Gimp seems to do plenty well with a 20 inch 260. 27-2800 should still be achievable with 140's no? go with the factory length and whack a suppressor on the end. Lop of an inch is you fancy it should still have you clear of the flutes. My rifle is an 18" plus can, honestly I dont think an extra 1 or 2 inches would make any practical difference in the bush
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