Rated SPCII?..I personally have resisted unless the barrel is like $50 to go other than 1-11 as the ARP barrels are so cost effective. For hunting I doubt you would see much difference though.

 

I've got a older pacnor 1-10" and my son and buddy both have arp 1-11" barrels and they all shoot the same loads equally well.

 

Depends on barrel rifling specs, chamber. 1:11 seems to be the sweet spot. Watch out for older 10 twist barrels with the obsolete SAAMI chambers.

RRA, BARRETT, and LWRC are three companies using 10 twist and SPC II chambers that perform well.

That at said, the sponsors here have great products with a lot of time involved in the 6.8.

 

From what I have researched so far, the twist is not nearly as important as the chamber. The SPC2 chamber design gave the freebore it needs for better hand loads, with better velocity while keeping down excessive pressures. Somewhere I have read that until you get down around 1:4 twist does fast twist to rifling have much bearing on chamber pressures. Also, the ratio of lands to gooves plays an important part as well. Personally, I would not worry too much about 1:10 over 1:11 twist.

The faster 1:10 twist can stabilize a little bit heavier (longer) bullet than 1:11 or 1:12.

 

... Also, the ratio of lands to gooves plays an important part as well. Personally, I would not worry too much about 1:10 over 1:11 twist.

The faster 1:10 twist can stabilize a little bit heavier (longer) bullet than 1:11 or 1:12.

The ratio of lands to grooves is extremely important. You need enough land area to securely grip the bullet at velocity but not enough that it causes too much friction/resistance. This is where the 5 and 3 land rifling shine as they distort the bullet less than trying to squeeze the bullet from opposing sides that an even number of lands will do.

The 1:10 twist barrels with 4 grooves are generally better than the 1:10 with 6 grooves.

SPC II or other improved chamber is also a good feature to have as it will reduce chamber pressure. The 10 twist does have the potential to stabilize longer, heavier bullets.

Additionally if the cost of the barrel the OP is looking at is more than about $150 my opinion would be go get an ARP 14.5 which is $205 shipped.

 

What Works For Me

I am a big believer in the faster the twist the better. This,of course,within reason. I like my 223Rem's with a 1:7 or 1:8. Anything slower is not for me. Same with a 308Win. 1:10 ONLY. In 6.8SPCII I want a 1:10 although I have a Bison that shoots great.

My reasoning is pretty simple. I feel that the bullets terminal ballistics is much better with a bullets rotational velocity right up there. EXAMPLE: My 85gr Barnes @ 3000fps out of a 10 twist bbl is spinning at 216,000RPM. Out of a 12 twist bbl it will "only" be spinning at 180,000RPM. I believe that the difference means quite a lot in the bullet opening rather quickly and starting a shock wave close to the surface of the animal where it entered.

You people shooting the 120gr Hornady SST's. IMO the rotational velocity of the bullet will make a lot of difference on the wound characteristics. I will be shooting this bullet out of a 1:10 twist bbl .... however .... it will be leaving the 10.5" bbl at 2250fps. This bullets rotational velocity is "only" 162,000RPM. I'm hoping that this will hold it together somewhat and keep the jacket and lead core together. If this was coming out of a 12 twist bbl the rotational velocity would "only" be 135,000RPM. IMO,with this combo that bullet should perform excellent.

Remember also that the forward velocity of a bullet slows down pretty fast. The rotational velocity does not. Even at the extended ranges the bullets rotation only slows a couple hundred RPM's. --- pruhdlr

 

I am a big believer in the faster the twist the better. This,of course,within reason. I like my 223Rem's with a 1:7 or 1:8.

Did you know that the M855 has a steel penetrator that is unstable, and is the only reason for the fast twist in the later M16A2 barrel? It has nothing to do with a heavier bullet.

 

Formula for information:

A bullet fired from a rifled barrel can spin at over 300,000 rpm, depending on the bullet's muzzle velocity (MV) and the barrel's twist rate.
The general formula for calculating the rpm of a rotating object may be written as

where

is the linear velocity of a point in the rotating object (in units of distance/minute) and C refers to the circumference of the circle that this measuring point performs around the axis of rotation.
For a bullet, the specific formula below uses the bullet's MV and the barrel's twist rate to calculate rotational speed:

• MV(in fps) x (12/twist rate in inches) x 60 = Bullet rpm

For example, a bullet with a muzzle velocity of 3050 ft/s (930m/s) fired from a barrel with a twist rate of 1 in 7-inch (180 mm) (e.g., the M16A2 rifle) spins at 313,714 rpm.
Excessive rotational speed can exceed the bullet's designed limits and the resulting centrifugal force can cause the bullet to disintegrate in a radial fashion. from Wikipedia.org (cut/paste)

 

I Use .....

..... ---> MV X 720 divided by the bbls twist rate ='s bullet RPM.

A solid copper bullet will not be pulled apart by centrifugal force. Generally,a copper plated bullets rotational velocity has to get upwards of a half a million RPM's before they will actually come apart in flight. This,unless you have a very rough bbl. Now......... hit one blade of grass,different story. --- pruhdlr

 

Rotation? ? We don't need no stinkin' rotation!!

50 grain 223 VMAX at 3750 out of a 1:8. Like an atom bomb whan it hits a PD but out of 200 fired during load develpment two never reached the target. I'm moving to Noslers with a heavier jacket.



Nothing like a comet tail to get your attention.

Greg

 

What chambering were these 50's hitting 3750?

Heinous typos thanks to autocorrect.

 

Out of a bolt gun, not an AR, with a slower twist barrel burning 30% more powder. No doubt it is faster.

Greg

 

That is one thing about the 6.8 we can't get enough speed out of them to blow up a bullet from the roational speed. I prefer a 1:9 for the 22's since I use them mostly for varmints and the liitle bullets can handle that normally. This one is just s a bit hot for that without bullets selection coming into play. It was built to shoot slightly heavier varmint bullets .

If I were indutrious and curious I'd do a 1:7 for pure long range with the good target bulets and then shoot some little ones to see what the speed limit is. As it is I'll settle for what I'm getting especialy since the accuracy is there at speed too. I could see a 1:9 in the future as they are now available and I can handle a wait of three weeks or so from Black Hole. Maybe a Savage in this one to go with his little brother.

Greg