The L42a1 is a No4T converted to 7.62 NATO using a 144gn proofed to 19T. When the No4s were sent in for proof as range rifles many failed the receivers cracked and we were out of pocket. SAAMI has no footprint in the Britishicon Military. SAAMI specs for the 303BRIT are plain wrong which is why there are so many problems using American products in this calibre. NATO spec sheets are different to SAAMI specs datum points being one. The reason my rifle failed the lug area was to small for the load size (pressure) This manufacturer has increased the action size three times since the original release to handle the heavier loads. Mine was a very early manufacture.