Jump to content

So just how capable is a 26" barrelled,magazine fed .308 out to 1000yds?


MJR

Recommended Posts

Not wanting to hijack the Long Range Rifle thread whats your opinion on this question? I realise a 26" barrel is not the ultimate for long range, I know a magazined action is not as strong as a single shot but for someone wanting a multi purpose rifle how much 'real world' difference is there?

Link to comment
Share on other sites

mjr,

 

dont know i have a 26 inch barrelled 308 as well and would like to know what sort of muzzle velocity have you got to acheive to keep a 150 or 155 grain bullet supersonic at 1000yds as that seems to be a basic balistics requirement of 1000yd shooting .

 

graham.

Link to comment
Share on other sites

Based on my copy of Exbal, for the following 150-155 bullets:

 

Berger 150 FB needs 2850fps to stay supersonic @ 1000yds

Berger 155 VLD needs 2450fp............"..............@ 1000yds

Lapua 155 Scenar needs 2300fps......."..............@ 1000yds

Sierra 155 Matchking needs 2650fps.."...............@ 1000yds

 

At the normal 308 velocities you will have no problem keeping all of the above supersonic out to 1000yds.

 

Ian.

Link to comment
Share on other sites

Ian,

thanks for that. The Lapua bullets seem slow, I expected them all to be circa 2800 ft/sec.

Lapua Scenars have a much higher BC than the rest, hence a lower velocity is required to keep them supersonic at 1000 yards.

However have to agree 2300 fps does seem low.

Cheers

Dave

Link to comment
Share on other sites

Surprised me too, but at 2300 with the Scenar (compared to 2800), you're giving away over two and a half mins (25") in the wind which any target shooter wouldn't be happy with. That'd be a massive difference in scores and a near impossible task on small furry/feathery things in switchy conditions

 

Chris-NZ

Link to comment
Share on other sites

Fellows,

 

I’m sure Ian’s 2300 was a typo.

 

As an aside; you can’t really talk of Mach without considering the air temp (air temp is the primary determinant of Mach velocity -ie the speed of sound varies with air temp).

 

At a station pressure of 1000mb; a 155 Scenar launched at 2800fps will go subsonic roughly as follows:

 

Minus 5 Deg C 930 metres

 

Plus 5 Deg C 950 metres

 

Plus 20 Deg C 980 metres

 

 

That's why you might find that a round that does OK at 1000yds on a warms winter's afternoon goes to ratsh't when the sun goes down and the temp drops a few degrees :blush:

Link to comment
Share on other sites

We shot 1000 the other day at Bisley and were adding 2-3MOA more than mid Summer.

 

The wind was slightly quartering towards us but it's still 10%.

 

On the plus side you can get away with a hotter load and the barrel cools down quicker between strings :wub:

 

Cheers,

 

Phil

Link to comment
Share on other sites

  • 8 months later...

Just noticed this thread being read, so re-read it myself.

 

Spotted Ian's last point:

 

You have got the wrong end of the stick guys, due to its high BC, 2300fps is the "minimum" velocity needed to keep the 155grn Scenar supersonic at 1000yds. :)

 

Ian,

 

I think there's a data error in there somewhere.

 

A Scenar needs to be launched at at least 2650fps to get to 1000yds and still be supersonic - and then it would only do so if the temp was 25 Deg C or higher.

 

On a 10 Deg C day you would need all your shots to be launched at over 2700 fps to do the same.

 

On a 0 Deg C day you'd need all MVs to be 2750fps + to get it there.

 

- and all those MVs need to be the MV of the slowest shot of your MV ES; ie you need a fudge factor higher for your average MV -say 2800fps in the last example.

 

:blink:

Link to comment
Share on other sites

Just noticed this thread being read, so re-read it myself.

 

Spotted Ian's last point:

 

 

 

Ian,

 

I think there's a data error in there somewhere.

