I've been eyeing up the Primaris Marines from GW's new Dark Imperium box set (https://www.games-workshop.com/en-GB/Warhammer-40000-dark-imperium-eng-2017) with green eyes, partially because I've always been a fan of true-scale marines and partially because of those smexy new bolt weapons they're all carrying. Given their new size, they *might* just be useful enough at 54mm scale to act as real bolters, rather than the current weenie 40k bolters in the massive ham-hands of Inquisitor models.
I borrowed a bolt rifle arm off a friend and did some bluetack and photoshopping, and I think the results speak for themselves.
(http://www.dreadquill.com/wp-content/uploads/2017/06/primaris-54mm-comparison-1.jpg)
(http://www.dreadquill.com/wp-content/uploads/2017/06/primaris-54mm-comparison-2.jpg)
(http://www.dreadquill.com/wp-content/uploads/2017/06/primaris-54mm-comparison-3.jpg)
(http://www.dreadquill.com/wp-content/uploads/2017/06/primaris-54mm-weapon-comparison.jpg)
I'll be keeping my eyes to the internet for anyone selling Primaris weapons by the sprue I think!
This answers a question I had as I love the look of the bolt rifle! I too will be watching out for them to appear!