Re: Never get tired of hearing this blokes crack(!)
Posted: Wed Apr 08, 2015 7:38 pm
Due to one of these historical anomolies, TR rifles are usually fitted with barrels whose internal dimensions are specified slightly undersize. (This also applies to the US and British Commonwealth equivalents and those used by Palma Rifle competitors in the US.) Whilst SAAMI, the ruling body for .308 Win specifies 0.300" bore dia. and 0.3080" groove diameter, the barrelmaker bores / cuts them on the small side, eg 0.298" or 0.299" bore / 0.3078" groove. This increases pressures and MVs and is a hangover from the days of military issued ammo and undersize bullets and was needed to get enough velocity for 1,000 yards. If you have an early 1st gen TR rifle, especially the number 4s with Enfield Lock barrels, these were seriously undersize to suit the old 145/146gn RG 7.62 bullets that often ran as small as 0.3077" diameter.
The 155gn Sierra MK used in the RWS ammo usually runs a little over its nominal 0.3080 around 0.3082" and doesn't need a tighter than SAAMI barrel, but the rifles were already there with them when the NRA went to RUAG. The load used was developed specifically with this situation in mind using several TR shooters' rifles with varied round counts and makes of barrels when the testing / procurement was done and the charge was adjusted to stay within safe pressures.
As pointed out, this batch appeared to be over-pressure when fed in tight barrels, but would run at lower pressures in a normal CIP / SAAMI specified rifle and therefore should be safe. Run the usual RWS ammo down 30-inch barrel FTR custom built rifles where the norm is to use SAAMI dimensioned barrels and MVs are often down on the TR 2,925-2,950 fps norm. If it (the over-pressure stuff) has reappeared under a different name, it's not being stupid or unreasonable to advise those with TR rifles not to use it even if it does seem a strange request to the non-TR shooter. The fault doesn't lie with the NRA when a supplier gets it wrong. Incidentally, it's not only out of spec ex-NRA / RWS that can create overpressures in a true TR rifle in unworn form, a maxium pressure .308 Win factory load could do so too for the same reason.
Although chamber form could affect this either way, this isn't a chamber neck issue as per the notorious Rule 150 issue, it's the powder characteristics and charge weight in relation to the bullet / bore match.
The 155gn Sierra MK used in the RWS ammo usually runs a little over its nominal 0.3080 around 0.3082" and doesn't need a tighter than SAAMI barrel, but the rifles were already there with them when the NRA went to RUAG. The load used was developed specifically with this situation in mind using several TR shooters' rifles with varied round counts and makes of barrels when the testing / procurement was done and the charge was adjusted to stay within safe pressures.
As pointed out, this batch appeared to be over-pressure when fed in tight barrels, but would run at lower pressures in a normal CIP / SAAMI specified rifle and therefore should be safe. Run the usual RWS ammo down 30-inch barrel FTR custom built rifles where the norm is to use SAAMI dimensioned barrels and MVs are often down on the TR 2,925-2,950 fps norm. If it (the over-pressure stuff) has reappeared under a different name, it's not being stupid or unreasonable to advise those with TR rifles not to use it even if it does seem a strange request to the non-TR shooter. The fault doesn't lie with the NRA when a supplier gets it wrong. Incidentally, it's not only out of spec ex-NRA / RWS that can create overpressures in a true TR rifle in unworn form, a maxium pressure .308 Win factory load could do so too for the same reason.
Although chamber form could affect this either way, this isn't a chamber neck issue as per the notorious Rule 150 issue, it's the powder characteristics and charge weight in relation to the bullet / bore match.
