1:7 vs 1:8 for service rifle

[Grig]

First time post although I have followed this forum for a few years and gained much knowledge. Thanks. Question: I have been a smallbore 3p shooter for a while (I'm 60). I am getting into high power service rifle competition. I am putting together an AR to that end. I have a lower ready to go. I am ordering an upper from White Oak. The service rifle upper from them I can get in either 1:7 or 1:8 twist. I don't plan on shooting heavier that 77gr SMKs but maybe I should. (I reload.) I shoot a lot of 55gr bulk Hornadys (bought 5000 bullets few years back). In short, which twist? I friend of mine says stick w/1:7 and you can shoot 80gr and heavier out to 600 yds. I was leaning towards the 1:8. Does it make a difference? Does an 80 grainer cheat the wind better than 77s? Thanks for the help..

 

[chkunz]

I have some experience that may be helpful. I have shot the M14 in the National Match Course since they dug the river but I have been shooting an AR match rifle now for several years and have been shooting 1:8 White Oak 20 inch and 26 inch barrels with good results. They shoot 77 SMK, 80 SMK, and Hornady 75 A Max bullets really well. I have not tried the 90 SMK in the 1:8 and do not think that would work, 1:7 would probably be a better choice for the 90 SMK. The 77 SMK was designed to be the heaviest bullet to be shot our of the magazine and it does really well even at 600 yards but the wind drift at 600 yards favors the 80 SMK. I would also recommend that you try the 75 A MAX at 600 yards. Some folks go with 1:7.5 and that is worth considering for your application. I have a report that my son and I wrote where we did considerable testing in this area. Send me a PM if you would like a copy.

 

[mac86951]

I really enjoy my white oak barrel, I selected a 1:7, however within 600y I'd recommend a 1:8. The 80gr Sierra is a single load only and anything else fed from a magazine will be lighter.

 

[Erud]

Both 7 and 8 twists are extremely common in HP shooting. Either one will handle bullets up to 80 gr without any trouble. You may be able to shoot 90's in the 7 twist, but most have decided that they are not worth the trouble for SR shooting. Just order whichever one is available or cheaper, you will not be able to tell the difference in target.

Good luck,
Erik

 

[Grig]

Thanks for the replies. I tend to be particular about these things and didn't want to overlook something.

 

[1lnbrdg]

If you enjoy shooting XTR, then go with the 7-twist. This rifle is really fun for 100 / 200 short range courses but the fun really starts when you get a full-distance 600yd range.

The 80gr Sierra shoots fine in an 1/8 twist but the 80 A-Max and the Berger 80.5 and 82 seem to need the 7-something twist to stabilize.

Having said that, 2 different times, I've had button-rifled barrels advertised as and marked as 1/8 that were closer to 1/8.5 twist and they wouldn't stabilize the 75gr Hornady BTHP, the 77gr Nosler or Sierra and weren't even close to stabilizing the 80gr bullets. It was very frustrating, if the temp/humidity were decent, the 75/77gr bullets worked but other times, they didn't.

All of my barrels now say 7/something twist and I haven't had the problem anymore.

 

[akajun]

either will work, but I would recomend the 1/7. Also, ditch the 55gr, shoot 77's at 2-300yds, and 80, or prefereably the 80.5 or 82 gr bergers at 600.

 

[Berger.Fan222]

either will work, but I would recomend the 1/7. Also, ditch the 55gr, shoot 77's at 2-300yds, and 80, or prefereably the 80.5 or 82 gr bergers at 600.

I tend to agree with this advice. Lots of good bullets in the 75-82 grain range: Sierras, AMAX, Noslers, etc. if you can't find the Bergers or prefer to shoot less expensive bullets.

 

[Grig]

Went with the 1:7. Thanks for the input. Will get the White Oak upper sometime near the end of October, hopefully.

 

[chkunz]

Probably the right decision. The 1:7 will be better for the 600 yard ammo with the heaver bullets and the 1:8 would be better for the 200/300 yard mag length ammo. Life is full of compromises but in this case it may be more theoretical than practical. Your XTC target was designed when the rules required the 30 06 round and is a very large target for the 223.

 

[DR1586]

I shot service rifle for a while. Started with a TRW M-14 and then switched to an AR. I shot nothing but 1:8s, using 77SMK, 80SMK, 75 HPBT, and 80 AMAX. I never felt like I lost anything by using a 1:8. Either way, the barrel twist won't buy you any points. So go with what you think is best, and practice with it and know your zeros. Before long you won't remember the twist when you're hammering X's. PM me if you have any more questions.

 

[people]

I have shot both and 1:8 is all I use now. I do not shoot anything larger than 80gr.