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Range Report Newest 6mm Dtacs, less drop than previous ones.

rc2125

rc2125

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Minuteman
Oct 24, 2007
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Granger, Indiana
Just got to run some of the latest 6mm 115 coated Dtacs over the weekend. Coated ones were just finished last tuesday. The tips on this batch of 500 are all "perfect", compared to my previous batches' tips (which were pretty distorted and ugly). Confirmed at 700,800,900 and 1000 yards, they drop .4 mil (or just over 1moa) less than the "old" ones. Wondered if anyone else has ran any yet and may have noticed the same difference?? No other variables whatsoever involved, shot several 5 shot groups of each bullet to compare.....same batch of brass/powder, all rnds loaded at same time with same setup, etc. Pretty considerable change, just from more pointed/uniform tips.

I had to use .620 BC in JBM to exactly match my real range data. 3010fps, 200yd zero, -6.3mil/21.8moa @1k.
 
Re: Newest 6mm Dtacs, less drop than previous ones.

What kind of stick are you pushing those pills out of? 3010 fps is very fast. Is it a 243 AI?
 
Re: Newest 6mm Dtacs, less drop than previous ones.

.62bc is a significant increase over the .54 listed in Bryan Litz's new book.

I was convinced the 105 berger vld @ .532 was the way to go in the 6mm.
 
Re: Newest 6mm Dtacs, less drop than previous ones.

It is just my luck that they would be improved after I bought 4000 in November. hehehe. That's OK, I have faith in the old ones.
 
Re: Newest 6mm Dtacs, less drop than previous ones.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RC2125</div><div class="ubbcode-body">I had to use .620 BC in JBM to exactly match my real range data. 3010fps, 200yd zero, -6.3mil/21.8moa @1k (>1700fps @1k, supersonic to just under 1900yards). </div></div>

That seems too high. I have to ask: did you input the actual environmental conditions you were shooting in or did you just use the JBM defaults? This can make a huge difference, especially if the shooting was done in warm weather.
 
Re: Newest 6mm Dtacs, less drop than previous ones.

Just got off the phone with them and they said it gives about a .010 boost in BC. So .620 might be a tad high. Of course you'll need to verify it at the range, but you might try .595 to start. They also said they are going to be alot more uniform than in the past. Hope that helps a bit.
 
Re: Newest 6mm Dtacs, less drop than previous ones.

From a prior correspondence with David Tubb:

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Some info for future references.

DTAC 115'S are only available in a closed nose configuration.
Testing indicates that the BC using G1 is improved approx 30 points at 2600 fps and 15 points at 1700 fps.</div></div>

Using my measured results of the old, non-pointed bullets as a reference, this would result in a G1 BC of ~.581 at 2600 fps and ~.537 at 1700 fps.

It's about a 4% increase over the old non-pointed bullet which is consistent with my measurements of pointed vs non-pointed bullets. The average G1 BC of the new pointed bullets will be close to .563 (average from 1500 to 3000 fps) and the G7 BC will be close to .288.

If you're observing a trajectory that suggests a BC of .620 (10% higher than expected) there's probably some error in your calculation (no offense). Deriving BC from drop data is very sensitive to uncertainties in many variables including atmospherics, range, true scope adjustment, etc.

-Bryan
 
Re: Newest 6mm Dtacs, less drop than previous one

Anyone got the G7 BC on the DTAC's?

Thanks
Rath
 
Re: Newest 6mm Dtacs, less drop than previous ones.

Sierra has pretty well perfected pointing the 2156 155 gr SMK bullet. It looks like dtubb added this capability to his DTAC 115.
 
Re: Newest 6mm Dtacs, less drop than previous ones.

I am still using the older moly 115DTACs and a G1 BC of 0.585 worked pretty well at long range. If anything, it occasionally seemed low. I was using ExBal software for the calculation. Reforming the tips with a Whidden tool increased the BC slightly, perhaps to almost 0.600.
 
Re: Newest 6mm Dtacs, less drop than previous ones.

