Bofors 105mm L/62 rifled gun retrofit to existing turreted tanks??

G'day gents.

Can I request the assistance/input of our resident 'Tank' experts/enthusiasts please?

I'm intrigued with the Swedish adoption of the Bofors 105mm L/62 rifled gun, which they developed and employed on their Stridsvagn 103 tank.
From what I'm able to ascertain, this gun was a development of the British Royal Ordinance L7 105mm L/52 rifled gun (??).
Now it appears obvious with its increase in barrel length (L/62 verse the L7's L/52), that its velocity/penetration capability was a marked improvement over that of the venerable Royal Ordinance L7, whilst using the standard/existing ammunition as the British 105 mm L7.

My question to our resident 'Tank' experts/enthusiasts is this -
If the performance of the Bofors 105mm L/62 rifled gun gave a better 'bang for bucks,' whilst using the standard/existing ammunition as the British 105 mm L7, is there any reason that the Bofors 105mm L/62 rifled gun couldn't be adopted, as a retrofit to conventional (turreted) tank designs - like the Centurion, Leopard 1, M60 etc...?
Now I know and appreciate that the longer barrel arrangement could/would add to issues of turret/vehicle balance, and of course the potential of ploughing of the gun barrel into the ground etc. But when I reflect on what the Israelis did with their M50/M51 Sherman - fitting a large counterweight at the turrets rear, could the Bofors 105mm L/62 rifled gun been feasibly incorporated into a turreted tank of the era? I'm thinking that many a army, with its 105mm ammunition stocks, could have potentially held off the seeming race to replace their 105mm tanks with 120mm tanks, had they been able to have fitted Bofors 105mm L/62 rifled gun. Add to this the seeming serge in advanced 105mm anti-tank rounds by the likes of Israel.....

I'd appreciate your comments and technical expertise gents!

Regards
Pioneer

The length of the Swedish gun's barrel only confers a marginal increase in penetration over the standard L/52 L7 gun.

To increase the penetration substantially what would be required would be either:

a) Longer barrel and a larger chamber;
b) A faster burning propellant;
c) An APFSDS round

The longer barrel with a larger chamber would allow a larger charge to drive the round to higher muzzle velocities.

A faster burning propellant, would allow higher chamber pressures, which in turn would drive the round to a higher muzzle velocity.

An APFSDS round, allows the round to retain it's muzzle velocity for longer, allowing velocities to fall off much slower than a larger, full diameter HEAT/AP or a reduced diameter APDS round does.

The Swedes decided when designing the Strv103 that they would utilise standard NATO 105mm rounds with a longer barrel. That way they could have a quid each way - they'd have a higher muzzle velocity but they'd still be able to tap the NATO supply system if they found their own ammunition supply system was unable to cope with any feared invasion of Sweden. The result was a marginally better armour penetration over the existing L7 but not substantially better.

Giving your gun a longer barrel is always a way to improve it's armour penetration with kinetic energy rounds. The Germans showed that, with the L/43. L/48, L/70 75mm guns they mounted on their AFVs in WWII (admittedly, they also substantially increased the chamber sizes as well). It would be possible to mount the L/62 Bofors gun in most tanks which mounted the L7, with some tinkering of the existing mounting's equilibrators. The extra 10 calibre lengths would not substantially increase the weight of the barrel to require the mounting to be moved. Why do so, though, when 120mm guns are available and they have substantially higher muzzle velocities than the L7?

"An APFSDS round, allows the round to retain it's muzzle velocity for longer, allowing velocities to fall off much slower than a larger, full diameter HEAT/AP or a reduced diameter APDS round does."

More importantly, it allows for stabilization of a projectile with a higher ratio between length and diameter. You cannot really spin stabilize at a L/D or 20.

Thanks gents for both your reply and explanation!
If you don't mind, I would still like to ask if the Bofors 105mm L/62 rifled gun couldn't be adopted, as a retrofit to conventional (turreted) tank designs - like the Centurion, Leopard 1, M60 etc...?

Regards
Pioneer

Pioneer said:

Thanks gents for both your reply and explanation!
If you don't mind, I would still like to ask if the Bofors 105mm L/62 rifled gun couldn't be adopted, as a retrofit to conventional (turreted) tank designs - like the Centurion, Leopard 1, M60 etc...?

Regards
Pioneer

Click to expand...

I believe I answered that question. It would be possible to mount the L/62 barrel in most tanks which could take the L/52 L7 gun.

