6xc freebore
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I have no experience with the 115's but I shoot the 105 Hunting VLD's .025 off the lands with my XC. I have .093" free bore. This puts the 105 perfect in the neck of the case in my opinion. Just a tad (few thousandths) ahead of the neck/ shoulder junction. I think the 115's would be too deep but in reality, the 105's will out perform the 115's all the way to 1000 yards if you look at a good ballistics program. Unless you are one of the few that can get the velocity up on the 115's without all the pressure.
Dan
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I did look up in my ballistics program and the 105 hybrid does drop less and is on par with the 115 drift wise. I guess I need to just stick with the 105. I would like the ability to chase the lands and wonder if I can do that with the 105s
Should I plan on the 7.5 twist or the 8
I shoot an 8 twist with great results. These things shoot really well with little effort. You could always switch to the 115 after a few thousand rounds when you cant reach the lands with the 105's. You might gain a little more life but I would think the better life of the barrel will already be lost. It really depends what you want from the rifle accuracy wise.
Dan
Contour wise I am going with a 27" Heavy Palma. The first 5" will be straight. This will give me the ability to set the barrel back and rechamber when the throat finally gives out.
If you take a look at JBM ballistics the pointed DTACs have a usable G1 BC of .590 and a G7 of around .300 at a MV of approx. 3000fps which I get easily with my 6XC. The Berger 105 Hybrids and the hunting VLDs have a G7 BC of .278. Even if you point the Berger's they are not really superior to the DTACs.
They are when you consider most people get 3100-3150 fps with the 105's
That extra fps will make the 105's outrun the 115's even in the wind on all ballistic programs.Dan
Using a Oehler model 43 at 1000 yards and shooting whatever sample mfg at the same time that I shoot the bullet I am trying to test results in a best as one can expect test platform - sort of an apples to apples comparison. Determining a BC coefficient is a lot like cooking some batches/tests yield slightly different #'s. However when you shoot tests with all pertinent samples then you get an actual difference between bullets A/B/C/D at that point/condition in time. This is the only way to get a true definitive difference.
l like G1 at 1000 yd numbers but it really doesn't matter - all one does is hit a key in the oehler 43 program to yield a different coefficient based on bullet form.
From my testing (more to come shortly) a 105 hybrid is approaching 70 points less than the next generation (N/G) 115 DTAC. It is my belief base on this different design which will adequately be stabilized in a true 8 twist barrel at sea level conditions.
When running in my ballisitics program and shooting the 105 at 3300 fps verses the N/G 115 at 3050 the N/G 115 drifts approx. 3% less at 1000 yds.
Makes it a no brainer IMO
Dtubb
l like G1 at 1000 yd numbers but it really doesn't matter - all one does is hit a key in the oehler 43 program to yield a different coefficient based on bullet form.
From my testing (more to come shortly) a 105 hybrid is approaching 70 points less than the next generation (N/G) 115 DTAC. It is my belief base on this different design which will adequately be stabilized in a true 8 twist barrel at sea level conditions.
When running in my ballisitics program and shooting the 105 at 3300 fps verses the N/G 115 at 3050 the N/G 115 drifts approx. 3% less at 1000 yds.
Makes it a no brainer IMO
Dtubb
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You numbers are within the margin of error IMO..
105 - .550 G1 1000 yd
115 - .580 G1 1000 yd
The numbers can vary slightly but this would be the average from several test sessions.
What would be the proper freebore and twist rate to take advantage of the new 115 but still be able to shoot the 105s
Currently using a .160" straight section with a 1.5 degree lead for the 115.
This would leave a 105 seated in about the last 1/2 of the case neck.
David,
Thank you for jumping in on this topic. You will have more valuable information and real world experience than a few of us put together.
You've sparked my interest in the 115 gr bullet once again. I did a fair amount of research on the 105 vs 115 grain bullets before I decided on the XC cartridge. I couldn't make my numbers (based on others data) match what you have said. I lost all interest in the 115 when it appeared most of the people that did testing with it showed pressure (ejector swipes, hard bolt lift) at a relatively low velocity. Most stopped (115gr) load development at a velocity node of anywhere between 2900-3050fps, as you have done yourself. The data most present on the 105vld class bullets put the velocity around 3150-3250fps. My JBM calculations showed the lighter bullet actually fairing out slightly better, and I mean very slightly Can you explain where my numbers are wrong? To be honest, it's so close that I still want to give the heavier bullets a try. Do you feel a 115 would stabilize from my 26" 8 twist at 2950-3000 fps? Thank you again for your knowledge!
Dan
Thank you for jumping in on this topic. You will have more valuable information and real world experience than a few of us put together.
You've sparked my interest in the 115 gr bullet once again. I did a fair amount of research on the 105 vs 115 grain bullets before I decided on the XC cartridge. I couldn't make my numbers (based on others data) match what you have said. I lost all interest in the 115 when it appeared most of the people that did testing with it showed pressure (ejector swipes, hard bolt lift) at a relatively low velocity. Most stopped (115gr) load development at a velocity node of anywhere between 2900-3050fps, as you have done yourself. The data most present on the 105vld class bullets put the velocity around 3150-3250fps. My JBM calculations showed the lighter bullet actually fairing out slightly better, and I mean very slightly
Can you explain where my numbers are wrong? To be honest, it's so close that I still want to give the heavier bullets a try. Do you feel a 115 would stabilize from my 26" 8 twist at 2950-3000 fps? Thank you again for your knowledge!Dan
Attachments
Dan,David,
Thank you for jumping in on this topic. You will have more valuable information and real world experience than a few of us put together.
You've sparked my interest in the 115 gr bullet once again. I did a fair amount of research on the 105 vs 115 grain bullets before I decided on the XC cartridge. I couldn't make my numbers (based on others data) match what you have said. I lost all interest in the 115 when it appeared most of the people that did testing with it showed pressure (ejector swipes, hard bolt lift) at a relatively low velocity. Most stopped (115gr) load development at a velocity node of anywhere between 2900-3050fps, as you have done yourself. The data most present on the 105vld class bullets put the velocity around 3150-3250fps. My JBM calculations showed the lighter bullet actually fairing out slightly better, and I mean very slightly
Dan
I reread my post and corrected my wind drift prediction - somewhere I flipped my BC improvement to a wind drift percentage. The wind drift would be slightly better as your JBM calculation predicts.
From my current testing I feel that the N/G 115 will be adequately stabilized in a true 8 twist (the older 115 would not be stable/accurate at a sea level atmospheric)
Do you feel the 8 twist is enough or should one go 7.5?
I found a reference that says use a
3/4 degree lead with about .050″ of straight section - This is quoted so that both the 105s and 115s can be used.
What would I gain or lose going with this setup?
In the past tried 3/4 and 1/2 degree leads and ended up going back to a 1 1/2 degree lead. IMO it is very difficult to get measurements on bullet seating depths in relationship to the bullet's engagement into or just off of the rifling when using a 3/4/ 1/2 degree leads. I would go with the faster twist in the preceding post question.
How would it hurt to back the lead off to only .100"?
Seating the full diameter at the base (boattail excluded)of the bullet past the neck shoulder junction (Donut/constriction) is not conducive to good accuracy.
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