Must have been a really, really poor design or Russian troops that were sensitive to recoil or just issued PPSHs, considering they used the x54r in the M38/M44, that size wise equal the SKS. The CKC-31 in x54r I could see excessive recoil and muzzle flash. From what I understand, the only real difference in the x41 and x39 was a slightly different powder and 2mm shaved off the neck.