I recall reading that the US Army was considering fitting M1s with longer 105mm barrels in one of the old Osprey Vanguard series books on the M1 Abrams. Yet from what I've read elsewhere the increase in muzzle velocity provided by the L/62 barrel versus the standard L7/M68 barrel isn't all that impressive. It probably was decided such an effort wasn't worth the trouble especially when considering that the M1E1 with the 120mm XM256 was being tested at roughly the same time.

Kadija_Man said:

Pioneer said:

Thanks gents for both your reply and explanation!
If you don't mind, I would still like to ask if the Bofors 105mm L/62 rifled gun couldn't be adopted, as a retrofit to conventional (turreted) tank designs - like the Centurion, Leopard 1, M60 etc...?

Regards
Pioneer

Click to expand...

I believe I answered that question. It would be possible to mount the L/62 barrel in most tanks which could take the L/52 L7 gun.

Click to expand...

Sorry my friend, so you did.

Regards
Pioneer

Pioneer said:

Kadija_Man said:

Pioneer said:

Thanks gents for both your reply and explanation!
If you don't mind, I would still like to ask if the Bofors 105mm L/62 rifled gun couldn't be adopted, as a retrofit to conventional (turreted) tank designs - like the Centurion, Leopard 1, M60 etc...?

Regards
Pioneer

Click to expand...

I believe I answered that question. It would be possible to mount the L/62 barrel in most tanks which could take the L/52 L7 gun.

Click to expand...

Sorry my friend, so you did.

Regards
Pioneer

Click to expand...

Actually he didn't answer your question. Just gave you some reasonably informed, backwards analysis, armchair general opinion that failed to take into account crucial issues and so was therefore just a nicer looking version of BS. But still BS.

Firstly you can extend the barrel of any gun but you need to compensate for this. The key issue in relation to the L7 gun in the S-Tank is it doesn't have trunions. Because the ordnance (which is the barrel, the trunions and the breech) is fixed into the hull of the vehicle it can't elevate or depress by itself (the entire vehicle has to pitch to provide elevation and depression). Usually a gun ordnance has trunions which are circular extrusions that the ordnance rotates around to provide elevation/depression. If you extend the barrel then you are changing the centre of gravity of the weapon. Ideally the ordnance is balanced on the trunions so rotation is easy. If it isn't then the you will need to add balancing gear or a very powerful elevating mechanism to counter the moment arm of the barrel (or breech). So if you just go and extend the barrel of the gun in an exsisting tank then you are going to change the CG of the ordnance. A simple way of compensating for this is to add a counterweight at the breech. But apart from being wasted mass it can also consume a bit of volume, which is usually at a premium inside a tank turret. And you will also need to manage the CG of the turret as changes to this through a longer barrel can effect the turret rotation mechanics.

Secondly (and there are more than two issues of BS in the above responses, but I'll leave it at only two) extended barrel length does not automatically provide a velocity boost. You can reach a point where the friction of the bore becomes more than the remaining force in the propellant gases leading to the projectile actually being slowed down. Also another advantage a longer barrel can provide is enhanced spin stabilisation of the projectile via longer rifling. This reduces dispersion and can be quite signficant at longer range compared to a projectile from a shorter bore where there may not be much difference in velocity.

Ok gents, going over some older topics I initiated some time back, and just wondering if anyone has any performance data or Swedish write-up of the Bofors L74 10.5 cm L/62 rifled gun, so that I can compare it to the L7 105 mm L/52 gun???
After all there must have been some marginal performance gains for the Swedish Army/Government/Bofors to invest $$$ in the L74 10.5 cm L/62 development and fielding!

I also found this write-up (I know and appreciate the source) in relation to the Rheinmetall Rh-120 120mm L/44 and L/55, which I think gives some precedence to my inquiry:

The German government began the development of the Leopard 3, although this was canceled after the fall of the Soviet Union.[39] On 29 October 1991, the governments of Switzerland, the Netherlands and Germany agreed to cooperate in the development of a modernization program for the Leopard 2. Part of this program included the introduction of a longer 120 mm tank gun,[40] a cheaper alternative to a brand new tank gun,[41] increasing the maximum range of the gun by an estimated 1,500 m (1,600 yd). Although the gun is longer, allowing for a higher 580 MPa (84,122 psi) peak pressure from the propellant, the geometry remains the same, allowing the gun to fire the same ammunition as that fired from the shorter version.[42] The longer barrel allows ammunition to attain higher velocities; for example, with new kinetic energy penetrators ammunition can reach velocities of around 1,800 m/s (5,900 ft/s).[43] The new barrel weighs 1,347 kg (2,970 lb).

Click to expand...

(Source: https://en.wikipedia.org/wiki/Rheinmetall_Rh-120)

Regards
Pioneer

There's a website on Swedish tanks with lots and lots of original documents somewhere, you should be able to find it by looking for those WW2-era Swedish tanks and other Sweden taking-specific keywords.

