DTAC 115 in 1x8?
- Thread starter swd
- Start date
I think that the general consensus is that a little tighter twist is needed for 115s. An 8" twist is good through 108s. I am having a 7.5" twist, 6mm Remington Bartlein installed on a Remington 700 long action to shoot the Berger and DTAC 115s.
At 243win velocities you SHOULD be able to stabilize the 115's, although 1-8" isn't ideal its not too far off. The best twist for the 115 DTAC at around 2900-3000fps is 1-7.8"
hope that helps,
-Steve
hope that helps,
-Steve
Higher altitudes and cooler temps the 8twist will be marginal with 115's.At sea level and warm temps it's probably going to dissapoint you.It's always better to over stabilize,at least if your not way over.Broughton's on top of spin requirements for most cartridge and bullet combo's, and would be happy to steer you in the right direction.
Tubb says he has no problems with 8-twist barrels. I've had both 7.5 and 8 in .243 and 6XC shooting DTACs (coated or bare) from 2880 - 2990 fps with great accuracy. Most all of my shooting is at or near sea level in temps from 35-100+ deg.. I am shooting Across the Course and Long Range competitions so my requirements may not be as exacting as for someone shooting Benchrest.
rcw3
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A true 8" twist will work with the DTAC 115's, but it's close. A cut rifled Bartlein is a true 8" twist, but I had a Broughton (button rifled) 8" twist (that was not a true 8" twist) and it did not properly stabilize them.
One of the original reasons I went with the 1:7.8" twist with the first Bartlein I had made up is I wanted a little "margin for error" built into the twist rate for the DTAC 115's and I never had any problems with any of the 7.8" twist barrels with the DTAC 115's.
I would never go tighter than a 7.5" twist because the twist starts to get too tight and other isssues begin to appear when you start running a 6mm twist tighter than a 7.5" twist (i.e. we did some 7" twist 6mm's and had problems with all of them in that they tended to presssure up fast and had a lot of presssure even with moderate loads). There's a point where a real fast twist rate becoms an impediment to pressure relief and projectile velocity and in a 6mm, it's not to far away from a 7.5 twist.
Robert Whitley
One of the original reasons I went with the 1:7.8" twist with the first Bartlein I had made up is I wanted a little "margin for error" built into the twist rate for the DTAC 115's and I never had any problems with any of the 7.8" twist barrels with the DTAC 115's.
I would never go tighter than a 7.5" twist because the twist starts to get too tight and other isssues begin to appear when you start running a 6mm twist tighter than a 7.5" twist (i.e. we did some 7" twist 6mm's and had problems with all of them in that they tended to presssure up fast and had a lot of presssure even with moderate loads). There's a point where a real fast twist rate becoms an impediment to pressure relief and projectile velocity and in a 6mm, it's not to far away from a 7.5 twist.
Robert Whitley
Robert (rcw3) is correct. It would be better if twist was expressed in helix angle rather than turn/inches. In smaller calibers, it is risky to use tighter than a 5.5° helix angle and better avoided. A 7.5" 6mm barrel is 5.74° and will work only if the barrel is very smooth and close attention is paid for problem indications. A 7.8" 6mm barrel is 5.52°. Certain rifling forms, like 5R or polygonal, may help in this regard by reducing bullet stress and engraving force. The following are approximate numbers for 5.5° twist.
.22 - 7.2"
6mm - 7.8"
6.5mm - 8.5"
7mm - 9.1"
.308 - 9.9"
As the caliber (bullet diameter) increases, the increased moment arm allows the bullet to be rotated more easily, offsetting the increased rotational mass. A formula could probably be developed that would model the bullet's mass distribution and velocity to predict required twist under a given condition. The Miller twist formula is a good approximation but only characterizes several key factors. Until then, paying attention to what experienced, serious experimenters like Robert Whitley or Bryan Litz have to say is your best bet.
.22 - 7.2"
6mm - 7.8"
6.5mm - 8.5"
7mm - 9.1"
.308 - 9.9"
As the caliber (bullet diameter) increases, the increased moment arm allows the bullet to be rotated more easily, offsetting the increased rotational mass. A formula could probably be developed that would model the bullet's mass distribution and velocity to predict required twist under a given condition. The Miller twist formula is a good approximation but only characterizes several key factors. Until then, paying attention to what experienced, serious experimenters like Robert Whitley or Bryan Litz have to say is your best bet.
My oldest 6x47L is chambered in a Bartlein .237" bore 1:8, and it's probably the most accurate rifle I own with DTAC 115s. My other two 6x47s both have Krieger .236" bore 1:7.5 bbls, and neither will match the Bartlein for velocity, though both are very accurate. With slightly tighter bores & faster twist, it's no surprise that they start to show pressure at lower velocities. I used the 1:7.5 tw. bbls. because I had several in stock and there was little or no demand for them at the time.
I've also shot a number of decent 600 & 1000yd. groups with Berger 115VLDs out of the 1:8 Bartlein, though I've yet to get them to shoot as well as the DTACs out of either of the 1:7.5 bbls. Probably just need to spend a little time experimenting with the seating depth of the VLDs - they shoot best out of the 1:8 Bartlein when jumped at least .020".
Most of my shooting is done at 2600' MSL, typically with low humidity and temps in the 40-95*F range.
I've also shot a number of decent 600 & 1000yd. groups with Berger 115VLDs out of the 1:8 Bartlein, though I've yet to get them to shoot as well as the DTACs out of either of the 1:7.5 bbls. Probably just need to spend a little time experimenting with the seating depth of the VLDs - they shoot best out of the 1:8 Bartlein when jumped at least .020".
Most of my shooting is done at 2600' MSL, typically with low humidity and temps in the 40-95*F range.
Hi Dennis, long time no hear from you, hope you're doing well.
Following your last thread, I am amazed that your Berger 115 VLDs are shooting well jumping over 20 thousands in an 8 twist, or anything else, for that matter.
What speed are you running them at ?
Andy
Following your last thread, I am amazed that your Berger 115 VLDs are shooting well jumping over 20 thousands in an 8 twist, or anything else, for that matter.
What speed are you running them at ?
Andy
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