I've been doing WAY too much reading and it seems to my amateurish student self that with the latest Hornady ELD-X bullets that 7mm-08 matches or even exceeds the performance of the 6.5 Creedmore at long range.

From my basic calculations using my free Strelok ballistics calculator they have virtually the same velocity at 1500 yards (after which they both go transonic)

The reason that I am researching this is because I have a new rifle coming, an RPR, chambered in .243.  I would like to "get my sea legs" using the excellent .243 and when the barrel is getting a little long in the tooth make a swap.  I've looked at .260 Rem, 6.5 CRD, and now at 7mm-08.  It seems like the 7mm should JUST edge out the 6.5 across the board (ex. a tiny amount of wind drift) even with the 6.5 having an initial velocity advantage of approx 200ft/sec.

I'm sure I'm messed up like a soup sandwich.  Why is that?  This is getting way farther down the rabbit hole than my current knowledge level.

7mm
Ballistic Coefficient (G1) .675
6.5mm
Ballistic Coefficient (G1) .610


In the end, with all else being equal, which should reliably be able to be pushed just a little farther than the other and still ring an 18" steel gong?

Some of your info is a little off. The .675 bc is for the 175grain 7mm bullet and that isn't going to work in a 7mm-08.  The ELD-x 143 is a .625 which is higher than what you have listed as well.

From what I have seen the strelok calculations are off at longer ranges as well


Fwiw it's worth I've shot a few hundred of the 140 eld and I'm using a higher bc than what they claim.  

What about 7mm SAUM?  It's starting to make a comeback in F-Class, now that the newer VLD bullets are proving to be up to the task of matching or exceeding 6.5mm performance.





It's not hard to get 3,000 fps MV with a 180gr. projectile, and due to the longer neck and lower case capacity relative to the 7mm WSM, people are reportedly getting better barrel life (> 1500 rounds seems to be common.)





I'll take 3,000fps vs. the 7mm-08's 2700 fps all day when I'm looking to reach out and touch something.



With a good muzzle brake like a VAIS, the 7mm SAUM recoil will feel like your .243



 

Comparing paper details is pointless here. There is so little practical difference between a 7mm anything and a 6.5mm anything of similar case capacities that it's just pointless to discuss. As a matter of practicality, you can hit the targets well past 1000m with a 6.5 somethingsomething just as well as you can with a 7mm somethingother. I've shot and still do shoot both in competition and the real difference for me between them is recoil and MV. A 260 kicks just enough less than a 7-08 to be noticed and the bullets move just marginally faster. Neither was really any better at hitting the kilometer gong than the other IMO. My 7mm BR recoils harder than my coaches 6.5 BR (which I shoot for 1 specific class) and the 6.5BR uses slightly lighter bullets moving slightly faster in every loading. Other than that the 7BR and 6.5BR are functionally identical.





I like 7mm. Bores last a little longer than 6.5's which is a big deal for me. BC's are right there with 6.5's if not a little better. Bullet selection is pretty vast too. 6.5mm has a special place in my heart but I've always found it to be more expensive in the end and I standardized on 7mm and for metallic silhouette I get a lot more area on the rams that a hit will cause it to fall. More ramentum.  





My advice: Stop what you're doing now comparing paper statistics and simply decide if you wanna join the fanbois on either side. If you're particularly recoil averse then the 6.5 is the way to go. If you want to be tacticool, 6.5 is the way to go. If you want an easy time of it, in my experience, 7mm is easier to deal with. YMMV.

 

 
The only way I'd do a 7saum is on a long action.  It really needs the long action to take full advantage of the heavier bullets.


 

He's also shooting an RPR so 7saum is not even an option there.  

