New bullet coming from David Tubb with a G1 BC of .620

[zipollini]

Excuse me if this has already been posted elsewhere

Was just looking at David Tubb's Facebook page and found the following post

"To clear up the rumors: I'm working on a new bullet. In the meantime, I still have DTAC 115s. Working on updating the website now because it says we are out of stock. Call 806-323-9488 to place an order for DTAC 115s if you need more. The new bullet is an improvement on the old bullet but is the same weight. New 115 bullet will be ready within the next 3 months.

Our tests reveal approximately 8% improvement in BC. The new 115 will be just as friendly of a bullet as the current 115. When the current 115s are gone the new 115 will be replacing it because it shoots better."

He states that it will stabilize in an 1:8 twist or faster barrel and has a G1 BC of .620 !!!

Present DTAC 115s have a G1 BC of approx. .585.

 

[jaygorski]

Oh really?

 

[Laurie]

Yes, that'd take a bit of doing, maybe just as a single value high velocity BC, but I don't see it happening as an average value. .620 average would beat any other 6mm bullet by a large margin and match Bryan Litz's tested value for the heavier, longer 6.5mm 140gn Berger Hybrid.

Bryan Litz gives the existing 115gn DTAC G1 / G7 values of 0.538 / 0.276 based on experimental findings. An 8% improvement raises that to 0.581 / 0.298, not at all bad values for a 'six'.

Taking a reasonably high 6mm performer, let's say a 6XC that gives 105gn bullets 3,150 fps, the equivalent MV for a 115gn job is 3,010 fps (both combinations produce 2,314 ft/lb ME). Run them through a ballistics program and you get 1,000 yard retained velocities and 10mph true-crosswind values of:

105gn Berger VLD .................... 1,594 fps / 68.9-inches drift

105gn Berger Hybrid ................. 1,626 fps / 66.5-inches drift

115gn New DTAC ..................... 1,607 fps / 65.5-inches drift

using tested G7 values for the 105s and the estimated 8% improved G7 for the DTAC. So, if the promised improvement is delivered, it puts the DTAC on a roughly equal footing with the better 105s. I could never get the existing DTAC to shoot very well for me in a 1 in 8-inch twist 6XC barrel and got much better results with the 105gn Berger and 107gn Sierra MK, but as always, if your barrel likes a particular bullet better than others so far as groups and long-range elevations go, well use that one.

 

[zipollini]

Laurie - The Litz number you quote is for the older open nose DTACs. The close nosed DTACs G1 is around .585 and is listed at .591 on JBM ballistics

From David's Facebook page

"Stephen Fox What is the G1 BC? I know depends on mv, etc, but what's the stated bc? Thanks

April 4 at 7:30pm

David Tubb Around .620

2 · April 4 at 9:18pm

Most folks have found that a G7 of around .300 works for the pointed DTACs.

http://www.scout.com/military/snipe...03-why-6mmm-berger-hybrid-instead-of-dtac-115

 

[jaygorski]

The current BN coated DTACs I have are right on at 600yds using Hornadys Ballistic calculator, so I'd have to say the .585bc is correct.

 

[swd]

The .585 number with the pointed DTAC's has been dead on for me too.

 

[alf]

I use .585 for my pointed Hybrids....tested to 1300+......

 

[CacheCropp]

Yes, that'd take a bit of doing, maybe just as a single value high velocity BC, but I don't see it happening as an average value. .620 average would beat any other 6mm bullet by a large margin and match Bryan Litz's tested value for the heavier, longer 6.5mm 140gn Berger Hybrid.

Bryan Litz gives the existing 115gn DTAC G1 / G7 values of 0.538 / 0.276 based on experimental findings. An 8% improvement raises that to 0.581 / 0.298, not at all bad values for a 'six'.

Taking a reasonably high 6mm performer, let's say a 6XC that gives 105gn bullets 3,150 fps, the equivalent MV for a 115gn job is 3,010 fps (both combinations produce 2,314 ft/lb ME). Run them through a ballistics program and you get 1,000 yard retained velocities and 10mph true-crosswind values of:

105gn Berger VLD .................... 1,594 fps / 68.9-inches drift

105gn Berger Hybrid ................. 1,626 fps / 66.5-inches drift

115gn New DTAC ..................... 1,607 fps / 65.5-inches drift

using tested G7 values for the 105s and the estimated 8% improved G7 for the DTAC. So, if the promised improvement is delivered, it puts the DTAC on a roughly equal footing with the better 105s. I could never get the existing DTAC to shoot very well for me in a 1 in 8-inch twist 6XC barrel and got much better results with the 105gn Berger and 107gn Sierra MK, but as always, if your barrel likes a particular bullet better than others so far as groups and long-range elevations go, well use that one.

