Optimal Twist for 6.5CM and 260 Rem

D

daved

Full Member
Full Member
Minuteman
Mar 28, 2013
163
21
Las Vegas, NV
#1
I've been doing some research for a custom build in 6.5 - leaning towards the CM but haven't ruled out the 260. One of the things I've noticed is that 6.5 barrels from Bartlein are offered in 8, 8.5 and 9 twists but the custom tack-drivers from GAP use 8.2. I was curious as to whether there is any difference between this custom twist and the standard ones in terms of accuracy.

Thanks for any comments,

Dave
 
#3
Great thread. I hope to get some info on this subject as well. I've used the 8twist for the 140 vld with good results. I've been working with a 8.5 twist recently w/ the 140 vld and also good results. What is the 8.5 twist optimum for?
 
#4
I run an 8.5tw on a 6.5x55 with 140g Hybrids with absolutely no issues. I'm basically at sea level. If you do the math on stability (and believe it) the only time an 8.5tw won't work most of us won't be outside and I'm not sure you'll find those conditions in the contiguous 48.

L
 
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#7
A 1:8.2 sounds like a good compromise to keep in stock as it’s faster than 1:8.5 and just a little slower than 1:8 and cheaper than stocking both, thereby, making it easier to sell to customers that read something on the internet and want one twist over the other because of it, verses real world experience with both twists. IIRC, it was Obermeyer that said an 1:8.7 is all that is needed for the 139-142 class bullets in .264 but how many of those do we see. FWIW, I have both a 1:8.4 and 1:8 because that was what was available at the time and I have never had any issues with any of the heavy weight bullets with either in DA's down to -1000'.
 
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#8
My barrel is a 1:8" and my buddy has a 1:8.2". Both are barreled actions by GAP...both shoot the SMK 142 great...other bullets shoot great too, but we've went with the SMK due to price and availability. (Everything shoots good through it to be honest...)
 
#9
I would only run a 1-9 twist if your not shooting bullets over 120 - 130gr. The 130's should shoot thru a 1-9 but I haven't done any twist rate calc's on them. If your shooting around the 140gr. bullets a 1-8.5 would be my minimum. You won't see any real performance increase for the faster twist other than maybe piece of mind.

GAP using the 1-8.2 I feel the reasoning is it bridges the gap between the 1-8 and 1-8.5 so it kinda satisfies everyone.

I've got a 1-8.5 on one gun and a 1-8.2 (maybe it's a 1-8.3) on another gun.

I've shot 120's, 123's, 130's, 139 and 140gr. bullets thru both guns and cannot tell a difference in how they shoot. Both guns are chambered in .260 Rem. and are bolt guns. GAP built me a GAP10 and it's also in .260 Rem. and again I cannot tell any difference.

Later, Frank
Bartlein Barrels
 
#11
Over the last 2 years, our club has ordered over 100 8.5 twist 4 groove and 5Rs in 6.5mm from Bartlein. We have yet to find a reason to switch.

Personally, I prefer a 4 groove over a 5R in this particular caliber.
 
#13
For me, I loved how nice the Swedish Mauser cut rifled barrels are, and wanted 4g, my last few Bartleins shot lights out, no reason to change, but I doubt many could tell any difference. Just my opinion. If your rifle is smithed right, a Bartlein with the right twist, load, and shooter will do as expected, and maybe then some!

As a side note, I had a Sako 75 sporter, 9 twist OEM, it shot 139s and 140 Amax, no issues, only grouped at 100, using 130 ABs it shot 1/2 MOA. I would never build a 9 twist unless you were sure you were shooting 130s and under. I had a 6.5-308 done before the 260 was Saami'd, it was ordered 8, but I received a 9, it never shot 140s when I tried, 100-129s did fine. Plenty of folks use 8.2-8.5 w/success, and it is conceivable they might squeak a few fps more and perhaps, a miniscule less metal fouling occurs.

Again, for me, it's 8 all the way, and that is for 260, Creedmoor, or 47. If I were using a 284 or 06 case, or 264 WM, or WSM, an 8.5 or even 8.7 might make good sense to keep pressures in check, as you are increasing RPMs simply by more FPS, so they can get by with a little less rate.
 
#14
Layton,

I have had two 5 grooves shoot right under 1/2moa, but everyone of my 4 groove 260s shoots 3/8ths or better. Normally in the .2s, and my Polarbear 2.0 rig is in the .1s after the 20th round down range.

My first KMW 260 was a 4 groove....that thing was the magic stick. I am sure it had a lot more to do with Terry Cross's pixie dust he sprinkles on his builds, but that rig drove like no other. The test targets were in the .1s after like 7-10 rounds

The 4 grooves seem to break in better, shoot faster, and just drive lil holes.

