I don't see why the mag length(2300fps) load wouldn't work. 

Out of a 20" inch gas gun with a generous throat I think one could get the same velocity.

Depending on the freebore the long load(2400fps) may work too. My long range .223 and 6.5G ARs I load long and single feed without issue.

You do need a 10twist or faster barrel. 

Keep in mind too, my rifle weighs 17lbs and has a good brake I can fire a ton of these without a problem . I don't know what the recoil would be like on an AR10.

thanks for taking the time to put all the data together , I found it interesting .

Very impressive, it's obvious you love your research as well as the act of pulling the trigger.

I have tried to locate this info for some time so thank you for the work. To date, I've been doing 175's in my GAP10 308.
I use a single round manual feed block as opposed to a magazine. Will be interesting to see how long of a round I can go.

Thanks again.

Yay, opinion thread!! and good discussion OP. Here's my take:

So.......controlled conditions and number comparisons are one thing - it gets different in application under non-controlled conditions. I think that the real reasons why there is almost zero justification to purchase .308 for precision shooting over a 6.5 come out when you get the shooter in dynamic or unstable conditions.

Many of us shot .308 (both standard 175gr as well as more efficient loadings) in tight competitions for a long time before making the switch to something better. We can tell the difference for certain. It's the significant recoil reduction, the edge during the rushed wind read, the advantage for partially-obscured UKD targets, and the extra speed for movers that all come together and just flat out work better. In my case, I estimated that moving to a more efficient cartridge from .308 improved my hits by ~10-15%. That's a lot.

I also think that a paper/controlled efficiency comparison between the .308 and any 6.5 variant on the same case should use bullets that are scaled for the case capacity (the idea is to approach 2900fps with 22-24" barrel length). In the case of the .308, the proper bullet is the 155gr Scenar (which, when driven to 2900fps, is remarkably similar ballistically to 140gr Amax at factory velocity out of a Creedmoor). The optimum bullet for the Creedmoor case is something like the 123gr Scenar (or a high-BC 130gr). Yes, you can still hit everything with a 140gr going slow, but the point is to get the velocity and recoil edge that a lighter, but high-BC, projectile can give you.

All of this gets amplified when you move to a 6mm, which is why they are the winners in most of the big steel (and paper!) long range matches. I'm staying with the 6.5 discussion for now, simply because of comparable terminal ballistics. If what I am getting at isn't true, then the aggregate results would show .30 cal as remaining competitive at all levels. They aren't.

All of this said, there is zero replacement for consistent time on trigger with feedback. In any quasi-practical match with targets to 800+yds, a wind-reading wizard who shoots 10,000+rds of Black Hills 77gr .223 per year is going to kick the ass of some tinkerer who changes his 6mm Whizbang handload every month. That's just experience, which trumps gear and cartridge every time.

So what velocity, drift, and flight time figures do you have for the .308 155gr. Scenar and 6.5mm 123gr. Scenar at 500/750/1000 yds do you have to put up for comparison to the OP's data? Would like to see your data that supports your assertion.


Thanks.

 

This has nothing to do with competions or skill level of the shooter. It is simply data.


I have clearly illustrated the effects of unstable dynamic conditions. One can look at the data and determine what is important to their needs. 

A guy who target shoots for fun, can load good lower SD ammo,  and has time to properly range targets is served quite well with a .308 using a proper bullet.

A guy trying to be competitive that doesn't have the luxury of time, exact distance, fast follow ups and require the highest possible number of hits will be better served with a flatter shooting, lighter recoiling cartridge.

 Understand I could have used 130s or 123s but they would have resulted in the 230s looking better due to wind drift problems. 155s from the same bbl length would have more for wind drift than my slow 230.

I could have bumped up the velocities to 26-28"" barrel lengths but the results would have been the same and my 230 velocities would have been a guesses rather than real life numbers.

That will be difficult to make a good comparison without the same conditions. 
He would have to use 20" velocities and the same atmospherics I did.

You can look at the 178eld for a preview, the 155 will have more drift, a lower hit percentage, a longer danger space, less sensitive to ES/SD, a greater velocity loss.

"A 140gr 6.5mm bullet scaled up to 30cal is a 230gr bullet, so the 230gr bullet is the proper bullet to compare to a 140 6.5mm for long range performance not a 175. "

What measurement or criteria was "scaled up" to come to this conclusion?

Thank for the info.  Really great post.

It is the work of Bryan Litz.

It goes like this: (not the work of Litz)when you scale up something by a linear dimension(like caliber) the volume goes up with the cube of the linear change, the weight goes up with the volume.

The linear scale factor between calibers 7.62 and 6.5mm is 7.62/6.5=1.1723.  So the 7.62 is 1.1723 times bigger in diameter than the 6.5mm.
The the scale factor for the weight of the bullet will be 1.1723³ which is 1.6111. 1.6111 x 140gr = 225.6gr

130gr 6.5mm scaled to 7.62 would be 1.6111 x 130gr = 210gr
123gr 6.5mm scaled to 7.62 would be 1.6111 x 123gr = 198gr

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6mm scaled to 7.62 would be 7.62/6 = 1.27. For weight it would be 1.27³ =2.048 scale factor so.....

108gr 6mm scaled to 7.62 would be 2.048 x 108= 221gr
115gr 6mm scaled to 7.62 would be 2.048 x 115= 235gr


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6mm scaled to 6.5mm would be 6.5/6 =1.083... for weight scale factor 1.083³ = 1.2714

108gr 6mm to 6.5 would be 1.2714 x 108 = 137gr
115gr 6mm to 6.5 would be 1.2714 x 115 = 146gr


So you can see anything under 200gr in 30cal is not a fair comparison vs. any of these sleeker calibers. To be fair you scale up the same shape bullet to the caliber. Obviously the shape of the bullet has a huge impact on how well it cuts through the air, you want the same shape and proportions as the other low drag bullets, in 30 cal those proportions result in bullets that are 215-230gr(in copper jacket lead core type).

Do you have a ballistics calculator? Hopefully so, and you can run your numbers for whatever atmospherics and load speeds you like. The model inputs for those bullets are well known, so have at it. The paper data are out there for everyone to play with.


However, in case you missed it, the point of my post is to bring up how things tend to work under realistic shooting conditions on a non-square range - and what works best under those conditions. The ultimate measure of what is best is proven by what is used at the high levels of competition. No way around it.

If you are simply interested in the paper numbers of pure bullet/load performance (and none of the other factors) from a hobby/engineering perspective, then maybe check out which cartridges/bullets/velocities are competitive (i.e. work the best in the wind and at distance) in F-Class and other benchrest-type games where much of the shooter's influence is removed from the equation.

There was talk of limiting bullet weight in FTR because the heavies had an unfair advantage.

It's understandable when you have some poor sap shooting 155s with quite a bit more drift at 1k than the 230Hybrid. 


The 155 scenar needs 3275fps to have the same wind drift as my 2300fps 230gr @1k.
Don't think you will get 3275fps out of a 20" bbl.

230@2300fps
Attached File



155@3275fps
Attached File