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6.5mm versus 7mm / .284"


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The more competitive the competition,and thecloserthe distance gets to 1000y,the more the balance swings to the better 7mm cartridges.

For club/pure enjoyment/ reactive gongs.....and  sub 750y  informal shooting, with multiple shots,the  best of the 6.5s are probably easier to shoot enjoyably.

Ballistics balanced against recoil. In a heavy rifle (20lb), it's close,between my two -7Shehane and 6.5x55 Ackley....but goes as above...chips down,Shehane.

gbal

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You will see a worthwhile ballistic advantage running 180gr bullets in something like a straight .284 Win compared to running 140gr in something like a 6.5x47 or 6.5 Creedmoor.

Depending on exactly what level of target shooting then dont rule out a good 6mm, potentially easier to shoot well and some of the best 6mm chamberings are seriously accurate and when shooting the 105-110gr class of bullet give up very little/nothing to a 6.5 running 140's in terms of ballistics out to 1000yds.

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I shot my 7mm saum today at a 1000yds and it went pretty well until I made a school boy error and dialled the wrong way.what a doughnut.i made 4 great elevation shots that were off the edge of the fig11 that would of killed my score.last detail I then had a misfeed and didnt get my last shot off before targets went down.just to pee me off futher I did it again on the next COF and lost my way and stopped shooting.i checked after and I ended up 5 moa right.what a complete balls up.only ever dialled wrong once before today :wacko:.Oh well nevermind.

Sorry to waffle on.

You won' be disappinted with a 7mm if you dial in correctly :D

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7mm has the edge on ballistics.  6 or 6.5mm are cheaper to shoot, can be nicer to shoot and something like small primer CM running 3000fps from a 28 inch barrel with 139/140s or even a 123 Scenar driven hard won't be that far behind a good heavier 7mm as higher velocity makes up the differences well.

Ultimately, 7mm BC takes some beating on performance alone.

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I run a Dta 260 rem factory barrel in my covert (26” from memory). I happily throws 139 - 140 gr bullets out to 1200 m. It has raised eyebrows on long range shooters with far more experience than myself. 

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To beat a good 7mm bullet (like the 180 Scenar L) you'll need to push a 6.5mm bullet to top speeds and pressures. Doing so will likely mean reduced brass life and kaning your barrel with very high energy powders.

the heavier 7mm bullet will beat the wind better all at lower speeds & pressures, giving you better overall barrel life.

just look at the differences between a 6.5x284 and a straight .284win - I'd say you'll get better performance downrange and better barrel life with the .284

 

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2 hours ago, meles meles said:

*eagerly awaits pictures of the 7/300 WSM*

If the left hand Defiance Deviant action I have been waiting for 13 months ever turns up I will be happy to oblige.

It will go well with the Bartlein and Manners T4 Carbon Elite, its out of the factory now so shouldn't be long. I think my customers middle name must be Solomon :)

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On 26/02/2018 at 3:06 PM, meles meles said:

It seems the 7mm is the way to go, but now we have to decide which flavour of 7mm.  Decisions, decisions...

 

*Scurries away to swot up on 7mm Rem Mag, 7 WSM, 7 SAUM, .284 Win   *

In the last year or so I've been exploring longer range with a 6.5 Creedmoor and I recently converted a spare slot to 7mm for an idea to stretch things towards some ELR. This means I've no doubt had some similar thoughts to you. Now [I think :)] I've narrowed it down to 7 SAUM and the relatively new 28 Nosler. (Thinking behind it goes something like: 7 SAUM tends to the best "all-round" package v the all new, all out, no compromise "bad boy" in the world of 7mm.)

Anyway, have you thought about putting 28 Nosler into the mix?

(And might anyone else, this side of the pond, have had any experience of the Nosler (or perhaps just like to give us a few ideas about it anyway)?)

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I'm not well versed in either bore size.  I am wondering how "pedestrian" a 7mm has to be before it loses out to a 6.5?

The reason for this question is that as a .308 shooter, I've always had a hankering for a 7mm-08 - would this be enough cartridge to produce a meaningful benefit over, say, a 6.5 CM?

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55 minutes ago, meles meles said:

We hadn't heard about .28 Nosler....

My advice would be to forget you now have!

Nosler sees itself as a modern US equivalent to H&H, Rigby and such selling upmarket rifles and its own design cartridges at inflated prices. (Rigby etc it is NOT as while it markets  nice rifles, they're hardly hand-built by craftsmen.)