I agree. I'm not convinced there's enough meat on the bone here to switch to 115's for me. I've been researching 6XC, 6x47 and 6 Creedmoor for little while now, trying to decide what to re-barrel from 308 for PRS. If I intend to focus on 115's, I need to choose a suitable reamer with more freebore and possibly consider a slightly faster twist than 1:8". This may affect my ability to shoot the 105's well, so I better hope I can get one of the two 115's to shoot well!

For that trouble, here's what I see in JBM, using a 200 yard zero, 10mph-90 deg wind and the velocities given by Laurie above.

Berger 105 Hyb - G7-0.278, 3150 fps - 1000 yard drop is 227.8", wind drift is 63.6".

DTAC 115 pointed - G1-0.590, 3010 fps - 1000 yard drop is 246.6", wind drift is 64.3"

New DTAC 115 - G!-0.620, 3010 fps - 1000 yard drop is 237.4", wind drift is 58.9"

So the current DTAC offers no advantage as far as I'm concerned. Lower performance, hard to find, specialized chamber/reamer.

While new DTAC may offer some advantage, no one has one in their hands yet, so the 0.620 is hopeful, but not proven. If you're not concerned about drop because you're shooting the same known distances all the time, (like F-Class) then you may buy some additional wind drift with the new DTAC. For PRS, if I have 700 yard shot in a 12 mph wind and I estimate 680 yards and 10mph, using the velocities from above:

105 Hybrid will hit 6.6" Low and wind drift 1.8"
New 115 (@0.620 BC) will hit 6.9" Low and wind drift 1.7"

Think my next reamer will be designed for the 105 Hybrid because it is a proven bullet, can buy them now, can shoot numerous other 105's, 107,s 108's in same chamber.

 

[Laurie]

Think my next reamer will be designed for the 105 Hybrid because it is a proven bullet, can buy them now, can shoot numerous other 105's, 107,s 108's in same chamber.

Been there, got that t-shirt (going for the heaviest one-off bullet in the calibre for the paper BC) with a chamber optimised for 90gn VLDs in 223 (for FTR). It shot well most of the time with the sole three bullets available (now down to two and only one of them [occasionally] in the UK). It wouldn't shoot lighter bullets worth a tinker's cuss.

Subsequent 223s have gone with less freebore, less velocity for the 90s, but much more flexibility. I've had too many rifles built over the years in various calibres set up for one particular bullet - great if they perform as hoped ... disaster if the barrel doesn't like them and it constrains other choices.

 

[johara1]

I think you are splitting hairs with these number, The 115's shot good for me and trimmed and pointed shot better. then the 105 Hybrid came along and they shot better, till that lot ran out. I could never get any lot of Hybrids to shoot as good and some were very bad. The old 115 plugs along with a steady performance lot to lot, maybe that is worth something. jim

 

[EBaker]

Just looked on the Tubb Web Site. They are still showing the 115 DTAC's as "Out of Stock" for now!

 

[tbeasley]

I agree with Jim, the 115 Dtacs are easy to load for. Soft seat them +.006- .008 in lands and they come alive. I run them 3110fps in a 7.75 twist .243 and they shoot awesome. Run scope 0-500yds all over and they simply are there every shot.
Like the fact that they can be bought in a 500ct box.

 

[MOShooter]

Might be based on the same design as the 7mm 183s. Our competitions have a 3100 speed limit. With RL26 and new 115s I could push hard and still stay under that.

Scott

 

[calib]

Any new word about when these may come out

 

[CacheCropp]

I think you are splitting hairs with these number, The 115's shot good for me and trimmed and pointed shot better. then the 105 Hybrid came along and they shot better, till that lot ran out. I could never get any lot of Hybrids to shoot as good and some were very bad. The old 115 plugs along with a steady performance lot to lot, maybe that is worth something. jim

That's a good point. If lot to lot consistency is better, that is a significant factor.

 

[EBaker]

Still waiting on the last of the old DTACs to become available!

 

[calib]

I was told they were out of the old dtac. I pre ordered a couple boxes of the new dtacs that should be out end of the month

 

[EBaker]

Oh well! I have enough of the old ones to last the remainder of this year. Guess its time to try a different bullet. I will try the new DTAC as well.

 

[zipollini]

Just a quick update on the new DTACs. Just called David Tubb's company and they told me that they are out of all their DTACs and don't expect to see the new ones until next week or the week after ( week of the August 15th or 22nd). Unfortunately that is what they told me two weeks ago so we will see.

 

[swd]

Thanks for the update. New products never seem to get out on time. Let's just hope they're as good as we expect.