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chrisj
Reply with quote  #1 
I think D. Tubb should have been asked his opinion on the Lapua 6.5x47 case necked down to 6mm and compared directly to the 6xc. That would have been a much more appropriate comparison.
D.TUBB...if you read this...your thoughts would be greatly appreciated.

Chris
Moderator
Reply with quote  #2 
There was actually a post on German Salazar's Shooters Journal board by a guy who has been shooting a cartridge similar to the 6.5x47. He is actually very happy with it shooting the 123gr Scenars. I'm not sure what bullets David tested in the 6.5XC. I have no doubt that he's right about the need for more "boiler room" if you're trying to shoot the 139s, 140s, 142s.

"Although this is not a new cartridge it will obviously mitigate the tedius process of having to form the brass from something else, which is a plus. My father has been shooting this cartridge for nearly twenty years in both silhouette and most recently F-class. It is an excellent choice for highpower as it provides a very nice compromise of barrel life and accuracy without sacrificing much at 600 yards. He has been using 123 Lapuas at 600 with H4350 at a velocity of 2800-2820 fps quite effectively.This cartridge also works equally well with varget and the same bullet at the same velocity. Keep the throat short and the barrel at or above 27 inches and 2900 with varget is realistic. The 107 with varget or the 123 Lapua will do fine at 200/ 300 yards,and of course 120smk works well also. Before Lapuas were being used he ran 140 SMK at 2735fps on the rams in sillhouette with excellent results.

I however opted for a chambering in 6.5xc which is about .050 longer case OAL than the 6.5x47 and a neck length over three tenths which seems to have improved the barrel life even more. With the XC i'm duplicating the performance of the 6.5-08 at 200/300 yds. I switched to a 130 Norma at 600 yds USING H4350 at a velocity of 2825 fps.140 Bergers work well at 2715-2725 also. With 2000 rounds on a Kreiger 8 twist at 26.5 inches the throat has moved .050-.060 with 107smk and 123 lapua. The 130 norma has not been moved since the 600 round mark." P. Hayes

But we'll just have to see how it works with the lighter 6.5mm match bullets. FWIW, Quickload predicts 2950 fps with the 123 grain Scenar. When you think about it, if David is getting 3000+ fps with his 115, that's not much difference in bullet weight.

The 123 Scenar is a great bullet, and if the 6.5x47 can push it at 2900-2950 I think a lot of shooters will like it. However, a 6XC with the DTAC 115 would certainly have an edge in ballistics.
6Dasher
Reply with quote  #3 
Hi,


Ballisticaly the 6.5x47 with 123gr scenars should fill the gap between a 6Dasher and a 6.5x284. Yet with less pressure than a 6Dasher (plus no fireforming) and less recoil/more barrel life than a 6.5-284. No, it will not beat the 6.5-284 in the 1000y game, but it is a good intermediate for 300-600y matches.
DTubb
Reply with quote  #4 
Something to keep in mind.
All of these various bullet makers post a BC for their specific bullet(s).
Most all of these are based on the G1 drag function that "so to say" cannot be all for all bullets.
I have found from all my testing that the Sierra Infinity program (Bill McDonald's work) is the best answer to a specific bullet's true BC's (there are multiple BC's for any given bullet at specific velocity ranges). Most of my testing in the last year has been from from 200 to 1600 yards (where the 115 gr 6XC starts to go subsonic) using specific atmospheric readings over about 50 different firing sessions with the majority of my testing from 1000 to 1700 yards.
Using apples to apples(Sierra infinity) comparison this is what you should know. It is also worth noting that the Sierra program only assigns the BC to the bullet that the specific mfg is claiming - meaning Sierra doesnt want to stomp on their claims when if fact it should IMO since each bullet(s) has multiple velocity BC's.
The 6.5 123 gr Scenar has a true starting BC (max velocity range) of less than .520 and falls off from there.
Likewise the 338 Lapua (250 gr) that claims a BC of the mid .600's actually has a BC that is less than the 6.5 142 Sierra.
And not to keep the ball in the Lapua court the Berger BC's are actually even more inflated.
I have to hand it to Sierra - Keeping their nose out of someone else's BC claims is admirable but not realistic.
For me this means that until you shoot your specific bullet at multiple long range distances and come back with reliable feedback (using atmospheric parameters) then you dont really know what you actually have.
DTubb

KentReeve
Reply with quote  #5 
Dave,

Thanks for the BC treatise, but the original question is:

"I think D. Tubb should have been asked his opinion on the Lapua 6.5x47 case necked down to 6mm and compared directly to the 6xc."

Care to answer that one?
chrisj
Reply with quote  #6 
Not sure I buy into the fact that everyone else except Sierra inflates their B.C'S. My 139 Lapua's shoot higher than 142 Sierra's in my 6.5-284 and in my old 6BR Lapua Long..(same as 6xc before the 6xc came out..give or take a few thousandths here or there.) the 105 Lapua shot higher than the 107 Sierras. Unless all bullets are tested under the EXACT same conditions...the B.C. will vary.

Chris
Rust
Reply with quote  #7 
I'll go so far as to say the BC of the same bullet fired at the same velocity may vary from rifle to rifle. It would seem to me that an optimum match of twist to the bullet, uniformity of the bore diameter, land and groove dimensions, uniform twist the length barrel, an accurate chambering job and a good crown would all contribute to the bullet being stable on muzzle exit or at least stabilizing sooner in flight. And the twist would make the bullet "tip over" at mid trajectory to have the nose of the bullet closely follow the actual ballistic path of the bullet.

Reason I say this is I have seen the same bullet at the same velocity across the same chrono on the same day require differing come-ups out of two different rifles. The variance got greater past 600 yards.

As far as software goes, and BC, when this barrel was fresher, the come-ups predicted by the Pejsa software using the listed BC for the 139 Scenar and the G1 modeling function pretty much exactly matched at 600, 800, 900 and 1,000 yards. I figured that it would be close enough to get me on target, I wasn't expecting it to be right on the money.

Unfortunately I am not made of money so what testing I do is pretty much my own limited array of equipment and my own competition loads.
slappomatt
Reply with quote  #8 
chrisj, my findings and others at my local range are exact opposite of yours. i was told that the 107 smk's are about 2" higher at 500meters than the 105 bergers and thats almost exactly what I found as well.
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