This may sound stupid or weird to some...I've become anti-tacticool.  I hate it when folks jump on the bandwagon and buy something because it's the latest and greatest tacticooliest thing out there.  In fact I think it's fun to combining the new and the old and being able to do it just a little better/cheaper/easier/faster. That's one of three reasons I'm starting with the .243 on my RPR anyways.  Heck, I've stuck with the "old" .308 up until now.  I would still shoot it if it could hang at very long distances but it seems to hit a wall between 800 (my AR10) and 1000 (others bolt guns) yards as it hits transonic speeds and loses accuracy.

243 is very capable.  I'm on my 2nd 243 RPR barrel.  I beat the absolute piss out of my first one.  


 

There are some definite upsides to some of the "cool guy" rounds.  6.5x47 and the 6mm are easy to load for inherently accurate and have amazing brass life.

My ignorance about the RPR is showing.





I built my IBR gun on a Defiance Rebel XM (medium-long) action.





 

 
Currently only available in 308 bolt face.

Tell that to popnfresh and let him tell you what he does with his 308 bolt.

Well,

I don't know Mr. Popnfresh but I'd be glad to hear how to stretch out a .308 to farther distances in a way that it would be competitive with 6mm, 6.5mm and/or 7mm for long range competition.

That would actually save me time and money since I'm already set up for .308 on my AR and I could easily fit a .308 barrel on my RPR.

His set up isn't a standard off the shelf 308.  It's a long throat so he can shoot heavies and squeeze the most out of it.  Not exactly apples to apples.  All things being equal the 308 isn't going to be able to hang.  You could have a barrel that way for any round and squeeze more performance out of it.  Shooting 1000 with a 223 isn't hard in a bolt gun either. Heavy bullets seated way longer than they would in an AR makes a huge difference.

As was posted above, his is not off the shelf. He had work done to be able to hit those long distances. Has equipment to get real good data on his reloads. Have pm'd him in the past for his advice. I stayed with a bolt 308 since I was already reloading for my AR10. You will have to really know your skills to get way out there. Not impossible but more work than using a 6.5 creedmoor or similar. I did pick up a 6.5 creedmoor. Savage 10T. Not that expensive to get into it. Haven't reloaded for it yet. Building up brass since I can't find any. When you look at the ballistics between 308 and 6.5cm, its obvious the creedmoor is the winner. Plenty of articles out there. You can still enjoy your 308. If your going to try competition out to 1000 yards, you will be at a disadvantage going up against those with 6mm,6.5mm and 7mm. If your just enjoying shooting with the guys going out far, no reason not to give your 308 a chance. Will be trying my luck at 1000 yards sometime soon. Just a bunch of us giving it a try. Just fun. Both 308 and 6.5 will be coming along. Just to have fun.

When you mention "competition", that is where my .308 load would be a no-no unless you can single feed.

I am using 230OTMs(hbn coated) seated to 3.245" I average 2415fps out of my 20" barrel so the drop is more but wind drift numbers are very competitive with a .719/368 bc.


The 230 has more recoil of course though I can fire 100 in a couple hours with no problems

I just want to know when the 6.5 became "tacticool"?? Hahaha

Where are you shooting? Air temp prevents me from that many rounds and keeping my tube cool enough to make a decent shot after about 10 minutes @ that rate. We are about 90°+ these days. I thought you were close to Houston? I am in Dallas.

Utopia, was there Friday morning. I fired 75 rounds from my .308 and 50 rounds from my .223 AR, various ranges from 340 to 1050yds in 3 hours laying out in the sun 8am to 11am.

I run a 20" MTU barrel on my .308 heat doesn't seem to effect it much, though it doesn't get very hot either. According to my Kestrel it stayed around 80 the whole time there.

Now add in Nosler's new AccuBond Long Range offering for the 6.5, G1 BC 0.719 at 142gr.  



ETA - I did some digging and it looks like Nosler is letting marketing hype get in the way of facts.  It should read 0.572 based on some independent testing. http://www.scout.com/military/snipers-hide/forums/5531-range-report/13942210-testing-the-nosler-142-lr-accubond