Whats the optimum rate of twist for 140gr 6.5mm

Question:
Whats the optimum rate of twist for 140gr 6.5mm

Choices:
1 in 9"
1 in 8"
1 in 7"

 

1 in 8" assuming moderate to high velocity.

If you were using heavier like the 160 grain, or longer "low drag" bullets then a 1-in-8" twist would be best. Especially with a barrel length of 20" or less.

Depends on which 140. If you are looking at Remmy corelokts a 1x9 works well. If you are looking at one of the VLDs 1x8. Overall length of the bullet is an often overlooked issue with stability and proper twist.

If you define "optimum" as the slowest rate of twist that will dependably stabilize a 140 grain 6.5mm spitzer, then the answer is 1-9" -- provided that velocity is sufficient. With lower velocity 6.5's like the .260 Rem and 6.5x55, using a 1-8" might be advisable. However, at .264 Win speeds, 1-9" is all you need or want.

I'm Thinking of getting the DPMS Panther in 6.5 Creedmoor and was surprised to see it has a 24" barrel with a 1 in 7.5" twist. I'm assuming that is to compensate for the higher velocities of that new cartridge and the fact it was designed around the 140gr bullet.

http://www.dpmsinc.com/firearms/firearm.aspx?id=51

Lower velocity requires a faster twist to stabalize the same weight bullets. The 7.5" twist is probably best.

Terry

Sadly, the 6.5 is an often overlooked but very versatile caliber with uses ranging from long range varmiting to medium to small game to 1000 yd benchrest competitions with some 140 gr. match bullets having ballistic coefficients of over .525. If the rifle is to be used in such long range competitions at least a 1 in 8 might be needed, but such a rate might tend to handicap the performance of bullets of with weights of 100 grs or lower.

So when push comes to shove, if the rifle in question is 20 lb. bench gun that will only be used in ultra long range competitions a 1 in 8 or even 1 in 7 would be appropriate. But to take advantage of it's versatility with all bullet weights, I would probably go with a 1 in 9 or even 10.

F. Prefect

I just finished watching a "Best of the West" TV show on the Outdoor channel. It's a long range hunting show. The guys have custom rifles and really know their stuff, dope the wind properly and make some really fantastic long range kill shots on big game.

Berger is the bullet sponsor and they exclusively shoot the VLD hunting bullet.

The hunter they guided killed a nice bull elk at 725 yards with a 6.5 mm round. I assume it was a 6.5 Remington, they didn't specify. The bull dropped as if someone shot it in the head with a bang stick at a slaughterhouse.

The sectional density of the 6.5 mm bullets puts them right up there with the .416 Rigby; they plow through like a freight train.

quote:

Originally posted by rcamuglia:
I just finished watching a "Best of the West" TV show on the Outdoor channel. It's a long range hunting show. The guys have custom rifles and really know their stuff, dope the wind properly and make some really fantastic long range kill shots on big game.

Berger is the bullet sponsor and they exclusively shoot the VLD hunting bullet.

The hunter they guided killed a nice bull elk at 725 yards with a 6.5 mm round. I assume it was a 6.5 Remington, they didn't specify. The bull dropped as if someone shot it in the head with a bang stick at a slaughterhouse.

The sectional density of the 6.5 mm bullets puts them right up there with the .416 Rigby; they plow through like a freight train.

I seem to recall that at some point in time the 1000 yd benchrest record was held by 378 Weatherby neck to 6.5 firing a very long and slender 6.5 mm bullet weighing approx. 155 grains. With it's low surface area exposed to the wind and high BC, it sliced through the air very nicely. But today, the military's new .338 Laupa snipper cartridge shoots a bullet that is claimed to have a BC of over .920! Now that's what I call efficient. I'm sure if that cartridge and bullet combo does not already own it's share of records, it soon will, but it will have to be in the unlimited category as the rifle weighs close to 20 lbs and has a semi-automatic action!

FP

quote:

the military's new .338 Laupa snipper cartridge shoots a bullet that is claimed to have a BC of over .920! Now that's what I call efficient.

Who is making this bullet?

quote:

Originally posted by OKIE1:

quote:

the military's new .338 Laupa snipper cartridge shoots a bullet that is claimed to have a BC of over .920! Now that's what I call efficient.

Who is making this bullet?

Looks like it may be a "calculated" BC yet to be proven by Doppler radar designed by Lutz Moller and manufactured by the German company CNC. Designated LM-105 the mono metal 292 gr bullet has a MV of just above 3000 fps.

