Back to the issue at point.
Many times, a rifle would be marked DP simply bcause they needed drill rifles and didn`t have enough. These would be looked after at a lower standard, of course, appearance being everything in drill. Sometimes, DP rifles would be rebuilt and issued for live-fire use, given that rifles were needed. Remember, Parliament has kept the Army as broke as possible for the last 350 years: since the end of the Civil War.
NOT ALL DP rifles are unsafe to fire. I have a DP SMLE Mark I*** which I have been shooting for the last 45 years with no problems. Out of respect to something more than a century old, I keep my pressures sane, that`s all.
British rifles were proofed for a SERVICE pressure of 18-1/2 Imperial Long Tons per square inch which is 41,440 pounds per square inch. That is the standard pressure which you were supposed to get from military mmo: a 174-grain bullet at 2440 ft per second, fired with Cordite, which is hot stuff. The Imperial Long Ton is made up of 20 hundredweights (c`wt) each of 112 pounds, each cw`t being 4 quarters each of 28 pounds, each quarter being of 2 stone of 14 pounds each. The overpressure required was obtained by using a fully-loaded Mark VII-type Ball round with the bullet replaced with a 215-grain RN slug of the old Mark VI type. This was the Proof round Mark III - Q Mark III. It generated about a third overpressure. Following this Proofing, the rifle was subjected to a SECOND proving, this with a Mark VII Ball round which had been dipped in lightweight motor oil (Rangoon Oil) and allowed to drain for a few seconds. This put ALL of the thrust onto the bolthead and MATED the locking-lugs into the locking-recesses of the rifle. THIS is why you shouldn`t go changing bolts about in Lee-Enfield rifles: because they are individually MATED as sets.
At times, OLDER rifles would be DP-marked even though still safe to fire. This likely is how my Mark I*** became DP`d...... before it was scrapped. I rebuilt it from scrapped parts at the time that the British were clearing out most of their remaining SMLE stuff, selling it for scrap.
The marking to be absolutely TERRIFIED of is a two-inch "ZF" painted on the right side of the Butt. This means that there is something terribly amiss with the rifle (the "Z") which cannot be cured at anything short of Factory (the "F") level.
DP is not a death sentence for a rifle, although ZF IS a death sentence, the Factory now having been turned into a Museum and a housing estate.
Hope this is of some help.
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