7mm to shoot a mile.

[Big Al]

I have a deposit for a build but Im in the final throes of the the planning stage, my customer wants to shoot to a mile, how seriously or frequently Im not really able to ascertain but I feel I must do the best job I can in ensuring the final cartridge choice is suitable and if not that we are all aware of its limitations.

The initial case that forms the starting point for this discussion is the 7mm Practical which my customer has suggested

http://www.ballisticstudies.com/Knowledgebase/7mm+Practical.html

I would like to ask those with long range experience of the bigger 7mm's what would their preference be for a case suitable to be used in a tactical style rifle that will more often be used mainly in the 800-1000 yard range but with the capability to shoot these milk jugs at a mile. 

Ive taken a look at the hot 7mm's being used in F-Class but as always there are many and things like barrel life, ease of obtaining brass and dies, level of case prep and forming, brass life as well as the all important inherent case accuracy must come into it.

I would be grateful for your thoughts on this one guys.

[OSOK]

I shoot 7's alot and past 2,600 yards when i can , Most 7mm rounds will cope with a mile and when not shooting 2 & 15's most will give a decent barrel life . The choice here is do you push hard and get there with less elevation etc or not so hard and use more as then the correct scope and rail is key to the build so your not having to rely on holdover , So the delivery system when it's only a mile is not that important .

 

If he needs to mag feed then you have less options but due to only needing a mile keep it simple with a case that doesn't need fire forming .

 

I have , 7/270 wsm , 7X68 Imp and a 7mm Norma Mag being built now but a normal straight 284mm will murder a mile !

 

It's better to run with whatever gives him the best group with the lowest extreme spreads and not chase velocity as ES's of over 15 are not worth pursuing .

 

Hope this helps

 

OSOK

[NigelM]

I have been going down a similar route and have done a lot of research over the past few months.

 

It seems to boil down to either finding a bullet which is consistent and stable as it goes subsonic like the 180 Berger, or trying to stay supersonic to that distance and putting up with the recoil or building very heavy. I looked at Nathan Fosters 7 Prac and well as the straight 7-300WM. Might even end up still trying one eventually, however have now made the decision to run a 180 Berger in my 280AI and see what happens.

[trucraft]

So many choices. Something bad ass 7 mm LRM or 28 Nosler? https://load-data.nosler.com/load-data/28-nosler/

 

http://www.longrangehunting.com/forums/f19/gunwerks-7-lrm-59112/

[Blue Haze]

7-270 WSM pushing hard on a Berger 180 Hybryd.

 

Push on for 3100 fps when playing at ultra long range, and back off to 2900 fps when closer in to save on barrel and brass life.

 

Easy to get brass, bullets & powder. Lots of load data and little brass prep.

[tisme]

I've used a 7-08 out to a mile a few times, good on barrels and 162gr ELDs make a good splash.

[Ronin]

I think most 7mm will make a mile.

 

As Greg points out, low ES is the absolute must for accuracy at this range.

 

I cant say ive ever shot a 7mm to a mile, but I have shot several 338's at this distance.

 

For, me, I would use a 284 Shehane, as from experience this is one of the easiest cartriges to get shooting low es and superbly accurate to boot, with bullets available in the upper .7's BC

 

 

You could use a 338 LM base parent case and neck down to 7mm, though if you were using a 338 based case, id personaly use a 338 diameter bullet in one of the high end LTS from LM or GSC with BC in the .9 / 1 region which makes scope choice easier.

 

 

You also need to consider spotting bullet splash, which is a heap easier with larger bore guns.....

 

Really depends on the customers pocket, availibilty of brass for the chosen cartridge and of course bullet choice.

[Scrumbag]

I have no experience of it but would a 7-.300WM work well I think.

Quite a bit more case capacity than the 7mm Rem Mag and apparently 300WM brass is easy to re-size.

 

I've been trying to work out how to stretch a 7x64 a fair way but it needs more velocity for the best 7mm projectiles.

 

Scrummy

[Izzy]

Al

 

Forgive me I don't normally post, lot of good advice above. I have a 284 shehane and shot it to 1760 yards, from my experience a 175g bullet will get there but it's not a particularly satisfying signature when it does. If your client likes fiddling with cases and loading then plenty of options listed above will be fine to a mile and frankly tactical sized targets under 1000 will soon become a bit boring and a waste of barrel life/components. For a mile I would want more poke than straight 284, fast and heavy is where I would be and just have to suffer the barrel life.

 

If they would rather shoot than spend time forming cases then I would canvas opinion on a 7mm rem mag and 180g+ pills @ 3000 fps+.

