Optimal 6.5-06 twist rate

brasscollector · September 28, 2016, 04:28 PM

Going to finally get into the 6.5mm and decided on a 6.5-06. Barrel finisher said he can get 7,8,9 or 10 twist. Plan on shooting 120s-142s or heavier. Not too concerned with lighter/varmint bullets, I've got other rifles for that. I see berger recommends 8" for their longer bullets, would that be my best option?

emcon5 · September 28, 2016, 05:03 PM

1:8 should be good up to 160 grain bullets.

TMD · September 28, 2016, 05:25 PM

1/8 is the standard in the 6.5 Creedmoor with 120-142gn bullets. If that's the weight range you plan on using then go with it. With the added velocity from the 06 case I wouldn't be surprised if a 1/9 worked great as well.

emcon5 · September 28, 2016, 09:46 PM

You can also run the numbers:

http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

Llama Bob · September 28, 2016, 10:42 PM

In general 1 in 8" twist is suitable for most 6.5mm applications. However, if you're going to shoot very long 140gr bullets like the Berger 140gr hybrid, and want to be 100% sure of stability at low elevation and cold temperatures, I'd go 1:7". For the vast bulk of 140gr bullets, in the vast bulk of atmospheric conditions, 1:8" is fine.

160s tend to be stubby round noses things that stabilize better than the 140s.

There is really no accuracy (or other) downside to fast twist however, so if I was in your shoes I'd order the 1:7".

hooligan1 · September 29, 2016, 04:25 AM

1:8" twist is really optimum for this cartridge, although I haven't tried anything heavier than 140's as of yet...
That's the cool thing, the 6.5 has a ton of cool bullets to test and try...

brasscollector · September 29, 2016, 08:54 AM

Quote:

want to be 100% sure of stability at low elevation and cold temperatures, I'd go 1:7"

I'm seeing a lot of votes for 8" twist but this is what had me pondering to begin with. If over-stabilization is not a concern (7" creates 2.0+ on jbm's calculator) then perhaps 7" twist might be the trick. I'm from Wisconsin where most of my shooting is done between 750'-900'. Also, for about 4-5 months it gets a little chilly here but not too bad

. I would say that the 140s-143s are going to be the main diet. Might even look for some boutique bullets but limited searching hasn't turned up much if anything longer/heavier than a 143gr VLD.

taylorce1 · September 29, 2016, 11:05 AM

You never said what action you're using to build a 6.5-06 on? Not all actions are created equal, and more importantly not all magazines (Just ask Hooligan1). With 6.5 bullets you tend to run out of magazine space very quickly, that is why there aren't currently bullets with higher BC's much over 140 grains. If you're worried about magazine space simply switch to a 6.5-284 and you'll have the same case capacity as the 06 but in a shorter package.

1:8 is going to be the standard twist to stabilize the mass produced bullets offered. Simply because the majority of cartridges offered are used in short actions and AR10/15 rifles where COAL is a major issue. Like you said unless you're going to run boutique bullets you shouldn't ever need to worry about a faster twist like 1:7 twist.

brasscollector · September 29, 2016, 11:10 AM

Older savage flat-top LA. Probably going to get a 26-27" heavier barrel. I always load for accuracy. Any velocity increase afforded by the longer barrel is simply a bonus.

taylorce1 · September 29, 2016, 12:08 PM

Savage have generous magazines and COAL shouldn't be much of an issue. I'd probably load some dummy cartridges up with the Hornady 140/143 ELD bullets at the max length that'll feed reliably from your magazine, then have your gunsmith cut the throat to have you .020-.030 jammed into the lands at that length. That'll give you some room to chase the lands as your throat wears out.

I'd use the Hornady bullet over others as it has good BC and the ogive is further forward than the Berger or other VLD bullets. To me the hornady's seem to be the best middle ground choice for setting up a barrel. Plus they usually have a very consistent tip to ogive measurements.

Llama Bob · September 29, 2016, 12:13 PM

Quote:

If over-stabilization is not a concern...

I would challenge anyone to produce even a single example where over-stabilization produced any kind of scientifically documented problem in small arms (not tanks, artillery etc.). I don't think they can.

There are two potential problems with fast twist rates:
1) Bullets that spin too fast and come apart. This is not going to be a problem at the velocities a 6.5-06 can produce, although it can happen in e.g. .22-250.

2) VERY small decreases in accuracy (on the order of a few hundredths of a MOA) due to the bullet shift from rotating around center of shape (in the barrel) to rotating around center of mass (in air). This effect falls to zero with bullets with modern jacket uniformity.

Since neither of these problems seems to apply for your application, I would err on the side of fast twist.

Llama Bob · September 29, 2016, 12:21 PM

Just as a point of reference, I regularly shoot a rifle with a stability factor of well over 6 with no adverse effects (.45-90, 400gr, 1" bullet length, 2100 ft/s, 1:20" twist, up to 100deg at 1 mile elevation). This has no measurable impact on accuracy (sub-MOA), terminal performance, or trajectory relative to computed trajectory.

