The MOD arbitrarily & arguably without technical justification decided on a joule limit for projectiles fired on their ranges, on the premise that establishing that limit would contain shots within the safety template of the ranges. Among others for example some F Open shooters, the 90-220 grain .30s used by some match rifle shooters exceeded that limit. Shooters operating in that velocity range, ie above the joule limit are required to prove that they have their firearms zeroed correctly at short range (the distance dependent on the venue) before being permitted to shoot at maximum distances. They have not been reined in.
Not the same warnings or situation.
The NRA found that due to the widespread use of undersized bores for .308 match rifles and converted No.4 rifles , some with bores of .306 or smaller, due to the often undersized bullets of 7.62 NATO ammunition previously used, that rifles were being subjected to excessive pressures when max power handloads were used instead of supplied 7.62 ammo.
The Birmingham Proof House and Radway Green ran extensive testing of these undersized bores and published a full explanation of the dangers. The result was a probition against use of undersized bores for converted No.4 rifles if used in competition, and a re=proofing of any No.4 conversions if used with any ammo that generated pressures above a certain limit.
Warnings against use of higher pressure long range match ammo in the converted No.4 were not new, but the increasing pressure levels of match ammunition brought the situation to a head.
There are rules in place on permissable bore size and more importantly throat and neck clearances for rifles to be used at Bisley in NRA sanctioned matches where the NRA supplies the new matchgrade ammunition.
This is in large part due to the contracted ammunition not meeting the velocity requirements until the manufacturer increased the charge and chamber pressure to maintain supersonic velocity at the maximum range of the match.
http://www.google.com/url?sa=t&sour...4tGECA&usg=AFQjCNET_SjbN5npS7oTcttNFb0ql2Ye5w
Chamber pressure limits were set at 3650 BAR (about the max deviation level of M80 Ball) for all but a few rifles of the general type.
BRITISH PROOF AUTHORITY MEMORANDUM JUNE 1999.
.308 Win Target Rifle Proof
The effect on chamber pressure of reduced dimensions, not complying with the
minimum specified by the CIP, was investigated and quantified by the
'Pressure Trials Consortium' whose report was published in March 1998. This
report indicates that pressures can be elevated to potentially dangerous
levels with certain barrel/chamber/ammunition combinations. The matter
having been raised at a recent CIP Sub-Panel Meeting will be subject to
study by a special committee of that organisation.
In the meantime, so as to allow proof to continue on barrels not complying
with CIP minimum dimensions it was agreed with the NRA that any deviation
from the minimum dimensions set by the CIP must be limited so as to ensure
that chamber pressures remain within the maximum average allowed (Pt-max) by
the CIP of 4150 bar when using CIP approved ammunition that does not exceed
an average pressure of 3650 bar. This maximum of 3650 bar is as measured in
a CIP pressure barrel using the CIP Radial Transducer method.
An attestation that ammunition does not exceed an average pressure of 3650
bar should be obtained from the ammunition supplier or manufacturer.
The practical application of data from the Pressure Trials Consortium's
report has been applied in setting these limits on deviation for barrel and
chamber dimensions.
The minimum acceptable dimensions are:- (see page 74 for CIP data)
GI- Throat = 0.3085 ( 7.8359 mm)
F- Bore = 0.298 ( 7.5692 mm)
Z- Groove= 0.3065 (7.7851 mm)
These smaller dimensions than permitted by the CIP will be acceptable to the
British Proof Authority on the following basis:
1) Certification in writing to the proof house confirming the actual
dimensions of G I, F & Z on submission for proof
2) The barrel will be marked .308 Win Non Standard as will the dimensions
not complying with the CIP minimum, e.g. G l = 0.3085, F= 0.298 & Z =
0.3065.
3) A mandatory Proof Certificate will be issued that will show the calibre
as .308 win Non Standard, the dimensions not complying with the CIP minimum,
and the statement 'Only CIP approved.308 Win ammunition producing a maximum
average pressure (Pt-max) of 3650 bar (CIP Radial Method) should be fired in
this barrel.'
NRA Rule 150 , Barrel and Chamber Dimensions
For the reasons given below, and since it is possible that different standards may have been used in the
last few years to test the compliance of Target Rifle chambers with Rule 150, the NRA Council have
decided that all TR chambers are to be re-checked this year. All target rifles whose chambers comply will
be marked with a green coloured ‘sticker’. Please note that the previous ‘stickers’ (blue or orange) will no
longer be valid.
All competitors should therefore have their chambers tested as soon as possible. Chambers may be
checked in the NRA Armoury or by other accredited gunsmiths. The names of accredited gunsmiths are
available from the NRA Armourer. Testing in the NRA Armoury will be free of charge unless the test round
is marked or pushed back, indicating a failure, in which case a charge of £1 will be applicable to replace the
test round and the chamber must then be rectified and re-submitted for test.
The rules on barrel and chamber dimensions for NRA Target Rifle are set out in Rule 150 of the NRA
Bible but reference must also be made to the current agreement between the NRA and UK Proof Authorities
in respect of the minimum permitted bore, groove and throat diameters on 7.62mm/.308 Target Rifles
submitted for proof.
Rule 150 Barrel states that the barrels of all Target Rifles must be suitable for firing either:
(a) the standard 7.62mm x 51 NATO military cartridge, or
(b) the .308 Winchester commercial cartridge.
The references to the .303” Mk 7, 5.56 x 45mm and .223 Remington cartridges in this rule are not relevant
as these calibres/cartridges are not permitted for use in TR during the Imperial Meeting.
The implication is that the chamber dimensions must comply with the CIP minimum chamber drawing
other than the exceptions outlined below. For all practical purposes the CIP and SAAMI drawings for
minimum chamber dimensions may be considered identical. Effectively, therefore tight chamber body
dimensions and or tight necks are not permitted.
The exceptions to this, as agreed with the Proof Authorities, are:
Minimum Bore Diameter : 0.298 inches
Minimum Groove Diameter : 0.3065 inches
Minimum Throat Diameter : 0.3085 inches
Maximum Cartridge Loaded Length : 2.800 inches
•
The restriction on bore, groove and throat diameters are not directly specified in Rule 150 but are
governed by the minimum diameters that are acceptable to the UK Proof Authorities on submission of a
target rifle for proof. In addition there is a maximum pressure restriction on the ammunition which is, of
course, outside the competitor’s control with issued ammunition.
The restriction on cartridge loaded length is specified by Rule 150 with reference to the 155 grain RG
projectile, i.e. if a cartridge loaded with this bullet to an overall length 2.800 inches is loaded into the rifle
chamber, the bullet must not be in contact with the rifling.
In practice compliance with the throat diameter / length restriction is checked using a dummy test
cartridge. If the bullet of this test cartridge is “ring marked” or pushed back into the case either the throat
diameter is too small, or the leed is too short, or both, and the rifle may not be used until the chamber has
been rectified.
I'd read years ago that there had been a flap over a police marksmanship team having cheated in a match by using custom assembled handloads to give them an edge, and warnings involving the No.4 action mentioned concerns raised by the British police.
The Enfield Envoy is not a conversion, being built from selected newly manufactured actions, so that rifle is less likely to suffer damage so long as CIP maximum acceptable pressures are not exceeded.
Handloading was far less common among UK target shooters till recent years, and the NRA now strictly controls all ammo used in competition to avoid incidents.
The Joule limitation was a different matter involving magnum caliber rifles. In part due to damage to backstops and range equipment as well as fear of overshooting.