[shooter mcreid]

Personally I would think the 7 saum would be a good option if the shooter is able to get the brass. It has the reputation of being efficient and seems to win comps often (In Australia at least). I have been using the 180VLDs at a conservative speed of 2950fps and the 183 sierras at 2920fps. My balistic app tells me both will still be supersonic at a 1800 yards (only just for the VLD). At these speeds the cases last for many firings but can also be stoked up to the 3100fps if needed. I have found accurate barrel life to be between 1000 and 1200 rounds when used for f class string firing.

[Big Al]

Thanks for the input so far guys.

 

My customer came to me having done some research himself with the idea of 7mm Practical, I was hoping that I would get some answers in relation to that cartridge and why (if there was a good reason) we shouldn't go 7mm Practical.

 

Thats where we are at present, Im lead to believe that brass will be easy to get and prep is not difficult so we must start at this baseline unless there are good reasons to go another route. I appreciate everyone has a favourite, I was hoping to get reasons why that favourite was a better choice than a 7mm Practical.

 

Keep it coming please

[Ronin]

Having read Nathans write up I see no real benefits of this 300 Winmag based cartridge over a 300 WSM based one.

 

The obvious flaw is the belted case and resizing issues that will happen after two firings - your customer will need a specialist forming collar to size the brass to the belt.

 

The other issue is the fact the case is ineficient compared to the WSM case (in my opinion) and you will attain similar velocities for less powder with the shorter case.

 

While quality brass is available for the Win Mag, its also available for the 300 WSM and case forming for the Winnie would appear to require more complicated steps than simply necking down 300 WSM to accept the 284 projectile .

 

The WSM based case is inherantly accurate too, as proven over years of use by F Open shooters as it has been in 7 / 300 WSM form the go to case for many years.

 

The Practical may be an excellent hunting round, but in the write up the author admits throat erosion is an issue and low volume shooting is used to avoid this (its essentially a hunting round of similar veign to the Shooting Times Westerner)

 

Interesting project though and it sounds like your customers mind is set anyway, id just pursued them to have a spare barrel set aside too for when fire forming is done....

[OSOK]

I have to agree with Ronin , The belted case is enough justification for me not to do it and there are lots of better cases to pick from . From a personal point , if WSM was used I'd neck up from 270 rather than size down from 300 as I've tried both and never found an advantage in the longer neck theory.

 

Regarding seeing signature, this always depends upon the type of ground and not an extra 200 ft/sec and joking apart the most common reason for not seeing strike at these distances is not looking in the right place .

 

As I've previously said , A mile is comfortable for most 7's with the right scope and rail combo so there's no need to go too big on the case , go with proven method that gives very low spreads . Look no further than 284's , saum's or wsm's as there's a reason why their successful in competition.

 

OSOK

[Scotch_egg]

Ronin/OSOK

 

I have just read a link on Nathan Fosters website where he professes the idea behind the practical is to neck size only. Therefore negating the associated issues with a belted cartridge.

 

http://www.ballisticstudies.com/Knowledgebase/7mm+Practical.html

[duey]

A 300 winmag case will require a special collet die to resize the area directly above the belt, especially if the brass is pushed hard, I know as I shoot winmag and had issues with tight bolt that was only solved with the use of said die after every third firing

I know of someone that achieves over 2000yds with a 284, with berger 180 vld, so why not just keep it simple as OSOK has said

[OSOK]

Scotch_egg , I've not looked at the write up but to neck size only wouldn't in my opinion ' Negate ' the belt issue it would just be pretending it wasn't happening . Many years ago I had a UA in 300 win mag and duey is bang on with the collet die as normal resizing dies don't get into the belt / body junction ...... You can probably tell that I'm not a fan .

 

OSOK

[Chris-NZ]

The local NZ Hunter boys build many big Sevens. They avoid anything with a belt on it.

 

A current favourite is the 7 FatMax: a .300 Norma necked down. Very efficient design and is the biggest performer you can build on a med length action.

Their other one is the 7 Stumpy which is a .300 Blaser necked down. It's basically a 2.5" RUM.

Either of these will do the mile but they would always do a .338 for that use.

 

BTW, Nathan Foster makes for an interesting read but despite what he claims, his true long range experience isn't a patch on that of the NZ Hunter crew.

[Blue Haze]

Repeat post

[Blue Haze]

Trying another tact - what velocity does your customer expect out of the 7mm Practical? I very much doubt it will much beat a WSM loaded to the hilt with RS70...

 

My reasoning is this - there are many in F-Class to whom brass prep, barrel life and cost is almost no object - they will use and do anything that gives an advantage. Why then do we not see cartridges like the 7mm Practical in F-Class, but load of 7-270/300WSMs?

 

I'd be advising your customer to say that 7WSM will do everything that the 7 practical will, but with less powder, longer barrel life, easier brass prep and easier to size cases.

 

For example the 7mm BoBo will only achieve 3120 fps when loaded to 4000 bar. At the same pressure the 7WSM only gives up 30 fps... So my answer is, why WOULD you use the practical?

