Discussion in 'Main Message Board' started by Sniper338, Aug 25, 2017.
Title says it...
What can yall tell me? 7x47 lapua vs. 7mm08... for a bolt gun..
Depending on IF you use .308 Palma brass necked down, which also has the S/R primers like the 7 x47, will then make it more of an "apples to apples" comparison. The 7-08 will hold "about" 10 pct. more powder. That should be about the only difference I can see. They both should shoot extremely well. I am presently embarking on a project to build a 7-08 Ackley. I will be shooting 180 Hybrids and my "target" is 2750-2800, which using RL-16 I should easily obtain. The regular 7-08 will be about 75f.p.s. (or so) slower.
You will be pleasantly surprised with the 7-08 AI.
The 7-08AI and the 7-47 both require a very expensive set of dies and fire forming the 7-08 not so much. But I do like the idea of not having the brass to cut to OAL every time you shoot it.
I am a B-I-G Ackley fan. I have 2 / .260 Ackleys right now and have owned / shot several more. Forming a .260 Ackley from .308 Palma brass is a lot of work, however, going from .308 to .284 is a simple proposition. When you neck down, always use body dies, they are worth their weight in gold!
I have shot many Ackleys. According to my calculations, I won't have too big of a stretch to go sailing past 2800f.p.s. However, I am not a fan of pushing things to their limit. That's why my target is 2750-2800, hoping that about 2775-2785 is where the accuracy node will be. I have shot enough Ackleys to just about know where I need to go. My reamer will have a .270 freebore so those Hybrids will be W-A-Y out there! AND my barrel will finish at 30".. With RL-16 powder, I believe (not positive) that the 2775 "target" will actually be the "middle" node, not the high end.
7-08ai can use Lee collet dies . I've been using the Lee on 2 different 7-08 Ackley for many years . Go with the 7-08 Ackley, very easy to resize 308 and get the neck clearance you want
Hope this makes sense , no coffee yet , late start.
I suppose it would depend on what your expectations are. The 6.5 X47 Lapua is a great platform to neck up or down but what you see is what you got as it is already a well designed case.
The 7-08 is a fine cartridge as well but it can be improved on. That takes it up another notch. But then there is still the .284.
The 7x47 is very efficient. Really drives bullets fast considering its size. Don't let the smaller size turn you away. There is a very good article here about it and barrel lenths.
The rule of thumb on this matter is that all other things (peak pressures, barrel lengths, use of appropriate powder grades with equivalent specific energy ratings) is to take the percentage change in case capacity and divide it by four to get the percentage change in MV.
The 7mm-08 case has around 15% greater capacity than the 7X47L equivalent, so will produce 3.5-4% higher MVs; the 7mm-08AI offers a 20% increase, so will give 5% higher MVs.
As we're talking reformed small primer 308 'Palma' brass here for the sevens, the three versions can all be run at the same pressures. Using LRP Remington, Lapua, Winchester etc brass would see the two 7mm-08 versions loaded to 3-5,000 psi less than the 7X47 Lapua to get half decent case life.
So, if the 7mm-08AI gives around 2,800 fps with the 140gn Hybrid, Benjamin's objective, the standard non-improved version will give around 30-45 fps less at similar pressures in the same chamber and freebore; the 6.5X47L based version around 140 fps less all other things being equal.
I run the standard 7mm-08 in a 31-inch barrel F-Class rig. Can't say what the freebore is as it was manually 'throated' to see a 168gn Berger VLD optimally seated and just 'in' the lands. (COAL = 2.975"). As it turned out, the barrel doesn't like this bullet much, so I've ended up using the new 160gn Sierra TMK at 2,830 fps over nearly 50gn of Viht N160 in reformed 'Palma' brass, a relatively mild load and which should keep barrel life good. If my wind reading is on form, I give 6.5X47Ls, Creedmoors, and 7mm SAUMs and WSMs a good run for their money in 500/600 yard matches on a range well known for 'tricky' winds.
The only LRP brass I use now is for my 200/300 yard load of the 150gn Lapua Scenar L also at not much over 2,800 fps over Czech Lovex SO65, a relatively slow burning and bulky single-based powder. The Scenar is a very high drag model for its being a relatively recently introduced seven, but the combination shoots very small groups indeed and works well to 300 yards in F competition too.