Nosler's proprietary cartridges are nearly all seriously over-bore capacity as they're designed to produce a headline grabbing MV figure for marketing reasons.

Rifles and ammunition generally get a good press from American shooting journos - not surprising as the individuals concerned do their 'testing' on live hunts of exotic species in exotics places with five star accommodation and catering for several nights at Nosler's expense.  Say anything remotely negative in print and that gravy train will never be boarded again.

Here are the case water capacities of a range of 7mm cartridges in grains weight:

7-08 ................................................  55gn

284 ................................................. 66gn

280 Rem / 7X64 Brenneke ..............  69gn

7mm RSAUM .................................. 73gn

7mm Rem Magnum / WSM ............ 81/82gn

28 Nosler ...................................... 95.9gn (Nosler data)

7mm RUM .................................... 112gn

 

The 7mm Rem Mag has been used as an off the shelf example of an over-bore capacity design for decades, although it is less so these days given the arrival of much slower burning powders such as Hodgdon Retumbo. Nevertheless, it is a big high case capacity cartridge for the calibre. With a 17% capacity increase over it for the Nosler, you burn a lot of extra powder for a very small MV hike, but at the expense of even worse barrel life. OK for people who fire less than 20 rounds a year in a sighting-in session then a couple of elk or moose hunts, but really, really useless as range tool.

To compound it, while you can get 7mm RM brass at reasonable prices easily, and SAUM and WSM brass for somewhat more with some hunting around for suppliers, the 28 Nosler is only supplied by Nosler at Nosler prices. (Actually, they're probably made by Norma under contract.)

Sportsman Gun Co currently has an offer price on it of £94.99 per pack. Not unreasonable? Note the pack size - 25 cases so £379.96 / 100 (+ P&P  :)

I could go on, but ............................... !!

 

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1 hour ago, Bushdog said:

I'm not well versed in either bore size.  I am wondering how "pedestrian" a 7mm has to be before it loses out to a 6.5?

The reason for this question is that as a .308 shooter, I've always had a hankering for a 7mm-08 - would this be enough cartridge to produce a meaningful benefit over, say, a 6.5 CM?

 

I researched this in some depth a few years ago before rebarrelling a 308 FTR rifle to 7mm-08, subsequently done with a 31-inch Bartlein fluted 9-twist - thank you Mik Mak and Dolphin Precision for a good job!

In factory or custom sporting rifles, the 7mm-08 is severely limited by magazine length and the SAAMI COAL of 2.800". That's why factory ammo is mostly 140gn PSP with one or two 150gn offerings. Despite this, it is reckoned by many to be one of the best light/medium deer cartridges on offer, a 7X57mm Mauser for modern rifles and today's expanding bullets.

As a range / prone deliberate competition tool, it needs to be on a long action or a short action used single-shot in both cases with an extended freebore chamber. The match 7mm-08 needs to run at around 2.95-3" COAL for mid-weight bullets such as the 160gn Sierra TMK, 162gn AMax / ELD, and 168gn Berger VLD, and slightly more for 175gn and heavier models. (The same of course applies to 260 Rem with 140-150gn bullets among the 6.5s.) The cartridge will handle 175/180s in match form, but the case capacity is marginal for the slower burning powders used - my opinion is if you want to shoot these bullets go up a step in case size to the 'straight' 284.

If you take the 168gn Berger VLD as the default bullet - I did and the barrel was chambered around it set at 2.99" COAL, pity the Bartlein has never liked this bullet much! - you have an aerodynamically efficient design with 0.925 form factor giving 0.322 G7 BC (Litz). That's a not unimpressive figure considering the darling of the 'Effers' shooting big boys' sevens, the 180gn Berger Hybrid is rated at 0.345, only 7% higher. However, look at the 6.5mm competition and the obvious comparison is with the same source and  similar vintage 140gn Berger VLD whose form factor / BC values are a not too different at 0.936 / 0.307. (Actually, taking these figures from Bryan Litz's Ballistic Performance of Rifle Bullets 3rd edition, Bryan has revised one of both as the two bullets had identical BC values when I did the research using data from the 1st edition.)

