View Single Post
Old January 12, 2020, 16:33   #28
Old Fart
Platinum Contributor
yovinny's Avatar
FALaholic #: 7679
Join Date: Oct 2002
Location: Wastelands of Western Kentucky
Posts: 6,899
Originally Posted by lockjaw View Post
They? You mean NATO... which included the US?

One of NATO's requirement for the new round to replace 7.62 NATO is that it must penetrate a steel military helmet (same requirement of 7.62 NATO). The steel projectile made this possible. The steel projectile also compromised the ability for the SS109 round to fragment.... and provided a convenient spin in stating that it was "more humane." It was surely not designed to be "less lethal."

So, yes, "they" (Belgians) designed the SS109 (US calls it XM855... pretty sure I stated XM855/SS109 earlier) round around 1/9, as I stated earlier. Also, as stated earlier, "they" used 1/7 as a compromise to stabilize the significantly longer tracer XM856 round (don't recall what the NATO equivalent was called). and no, it wasn't just in arctic conditions. 1/9 marginally stabilizes the longer rounds in most condiitons, and is very temperamental resulting in inconsistent performance. Tracer rounds need to reflect the performance of M855/SS109 as cloe as possible in all conditions. I challenge you to shoot M856 tracer rounds at 100 - 300 yards through a 1/9 twist AR barrel, and compare to performance of M855. You might find the results amusing and/or borderline shocking (I have done it). I'm a dork, I find this stuff interesting.
SS109 came out of FN testing for a longer range bullet in the FNC with 1:12 twist.
It Swedish testing with the 1:12 fnc (long before equivalent tracer ammo was thought of) it displayed a tendency to tumble almost immediate on impact with soft tissue.
Sweden's testing board ruled that such tendency would be considered inhumane, as at that time there was also talk of updating the 49' Geneva agreements on such things.
Sweden asked FN to change the twist used to one fast enough that tumbeling would be all but eliminated in soft tissue, ie make it less lethal.
The German helmet (3.5mm mild steel) penetration test was previously easilly passed by ss109 out of 1:12 twist fnc.
The US submitted the m16a1 (1:12) with xm777 ammo to NATO testing. While judged much superior in terms of incapacitation and lethality in soft tissue, it was less effective at the penetration testing. This stemed from the fact that they had production issues and couldent keep the penetrator core strait and centered in the lead core and jacket.
If your interested in this stuff, you should really search out and read some of the info and history for the 1980 nato findings and the compromise the US made to keep NATO happy...
yovinny is offline   Reply With Quote