Paul,
Lilja is as good as any of the best 6.5 barrels. They are a family run business who stand by their quality. They manufacture barrels for civilian national/international matches and are the choice for DEVGRU's recon rifles (the 'M4 Navy' profile - they have a slightly longer 18.8" equivalent profile in Grendel called the '319'). They stamp their barrels with their logo (see their website) so you know it's legit.
Grendel has the smallest case of all the popular 6.5 calibres. That's why it can fit in AR15 mags and use its relatively fragile receiver. Because of this however it is a relatively slow calibre. If bullet expansion is designed as low as 1,500fps then 400m will be its max effective range. Some bullets need at least 2,000fps which is only about 200M in Grendel. This doesn't take into account bullet placement of course and these are broad benchmarks. Also the bullet is influenced by the wind more than the other 6.5 calibres. If long range hunting is your thing then the calibre is not a good choice, regardless of barrel length. 20" and longer is almost compulsory for what you are planning. If longer than 20" you may as well get an AR10 in a larger calibre, with a more normal length barrel typical of an AR. Or get a bolt gun, which will be around 22-26" length. And if you get a bolt gun you may as well get it in a larger calibre. Again, all this for long range hunting.
But surely you can get closer than 600M for the shot.
Lilja is as good as any of the best 6.5 barrels. They are a family run business who stand by their quality. They manufacture barrels for civilian national/international matches and are the choice for DEVGRU's recon rifles (the 'M4 Navy' profile - they have a slightly longer 18.8" equivalent profile in Grendel called the '319'). They stamp their barrels with their logo (see their website) so you know it's legit.
Grendel has the smallest case of all the popular 6.5 calibres. That's why it can fit in AR15 mags and use its relatively fragile receiver. Because of this however it is a relatively slow calibre. If bullet expansion is designed as low as 1,500fps then 400m will be its max effective range. Some bullets need at least 2,000fps which is only about 200M in Grendel. This doesn't take into account bullet placement of course and these are broad benchmarks. Also the bullet is influenced by the wind more than the other 6.5 calibres. If long range hunting is your thing then the calibre is not a good choice, regardless of barrel length. 20" and longer is almost compulsory for what you are planning. If longer than 20" you may as well get an AR10 in a larger calibre, with a more normal length barrel typical of an AR. Or get a bolt gun, which will be around 22-26" length. And if you get a bolt gun you may as well get it in a larger calibre. Again, all this for long range hunting.
But surely you can get closer than 600M for the shot.