Nevertheless, the armour piercing capabilities of CPBC ammunition is okay, within its limits.
I was snooping around The Nathan Okun Naval Gun/Armor Data Resource webpage, and came across a ready reckoner for armour piercing capabilities. This is essentially a tabular presentation of the programmable calculations that Okun presents. I am fairly sure that you would be familiar with them, but wasnt sure....
I wanted to see just how bad the CPBC ammo was in comparison to the 5.91' AP rounds you were talking about. I was particulalry interested in the relative performances at the 10-12-14000 yds ranges
Hi Parsifal,
the ww2guntables are indeed based on Nathan Okuns M79APCLC (for deck armour) and facehad (for face hardened armour). It also used wiggle matched McTraj ballistic estimations of the projectiles in question. In my view this is a reasonable approach altough there are multiple, unfixed issues worth to keep in mind:
1) Lundgren didn´t actualized on the more recent versions of Nathans facehd, his use of an older facehd version is therefore problematic
2) M79APCLC does not sim CPBC. Nathan Okun is pretty clear on this. The program (used for deck penetrations) is based on the US 3" M79 AP-shot ammo (without cap and with inert filler, a thick bodied armour piercer) and it´s respective performances against ductile, homogenious armour. It is reasonably accurate for all other,
decapped AP-rounds (error is negliable) but if You use it for CPBC (or HE for that matter) it will always sim as if they were true AP´s (but decapped) with resulting greater penetrative ability. Unlike Nathans Facehd, where You may choose between projectiles, You can only enter weight, size, striking velocity and obliquity of the projectile into M79APCLC...
Another problem encountered in our specific comparison, just from a first impression are the inconsistent ballistic performances (plotted #1 vs #2 with curvefinder). A comparison with NaAB gives these ballistic performances:
------6"/50BL MK 13-------------15cmL60C28-------
range----velocity----fallangle---velocity----fallangle
2500y----2347fps----1.79------2636fps----0.54----
5000y----1976fps----2.51------2195fps----2.16----
6000y----1839fps----3.47------2022fps----3.43----
7500y----1649fps----5.31------1798fps----4.29----
10000----1384fps----9.32------1466fps----8.28---
15000----1099fps----22.51-----1097fps----20.34--
16000----1077fps----25.31-----1069fps----23.45--
17500----1061fps----30.86-----1046fps----28.3---
20000----1062fps----38.23-----1040fps----36.51--
25000----1132fps----55.9------1094fps----52.38--
26000----out of range----------1110fps-----55.45-
28000----out of range----------1159fps-----63.5--
30000----out of range----------out of range-------
Two things are notable:
A) NaAB and ww2 guntables are both based on exterior ballistic computation, not on primary sources. As a result, both approaches show differing results, reflecting the different programs in use.
B) The 112lbs 6" round starts with less muzzle velocity but is able to keep the energy much better than the lighter 5.91"/60. The 5.91"/60 uses 8.5 crh windscreens but the bottomline is that the higher sectional density -an advantage inherent for the 6" round- greatly enhances it´s energy retention. There is a trade effect for this: Higher angles of fall. Higher angles of fall are welcome against deck armour but here again M79APCLC clearly overstates CPBC performances in this regard so we have to be very careful with the deck penetration figures suggested by ww2 guntables and NAaB (the latter program does share the same methodological approach, using Nathan Okuns M79APCLC for all deck related computaions).
From your discussion, I get the understanding that the AP capabilities of the british round were not good at oblique angles, because there was a tendency for the British round to "bounce off".
That is an interesting side aspect worth to be mentioned. The Royal Navy had by ww2 the best sloution for a virtually indestructable delay fuse. The specifications called for a fuse able to work even if the projectile bounces off (every condition other than base first, which would be asking perhaps to much), beeing rejected by armour, incredible.
But what I wanted to mention with the soft AP-caps is that by ww2 standarts and in case the projectile engages face hardened armour (rare on cruiser belts but quite often used for CT, barbettes and turret faces), soft capped projectiles don´t work anymore, regardless of obliquity. Against KC-type armour of pre ww1 standart, they work, given a low obliquity. Against 1930 period face hardened armour, soft caps will always be shattered before they can accomplish destroying the facelayer of the plate. A shattered projectile will still be able to hole the armour and considerable parts of the projectile up to the forward burrolet may pass the plate but the effect of the burst is always outside or mostly so, unlike a true APC, which may achieve full penetration in a condition fit to burst (effective penetration in Nathans definition).
However, they do always work againt homogenious armour (all deck armour and most cruiser belt armour other than US cruisers and PBB´s) in cases for obliquities lower than 20 deg and they also help improving the "normalization" of the projectile.
Finally, the british gun designers never aimed for extreme performance. They always kept a weather eye on barrel life, and this was achieved mostly by not overstressing the barrels with super high muzzle velocities. Whereas the british guns had a barrel life of 1100 EFC (equivalent full charges) the German gun was less than half that, at 500 EFC.
Worth to consider. Agreed.
The Barent Sea is an example of 6"CPBC inflicting serious damage to Hipper. But 6" CPBC didn´t engaged armour in this event. Hipper was on flank speed and the depression of the self induced wave exposed the amidship region. During it´s turn she heeled over and these two events made it possible that a 6" CPBC could strike below the main belt. The projectile entered the hull and exploded in a liquid outboard wingtank. Splinters defeated the 20mm torpedo bulkhead and serious flooding to one boiler room commenced. Another boiler room was flooded progressively via drainage and bilges later as a consequence of this hit. The other 6" rounds hit the hangar and the foreship, starting a fire each.
best regards,