7mm-08 and 7mm-08AI question
- Thread starter Heman
- Start date
I had a BIG write up on the 7mm-08A.I. using 180 Hybrids. With 53.0g of RL-26, I was getting 2910f.p.s. I had an unusual experience. Just below 2700F.P.S. with RL-16 I would get excellent accuracy. However, anything, and I mean ANY VELOCITY above that, resulted in terrible accuracy. Having said that, I believe it was the barrel. Most barrels have at least 2 nodes (upper / lower) that they will shoot well in. Mine was the exception.. Mine would ONLY shoot at the lower node. The problem I had was that at the lower node I could only get about 30 or so rounds of excellent accuracy. The barrel would "gum up" from dirty powder residue so badly it destroyed accuracy in short order. The "gunk" was so bad that when I cleaned it, the "loose" carbon poured out of the end of the barrel like black syrup! You NEED pressure to burn any powder cleanly. I could not raise enough pressure at 2690 with RL-16 to burn clean.. So that was the end of my "experiment"!
XTR
F-TR obssessed shooting junkie
Shawn, I don't recall if @ShootDots write-up was the only one or not. There have been some folks in Oz experimenting with it for F-Open too. I know there are some write-ups in here somewhere. Haven't got time to dig them up right now.
I seem to recall that for Open they weren't able to consistently get the 180s up to where they wanted.
I've never experimented with mine beyond the 162.
I seem to recall that for Open they weren't able to consistently get the 180s up to where they wanted.
I've never experimented with mine beyond the 162.
I shoot a 'straight' (but long freebore) 7-08 and a 'straight 284' in F-Class with a bit of 600 and 1,000 BR thrown in for the pair. The idea behind the 7-08 was a modestly recoiling accurate short to mid-range rifle with good barrel life to share the workload with the 284 rather than use this cartridge at every distance. The 7-08 has a 31-inch Bartlein on a Savage PTA, the 284 being a 30-inch Bartlein on a Barnard 'P'. Both shoot very well.
Like you I did a huge amount of QuickLOAD and external ballistics program modeling and it was difficult to make a case for the straight 7-08 over equivalent size 6.5s. My original 'cunning plan' was to use the 168gn Berger VLD and the barrel was throated for that, resultant COAL around 2.97". This bullet has a near identical posted (Litz) BC to its 140gn 6.5mm equivalent, so in straight ballistic terms, you're looking to match potential 6.5 MVs to be in the same ballpark. In theory, with a larger bore and greater area of bullet base for the powder gases to push on, the 7-08 should outperform the same parent case 260 Rem, but it doesn't seem to work out like that in real life. The one big upside is enhanced barrel life for the 7mm, especially if you stick to the cooler burning powders.
So, if I could get 2,800 fps or a little more from the 168gn VLD, I'd be happy I thought, even though this forum is full of people claiming 2,900 fps or thereabouts from equivalent 6.5s and 140s. Unfortunately, the Bartlein didn't seem to like the 168gn VLD. The 162gn Hornady AMax initially looked promising, but I could only get it to group really well at too low MVs. At that time the new 160gn Sierra TMK appeared on our side of the Atlantic so I thought I'd try that, and quickly found my 'default bullet'. It really does perform well at apparently all distances at around 2,830 fps from a case full of Viht N160. The BC is a bit down on the 162 AMax and quite a bit lower than those of the 168gn Berger and new 162gn Hornady ELD-M. I might try the latter in 2018 just to see how it does in this barrel / cartridge, assuming I can find any as it seems ELD-Ms are thin on the ground in most weights / calibres in the UK. (I also sometimes use the 160 TMK in the 284 at around 125 fps higher MVs also over N160 for mid range matches when the weather forecast is 'iffy', or if wanting to take no chances for an important match will shoot the 284 mid range with the 175gn SMK (also at 2,825 fps - every 7mm loading I've tried seem to end up with this velocity).
As a short-range (300 yard) load I ended up using the relatively low BC but superbly made and consistent 150gn Lapua Scenar L over a European (Czech) powder called Lovex SO65, a single-based tubular number that is quoted by its makers as having the same burning rate as H. VarGet. But ... it doesn't (it's slower burning), is bulkier, and has less energy so is a rather limited use propellant that suits cartridges like the 7X57mm and 7X64mm more than 308 case based numbers. I was given a couple of Kg by a frustrated one-time user who couldn't make this powder work in anything he shot, and thought I'd give it a try in 7-08 having by then decided that the cartridge is best fed with relatively slow burning powders. (The loading manuals are a bit misleading in powder choices as they are usually orientated to 140/150gn SPs loaded to 2.8" COAL in 22/24-inch barrels for deerhunters.) Again, MVs are around 2,850 fps and short-range precision is as good as anything else I shoot including the 6BR. I'm going to give the old 150gn Sierra MK in its shiny new pointed form a go too next year as a possible 200/300 bullet, although I bought this bullet more for 7X57mm in a historic Mauser service rifle than for the 7-08. Even here in Europe, the SMK is a lot cheaper than the Scenar.
