Has the classic appearence of an obstructional burst to me. Would have been in the vicinity of the larger part of the burst & as that swelled up side wall split further in both directions, but more forward than to the rear. Also note the exact popint of the obstruction cannot necessarily be determined by point of burst. It quite possibly moved a bit forward under impact prior to the gas piling up enough to produce the burst. Best read I am aware of on this subject is to be found in Burrard. Proofs appear to be post 1925 Birmingham, but prior to 1954.