Some say a 5R will give you better barrel life, but after shooting against the other 20 to 30 260s rigs we have in the club, I don't really see that. We get about 2500 to maybe 2800 good competition rounds out of a barrel. Will the gun still shoot tight? Sure. However with the cost of bullets these days, I rather swap a barrel and squeeze out all the performance possible. Once it takes me 9mils + to get to 1K at Sac Valley, it is time to schedule a rebarrel.

Disclaimer: I am not a smith, nor a smart guy when it comes to this shit. These are just my observations and experiences. + the whole holiday day inn express thing.... :)
 
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#17
NorCal Vu said:
Layton,

I have had two 5 grooves shoot right under 1/2moa, but everyone of my 4 groove 260s shoots 3/8ths or better. Normally in the .2s, and my Polarbear 2.0 rig is in the .1s after the 20th round down range.

My first KMW 260 was a 4 groove....that thing was the magic stick. I am sure it had a lot more to do with Terry Cross's pixie dust he sprinkles on his builds, but that rig drove like no other. The test targets were in the .1s after like 7-10 rounds

The 4 grooves seem to break in better, shoot faster, and just drive lil holes.

Some say a 5R will give you better barrel life, but after shooting against the other 20 to 30 260s rigs we have in the club, I don't really see that. We get about 2500 to maybe 2800 good competition rounds out of a barrel. Will the gun still shoot tight? Sure. However with the cost of bullets these days, I rather swap a barrel and squeeze out all the performance possible. Once it takes me 9mils + to get to 1K at Sac Valley, it is time to schedule a rebarrel.

Disclaimer: I am not a smith, nor a smart guy when it comes to this shit. These are just my observations and experiences. + the whole holiday day inn express thing.... :)
Click to expand...

Hey Vu and Layton! I don't think the number of grooves has any bearing on barrel life with everything else being equal.

Faster or slower with the number of grooves? A difference of a 100fps from barrel to barrel is considered normal. Changing the groove size will have a bigger impact on pressures and velocities. If one barrel is .2640" on the groove and the other is .2643" on the groove that can cause a difference.....sometimes and I'll throw a but in here. What chamber reamer is used in one guys gun vs. what spec. reamer is used in another guys gun can have an impact on velocities as well.

Some years back I had a 4 groove, 1-8 twist, 6mm Rem. chamber barrel on one rifle and on another gun I had a 5R, 1-8 twist barrel on another in the same chamber. Both barrels where finished at 30". Shot a two man team match at a 1k yards with them. Same relay same conditions. The 5R barrel was like 30fps slower than the 4 groove in that particular case. Showed up at the match with the 5R having zero rounds on it/no break in etc.....I put the gun back together, remounted the scope etc...and with no zeros or test firing I put my come ups on the gun for a 1k and the gun was on paper. Touched up the scope and almost cleaned the target. We came in 3rd in the two man team match! My partner was my step son and was 13 at that time. He never shot a match before. I took him to the range and we practiced prone at 200 yards. At the match I just gave him his changes on the scope for him and told him when to pull the trigger.

Some say if you want hard core accuracy to go with conventional (English style rifling) and I do believe this to a certain extent. This is where the lands meet the grooves at basically a 90 degree corner vs. the 5R style rifling where the lands come down on a angle.

I do believe though the 5R style rifling with the odd number of grooves helps to fight against bullet failure. The bullet jacket doesn't get upset/distorted as much when it makes the jump from the case into the rifling.

That being said I've got both 4 groove and 5R barrels on my guns. I like both and don't see a ton difference.

Later, Frank
Bartlein Barrels
 
#18
Layton said:
I run an 8.5tw on a 6.5x55 with 140g Hybrids with absolutely no issues. I'm basically at sea level. If you do the math on stability (and believe it) the only time an 8.5tw won't work most of us won't be outside and I'm not sure you'll find those conditions in the contiguous 48.

L
Click to expand...

+1

A 8.5 twist will do everything a 8 twist will do.It's whatever you want.
 
#21
^^ There you have it guys. Straight from the man the makes the barrels.

For the last 3 to 4 years (maybe even longer) 90% of the custom rifles in our club have been powered by a Bartlein. I am sure Frank can find more precise numbers, but I think our barrel orders are split down the middle concerning 4 grooves or 5R, but they are 100% 8.5 twist.


Here are our match stats for 2013 so far.

If you scroll to the bottom of each month it gives you a break down in calibers.

As you can see, we like our 260s out here. :)

https://docs.google.com/spreadsheet/ccc?key=0AkJvfCOwH5YndGs5RHpVVkJfZ2ZERWc1bDJBYklERlE#gid=0
 
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#23
Anyone using a lilja 3 groove barrel on their 6.5? I was talking to a respected gunsmith in my area yesterday and he highly recommended a 3 groove lilja for a 6.5 creedmoor. If anyone is using one chambered in a 6.5, let us know your specs and how it shoots!
 
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