Gibbs

Boots Obermeyer may have a different opinion on 5R vs others as being bull, but he is pretty much the one that invented it many years ago. Several of the major barrel makers learned from Barrett Obermeyer on their practices. I agree it is all different and all subjective to one's opinion. This link: http://www.stockysstocks.com/servlet/the-666/Rock-Creek-5R-Cut/Detail gives a very good account of benefits of 5R barrel and there are probably others as well as there are others that stick with simple 4 or 6 groove patterns for their rifling. 1:10 twist will handle every bullet out there that you might want to shoot form an AR-10. Some might say they work their best on the 165 and 168 match bullets with boat-tails the best. What I have been told is that the heavier bullets need a bit faster twist to stabilize them well. In the 6.8 SPC they found that 1 in 13 twist would work on 90gr, 100gr and 110gr, but when you loaded in the 120 grain it was not enough twist to give the bullet performance that the bullet was capable of doing. In 6.8 SPC the 1:9 was ok, but was not able to handle the higher pressured SSA ammo as well, and some of it was due to the fact that the chamber was not set up as as SPC2 chamber. IE there was only 0.050" freebore on the original SAAMI specs of 6.8 SPC where most of the newer barrels and makers are using chambers with 0.100" freebore with the relaxed twist of around 1:11 and some out there of 1:12. In handloading you would see pressure signs with less powder in the tighter SPC1 chambers over the SPC2 chambers with the longer freebore. Kind of like the 5.56 NATO would be with it's longer freebore for hotter military rounds as opposed to the .223 Remington ammo. You could shoot 5.56 x 45 ammo out of a barrel just made for .223, but you could not (should not) do it very much as there are higher pressures. Gas systems have an effect on chamber pressures as well, since the hole for releasing the gas to move the bolt carrier is closer to the bore, they pressure at that point is higher than that of mid length or rifle gas systems. Further down the barrel those latter gas systems also take a little larger port hole for the gas block since there is less available pressure/gas at that point for bolt carrier movement. Taking these things into account, there are very nice .308 rifles out there in the AR platform that do exceptionally well with 1:10 twist and 4 or 6 groove rifling. They are, after all, somewhat designed for battle rifle conditions and as such if you look for extreme accuracy, you are better at looking at bolt action .308 over the gas operated semi autos like the AR series. The barrel I have is not really bad at all. I have been able to get a group at 100 yard of 0.366" using 150 gr Hornady SP bullets non BT with molly coating. I just think it would be (my opinion) a nicer shooting rifle and a bit easier on brass for reloading if I had a mid length gas system barrel on it.

a "looser twist" would refer to something like 1 in 11 or 1 in 11.25, or even 1 in 12. I remember reading one time, from a pretty knowledgeable barrel maker that the less twist it takes to stabilize a given bullet, the better. 1:11 is a bit "looser" than 1:10 and will still stabilize the 168 gr bullet very well. It would stabilize 150 grain without any issues at all. By "loosening" up the twist, you can reduce pressures slightly, as they did this with the 6.8 SPC. By going from 1:10 to 1:11 or even 1:11.25, this allowed for a bit hotter handloads.

Brownell has a 16" barrel 5R rifling 416R SS here: http://www.brownells.com/rifle-parts/barrel-parts/rifle-barrels/308ar-barrels-prod69784.aspx?avs|Cartridge_1=CTT_308 Winchester They are not 1:11 rifling, as I think those can be handloaded a bit better than 1:10 twist barrels. Not promoiting any website, but that link shows info as to button riflled barrels, all ready for mounting into a receiver. Just wish it were 1: 11 twist rather than 1: 10. I feel that the looser twist might open up with less pressure for handloading. My recent batch with 150 gr Hornady are pretty good groups using IMR 8208 XBR powder and magnum primers.

Many thanks!

Not many out there. Have seen a few 5R rifles, and have a 6.8 SPC that I put together with an AR Performance 5R barrel, and wanted to see if I could find one in .308 for my new LR 308. I actually started out looking for a mid length gas barrel as I really don't like the carbine length gas in the DPMS LR308 rifle I have. So, I figured if I can look for a mid length gas system, why not look for one with 5R rifling as well. Not a lot of choices out there. Boots Obermeyer made the first 5R barrels some years back and he cuts barrels pretty deep with his barrel making machinery, rather than using button rifling. What have you all heard for 5R barrels, 16" length mid length gas systems? Ranier Arms has some, but they say "Polygon" barrels and I am not well versed on that style.

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