What I took from the figure work was that with bullets having similar BCs, you need similar MVs to have comparable external ballistic performance between 6,5 and 7mm cartridges and as the 260 etc in long-throat (LT) match form would give a 140 0.264 bullet around 2,800 fps, that or more had to be the 7mm-08 objective for the 168 VLD. The Litz revisions ease that target a bit, but we now have the Hornady 140gn 0.264 ELD-M with a G7 BC of  0.322 as per the 7mm 168, and a 147gn version at a very impressive 0.355. (On the other side of the balance sheet, the new Hornady 7mm 162gn ELD-M is rated at 0.327, a little higher, and being a little lighter can be driven a bit faster, in theory anyway.

I then spent many happy hours modelling 260 Rem LT v 7mm-08 LT and the conclusion was that unless you really stoke the 7-08 up with hot burning double-based or high-energy powders, the 260 in long throat form has the edge as in QuickLOAD at any rate, an extra 50-100 fps is on offer. Since then, small primer 6.5 Creedmoor brass has appeared and we're starting to see some impressive claimed MVs for handloads for this cartridge in this form.

The other side of the equation is of course barrel life. I reckon that the 7-08 with single-based powders and warm but not excessive pressure loads should give up to 50% greater barrel life than hot loaded Creedmoors / 260s. (Say 3,000 rounds v 2,000, but with some of the MV claims for SR 6.5 Creedmoor and 140-147gn bullets, I frankly doubt if these rifles will see as much as 2,000 rounds through a barrel!)

In the end I settled on the 160gn  Sierra TMK at 2,830 fps from a compressed load of Viht N160 for mid-range F and for short-range F, the 150gn Lapua Scenar L at 2,850 fps using Lovex SO65, a modest pressure and ballistic performance load but one that will chew the centre out of the 300 yard F-Class target and produce groups in the twos with some high ones off the bench at 100 yards in nil/low wind conditions. I have avoided hot powders - RS60, N550, and suchlike - but have loaded 50 rounds up recently to try at 100 with Hunter, RS62, and N550 to see what level of MVs can be obtained. I've also just bought a couple of hundred of the higher BC 162gn Hornady ELD-Ms to see what their precision is like - the 160 TMK shoots so well in the rifle that it has to be an exceptionally good-grouping combination for me to replace it irrespective of the bullet's BC.

With hindsight, the 7-08 needs such relatively slow burning powders with >160gn match bullets, that I'd choose 7mm-08 AI now rather than the 'straight' version whose case is just a bit short on capacity. (The same applies to 260 of course.) 7mm-08 brass is no problem - Winchester is actually rather good, but the obvious source for the match shooter is Lapua .308 Win 'Palma' small primer - a single pass through a 7mm-08 FL sizer reforms it although it does thicken necks by a thou' so mild neck turning may be necessary for a 'minimum SAAMI' chamber.

 

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Thanks Laurie. Sounds like the longer (best BC) bullets may not be a goer in a short action magazine rifle, then.  That's a pity - I was pondering this as an alternative to .308 when my current barrel bites the dust.

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2 hours ago, meles meles said:

The more we learn about this subject, the more we think we should stick with our existing 7mm Rem Mag ( A Remington 700 in an AICS stock) for longer range shooting and keep the DTA for sub 600 yards and sub sonic rounds

 

As you have a rifle whose action and bolt are set up for magnum case-head cartridges and long COALs, the 7mm Rem SAUM would be worth consideration if and when rebarrelling comes due. This version of the short magnums appears to be gaining popularity rapidly these days, so this year's long-range match results should show if its day has finally come.

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17 minutes ago, Bushdog said:

Thanks Laurie. Sounds like the longer (best BC) bullets may not be a goer in a short action magazine rifle, then.  That's a pity - I was pondering this as an alternative to .308 when my current barrel bites the dust.

For this purpose the Creedmoor is the obvious contender as a smaller calibre 308 replacement, superior in every respect bar barrel life.

For the Creedmoor and also the 260 Rem in longer-range magazine fed operation, look at the 130gn Berger AR-Hybrid which I reckon may be a game-changer for such rifles in magazine operation. It's been developed for the 260 Rem for use in 2.800 COAL loadings in - as the same suggests - semi-auto match and tactical rifles and manages to produce an impressive BC despite having a shorter nose section than more traditional 6.5s. I'll give some a go in a long-throat 260 later this year including running them with really large jumps (as in 150 or more thou'). Not a cheap bullet though.

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Thanks again Laurie - kind of confirmed what I already suspected.

The .308's still got a bit of life left in it yet, but probably a 6.5 CM re-barrel is most sensible, when the time comes.

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