GGG 308 Ammo

[edcm]

Hi All
Has anyone chrono'ed the GGG 175gr ammo? Even better if it was with a 1 in 10 20 inch barrel!

Any reading would be great as i will estimate 25fps per inch as a guide.

It states 805m/s on the box but past experience with Hornady etc shows these to be wildly exaggerated.

Thanks Eddie

[Laurie]

Bear in mind that both the GGG and its RUAG predecessor are/were manufactured for a very particular set of internal ballistics circumstances - to produce just under maximum allowed pressure and 2,925-2,950 fps MV in a 30-32" barrel with a short freebore chamber and this is crucial, a barrel whose internal dimensions are smaller than the SAAMI standard 0.300/0.3080" land / groove diameter.

The reason for the 'tight-bore barrel' is largely historic and a throwback to the days of shooting issued military spec 7.62mm ammunition with undersize bullets. These raise pressures and also MVs. There are two effects of this situation - standard SAAMI spec ammunition may produce higher than maximum chamber pressures in a TR rifle; conversely using the NRA ammunition will produce significantly lower pressures and MVs in a non-TR/Palma rifle, especially when one is talking about off the shelf sporting rifles that have slacker chambers, in many cases massive freebore values, and of course up to ten or 12 inches less barrel.

I can't comment on the GGG NRA ammunition, but its RUAG predecessor manufactured to the same specification had over 100 thou' bullet jump to the lands in a low round count Howa 1500 Varminter with 22-inch barrel and produced under 2,600 fps. Well under that figure IIRC, but I'd have to look my range notes out to quote the actual value. ES was fine and it grouped superbly at short range, but at some 400 fps MV under-spec, it would struggle beyond 800 yards, or even 600.

The upside is that the original 155gn Sierra MK (product number 2155) as loaded in both versions is a superbly tolerant bullet, not only of lots of jump inside the rifle, but of trans and subsonic velocities in flight, so it makes the best of what would be a disastrous set of circumstances for many bullet designs.

[edcm]

Hi Laurie

Thanks for the reply. I am now confused, that this ammo will be impossible to gauge (even a rough idea) without a chrono, beacuse it is designed for 7.62 NATO rather that .308 (even though it says .308 on the box.) due to the possible massive jump.

Eddie

[Laurie]

Hi Laurie

Thanks for the reply. I am now confused, that this ammo will be impossible to gauge (even a rough idea) without a chrono, beacuse it is designed for 7.62 NATO rather that .308 (even though it says .308 on the box.) due to the possible massive jump.

Eddie

No not designed for 7.62 NATO, but for tight-bore / short freebore 308s. (the 7.62 reference is there to explain why TR rifle barrels are largely for historic reasons cut 'tight' by the barrelmaker.)

The key point is that your rifle should have a SAAMI standard 300/3080 dimensioned barrel as have nearly all factory rifles. It may also have a throat giving considerably considerably more freebore than the standard GB TR rifle with its Bisley 150 or Palma 95 chamber dimensions. This is the area ahead of the chambered bullet ogive that is cut as a slightly over bullet size cylinder until the angled beginning of the rifling lands start. Most commercial rifles have more freebore than TR rifles because they may be asked to deal with heavier / longer bullets and greater COALs than that loaded for TR / Palma. The RWS / GGG NRA cartridges are loaded to around 2.75" for instance around 60 thou' under the SAAMI maximum. They will not chamber the US 175gn Sierra MK bulleted M118LR round as a result as the freebore is 25 thou' or so too short.

Those twin conditions mean that a TR rifle produces higher pressures and MVs with any given ammunition lot than an equivalent rifle with same length barrel and SAAMI dimensions. Turn things around and put ammunition loaded specifically for TR rifles into an off the shelf commercial 308 Win rifle and it now produces less pressure and less velocity in the more generously chambered and dimensioned commercial rifle chamber and barrel.

That of course if before one factors in the 10 inch barrel length reduction between your rifle and that of a typical TR model. Assuming 25 fps / inch average change is likely an underestimate.

