopod but if I had to choose between the two, I'd go for the butt-spike. As nice as the Accu-shot is, it takes up some real estate and when deployed (NOT extended) it already has the butt elevated a good bit, see pic above. What I like about the butt-spike is that it's relatively low profile and you just extend from there....if that means something to you, maybe it doesn't but something to think about.