Both loads produce little recoil in a 20lb+ F-Class rifle making them very easy to shoot. They also allow the use of modern wide bipods with no loss of control or stability over a front-rest, and reduce the kit weight that needs to be humped around in an uphill moorland range that doesn't have vehicle access to all distances' firing points.
Having played around with 175s/180s, I came to the conclusion that the standard case is just that bit too small capacity to hold the required amounts of slow-burning single-based powders. The AI version would be a boon if running this bullet weight. The other answer would be to go to Reload Swiss RS60 (Alliant Re17), but I've done my best to avoid the hotter burning / high-energy grades. If I need to shoot this bullet weight, I use a 284 rifle.
For informational reasons, I'll test three higher pressure / MV loads with the 160gn TMK over the next few weeks using the soon to be lost to us IMR-4831, plus European manufactured Viht N550, and Ramshot Hunter. It should be feasible to get to 2,900 fps plus with the small primer brass, but even if it does so and works well, I don't intend to use these loadings in this rifle. (2,900 fps with the 160 is the equivalent of 2,735 fps with a 180gn bullet using ME generated as a rough and ready calculator, so is still a fair bit short of Benjamin's AI performance target.)
I know from earlier tests that RS60 / Re17 works well with this bullet and the 175gn Sierra MK and gives respectable MVs, but again have no desire to trade a significant amount of barrel life for the MV gains when I have a 284 that does it at lower pressures and temperatures with Viht N160 (160gn bullet) or N165 (175/180s). I also noticed that with half-decent performance loads with 175/180s that subjective recoil increased noticeably over the 150/160gn bullet loads to the point where I started to feel that one of the little cartridge's key benefits was being sacrificed for the extra ballistics performance.
I came to the conclusion some time back that if only ballistics are counted, it is better to keep the smaller capacity cases in 6.5mm calibre given their ability to produce over 2,800 fps MV with very high BC 140gn bullets. The 7-08's inbuilt advantage is barrel life over them. To start to get external ballistics advantages from a move up from 6.5 to 7mm, the AI variant of the 7mm-08 is needed at the very least, or a move up to the next case size - 280 Rem / 284 Win
The 7x47 Lapua does NOT need custom dies. They are easily made from 6.5 x 57 L dies.
For example, my 7x47L FL die is a Redding 6.5x47L die that has had the shelf that the bushing sits on opened to accept the 7mm neck. Easy peasy.
I always use inline seating dies cut with my reamer. But, a regular seater can be made with a 6.5x47L by replacing the sleeve that holds the bullet with a 7mm.
Making cases is no different than loading a factory Lapua 6 BR case: You run it over a 7mm mandrel (vice a 6mm mandrel), clean off the lube, load and go shoot.
It's stupid easy to load for. Think of it as a scaled up 6 BR.
I have two currently and am having a third built. If you have questions, feel free to PM me.
I assume you will be shooting as a single shot, or are you using a long action?
My virgin brass loads are as accurate as fire formed loads at slightly slower speeds.
As a single shot..
As always, brilliant, objective and well informed opinion Laurie, thank you.
So, I built my 7-47 for the 300-ish varmint matches that we shoot around here, for tactical matches that my son might shoot, and for general purpose east-of-the-Mississippi hunting.
My only contribution to this, really, was experimenting with freebore such that it would handle a wide range of bullets (110 flat base to 168 VLD) with the full diameter of the bullet above the donut, and fit into an AI 308 mag.
Here is the test rifle and a what I expect from it. It's a factory Tikka action, factory trigger, Manners stock (not bedded), but with a Broughton barrel. Weighs about 8 lbs. Built by Mike Ezell for me. Sorry can't remember the exact load for that group, but it's likely a 150 SMK pushed with 8208XBR. As I said, it's stupid easy to load.
I'm definitely not saying that the 7-47L is a panacea or even "better" than a 7-08. Just that I built it to fill a specific niche, that it does so very well, and that it is simple and straightforward.
my vote 7mm-08ai or move up to bigger gun
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