So after some mailing mishaps, @kneedeep (thanks for the help) supplied me with a 125HHT to compare PDRs with the 124hh I had on hand.
As some guessed, the an individual PDR band on the new has more volume vs the old(about 15%). As a total, the new with 2 PDR vs the old with 3, old has about 22% more than the new.
This still brings to question, why pressure out sooner?
While handling and measuring, a couple things jumped out. First, the boattail(BT) of the HHT has more surface area on the base and a lower angle from center line. This gives more area for powder gas to push against and less space to go around (possibly less dwell time at ignition). Secondly the distance from last full diameter at start of BT to nominal bore diameter(0.260) is about 4x longer on the HHT vs HH. Front shoulders/ogive(from nominal .260 to full diameter) on both are too close to measure a difference and are very near together(point to point).
Top is hh, bottom hht. Notice faint ring at black lines. Tried to line up high point at last PDR to show differences in length to nominal bore diameter of .260 and see boattail final diameter.
As some guessed, the an individual PDR band on the new has more volume vs the old(about 15%). As a total, the new with 2 PDR vs the old with 3, old has about 22% more than the new.
This still brings to question, why pressure out sooner?
While handling and measuring, a couple things jumped out. First, the boattail(BT) of the HHT has more surface area on the base and a lower angle from center line. This gives more area for powder gas to push against and less space to go around (possibly less dwell time at ignition). Secondly the distance from last full diameter at start of BT to nominal bore diameter(0.260) is about 4x longer on the HHT vs HH. Front shoulders/ogive(from nominal .260 to full diameter) on both are too close to measure a difference and are very near together(point to point).
Top is hh, bottom hht. Notice faint ring at black lines. Tried to line up high point at last PDR to show differences in length to nominal bore diameter of .260 and see boattail final diameter.