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[HK416]

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[JMP]

Yes, it has an over-sized "tactical" bolt knob installed and a muzzle brake has been added. It is also a short action. It probably also has a new trigger and possibly work on the receiver.

Going that route ends up at a pretty pricey level where I'd personally just get a real AI rifle if that's what you like. You pay a little more, but you get a spectacular rifle that will shoot great right out of the box. Also, the space ship looking butt of the stock adds quite a bit to the price. If you don't need the fancy adjustments, you will probably end up saving with a more basic version of the stock, which has plenty of adjustments for most. The one thing with AI stocks is that I think it is well worth the price to get the folding versions because they do an exceptional job with a folding stock.

[ar15barrels]

Can you guys ID any other parts on there?
Like is it an aftermarket barrel and bolt/bolt handle being used?

And my last question is the AAC-SD a short action or long action?

That appears to be the factory AAC-SD barrel.
That barrel came with a threaded muzzle from the factory.
The AAC-SD is a 308 so that will be a short action receiver and chassis.
The bolt knob is aftermarket, but I can't say whose it is from those pictures.
The bipod is an Atlas.
The scope mount looks to be a Spuhr.