 

A Scenar needs to be launched at at least 2650fps to get to 1000yds and still be supersonic - and then it would only do so if the temp was 25 Deg C or higher.

 

On a 10 Deg C day you would need all your shots to be launched at over 2700 fps to do the same.

 

On a 0 Deg C day you'd need all MVs to be 2750fps + to get it there.

 

- and all those MVs need to be the MV of the slowest shot of your MV ES; ie you need a fudge factor higher for your average MV -say 2800fps in the last example.

 

:)

 

BD, I am only going by what exbal says mate, when i entered your suggested 2650fps it gives a velocity of 1251fps @ 1000yds :)

 

Ian.

Link to comment
Share on other sites

I'm afraid the BCs those IMBAL calculations are based on are hopelessly optimistic. They use what ballisticians call the G1 drag curve model which in turn is derived from a flat-based round-nosed projectile closley resembling those by our great, great, great, (etc) grandfathers in the South African war. There are two problems with G1. First we don't shoot bullets like that at long range and two G1 BCs are highly velocity sensitive. The quoted Lapua 155gn Scenar BC of over 0.5 is reckoned to be correct at MVs above 3,050 fps, but it falls steadily in line with reducing velocity.

 

The guru on this a former US Air Force rocket scientist called Bryan Litz who is now Berger Bullets' ballistician and is currently in the process of designing a new generation of 'hybrid' ogive bullets for the company. (Expect a new 6mm 105gn match bullet in the next 12 months, and the first of a new range of super-high 0.308s in late 2011 or during 2012). If you want to read what he says about the REAL ballistics of 0.308" 155s, look at his 2-part article in TargetShooter online magazine:

 

Free Target Shooter Magazine homepage

 

and request the archived October and November 2009 issues.

 

Bryan developed a sophisticated 1,000yd velocity measuring system that records a bullet's speed at set points over a 1,000yd flight (using accoustic sensors feeding into a laptop instead of the incredibly expensive Doppler radar gear needed previously) and has produced data for around 175 different long-range match and hunting bullets in AVERAGE G1 and much better G7 data forms.

 

His findings for the 155s are:

 

 

Berger VLD ........................ 0.225 / 0.439

 

Berger 155.5 Fullbore .......... 0.237 / 0.464

 

Sierra Palma MK (old) .......... 0.214 / 0.417

 

Sierra Palma MK (new) ......... 0.229 / 0.447

 

A-Max .................................. 0.212 / 0.415

 

Lapua Scenar ....................... 0.236 / 0.462

 

The first value is the much better G7, the second the G1 averaged over a 3,000 to 1,500 fps flight path.

 

Run these through a G7 ballistics program such as those used by JBM or the free one downloadable from the Berger Bullets website and these are the MVs you need to keep them supersonic at 1,000yd (1,122 fps is the speed of sound).

 

Berger VLD ................ 2,815 fps

 

Berger 155.5 ............... 2,720 fps

 

Sierra MK (old) ............ 2,920 fps

 

Sierra MK (new) .......... 2,780 fps

 

A-Max ........................ 2,950 fps

 

Lapuas Scenar ........... 2,720 fps

 

BUT .................. !!!!

 

Life is never simple or easy here. Firstly as Brown Dog points out the speed of sound varies according to air pressure and temperature as does a bullet's rate of loss of speed. These figures are based on 'standard ballistics values' of 59 degrees F and 29.92" of mercury atmospheric pressure (sea level on a typical day). Shoot on a desert mountain 5,000ft ASL and in 100 degrees and you have thinner air and a fair bit more latitude.

 

Then there is the 'transonic' zone turbulence problem as the bullet approaches the speed of sound. Ballisticians say it starts between 1.4 and 1.3 Mach, but so far as long-range target shooters are concerned, the real problem starts at about 100 fps above the speed of sound, say 1,250 fps. What happens is that because of the bullet's curved shape some parts of the air flowing around it are accelerated and remain supersonic, but at other points it's slowed and become subsonic resulting in turbulence and extra drag - so the ballistic table results are inaccurate for the last hundred yards or so.

