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Discussion Starter #1
new to the 6.8apc.
I recently traded for a brand new upper. The barrel is stamped “6.8 SPC II 1:10”
I’ve read many people stating the 1:11 is the more common twist rate nowadays for the SPC II.
I picked up two boxes of XM68GD to sight in (I haven’t sighted it in yet). Will this ammo be okay? What other bullet weights should I try?
How else can I tell if my barrel is SPCII? Anything else to look for?
I will mainly be using this for deer hunting / hog hunting
Thank you all

64115


64116
 

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One of my 6.8's is a 1:10 barrel. Shoots 90 and 110 grain bullets fine.
 

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It should be fine but you may find that it likes heavier bullets better. Hornady 120gr sst etc
 

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The deal with 1:10 vs 1:11 twist had more to do with the land/groove ratio than than the actual twist rate. Most manufacturers that use 1:10 twist use the same barrel blanks that were developed for the 270 Win, which has a 6 groove barrel, and a higher land/groove ratio, which produces lower velocity for the same chamber pressure when compared to a 3, 4, or 5 groove barrel with a lower land/groove ratio. The fact that they also used a 1:11 twist made it easier to tell barrels apart. That's why the 1:11 is more desirable.
 

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With the way factory ammo is loaded these days the 10 twist should be fine. If you hand load and work up you will be okay there also.
 

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Have two 1:10 twists (along with three 1:7 twist) 6.8 spc II barrels which I use for shooting 110, 115 and 120 grain bullets. The 1:10 tubes will stabilize 130 grain pills enough for plinking but not precision accuracy.
 

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The difference between 1:10 twist and 1:11 twist in terms of pressure and velocity is miniscule. In practice I can shoot 1:11 twist 6.8 barrels next to 1:7 twist with a 110 grain bullet and see zero difference in accuracy or velocity. Litz conducted an experiment and found the effect of twist rate on velocity was on the order of 1.3 fps per inch of twist:


I claim that it doesn't matter at all, any ammo you can shoot in an 11 twist barrel you can shoot in a 10 twist, all else being equal. The only practical difference being that the 10 twist barrel can better stabilize some 120+ grain bullets better than the 11 twist. This will also give those heavier bullets higher practical ballistic coefficients (turns out that BC is a function of twist rate when you are close to the stability margin for a given bullet).
 

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This is another bit of information I have been wondering about. I am totally impressed with the knowledge of individuals on this forum. Everything from Constructor and the info he provided on the the differences in 6.8 SPC chambers, to Xman bullet info to scope info from multiple individuals to reloading and now barrel twist rate info.
 
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