You might ask why not shoot 6BR in 200-500 yard matches if I have one given its potential precision and its better external ballistics with a 105-108gn bullet than a 150gn 7mm at the same speeds? Again, barrel life. The 7-08 is my shoot in everything piece whilst having got a really successful 6BR going, I don't want to p*ss its barrel life away in short distance F matches where other things with longer barrel accuracy lives do well enough - I did that with my first 6BR some years back and started shooting it in 600 yard BR just as the round count neared 1,500 - after which point my 'aggs' steadily increased despite still getting the occasional good group that matched what it did initially.
As part of my maximise barrel life concurrent with acceptable ballistics philosophy, I use N165 in the 284 for my primary loads with 175 and 180gn SMKs and N160 with 160gn class bullets. The reason for the SMKs is twofold. I was offered 3,000 180s at a 'steal price' back in 2014 which is as we are today less than a third of the late 2017 UK price for 180gn Bergers (a quarter of that now being demanded for Hybrids here). I found that it took a lot of work to get the 180 SMK to perform well at long range, but seem to have got there with a lot of BTO batching, weighing, trimming and pointing. IME the 'new' pointed SMKs are MUCH better made than and very consistent indeed compared to this previous generation, although with 3,000 to work my way through, I've not had a need to acquire any in the 180gn weight. This runs at 2,855 fps in my 284 / 30-inch and is a little 'hotter' than I want or need so will likely download it in the future if I can find a lower charge / MV combination that shoots as well. However, I had some of the old 175 SMKs, nice tolerant tangent ogive designs and actually barely less aerodynamically efficient than much pointer and more finicky designs from other people. (0.948 G7 form factor v 0.946 for the Berger 180gn VLD.) 55.5gn N165 gives them 2,820 fps (again!) and quarter to third-MOA short-range groups with less recoil than the 180s. Despite having all the cheap 180s, this has become my default 284 combination except for 1,000 yards where I usually shoot the 180 SMK.
I did try the 175 and 180gn SMKs in the 7-08. Results were 'mixed'. The 175 could be a 'possible', but with N160 and N165 the main problem was over-compressed charges to the point where COALs became a) too long, and b) inconsistent. I used two lots of brass here - reformed 308 Lapua 'Palma' and the larger capacity 7-08 Winchester, both fully 'prepped'. I could get more powder into the Win cases hence its use here, the necked-down Palma being my default case for match use. N165 appeared to work better than N160 so I concentrated on that in follow-up testing.
In reformed Lapua brass 46.4-47.5gn N165 rising in 0.3gn steps gave 2,566 fps rising to 2,613 fps and 0.3-0.6" 100 yard five round groups with small ES values, some single figure. 47.3 and 47.5gn looked promising, at 0.3 and 0.35" 2,598 and 2,613 fps, 8 and 10 ES. 2,600 fps isn't a silly-low MV with this bullet, but it depends on the competition of course. If you're up against people shooting 180gn Hybrids at 2,800 fps plus or here in the UK, SAUM / WSM at 2,900-2,950 fps (even some in club matches) ............... I'm not saying you can't make this weight bullet work, but it'd need a bit more freebore and higher energy powders that wear the barrel out faster. (So why not use 284 instead with lower pressures and cooler burning propellants?)
Winchester brass allowed charges to go up to 49.2gn and MVs to 2,688 fps. Groups weren't bad, all under half-MOA in a 48.8-49.2 x 0.1gn series of five by five round batches, running 0.4-0.5 inch groups, but I expect third-MOA or less from this rifle, off the shelf Savage PTA action and AccuTrigger or no. The degree of charge compression was too great too even with use of a very long drop tube on the funnel. Recoil was noticeably heavier than with my 160gn TMK load. If I didn't have a 284 to shoot the same bullet without hassle at 130-200 fps higher MVs, I might have persevered, but there was no sense in doing so. With the compression / COAL issue too, ammunition loaded weeks or months earlier might have produced poorer performance too than these test loads shot within a day or so of loading them up.