 

Some bullets cope better than others at just above the speed of sound and/or going subsonic. The 168 Sierra doesn't, likewise all .308" A-Maxes apart from the new 208gn - it's to do with an overly steep boat-tail angle (don't ask!)

 

Then, there is muzzle velocity spread. We talk averages at say 2,900 but that might be 2,875 - 2,915 for individual bullets. Those at the low end crash and burn at 1,000, those at the top end just stay supersonic and go roughly where you aimed. So you need a cushion. This is why 7.62mm / .308W 'Target Rifle' has used 30-32" barrels since its inception in 1967/8 - it's to achieve 2,950 fps MV with a 155 in today's terms, and the current NRA RUAG ammo is tuned to give the old Sierra Palma MK 2,950-2,975 fps in a 'typical' TR barrel (tight internal dimensions as well as long) which ties right in with what Bryan Litz says about this bullet.

 

 

Right, so that's a load of problems. Solutions for 26" barrel users?

 

1. If you want to use 155s, don't use the old 155 SMK, or Hornady A-Max at 1,000yd

 

2. Don't use the 168s from Sierra, Hornady, Speer, or the 167 and 178 A-Max, or the 180 SMK - they all have 13-15 degree boat-tail angles and risk becoming unstable beyond the 800yd mark. Don't use the 167 or 185gn Scenars - they'll remain stable but are low BC. Bryan Litz's results for the 185 Scenar are way down on what Lapua quotes (he gets 0.247 G7 and 0.483 G1)

 

3. Use a high BC heavier bullet and/or one that has reputation for behaving well in trans or even subsonic flight. The best bullets on the market at the moment for general long-range 308W shooting are the Berger 175 and 185gn Target BT Long-Range models (not the same weight VLDs). Apart from having very high BCs, heavy bullets behave better at long ranges even though their MVs are lower. The three heavy Sierra MKs - 190, 200 and 220gn are superb long-range bullets and remain stable and relatively unaffected by wind in trans and subsonic velocities. That's why the 1,200yd Match Rifle shooters have used them for years and years (although about half have now switched to 210gn VLDs). The 175 Berger's BC values are 0.264 G7 / 0.515 G1; the 185 BT L-R's are 0.287 G7 / 0.560 G1.

 

4. Buy Bryan Litz's book "Applied Ballistics for Long Range Shooting". If you want to shoot at 1,000yd it'll save you money and time in the long run.

 

A lot of people reading this are going to query the take on a heavy slow bullet v 155 at high MVs. Here are the figures.

 

Let's assume you're getting 2,850 fps from a 155 in your 26" barrel rifle. The equivalent is 2,610 fps from the Berger 185 BT L-R and 2,575 fps from the Sierra 190gn MK (all give the same ME of just under 2,800 ft/lbs energy).

 

155gn Scenar, G7 BC of 0.236, 2,850 fps MV .............................. 1,000yd: 1,202 fps and 100" drift in a 10 mph wind

 

185gn Berger BT L-R, G7 BC of 0.287, 2,610 fps MV .................... 1,000yd: 1,276 fps and 87" drift in a 10 mph wind

 

190gn Sierra MK, G7 BC of 0.270, 2,575 fps MV ........................... 1,000yd:1,184 fps and 97" drift in a 10 mph wind

 

Not only do you get the higher retained velocity from the heavy Berger, but that's a big reduction in wind effect and that makes the shooter's life a whole lot easier.

 

Unfortunately, these Bergers cost an arm and a leg, and at the moment the 185gn model is as rare as rocking horse droppings as nearly every .308W F-TR long-range shooter in the country has switched to them. The 190gn Sierra performs better than its ballistics suggest because of its transonic flight tolerance. I know as I used them successfully at 1,000 at around 2,550 fps in a 24" barrel tactical rifle a few years ago.

