Below on the right is as close as I have ever come to a total case head separation in over 47 years of reloading.
The Winchester .303 British case was full length resized and fired three times with .009 head clearance. And yet a case neck sized only and fired with light loads was fired 32 times before the neck split.
It is the amount of head clearance and the case stretching beyond its elastic limits that determines case life, and not how many times the case is trimmed.
The 303, and I assume too other military rimmed designs, are special cases (no pun intended). As they headspace on the rim alone, you can allow large clearances at the upper body / shoulder level. In issue ammunition intended to be fired only once and chucked, any clearance smaller than that which would cause an instant case separation or rupture can be tolerated - and often is. This was a deliberate policy in the case of the British military 303s many of which have very slack and over-length chambers as it allowed acceptable functioning in the field with poor quality wartime manufacture ammo, corroded, dented, slightly bent, dirty etc cases, badly fouled chambers and so on.
There is a second factor that affects the Lee Enfield series of rifles that often causes even neck-sized brass to separate in only a few firings and which is load / pressure related. The weak action (especially the earlier Long Metfords / Lees and SMLE) and perhaps even more so the thin bolt whose rear-located lugs are of very different sizes / construction, the right-hand one being a very long job to double up as a bolt guide in the slotted receiver bridge when in the open position, allow the case to flex on one side under firing pressures. Sizing for minimal shoulder clearance and using mild loads is all that the 303 handloader can do for these rifles, apart from obtaining brass whose alloy and construction is such that it accepts a degree of stretching.
I never had a problem with 303 calibre Enfields, and some Norma brass that cost me a small fortune at the time as a beginning indigent fullbore shooter despite being in a close-out sale saw me through several rifles and an unknown, but large number of firings. The problem came when I took up GB 'Target Rifle' in the 80s and like many cash-strapped TR tyros of that era bought an ex club former 'Service Rifle' discipline No.4 Enfield that had been rebuilt in 7.62 by G E Fulton & Sons of Bisley for the switch from SR to TR in the late 60s.
I got my first incipient separation of Winchester 308 brass on its fourth firing and was shocked as it had been neck-sized throughout and I was using a very mild load. Enquiring about this and worrying about a faulty chamber or whatever, I was told this was normal for 7.62 Enfields. Within a box of 50 cases, the first victim would appear at the 4th or 5th firing, then it would be one or two for the next few firngs, but around the 8th or 9th it became much more frequent so I'd junk the survivors. Both the nature of the stretching / cracking and the large variation in life from a single loading intrigued me - it was never a straight ring around the case body, always higher on one side. I eventually came to the conclusion that the Lee bolt construction and locking arrangements allowed the bolt to twist in one direction under firing pressure and that in a box of 50 cases being loaded multiple times, random positioning in the chamber would see extremes of one or two cases positioned with the same side at any given point of the chamber / bolt-face on every or nearly every firing causing whichever section of case wall that stretched more to be rapidly weakened whilst at the other extreme one or two cases got a different position each time spreading the stretching out over more case wall and giving better life. Most were in between the extremes.
Why the problem in 308 and not 303? Simply, a very mild 308 load generates say 50,000 psi or a bit more whilst an equivalent modest 303 loading is 10,000 psi less, so the former gets a lot more punishment.
I of course have used the paperclip method for years and it is an excellent method. Having said so, I have seen a number of actual case head separation (NOT case rupture which is completely different and very dangerous) in both modern rifles and pistols and it is generally not a dangerous occurrence. The rear of the case seals the chamber and no hot gas/plasma comes back to the bolt. It just leaves the forward part of your case in the chamber causing a jam when another round is loaded. Still something which one should try to avoid.
That reminded me of a veteran and very harum-scarum character I used to shoot alongside on the local military ranges at the time I had my 7.62 No.4. To justify the description, the late Reg Collinson who'd started shooting as a teenage schoolboy Home Guard private during WW2 - a real life Private Pike of the
Dad's Army sitcom - was (and is) the only person I know who managed to have an accidental discharge of a firearm inside his own house. In fact he did it not once, but twice (on two separate dates) with a 38 Spcl target revolver. I can only conclude he was experimenting with Russian Roulette but missed!
When I first met Reg he shot a 303 Number 4 which apart from Parker-Hale match sights and a few Reg-performed (and usually dangerous) DIY 'improvements' such as a 'trigger job' that regularly produced random discharges until a proper gunsmith fixed it, was as God and His Majesty had issued it to some Tommy in the closing stages of WW2. Reg loaded and fired his brass until it separated ("Boxer cases are EXPENSIVE" he'd say) and then, and only then was it junked invariably in two pieces. So in a day on the range shooting maybe 50 or 60 rounds over 300-600 yards, Reg would have at least a half dozen separations, never any leaking gas or anything bad as you say except the shot would be a flier (or even more of a flier than many of his 'good shots')
This range saw a lot of interruptions to shooting as military parties marched to and from adjacent ranges across our usually allocated range which lay closest to the car park and during one unusually long one on a fine warm summer's day as we lazed around, Reg becoming increasingly irritated and restive at the absence of trigger-pulling, I produced a separated 303 case extractor from my bag for diversion and said 'You'll recognize this Reg' to the great man. 'You foolish boy carrying that thing around' he responded. 'These were only ever needed by Bren and Vickers gunners - you can always get the front half of the case out of a rifle chamber easily' quoth he. (..... and he should know)
As luck would have it, the red flag was hauled down and we restarted just at that moment and Reg (as usual) was the first to fire. There was an unusually long pause and fumbling with the rifle after the target was marked and Reg turned to me and said with some embarrassment 'Er, can I borrow your extractor Laurie. I've got a stuck separated case.' So, the moral of the story is there is (occasionally) some justice in the universe, or alternatively don't be too dogmatic in your assertions!