To give an example of what I'm on about, the final year of the NRA / RUAG contract for RWS branded 308 GB NRA match ammunition saw major pressure problems with the lot chosen for issue in that summer's Imperial Meeting at Bisley - pressures high enough to produce very hard extraction in most rifles and blown primers in some - a serious condition. That lot was withdrawn and replaced during the matches and returned to the factory as out of specification. RWS engineers retested the errant ammunition and found that although loaded too 'hot' for some 'tight' TR rifle barrels, it was OK in a standard dimension SAAMI test barrel. It was then repackaged under a different name and quite legitimately put on the market as 308 Win 155gn Sierra MK match-bullet ammunition. Some of that made its way into the UK retail chain at attractive prices and ended up being used by TR shooters at Bisley whereupon the NRA Had to put out an 'advisory' saying it MUST not be used in your average TR rifle built to normal specifications. Such rifles when proof tested are stamped as '308 Win Match - non standard' or something similar and the standard 308 Win proof loading reduced.

Back in the early days of using grotty military specification 7.62mm ball ammunition, some barrels were used with bores as small as 0.297" land and 0.305" groove diameters. Some of these early 7.62mm rifles are still around with original (although by now usually comprehensively shot out) barrels and can be downright dangerous with 308 Win full pressure ammunition. As ammunition and bullet standards changed / improved in the final days of the RG 155gn FMJBT sniper round sold to the NRA as 'Bisley Target', barrels started to be specified as somewhere around 0.298-0.299" bore (1 to 2 thou' undersize) and 0.3075-3078" groove diameter (third to half a thou' undersize). The 155gn Sierra MK used in the NRA ammunition is slightly oversize against the nominal 308 dia - usually miking at 0.3083"-0.3085".

Most if not all of the custom barrelmakers offer 30-calibre blanks in both stanadrd and 'tight' dimensions. Scroll down the Bartlein Barrels list here

https://bartleinbarrels.com/calibers/

and you'll see '30 cal tight' showing likely internal dimensions with standard 308 on the line below

So yes, you are correct. Until you can chronograph the ammunition in your rifle, you have little idea as to its actual MV. I would expect it to be around 2,500-2,550 fps, but nothing is a given in this matter as rifles are all individuals and if you have a military orientated tactical type rifle, it may have a barrel specified a bit on the tight side to provide satisfactory MVs and performance with military spec ammo.

[Furiouspilgrim]

GGG is normally on the HOT side. I’ll check what data I have on mine tomorrow. 20” 1 in 12.

[edcm]

Laurie

Thank you again I am now (partly) educated.

So my dilemma is that i now need to find a reasonably priced factory round that has a good BC that will fit a non tight barrel.
I hope to shooting at Orion in April, which normally makes me use 200 rounds or so.

Furiouspilgrim
that would be great if you can dig that out please.

Eddie

[20series]

I would recommend HPS Targetmaster ammo they do various weights of bullets.

https://www.hps-tr.com/en/targetmaster- ... n-from-hps

Alan

[rox]

Has anyone chrono'ed the GGG 175gr ammo? Even better if it was with a 1 in 10 20 inch barrel!

Most of what Laurie has described applies to the 155gr GGG 'Imperial' product, not the 175 gr. 175 gr would be illegal in TR competition, and it certainly isn't designed to achieve 2950 fps in typical TR chamber and barrel dimensions.

..

[IainWR]

Laurie, and others

While everything you say about the round that GGG make for NRA competition is correct, Eddie is asking about a different product.

The NRA round is marketed in a box of 20 laid out in 2 rows of 10, in 2-tone green/yellow, labelled 7.62mm Imperial 155gr match. Eddie's ammunition is in esentially the same box, but labelled .308" Win 175 gr HPBT. There is also a 168gr product similarly packed and labelled, and GGGs standard 7.62mm NATO round with a 147 gr bullet, that comes packed in brown cartons laid out 4x5 and marked 7.62x51 NATO. The 147gr bullet is GGGs own product, the 155 is, as you say, a Sierra 2155 MatchKing, and I suspect, but cannot confirm, that the 168 and 175gr are also Sierra bullets.

Hi All
Has anyone chrono'ed the GGG 175gr ammo?
Thanks Eddie

[edcm]

Hi Iain

Thanks for the response...... yes they are SMKs.

A really confused Eddie