 

The 175 and 185gn Berger work OK in 1-13" twist barrels, although 1-12" is better for the 185. The 190 SMK is fine in 1-12" too.

 

Laurie

Link to comment
Share on other sites

I made a mistake guys, i always believed the speed of sound to be approx. 1070fps which i now find thanks to Laurie's post not to be the case.

Exbal results, with Brians Litz's revised G1 BC now tells me that the Lapua 155grn Scenar needs 2780fps to be supersonic @ 1000yds :) more inline with Lauries and BDs findings.

 

Ian.

Link to comment
Share on other sites

Plenty of interesting external ballistics stuff but what about:

I know a magazined action is not as strong as a single shot

 

 

In terms of accuracy what do people think of the following statement?

If it's behind the lugs it doesn't matter.

Link to comment
Share on other sites

Laurie,

 

Great post. :)

 

Although Temp is the primary determinant of Mach and; rather counter-intuitively; pressure is not - as its effects get largely cancelled out by other factors. So, as you do, the 'minimum MV' statement must always be associated with a temperature.

 

( and your comment on MV spread was rather better explained than mine :):) )

 

The downside to the heavier 308 bullets; to my sensitive soul, is that they kick more! The difference between firing a 155 and a 180 or heavier is tangible (and I don't like recoil!)

 

 

In terms of accuracy what do people think of the following statement?

If it's behind the lugs it doesn't matter.

 

I think it's absolutely spot on. Fire it with a 2lb hammer.

Link to comment
Share on other sites

The downside to the heavier 308 bullets; to my sensitive soul, is that they kick more! The difference between firing a 155 and a 180 or heavier is tangible (and I don't like recoil!)

 

 

Yes, that's a really valid point, especially if the rifle is heavy sporter weight model like a Remy VS or PSS. A lot of American Fullbore (like our TR) and Palma shooters use the 175gn Berger BT Long-Range for club and 'American Rules' competitions, and 155s for those run under Palma conditions. They say that the wind drift reduction / recoil trade-off works in their favour with the 175, but not with the 185.

 

If using a 155 at long ranges (beyond 600yd), the three outstanding models are the new Sierra (no. 2156), Berger 155.5gn and Scenar. The Berger is a great bullet but priced at £48 / 100. A lot of people are doing very well with the new Sierra - a tip here is to jump them a lot, at least 30 or 40 thou'. This may be the best choice for people with long throated chambers or want to use the magazine and need the round at standard length. The Americans say they still work really well when jumped 70 and 80 thou'. The 155 Scenar is a proven good performer and widely available. if it suits your barrel, it's as good anything.

 

For short-range shooting - 200-600yd - the old Sierra (no. 2155) is still a really good choice. Beyond 600, you put yourself at a disadvantage shooting it.

Link to comment
Share on other sites

Nice posts (both) Laurie a good clear and concise explanation.

Liked the use of examples to better illustrate your point and gives us a clue what REALLY works.

Cheers.

Link to comment
Share on other sites

  • 2 weeks later...

My girlfriend shoots a 26'' barrelled .308 Remington 700 rifle,and at the last 1000 bench rest shoot at Diggle kicked all our arses.

I know this sound s like a tall story,but it really happened.

Not only did she win factory class,won light gun class too.

A lot of people say the .308 it dead,it certainly wasn't dead this day.

I do most of her loading/or set it up for her.

 

Moly coated 155 scenars

 

48.1 vit 150/just of the lands

 

They could actually soft seating into lands,a lot of powder and moly bullets ?.

 

Adrian

Link to comment
Share on other sites

Hi Adrian,

 

I will confirm that - Toni sure did kick all our arses. What's more, she just might win the UKBRA Factory Sporter Championship.

 

Might have known you'd try and steal a bit of her glory by claiming to have done her reloading - shame on you!

 

See you both Sunday?

 

Cheers

Vince

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use and Privacy Policy