On brass, I've used Winchester, Lapua 7mm-08, and reformed Lapua 308 'Palma'. The Win stuff performs well after batching / prepping, but I imagine its life would be poor with full-house loads. The Lapua 7-08 is heavy and has thicker necks than I like taking loaded round neck O/Ds out to around 0.314" only a thou' below the SAAMI maximum, although I've not suffered any obvious pressure issue with it. (But then I've hardly used it to date.) The reformed Palma brass has doner very well and with a re-anneal every third or fourth firing and hardly any neck working (Wilson bushing neck die + Redding body die) plus a near minimum SAAMI chamber I expect the life of two or three 50-ct boxes to exceed that of the barrel. Sizing it down to 7mm thickens necks to nearly 16 thou', so a neck turn to 0.014" is done. So far, no issues / problems and ES values are better than with large primer brass.
Like you I did a huge amount of QuickLOAD and external ballistics program modeling and it was difficult to make a case for the straight 7-08 over equivalent size 6.5s. My original 'cunning plan' was to use the 168gn Berger VLD and the barrel was throated for that, resultant COAL around 2.97". This bullet has a near identical posted (Litz) BC to its 140gn 6.5mm equivalent, so in straight ballistic terms, you're looking to match potential 6.5 MVs to be in the same ballpark. In theory, with a larger bore and greater area of bullet base for the powder gases to push on, the 7-08 should outperform the same parent case 260 Rem, but it doesn't seem to work out like that in real life. The one big upside is enhanced barrel life for the 7mm, especially if you stick to the cooler burning powders.
So, if I could get 2,800 fps or a little more from the 168gn VLD, I'd be happy I thought, even though this forum is full of people claiming 2,900 fps or thereabouts from equivalent 6.5s and 140s. Unfortunately, the Bartlein didn't seem to like the 168gn VLD. The 162gn Hornady AMax initially looked promising, but I could only get it to group really well at too low MVs. At that time the new 160gn Sierra TMK appeared on our side of the Atlantic so I thought I'd try that, and quickly found my 'default bullet'. It really does perform well at apparently all distances at around 2,830 fps from a case full of Viht N160. The BC is a bit down on the 162 AMax and quite a bit lower than those of the 168gn Berger and new 162gn Hornady ELD-M. I might try the latter in 2018 just to see how it does in this barrel / cartridge, assuming I can find any as it seems ELD-Ms are thin on the ground in most weights / calibres in the UK. (I also sometimes use the 160 TMK in the 284 at around 125 fps higher MVs also over N160 for mid range matches when the weather forecast is 'iffy', or if wanting to take no chances for an important match will shoot the 284 mid range with the 175gn SMK (also at 2,825 fps - every 7mm loading I've tried seem to end up with this velocity).
As a short-range (300 yard) load I ended up using the relatively low BC but superbly made and consistent 150gn Lapua Scenar L over a European (Czech) powder called Lovex SO65, a single-based tubular number that is quoted by its makers as having the same burning rate as H. VarGet. But ... it doesn't (it's slower burning), is bulkier, and has less energy so is a rather limited use propellant that suits cartridges like the 7X57mm and 7X64mm more than 308 case based numbers. I was given a couple of Kg by a frustrated one-time user who couldn't make this powder work in anything he shot, and thought I'd give it a try in 7-08 having by then decided that the cartridge is best fed with relatively slow burning powders. (The loading manuals are a bit misleading in powder choices as they are usually orientated to 140/150gn SPs loaded to 2.8" COAL in 22/24-inch barrels for deerhunters.) Again, MVs are around 2,850 fps and short-range precision is as good as anything else I shoot including the 6BR. I'm going to give the old 150gn Sierra MK in its shiny new pointed form a go too next year as a possible 200/300 bullet, although I bought this bullet more for 7X57mm in a historic Mauser service rifle than for the 7-08. Even here in Europe, the SMK is a lot cheaper than the Scenar.
You might ask why not shoot 6BR in 200-500 yard matches if I have one given its potential precision and its better external ballistics with a 105-108gn bullet than a 150gn 7mm at the same speeds? Again, barrel life. The 7-08 is my shoot in everything piece whilst having got a really successful 6BR going, I don't want to p*ss its barrel life away in short distance F matches where other things with longer barrel accuracy lives do well enough - I did that with my first 6BR some years back and started shooting it in 600 yard BR just as the round count neared 1,500 - after which point my 'aggs' steadily increased despite still getting the occasional good group that matched what it did initially.