[Laurie]

The Boo Boo had a few users in the early days of F-Class, but was soon replaced by the WSM which offers a lot better barrel life and less recoil for a small drop in MVs.

[Big Al]

Trying another tact - what velocity does your customer expect out of the 7mm Practical? I very much doubt it will much beat a WSM loaded to the hilt with RS70...

 

My reasoning is this - there are many in F-Class to whom brass prep, barrel life and cost is almost no object - they will use and do anything that gives an advantage. Why then do we not see cartridges like the 7mm Practical in F-Class, but load of 7-270/300WSMs?

 

I'd be advising your customer to say that 7WSM will do everything that the 7 practical will, but with less powder, longer barrel life, easier brass prep and easier to size cases.

 

For example the 7mm BoBo will only achieve 3120 fps when loaded to 4000 bar. At the same pressure the 7WSM only gives up 30 fps... So my answer is, why WOULD you use the practical?

 

 

I had my own opinion and used F-Class as the benchmark but my customer seemed very impressed with the 7MM Practical based on watching Youtube clips. Im not one for wanting to push anyone down a route the dont want to go but equally starting a thread like this may well provide enough data and evidence to confirm my own feelings.

 

In the end I will build whatever is asked of my but I think on a project like this which will be expensive it is worth exploring all options.

 

Im grateful for everyones input so far.

[Vermincinerator]

Any thoughts on using the 7mm Dakota case, longer then the WSM but shorter then the RUM.

 

Ian.

[NigelM]

I have been looking pretty hard at 7 SAUM, 7 WSM, 7LRM and 7 Practical for a similar project. What's interesting is the difference in powder capacity vs MV. There seems to be about 100 fps (3%) between the smallest (SAUM) and largest (Practical) yet the difference in case capacity is 14 grains (19%).

 

The practical is a pretty inefficient cartridge and those additional grains are doing little more than increasing recoil and throat erosion.

 

My conclusion is to go for a 7 SAUM. Most also believe it to be amongst the most accurate of the 7's to boot due mainly to the long neck and as a true short action chambering I can run it in short action and still seat the longer bullets without eating too heavily into case capacity.

[Laurie]

That's always the case - a basic rule of internal ballistics. A simple guide to calculate how differences in case capacity affect MVs is to take the % capacity change and divide it by 4 to get the MV change. (Everything else equal - ie same bullet, barrel length, peak pressure, use of a suitable powder giving full pressure at a near 100% fill-ratio.)

 

So a 20% larger case and powder charge give a roughly 5% MV improvement.

 

However, in any calibre, once you get to 'over bore capacity', the resulting gains of any further size increase become even poorer and when you start with 7mm SAUM size you're into that sort of territory.

 

A wonderful example (well 'wonderful' if you're a supplier of new barrels and large tubs of very slow burning powders) is the new .26 Nosler which must be one of the more ridiculous designs of recent years.

 

Using Nosler's loads data and comparing the 26 to the marginally over bore capacity 6.5-284 Norma, here's what you get, both using a 26-inch barrel and 140/142gn bullets:

 

6.5-284 (58.4gn water capacity under a seated bullet) ............. 52gn Alliant Re19 ........... 2,953 fps MV

 

26 Nosler (93.0gn water capacity under a seated bullet) .......... 86gn Viht 20N29 ............. 3,194 fps MV

 

Both use Nosler data for the powder showing the highest MV and both powders have excellent fill-ratios in the near 100% bracket.

 

So 59% case capacity and 65% powder charge weight increases actually give a 241 fps or 8% velocity gain, not the 15% that the 'quarter-rule' predicts and which likely applies between say 260 Rem and 6.5-284 if both loaded to the 260's 60,000 psi SAAMI maximum chamber pressure.

 

Of course when you want a tool to undertake a specific task such as shoot a mile (although the pretty well off the shelf 7mm magnums are more than ballistically adequate for that task), normal considerations often have to be thrown out of the window and every little extra benefit seized. This is definitely the case with the now annual US two-mile shooting competition with some pretty extreme large bore cartridges burning really large quantities of powder.

 

However, I don't think that the desire to shoot an elk say at very long distances compared to normal sporting shots really needs the 26 Nosler.

[NigelM]

Thanks for the informative reply Laurie.

 

Agreed the 26 Nosler is a bit mad. I did some calculations and worked out that the barrel life was likely to be around 400 rounds. I got to 600 for the 28 Nosler and about 1000 for the 30 Nosler. All based on case capacity vs bore sectional area and correlated to known chamberings.

 

A 338 Nosler might be an interesting proposition though. A non belted 338 fitting a standard chamber and magnum bolt face. I would think that's about optimum performance/efficiency for 96 grains of capacity.