I believe Norma's strategy to avoid core bonding in the tip area of their Oryx bullets, combined with tip skiving, is to readily initiate expansion at impact, at and above their advertised minimum impact expansion velocity of 1500 fps.
Fusion is advertised as having internal tip skiving, same as the Speer Grand Slam and Speer Mag tip bullets are / were advertised to be part of the design. It's unclear to me how Fusion accomplishes this with an electrochemical bonding process, but details on how core bonded bullets are manufactured are scarce as prior noted. Since there is no advertising mentioning the tip of Fusion bullets not being bonded, I would expect that area to be bonded, which may explain observed performance differences vs recovered Norma Oryx bullets for example, which have somewhat similar semi-spitzer profiles.
For standard non-bonded Hot-Cor design bullets including current production Speer Grand Slam bullets the process was advertised by Speer as eliminating any lead oxide film possibly present on lead wire used in other methods of manufacture of competing bullets, as well as any lubricant films between the lead wire and inner jacket walls. The key point here is lead oxide as mentioned is much more soft, and slippery, than non-oxidized lead - and machine lubricant residue speaks for itself. Thus, without core bonding or mechanical lock features (which a cannelure is an example of a not so strong type), there is a friction fit between the lead core and inner jacket wall. After impact of the spinning bullet without core bonding, release of bullet fragments can help reduce the friction grip. The non-bonded jacket when allowed to slip has a lower momentum than the core in terms of mass times velocity. Additionally the jacketed portion experiences drag on the jacket as the outer surface first.
Returning (yes) to this site with the recovered bullets with impact velocity figures alongside sectioned unfired examples, the second generation Speer Grand Slam bullets show expansion ceased at about the same point for the examples numbered 28 and 29, two .308 180 grain examples with impact velocity figures of 777 m/s (2549 fps) and 840 m/s (2756 fps). Also the expansion stopped before reaching the external jacket ring before the cannelure, which also means expansion ceased before peeling back to the cannelure and the partial internal ring of jacket material used as a mechanical lock for the non-Hot-Cor rear lead core section.
http://kjg-munition.de/Zielwirkung/Geschossbilder.htm
Now examine the Nosler Partition examples numbered 13 and 14. These are not bonded core design nor manufactured using the Speer Hot-Cor process. Both of these experienced core - jacket separation with the front core (and it doesn't appear the front core of example 14 was recovered) but the rear core and the mechanical locked jacket around the rear core experienced no slippage, as expected and advertised. Now example 15 doesn't appear to have experienced significant core slippage in the front core section.
The Swift A-Frame bullets with partitioned jacket and bonded front core in examples 16 and 17 don't appear to have experienced any core slippage. As advertised and expected.
All these bullets are of equal unfired diameter and weight, and have a similar range of impact velocities.
What I wonder about Speer is after being purchased by ATK, how much value was placed (and attention paid) to consistently having the "clinically clean" inner jacket surfaces for bullets produced by the Hot-Cor process, including the current production Speer Grand Slam, mentioned in their earlier advertising.
I'd enjoy seeing a link posted to the study on the Speer Grand Slam design with heel lock, posted as inconclusive, as Speer advertising indicates that original Speer Grand Slam design feature was used for at least 10 years before the second generation with the partial internal locking ring for the rear core, and was briefly mentioned by Speer again after the ATK purchase and third generation with a single lead composition Hot-Cor process core were marketed. Just because I'm quite familiar both conceptually and experientally with factors in design of experiment, weighting factors assigned to various elements of results, statistical analysis, and so forth, especially if that study included the heel lock in the original Speer Grand Slam design with the rear lead core not installed with the Hot-Cor process as well as the heel lock with the third generation Speer Grand Slam with a single lead core composition installed with the Hot-Cor process.
I can understand the deletion of the shallow external jacket ring above the cannelure on the heavy for caliber Speer Grand Slam bullets, as the examples shown at the web site included again in this post never experienced expansion to that point even at an impact velocity of 2756 fps.
Fusion is advertised as having internal tip skiving, same as the Speer Grand Slam and Speer Mag tip bullets are / were advertised to be part of the design. It's unclear to me how Fusion accomplishes this with an electrochemical bonding process, but details on how core bonded bullets are manufactured are scarce as prior noted. Since there is no advertising mentioning the tip of Fusion bullets not being bonded, I would expect that area to be bonded, which may explain observed performance differences vs recovered Norma Oryx bullets for example, which have somewhat similar semi-spitzer profiles.
For standard non-bonded Hot-Cor design bullets including current production Speer Grand Slam bullets the process was advertised by Speer as eliminating any lead oxide film possibly present on lead wire used in other methods of manufacture of competing bullets, as well as any lubricant films between the lead wire and inner jacket walls. The key point here is lead oxide as mentioned is much more soft, and slippery, than non-oxidized lead - and machine lubricant residue speaks for itself. Thus, without core bonding or mechanical lock features (which a cannelure is an example of a not so strong type), there is a friction fit between the lead core and inner jacket wall. After impact of the spinning bullet without core bonding, release of bullet fragments can help reduce the friction grip. The non-bonded jacket when allowed to slip has a lower momentum than the core in terms of mass times velocity. Additionally the jacketed portion experiences drag on the jacket as the outer surface first.
Returning (yes) to this site with the recovered bullets with impact velocity figures alongside sectioned unfired examples, the second generation Speer Grand Slam bullets show expansion ceased at about the same point for the examples numbered 28 and 29, two .308 180 grain examples with impact velocity figures of 777 m/s (2549 fps) and 840 m/s (2756 fps). Also the expansion stopped before reaching the external jacket ring before the cannelure, which also means expansion ceased before peeling back to the cannelure and the partial internal ring of jacket material used as a mechanical lock for the non-Hot-Cor rear lead core section.
http://kjg-munition.de/Zielwirkung/Geschossbilder.htm
Now examine the Nosler Partition examples numbered 13 and 14. These are not bonded core design nor manufactured using the Speer Hot-Cor process. Both of these experienced core - jacket separation with the front core (and it doesn't appear the front core of example 14 was recovered) but the rear core and the mechanical locked jacket around the rear core experienced no slippage, as expected and advertised. Now example 15 doesn't appear to have experienced significant core slippage in the front core section.
The Swift A-Frame bullets with partitioned jacket and bonded front core in examples 16 and 17 don't appear to have experienced any core slippage. As advertised and expected.
All these bullets are of equal unfired diameter and weight, and have a similar range of impact velocities.
What I wonder about Speer is after being purchased by ATK, how much value was placed (and attention paid) to consistently having the "clinically clean" inner jacket surfaces for bullets produced by the Hot-Cor process, including the current production Speer Grand Slam, mentioned in their earlier advertising.
I'd enjoy seeing a link posted to the study on the Speer Grand Slam design with heel lock, posted as inconclusive, as Speer advertising indicates that original Speer Grand Slam design feature was used for at least 10 years before the second generation with the partial internal locking ring for the rear core, and was briefly mentioned by Speer again after the ATK purchase and third generation with a single lead composition Hot-Cor process core were marketed. Just because I'm quite familiar both conceptually and experientally with factors in design of experiment, weighting factors assigned to various elements of results, statistical analysis, and so forth, especially if that study included the heel lock in the original Speer Grand Slam design with the rear lead core not installed with the Hot-Cor process as well as the heel lock with the third generation Speer Grand Slam with a single lead core composition installed with the Hot-Cor process.
I can understand the deletion of the shallow external jacket ring above the cannelure on the heavy for caliber Speer Grand Slam bullets, as the examples shown at the web site included again in this post never experienced expansion to that point even at an impact velocity of 2756 fps.
