With short (18-20") barrel, am I overly limiting my caliber choices?

Mark21

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Mar 19, 2008
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Took an intermediate distance course this summer (400-600 yards) and loved trying out the various 16" and 18" semi-auto .308s others brought to class. Given where I live, 600-800 is the limit I will be shooting at for the foreseeable future. So I went ahead and recently bought an AR10 lower and was talking to my smith about a short .308 using a Rock Creek barrel when he told me, "You already have a hammer of a .308. Try something new." [I have a custom Surgeon/Rock Creek 24" .308 bolt gun that he built, and also an 18" 6.8SPC AR15 that I used in that course]

Point made by my smith, but when I researched the rounds that may interest me (.260 Remington, 6.5 Creedmoor, perhaps .243AI) they all seem to be in the sweet spot with barrels around 24" or so. Seems an 18" .260 Remington doesn't really buy me much compared to a .308, except that I would have to reload a lot more using the former!

Thoughts from any guys out there that perhaps run shorter barrels in "alternative" calibers? Or should I leave those to longer barrels and just make the short .308, since it is a semi after all, so not exactly a dupe of my bolt-gun?
 
A few guys here have posted excellent numbers from short (17-18") 6.5 CM bolt guns running 123 Scenars and Varget and are getting ~2850fps without pressure signs. The 123 Scenar has a G7 BC of .265.

Right now I'm getting 2925fps out of 123 Scenars and H4350 with a 22" 6.5CM barrel on my JP but want to build a short/light upper too. I'm planning on having JP build an 18" 6.5 Creedmoor with and playing with the 123 Scenars, Varget, and H4895. Hoping for 2800-2825fps out of a handy short & light rifle.
 
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Look at it this way, if you go with a 6.5 caliber and push 123’s at 2750-2850 or 140’s at 2550-2650 it would take a 24+ inch barrel and a very high performance 308 bullet to even keep up with you in drop or drift. Go to JBM and run some numbers.