You should not forget that against APFSDS pure steel is more efficient than composite armour.
(...)
It is known that thickness efficiency of composite does not surpass, and at that time was significantly less, than steel against APFSDS.
It's not true.
Onces again - please read and use google translator on both articles about Burlinghton here:
http://www.wceo.wp.mil.pl/plik/file/WBBH/PH-W/PHW_4.pdf
http://www.wceo.wp.mil.pl/plik/file/WBBH/PHW3_tresc.pdf
We have some data there (with bibliography of course).
In 1978 Burlinghton special armour had mass Efficiency like 1,5 vs APFSDS and 3 vs HEAT in compared to homogeneous armor steel of the same weight.
So 1kg Burlinghton armour shoud offer protection like 1,5kg homogeneous steel armor vs APFSDs and 3kg homogeneous steel armor vs HEAT (of course it is only example).
So in fact -in reality - Burlinghton style multialyer armour had better efectivness then RHA plate at the same weight. 1kg Burlinghton armour works as 1,5kg RHA plate.
So Your sentence is not true.
heavier and more dense composition, and with steel there is no argument.
Yes they are - when we have 1000kg RHA plate it's still 1000kg RHA plate, when we have 1000kg Burlinghton armour (for 1978) then its act against APFSDs like 1500kg RHA and agains HEAT as 3000kg RHA. For that reson in western tanks there is very little pasive RHA, HHS, and SHS plates -less then other pasive material (ceramics, kevlar, others). In estern tanks most of LOS thickenss and weight takes cast steel and RHA plate. Two module with those reflecting plates in T-72B weight 781kg, for 11550kg turret weight...
And If you want to talk about armour mass please tak a look that if for erly burlinghton 1Kg Burlinghton armour = 1,5kg RHA vs KE and 3kg RHA vs HEAT then Leopard-2A4 turret with weight 16000kg (without crew, ammo, attachments) whit "special armour" weight equal 8900kg is like:
13.350kg RHA vs APFSDS and 26700kg RHA vs HEAT and it's the lowest ratio for 1978 not 1985. in reality it could be even better.
I was talking about thickness efficiency (since that is what we measure). Weight will not say much, without knowing volume increase.
I know for erly Leopard-2A4 gun mantled mask volumen, armour weight and others. And what?
Dimensions leopard-2 gun mantled mask are known, the same dimensions of blanks for L-44, FERO, and MG. And we know mass of gun mantled mask - 630kg. Rest is rather simple math base on qustion- how thick will be homogeneous steel armor block "inside" gun mask dimensions if it will be weight 950kg (630kg x1,5 vs APFSDS) and 1890kg (630kg x3 ve HEAT). The answer is:
a) 272 mm
b) 542 mm
So this protection offer by gun mantled mask should be:
a) 270 mm vs APFSDS
b) 540 mm vs HEAT
For 42cm thick gun mantled mask -it's weight (630kg) is only 7% whole leopard-2A4 turret "special armour" (8900kg)!
And try to consider if double thick (84cm) front armour on turret can be as 540mm vs RHA and 1084mm vs HEAT - becouse mass is fully posible in that volumen like in Leopard-2A4 turret. And if you have any doubt if so hight protection level against HEAT was avaible then go back to the article and ratio between KE and CE protection. Secon value was 1: 2,09 and as we can see -it's fully possible for leopard-2A4. For lower ratio mentioned in article for 1978r it was 1: 1.36 so protection can be like 540mm RHA and ~750mm vs HEAT as lower values.
And propably ineffectiveness Soviet HEAT warhed was reson why thre was rapid growth penetartion possibilities soviet AT weapons in late 80s -and it's very easy how APFSDS and HEAt warhed developers try to catch up the growth of armor protection:
Leo2A1; 1979- november 1984
380 (I batch) + 450 (II batch) + 300 (IIIbatch)
APFSDS since 1976 to 1984.
115mm:
3БМ28 - 380mm RHA
ЗБМ21 - 330mm RHA
125mm:
3BM22 (1976) - 380mm RHA
3БМ26 (1982) - 410mm RHA
3БМ-29(1983) - 430mm RHA
ATGM's, and GLATGM's:
9М 111-2(Fagot -1975) - 460mm RHA
Konkurs (1974) - 600mm RHA
9М111М (Fagot 1983) - 600mm RHA
9М112М (Kobra GLATGM ppk 1976) - 600mm RHA
9M112M (mod. Kobry from 1985) - do 700mm RHA
In this period propably Soviet inteligence haven't bigger idea about burlinghton - perforation level enought for APFSDs was around 450mm RHA (for typical 1300m max fire range) and for HEAT warhed about 600mm RHA (-150mm RHA up armor level necessary to kill tank) so 450-500mm RHA vs HEAT.
That protection level was expected by Soviet developers. But it was propably very underestimated against HEAT wathed (different specificity Burlihton armour then all older armours) -for the other side - protection level vs KE is in accordance with the fact what we know aboit erly M1 and Leopard-2 armour.
But propably after ~1984 some infos went to the east and we can see very fast and huge growth penetartion possibilities for Soviet AT weapons -the same we can assume that soviet developes finds how really good was Burlinghton armour and they try to catch up those problem after miss a of them:
Leo2A3;december 1984-december 1985
300 (IV batch)
Leo2A4; december 1985-marc 1992
370 (1985-1987 marc; V batch)
150 (1986-1989may; VI batch)
100 (1989-1990 april;VII batch)
75 (january 1991-marc 1992; VIII batch)
APFSDS since 1985 to 1990:
3BM32 (1985) 500mm RHA
3BM42 (1986) 450mm RHA
3BM48 (1990) 600mm RHA
ATGMs and GLATGM's since 1985 to 1994:
9M120 (1985) 800-950mm RHA
Wichr-M (1990) 1000mm RHA
9M115-2 (1992) 980mm RHA
9M133-1 (1994) 1200mm RHA
In that level on typical distance in western europe soviet developers suspected to find western tanks whit about more then ~550mm RHA vs KE and more then 850-1000mm RHA vs HEAT.
Hmm it looks that those value looks simillar to thats values:
And try to consider if double thick (84cm) front armour on turret can be as 540mm vs RHA and 1084mm vs HEAT - becouse mass is fully posible in that volumen like in Leopard-2A4 turret.
??
All is connect with each other - knowing leopard-2A4 (erly) mass and Burlinghton evectivness, Soviet AT weapons perforation etc.
And If we consider angle and LOS thickness then protection for that Leopard2A3 and 2A4 (erly) will be as ~430-480-540mm vs KE and 850-954-1084mm vs HEAT (turret sides at 30. and hull front - turret front ad 30. - turret front at 0.)
For 2A4 since 1986 it will be slighty bigger:
500-550-630mm vs KE and -1000-1150-1300mm vs CE ((turret sides at 30. and hull front - turret front ad 30. - turret front at 0.)
And If you think that more then 1300mm vs HEAT was impossible then remember about case when AGM114 hit M1A1HA turret during ODS. SC warhed whit perforation bigger then 1100mm (170mm diamtere x 6,5) was unnable to perforate those armour.
In 1991.