As part of my maximise barrel life concurrent with acceptable ballistics philosophy, I use N165 in the 284 for my primary loads with 175 and 180gn SMKs and N160 with 160gn class bullets. The reason for the SMKs is twofold. I was offered 3,000 180s at a 'steal price' back in 2014 which is as we are today less than a third of the late 2017 UK price for 180gn Bergers (a quarter of that now being demanded for Hybrids here). I found that it took a lot of work to get the 180 SMK to perform well at long range, but seem to have got there with a lot of BTO batching, weighing, trimming and pointing. IME the 'new' pointed SMKs are MUCH better made than and very consistent indeed compared to this previous generation, although with 3,000 to work my way through, I've not had a need to acquire any in the 180gn weight. This runs at 2,855 fps in my 284 / 30-inch and is a little 'hotter' than I want or need so will likely download it in the future if I can find a lower charge / MV combination that shoots as well. However, I had some of the old 175 SMKs, nice tolerant tangent ogive designs and actually barely less aerodynamically efficient than much pointer and more finicky designs from other people. (0.948 G7 form factor v 0.946 for the Berger 180gn VLD.) 55.5gn N165 gives them 2,820 fps (again!) and quarter to third-MOA short-range groups with less recoil than the 180s. Despite having all the cheap 180s, this has become my default 284 combination except for 1,000 yards where I usually shoot the 180 SMK.
I did try the 175 and 180gn SMKs in the 7-08. Results were 'mixed'. The 175 could be a 'possible', but with N160 and N165 the main problem was over-compressed charges to the point where COALs became a) too long, and b) inconsistent. I used two lots of brass here - reformed 308 Lapua 'Palma' and the larger capacity 7-08 Winchester, both fully 'prepped'. I could get more powder into the Win cases hence its use here, the necked-down Palma being my default case for match use. N165 appeared to work better than N160 so I concentrated on that in follow-up testing.
In reformed Lapua brass 46.4-47.5gn N165 rising in 0.3gn steps gave 2,566 fps rising to 2,613 fps and 0.3-0.6" 100 yard five round groups with small ES values, some single figure. 47.3 and 47.5gn looked promising, at 0.3 and 0.35" 2,598 and 2,613 fps, 8 and 10 ES. 2,600 fps isn't a silly-low MV with this bullet, but it depends on the competition of course. If you're up against people shooting 180gn Hybrids at 2,800 fps plus or here in the UK, SAUM / WSM at 2,900-2,950 fps (even some in club matches) ............... I'm not saying you can't make this weight bullet work, but it'd need a bit more freebore and higher energy powders that wear the barrel out faster. (So why not use 284 instead with lower pressures and cooler burning propellants?)
Winchester brass allowed charges to go up to 49.2gn and MVs to 2,688 fps. Groups weren't bad, all under half-MOA in a 48.8-49.2 x 0.1gn series of five by five round batches, running 0.4-0.5 inch groups, but I expect third-MOA or less from this rifle, off the shelf Savage PTA action and AccuTrigger or no. The degree of charge compression was too great too even with use of a very long drop tube on the funnel. Recoil was noticeably heavier than with my 160gn TMK load. If I didn't have a 284 to shoot the same bullet without hassle at 130-200 fps higher MVs, I might have persevered, but there was no sense in doing so. With the compression / COAL issue too, ammunition loaded weeks or months earlier might have produced poorer performance too than these test loads shot within a day or so of loading them up.
On brass, I've used Winchester, Lapua 7mm-08, and reformed Lapua 308 'Palma'. The Win stuff performs well after batching / prepping, but I imagine its life would be poor with full-house loads. The Lapua 7-08 is heavy and has thicker necks than I like taking loaded round neck O/Ds out to around 0.314" only a thou' below the SAAMI maximum, although I've not suffered any obvious pressure issue with it. (But then I've hardly used it to date.) The reformed Palma brass has doner very well and with a re-anneal every third or fourth firing and hardly any neck working (Wilson bushing neck die + Redding body die) plus a near minimum SAAMI chamber I expect the life of two or three 50-ct boxes to exceed that of the barrel. Sizing it down to 7mm thickens necks to nearly 16 thou', so a neck turn to 0.014" is done. So far, no issues / problems and ES values are better than with large primer brass.
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Laurie,
Thanks I've seen the big numbers but QL isn't letting me get there with powder combinations so I've wondered what is actually possible. I need to update to QL 3.9 so I can get the newer powder files.
The reason you looked at the 7mm-08 is why I'm thinking about it, but then I normally shoot my 223 for mid-range club matches and my 243 (which is my backup 1000yd gun) for bigger matches. More less this is just a thought exercise for a "MAYBE" type thing cause it is to cold to do anything else.
Thanks I've seen the big numbers but QL isn't letting me get there with powder combinations so I've wondered what is actually possible. I need to update to QL 3.9 so I can get the newer powder files.
The reason you looked at the 7mm-08 is why I'm thinking about it, but then I normally shoot my 223 for mid-range club matches and my 243 (which is my backup 1000yd gun) for bigger matches. More less this is just a thought exercise for a "MAYBE" type thing cause it is to cold to do anything else.
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