http://www.falfiles.com/forums/showthread.php?s=&threadid=49526
Topic: British Army Instructions for Headspacing
NZ L1A1 Collector
Moderator
Bronze Contributor
FALaholic # 45
September 08, 2002 06:40 Post #1
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Cartridge space adjustment
10. Having determined that cartridge space is incorrect and can only be adjusted by fitting a new locking shoulder a size is to be selected to bring CHS within the limits of gauge SM 651 (1.6325 in.) and SM 650 (1.638 in.). This will ensure that the rifle will have a maximum life available before a further change of locking shoulder is necessary. The method of selecting the correct size of locking shoulder is as follows:
a. With breech block removed from carrier and placed in the body the amount of longitudinal movement is to be estimated with the gauge SM 663 ( 1.643 in.) in the chamber. This movement indicates the amount the CHS exceeds 1.643 in.
b. For example, assuming the longitudinal movement is very slight and is estimated at 0.001 in. the factors to be considered are:-
(1) Difference between 1.643 in. and 1.638 in. = 0.005 in.
(2) Movement at 'b' above............................... = 0.001 in.
(3) Approximately half the difference between = 0.003 in.
the accepted limits of 1.6325 in. and reject....................(approx)
limit of 1.638 in.
(4) Total headspace wear to be taken up is ....= 0.0009 in.
(1) + (2) + X3) above
c. Remove existing locking shoulder as detailed in paragraphs 12 and 13, measure it with a micrometre or the gauge shown in Fig 1, then select a replacement locking shoulder 0.009 in. larger, in the standard or oversize range as required. It is advisable, though locking shoulders are numbered, to verify the dimension as-wear may have taken place on the existing shoulder and this must be considered on the change. A list of locking shoulders in the standard and oversized range is shown in Table 1.
d. Replace the selected locking shoulder as detailed in paragraphs 17 - 21.
e. When a correct cartridge space has been obtained ensure that the breech block and carrier are numbered to the rifle as detailed in S Arm D 117 Mod Instr No 3.
Note: There must be a slight forward movement of the carrier against the tension of the safety sear spring when the action closes over gauge SM 651 (1 6325 in.).
Locking shoulder Replacement
11. Locking shoulders are to be replaced for the following reason:-
(a) To adjust cartridge head space.
(b) To replace fractured or damaged locking shoulders.
(c) To replace loose locking shoulders.
12. Locking shoulders which have been driven out, or in, are liable to fracture in service, therefore it is essential that they must be pressed out, and in to prevent the possibility of fractures. To enable this to be accomplished, a tool for the removal o locking shoulders is shown Fi g 4002. A fixture and tool for the assembly of locking shoulders is shown in Fig 4003, 4004, 4005 and 4006. In Fig 4007 is shown the method of resizing the locking shoulder hole using a tungsten carbide ball, anvil and gauge plain cylindrical L22Al.
13. To remove the locking shoulder place the large plate over the body and position by the locating pins, ensuring that the slot is aligned with the head of the locking shoulder. Hold the plate with the body of the rifle in a large vice and place the second part of the tool on the outer jaw. Lead the stud of the tool on to the end of the locking shoulder as the vice is tightened and press the head through the plate. Remove locking shoulder.
14. The range of locking shoulders are issued in two fitting sizes, 'standard' and 'oversized'. The oversized are identified with a letter 'Y' stamped on the large head and are to be used when the locking shoulder hole in the body is found to be oversized.
15. With the locking shoulder removed determine whether a 'standard size' or 'oversized' locking shoulder ('Y') is required by gauging the hole as required by S Arm D 118 Table 2 Serial 4.
16. Should an 'oversized' locking shoulder (Y) be required the tungsten carbide ball is to be forced through the locking shoulder using the anvil and vice as shown in Fig 4007. The ball is to be forced completely through from either side or partly through from both sides ensuring that it goes past the 'halfway' from each side. The 'GO' end is to be accepted, the NO GO' is to be rejected.
17. To reassemble the 'normal' or 'oversized' (Y) locking shoulders, the rifle body must be placed in the fixture (Fig 4003); ease the two steadying screws at the top of the fixture and the clamping screw at the rear. Slide the body over the guide block ribs in the fixture, depressing the spring locating plunger to allow it to pass, until the rear reaches the stopping block. The plunger will automatically enter the hole for the locking shoulder under the influence of its spring. Screw the steadying screws lightly down on the body to align and prevent distortion and tighten the clamping screw at the rear of the fixture.
18. Enter the locking shoulder in the assembly slot guide the leading end into the locking shoulder hole in the body and push it down as far as it will go. Insert the press tool in the assembly slot with the flat on its upper surface to the front. Position the fixture under a press and exert sufficient pressure on the tool to force the locking shoulder down until the lug is fully engaged in its recess.
19. Remove the tool, release the steadying and clamping screws and-remove the body from the fixture.
Note: The body cannot be removed unless the shoulder is correctly seated in the body. If difficulty is experienced, retighten the steadying and clamping screws, replace the press tool and force the shoulder fully home.
20. Reassemble breech block to carrier and retest CHS. Interference between breech block and locking shoulder as the breech block moves forward is permitted, as long as the height of the locking shoulder above the inner bottom surface of the body does not exceed 0.011 in.
21. When an oversized locking shoulder is fitted a letter 'Y' is to be stamped on the body as shown in Fig 4007 using 5/64 in. steel stamps.
Thats all there is too it I hope this helps and dosen't confuse the issue.
__________________
Kevin Adams
Rifle, 7.62 mm, L1A1 Collector & Researcher.
NEW ZEALAND