September 28, 2016, 04:28 PM	#1
brasscollector Senior Member Join Date: July 26, 2015 Posts: 526	Optimal 6.5-06 twist rate Going to finally get into the 6.5mm and decided on a 6.5-06. Barrel finisher said he can get 7,8,9 or 10 twist. Plan on shooting 120s-142s or heavier. Not too concerned with lighter/varmint bullets, I've got other rifles for that. I see berger recommends 8" for their longer bullets, would that be my best option? __________________ He may look dumb, but that's just a disguise. -Charlie Daniels

September 29, 2016, 04:25 AM	#6
hooligan1 Senior Member Join Date: July 18, 2010 Location: Independence Missouri Posts: 4,585	1:8" twist is really optimum for this cartridge, although I haven't tried anything heavier than 140's as of yet... That's the cool thing, the 6.5 has a ton of cool bullets to test and try... __________________ Keep your Axe sharp and your powder dry.

September 29, 2016, 11:05 AM	#8
taylorce1 Senior Member Join Date: November 18, 2005 Location: On the Santa Fe Trail Posts: 8,242	You never said what action you're using to build a 6.5-06 on? Not all actions are created equal, and more importantly not all magazines (Just ask Hooligan1). With 6.5 bullets you tend to run out of magazine space very quickly, that is why there aren't currently bullets with higher BC's much over 140 grains. If you're worried about magazine space simply switch to a 6.5-284 and you'll have the same case capacity as the 06 but in a shorter package. 1:8 is going to be the standard twist to stabilize the mass produced bullets offered. Simply because the majority of cartridges offered are used in short actions and AR10/15 rifles where COAL is a major issue. Like you said unless you're going to run boutique bullets you shouldn't ever need to worry about a faster twist like 1:7 twist. __________________ NRA Life Member

September 29, 2016, 11:10 AM	#9
brasscollector Senior Member Join Date: July 26, 2015 Posts: 526	Older savage flat-top LA. Probably going to get a 26-27" heavier barrel. I always load for accuracy. Any velocity increase afforded by the longer barrel is simply a bonus. __________________ He may look dumb, but that's just a disguise. -Charlie Daniels

September 29, 2016, 12:08 PM	#10
taylorce1 Senior Member Join Date: November 18, 2005 Location: On the Santa Fe Trail Posts: 8,242	Savage have generous magazines and COAL shouldn't be much of an issue. I'd probably load some dummy cartridges up with the Hornady 140/143 ELD bullets at the max length that'll feed reliably from your magazine, then have your gunsmith cut the throat to have you .020-.030 jammed into the lands at that length. That'll give you some room to chase the lands as your throat wears out. I'd use the Hornady bullet over others as it has good BC and the ogive is further forward than the Berger or other VLD bullets. To me the hornady's seem to be the best middle ground choice for setting up a barrel. Plus they usually have a very consistent tip to ogive measurements. __________________ NRA Life Member

September 28, 2016, 05:03 PM	#2
emcon5 Senior Member Join Date: July 10, 1999 Location: High Desert NV Posts: 2,850	1:8 should be good up to 160 grain bullets.

September 28, 2016, 05:25 PM	#3
TMD Senior Member Join Date: August 9, 2011 Posts: 1,293	1/8 is the standard in the 6.5 Creedmoor with 120-142gn bullets. If that's the weight range you plan on using then go with it. With the added velocity from the 06 case I wouldn't be surprised if a 1/9 worked great as well.

September 28, 2016, 09:46 PM	#4
emcon5 Senior Member Join Date: July 10, 1999 Location: High Desert NV Posts: 2,850	You can also run the numbers: http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

September 28, 2016, 10:42 PM	#5
Llama Bob Senior Member Join Date: January 13, 2016 Posts: 337	In general 1 in 8" twist is suitable for most 6.5mm applications. However, if you're going to shoot very long 140gr bullets like the Berger 140gr hybrid, and want to be 100% sure of stability at low elevation and cold temperatures, I'd go 1:7". For the vast bulk of 140gr bullets, in the vast bulk of atmospheric conditions, 1:8" is fine. 160s tend to be stubby round noses things that stabilize better than the 140s. There is really no accuracy (or other) downside to fast twist however, so if I was in your shoes I'd order the 1:7".

September 29, 2016, 12:21 PM	#12
Llama Bob Senior Member Join Date: January 13, 2016 Posts: 337	Just as a point of reference, I regularly shoot a rifle with a stability factor of well over 6 with no adverse effects (.45-90, 400gr, 1" bullet length, 2100 ft/s, 1:20" twist, up to 100deg at 1 mile elevation). This has no measurable impact on accuracy (sub-MOA), terminal performance, or trajectory relative to computed trajectory.