I have mentioned this before, but seems relevant to the subject so perhaps worth repeating. Many years ago I purchased an H grade Lefever with twist bbls as a "Parts" gun. Stock was broken & taped, bbls were badly pitted & at somepoint the trigger plate screw had been replaced with one too long which prevented gun from closing properly (seller didn't figure out the problem there). At 14" down the left bbl it appearded it had been hit a blow on a sharp corner resulting in a dent & then fired. This resulted in the metal cracking at this crease for a distance of about ¼" following a weld seam, then turned forward at about a 90° angle for about an 1/8" with a little flap raised up forward of the crack. Behind the crack the metal was still depressed inward into the bore. As I considered the bbls worthless anyway I decided to experiment a little. I ran a dent plug under the dent, raised the part which was depressed & beat back down the raised portion. It then became very hard to tell the crack was there. I then tied it to the "Firestone Proof House" & proceded to fire several factory 3¼de-1 1/8oz loads through it (by remote string from behind a large walnut tree) examing the bbl after each shot. As nothing occured I then stepped up to some 3 3/4de- 1¼oz factory "Express" loads & fired several of these. Again nothing happened so I tried a few handloads consisting of enough Unique powder to give 1 3/8oz of shot about 1125-1150 fps, again nothing. Remember this gun was "Pre-Cracked". After this I simply put it back in the cabinet in case I needed a part for one of my other Lefevers (so far haven't) & right now, even knowing where to look I can only find that crack with aid of a magnifying glass. I had erronously assumed when I fired those shells that crack would open back up wide. It had apparently taken the "Obstruction" of the dent to do it in the beginning. When the obstruction was removed there simply wasn't enough pressure that far down the bbl to even raise that little flap, much less burst a sound bbl.
It does seem to me to be true that all bursts forward of the chamber, if a proper examination & annalysis is carried out will prove to be from either an obstruction, or a bad internal flaw within the metal. Fortunately these internal flaws are seldom encountered, most having come to light in the construction of the bbl & been discarded. Of those which slip through & often go for years before a problem, in spite of all the warnings of bad welds, rust from galvanic action of the disemilar metals etc, etc, of twist & damascus they seem more commonly encountered as seams in fluid steel. Just my take on the situation.
Although over the years I have personal knowledge of a good number of twist & damascus bbls (some in poor condition & of questionable ancestry) having been used with an indiscrimanate choice of all manner of factory shells, I personally do not follow this pattern. I have never been much of a high volume target shooter, but if were to do so I would stick to loads in the 6-7K psi range. For hunting loads, which may see cold weather use I load to about 7.5K psi & set about 8K as my max. Have done this with both Damascus & Twist & reached the age of 70 with nary a problem. I may be wrong, but simply do not believe in those "Super Low" pressure loads of smokeless with pressures below 6K for any purpose. My belief is one is running an unnecessary risk of leaving a bore obstruction.
