Kinda pricey, I use Wheelers Level Level Level which was under $20 back when I got it, but there are clones that are less than $10 now. Simple tool, but works great, maybe not competition accurate, but it does a good job on all my rifles.
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I ordered this one recently on Amazon $15.99, because a couple rifles didn't have a flat spot to use the magnet on and ARs are aluminum. Vials were loose, but some black RTV silicone fixed that. I was going to send them back but the others are more and the ones that are not are plastic.
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