There have been some long ongoing threads about doing this here somewhere. I know someone in Oz tried it. Bottom line as I recall (i could be mistaken) was that you just could not quite get there velocity wise to be really competitive.
Yes, the problem is that the 7mm-08 finds it harder to match 260 etc 140gn MVs than one would expect. The 168gn 7mm Berger VLD and its 140gn 6.5mm equivalent have similar BCs (in Bryan Litz's early results they were identical; now with revisions the 7mm is given a modest advantage). So you need to match 6.5 velocities to give the same external ballistics, improve on them to do better, and that's not easy, or maybe not even possible.
I rebarrelled one of my 308 FTR rifles to 7mm-08 three, four years ago with a 31-inch 9-twist Bartlein. It's throated for optimal seating of the 168gn Berger VLD. COAL a whisker short of 3-inches, so long. At the time, I knew the -08 AI offered enough extra performance to make it a superior option, so go for it Alex Wheeler, but this was at the time of the great cannot-get-anything tools and components shortages, and it would have taken forever to get a reamer and dies, so I went slightly reluctantly with the 'straight' version.
My objective throughout was to have an effective tool for short / mid-range but without running 'hot' powders at mega pressures (as so many 6.5mm shooters do) for maximum barrel life in a rifle that sees a great deal of use. (In any event, I have another threaded and chambered Bartlein in 6.5X55mm for this rifle that will go onto it eventually.) This is a (relative) budget job - Savage PTA action untouched from the factory; Dolphin Precision alloy chassis stock with a DIY two-pack epoxy glue bedding job (valve grinding paste and mating the pair work just as well); two forends 3-inch (for bench and occasional F rest use) and FTR (for bipods). The bipods used are super-wide footprint Tier-One 'Carbon' and Shooting Shed 'Stotteben' models with two thirds metre footprints at low settings and used for nearly all my F-Class shooting these days - the energy / breath saving in not carrying a full-weight F rest and heavy sand rear bag around have long paid off here and I have long proven to myself that I shoot just as well of them as with a rest, especially with this mild number.
As it turned out I just couldn't get the 168gn VLD to group well enough. The 162gn AMax was used with some limited success for a while, but still wasn't good enough, and MVs weren't high enough either being in the 2,700s. One issue is to ignore everything printed in loading manuals for the cartridge - their data are entirely geared to standard freebore 140gn loads that work well with medium-fast burning rate powders. It took me a while to get my mind around this and start with a clean sheet of paper. Then Sierra introduced the 160gn TMK, a very well made bullet, reasonable BC (0.293 G7) and form factor (0.968) according to Bryan Litz in his latest edition of Rifle Bullet Performance. This bullet shot well from day one jumped 15 thou' and with mildly compressed loads of slower burning powder got over the 2,800 fps mark, my final load running at 2,830 fps last time I checked it. 1,500 rounds on I've never redone the seating depth despite whatever may have happened to the throat and it shoots just as well as it did when set up for the barrel at ~300 rounds down it.
While on bullets, Hornady's new 162gn ELD-M is given remarkably high ratings by Litz - 0.877 form factor and 0.327 BC. The changes in its shape from the old AMax of the same weight are to a layman like me minor and subtle but have made a surprisingly great improvement! That BC is where many 180s are! However, it is a true VLD with an Rt/R value of 0.5 compared to the jump tolerant Sierra TMK's 0.84 which is identical to that of one of my other favourite sevens, the venerable 175gn Sierra MK - a much underrated and underused bullet. Anyway, I've just bought a couple of hundred ELD-Ms to see if I can make them shoot well ... or at all.
In keeping with cooler powders and good barrel life, the 160 TMK has been used entirely after initial tests with Viht N160, a 47 point something gn charge mildly compressed after pouring slowly down a Forster five-inch drop tube funnel. This is in necked-down 308 Win Lapua Palma small primer brass with Rem 7 1/2BR primers. Necking it down thickens walls by around a thou', no issue for a factory chamber I'd think, but in a minimum SAAMI chamber, I give them a mild neck-turn to return them to where Lapua 7mm-08 brass is, followed by annealing. ES and SD are good, but not spectacularly so, same as you get with a good 'straight 284'. Shooting the rifle and TMK combination in 600 and 1,000 yard BR matches, shows very good elevations, of 0.1-0.3 MOA despite use on a range that sees wind induced elevation changes.
My other load is my short-range one - Winchester ('prepped') brass or necked down 1980s Norma 160gn thin-neck 308 Win - Russian primer, relatively low BC 150gn Lapua Scenar L bullet and enough Lovex SO65 to give 2,850 fps MV. A very low pressure load! With Litz form factor 0.991 and BC 0.268 this is a ballistically workmanlike design rather than outstanding ......... but are the bullets consistent out of the box? ..... and do they shoot at 100/200/300 yards? Stock Savage PTA or no, this is a one-hole 5-round 100 yard bench set up and I've had some outstanding 300 yard F scores with it. I can do better with a custom-built 6BR bench rest 'Light Gun' in 300 yards F shot off a bipod, but there's hardly anything between them (and the 6BR barrel life is saved for the benches anyway). Lovex SO65 is an extruded Czech powder which I see is now available through somebody in the US. It is shown in Explosia's burning rate chart as same as VarGet - it's not and nowhere near. It's also bulkier and much lower specific energy than VarGet, so is closer to Viht N150 or maybe even IMR-4350 in real-life performance. Again, a slightly slower burning powder for the bullet weight than seen in most manuals.
I did try heavier bullets - 175 and 180gn SMKs with N160 and N165. Throated as it is, the 175gn MK is seated pretty close to optimal; the 180s need yet more freebore. Both, especially the 175, showed promise and N165 proved better than N160. The standard case is really short of space now and excessive compression became an issue. Even with the much higher capacity Winchester brass and heavy neck tension, use of a 20-inch drop tube, etc, etc COALs were all over the place with the charge pushing back against the bullets - I was barely shy of 52gn N165, so can hardly wonder at that. The 7-08AI or other improved form and with a bit more freebore might have worked well here. Recoil was noticeably stiffer than with the 160/N160 load and as I have a heavier Barnard 284 that shoots the 175 SMK at ~2,850 fps with good results for my 800 and longer distance matches, there's not much logic in going down the 'standard 7mm F bullet' route with the smaller cartridge.
To see how it will do with some faster loads for those less concerned about barrel life, I loaded up three lots of 160gn TMKs in reformed Palma brass late last year with hotter powders such as Viht N550 and Ramshot Hunter, but haven't yet got around to bench-testing them. 2,900 fps should be easily 'on', but how well faster loads will group .......... ?
Anyhow, soon we'll have real accuracy and velocity data on it.
(After the rebuild cost and that of the brass and dies, the good news though is that it costs me nothing as I have enough bullets and suitable powders to see me through a barrel, maybe even two barrels. 