I believe the highest confirmed BC is also a mono-metal Lost River Ballistics 270 gr J40 also manufactured by CNC with a BC of .871. Amazing stuff.

FP

quote:

I seem to recall that at some point in time the 1000 yd benchrest record was held by 378 Weatherby neck to 6.5

No, the 6.5 WWH (Weatherby-Wright-Hoyer) was a .300 WBY necked to 6.5 -- very similar to a 6.5 STW. This is about the largest case used on a 6.5 that provides any practical boost in performance. Using the .378 (or Rigby) case would provide only marginal and impractical added velocity compared to the 6.5 WWH or 6.5 STW. But it would impress your friends.

quote:

Originally posted by Stonecreek:

quote:

I seem to recall that at some point in time the 1000 yd benchrest record was held by 378 Weatherby neck to 6.5

No, the 6.5 WWH (Weatherby-Wright-Hoyer) was a .300 WBY necked to 6.5 -- very similar to a 6.5 STW. This is about the largest case used on a 6.5 that provides any practical boost in performance. Using the .378 (or Rigby) case would provide only marginal and impractical added velocity compared to the 6.5 WWH or 6.5 STW. But it would impress your friends.

You are correct, it was the 300 case.

I guess I got it confused do to an article I read somewhere dealing with the development of the 378/460 Weatherby cartridge which are the only Weatherby cases (other than the .224) that are not derived from the 300/375 Holland and Holland magnum case.

As the story goes, and I cannot verify the veracity, back in the early 50s some agency in the Defense Dept. solicited the help of Roy Weatherby to produce a cartridge that would yield 7000+fps velocities from a 55 gr. .224 bullet for the purpose of determining the effects of such a high speed projectle on various types of armour being developed at the time.

I have no idea whether or not they suceeded, but shortly thereafter the 378 Weatherby was introduced, followed by the 460 3 or 4 years later. Again this is totally unsubstanciated and one can only guess what kind of pressures such a round would develop, but it seems like the wildcaters just keep on necking down like there's no end in sight. However, as you suggest, I would think there would have to a limit somewhere at which time the ??/378 becomes a grenade rather than a rifle cartridge.

F. Prefect

My PAC-NOR barrel chambered in 6.5 Swede that I put on my Ruger action has a 1:8 twist, shoots 120 and 140g Sierra Matchkings, Gamekings and ProHunters superbly.

Here. I'll screw with your head a little. I built a 6.5x284 with a 26" Krieger barrel that has a 8.5" twist for the 142 grain SMKs.

I have 3 Swede Mauser's and if I recall, their twist when converted to inches is like 1 in 7.6 or around there?

quote:

Originally posted by tywt:
I have 3 Swede Mauser's and if I recall, their twist when converted to inches is like 1 in 7.6 or around there?

That's why the Swedish Mauser's are the most accurate military rifle.

quote:

I guess I got it confused do to an article I read somewhere dealing with the development of the 378/460 Weatherby cartridge which are the only Weatherby cases (other than the .224) that are not derived from the 300/375 Holland and Holland magnum case.

Don't forget the .220 Weatherby Rocket and the .240 Weatherby. While the Rocket is based on the .220 Swift IIRC, the .240 is an entirely unique case. Many people think it is simply a .30-06 with a belt, but while the head is identical in diameter to the '06, the body in front of the belt is smaller.

quote:

Originally posted by Stonecreek:

quote:

I guess I got it confused do to an article I read somewhere dealing with the development of the 378/460 Weatherby cartridge which are the only Weatherby cases (other than the .224) that are not derived from the 300/375 Holland and Holland magnum case.

Don't forget the .220 Weatherby Rocket and the .240 Weatherby. While the Rocket is based on the .220 Swift IIRC, the .240 is an entirely unique case. Many people think it is simply a .30-06 with a belt, but while the head is identical in diameter to the '06, the body in front of the belt is smaller.

The 220 Rocket? I didn't even know it existed. Does that give you a clue how old my reloading manuals are? I gotta check it out.

I had always wondered why in almost every popular calibur, Weatherby had a cartridge at the very top of the list, other than in the case of the .224 Weatherby Magnum which was easily "outclassed" by both the Swift and the 22-250. The 240? Just slipped my mind as many things are seeming to do as father time slowly takes it's toll.

F. Prefect