Anyone got the G7 BC on the DTAC's?

Thanks
Rath
 
Re: Newest 6mm Dtacs, less drop than previous ones.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DesertHK</div><div class="ubbcode-body">What kind of stick are you pushing those pills out of? 3010 fps is very fast. Is it a 243 AI? </div></div>

26" bartlein 5r, .236 bore, .243win, hbn coated dtacs, 41gr R17, lapua brass,.003 neck tension, .012 off lands, chrono about 6ft away, not the slightest signs of pressure(no trace system).

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: kombayotch</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RC2125</div><div class="ubbcode-body">I had to use .620 BC in JBM to exactly match my real range data. 3010fps, 200yd zero, -6.3mil/21.8moa @1k (>1700fps @1k, supersonic to just under 1900yards). </div></div>

That seems too high. I have to ask: did you input the actual environmental conditions you were shooting in or did you just use the JBM defaults? This can make a huge difference, especially if the shooting was done in warm weather. </div></div>


Something was probably off a bit then, or I fat fingered an entry.

These were bullets from the most recent batch that siera turned out for them, like 3 weeks ago now. Talked to D Tubb on the phone, and confirmed there were changes they had been working on now for awhile, and the tips should all be uniform with less of a hollow point hole.....which they are, and that they will drop noticeably less out towards 1k.....maybe what they consider "pointed"?

I just noticed they dropped less than the previous bullets at 600,700,800,900,1k yds, when shot "side by side" and wondered if anyone else noticed the same. Right around 14" less drop @ 1k
 
Re: Newest 6mm Dtacs, less drop than previous ones.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DRAM40A1</div><div class="ubbcode-body">It is just my luck that they would be improved after I bought 4000 in November. hehehe. That's OK, I have faith in the old ones. </div></div>

Same here have approx 3K to run thru and that will take me a while .
Good to hear there improving
 
Re: Newest 6mm Dtacs, less drop than previous ones.

Rath,
I measured the G7 BC of the old DTAC 115's to be 0.276.

Sendero_man,
The boron coating wouldn't affect the BC.

Based on what David said, my experience with pointing, and the observations made from those above, I would guess that the G7 BC of the new (more pointy) 115 DTAC's is close to 0.288.

Take care,
-Bryan
 
Re: Newest 6mm Dtacs, less drop than previous ones.

Scott,
The BC of the bullet is unaffected by the atmospheric conditions. The <span style="font-style: italic">air density</span> is affected by the atmospheric conditions, and that affects how the bullet flies, but the BC is the BC, period.

A ballistics program will account for the effects of the atmosphere on the trajectory of the bullet. There's no need to calculate and enter a 'corrected' BC.

-Bryan
 
Re: Newest 6mm Dtacs, less drop than previous ones.

Yay, a better DTAC, that will help make up for my poor shooting even more!
 
Re: Newest 6mm Dtacs, less drop than previous ones.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bryan Litz</div><div class="ubbcode-body">Scott,
The BC of the bullet is unaffected by the atmospheric conditions. The <span style="font-style: italic">air density</span> is affected by the atmospheric conditions, and that affects how the bullet flies, but the BC is the BC, period.

A ballistics program will account for the effects of the atmosphere on the trajectory of the bullet. There's no need to calculate and enter a 'corrected' BC.

-Bryan </div></div>

thanks a lot for the response. have to show this to some guys that insist that elevation and conditions change the BC of a bullet. now I know better.
smile.gif
 
Re: Newest 6mm Dtacs, less drop than previous ones.

The tips are very uniformed in the new batch. I haven't had a chance to chrono my load, but 43grains of H4350 took me 6.4mils to 1k at 70-75degreeF/ 2000ft. This post had lead me to also believe that the bc might be closer to .600, as I doubt that I'm pushing it over 3100fps. .243win

The 139scenars from my buddy's rifle(.260rem) at 1k still beat the 115 dtacs in wind drift by .3mills/5mph crosswind at 1k. I was shooting much flater though by at least a mil at 1k.
 
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