With any change of gun in a tank or indeed any armoured vehicle, the question is "Will the government pay for it"? Chances are poor with marginal improvements that any government will approve such project. Add to the cost of the gun any changes in training that will be required and junking of any spares that exist for the standard gun. Take a look into the search for an M-16 replacement.

lastdingo said:

There's a website on Swedish tanks with lots and lots of original documents somewhere, you should be able to find it by looking for those WW2-era Swedish tanks and other Sweden taking-specific keywords.

Click to expand...

Thank you for your reply lastdingo, I have to admit that I've tried this in without any luck

Regards
Pioneer

Thank's for your input Foo Fighter

In truth I hear what you are implying, but I'm working on the analogy, that if a low/ middle-ranked country/army already has and wants to retain a qualitative capability edge in terms of tanks [let's say Leopard 1A3/1A4] in its given region, and doesn't really need to excessively go overboard in terms of First-World/Superpower capability and costs of purchasing a new fleet of tanks and it's associated logistics, maintance and training infustructure [eg. Leopard 2/M1 Abrams/Challanger 2......] to gain that perceived 'needed'/'trend' of having the additional firepower of the 120mm tank gun; my thought process was/is that low/middle-ranked country/army could/would achieve a cost-effective qualitative increase in firepower with replacing the likes of it's existing Royal Ordinance L7 105mm L/52 gun with a Bofors L74 105mm L/62 gun, without having the costs of replacing expensive 105mm ammunition stocks......after all its not always the case that the low/ middle-ranked country/army is going to be facing up against the likes of Leopard 2's/M1 Abrams/Challanger 2's/T-90's....
On top of this thought is the knowledge and appreciation that while it was/is hip to adopt a larger 120mm gun (and hence whole new tank in the majority of cases), one didn't necessarily have to be square, as vast technological advances and investment continued to be committed and delivered in parallel with 120mm ammunition, did it not?
Hence my thought/analogy that a slight improvement in velocity/range of the L62 calibre gun and advancements in 105mm ammunition = a qualitative gain for an affordable net cost.

(P.S. Not wanting to detract from main topic, but in relation to your "Take a look into the search for an M-16 replacement." analogy Foo Fighter, it is my humble opinion that the US military failure to replace this assault rifle decades ago, has just as much to do with the inability of the US military really knowing what it wants to replace the ubiquitous M-16 assault rifle with period. I mean look at how many 'programs' have been formally conducted by the US Army.....to no avail!
They either don't give the 'M-16 Replacement' the priority it deserves; or it wants redicoulous 'weapons systems' that are something out of Hollywood movies like Terminator.......
Then there's the endless indecisiveness of the actual preferred calibre the new assault rifle is supposed to use......
On top of this is the toxic domestic US politics of not being able and willing to except that non-US rifle manufacturer's can and are better than the domestic designed assault rifles. Riding on the back of this domestic US politics is the irrefutable political/$$$ power of the US arms industry, who'd sooner undermind/destroy a government if their product, lobbying, collusion and corruption isn't excepted and adhered to.)

Regards
Pioneer

G'day.

1. Not implying anything.

2. Any nation unwilling to invest in new vehicles is unlikely to invest in a marginal/small improvement given that the spares and training will also have to be funded on top of the guns themselves, plus the cost of fitting the guns (Not a small cost in itself)

3. The M-16 replacement has of been cited to have failed due to not being of sufficient improvement to justify the investment required.

1. Not implying anything.

Click to expand...

My apology in that case Foo Fighter


Regards
Pioneer

No worries, written communication is never perfect. Have a great day.

Manuals just give a Vo increase of 50 m/s to the regular L7, so there rly was no point to put money into such an effort.

blockhaj said:

Manuals just give a Vo increase of 50 m/s to the regular L7, so there rly was no point to put money into such an effort.

Click to expand...

Thanks for the statistic blockhaj
So I guess I'm still stuck with the question as to why Sweden invested in the Bofors L74 105mm L/62 gun?

Regards
Pioneer

Pioneer said:

Thanks for the statistic blockhaj
So I guess I'm still stuck with the question as to why Sweden invested in the Bofors L74 105mm L/62 gun?

Regards
Pioneer

Click to expand...

The gun had to be scratch built since it was equipped with an integrated autoloader and other reasons, the configuration also allowed for a longer barrel, although not by too much, thus it was a nobrainer to get a little more omph from the construction by lengthening the barrel

Early on however, it was unclear what gun was to be used, some proposals fitted the british 84,3 mm 20pdr B from the Cent V, others with an indigenous Bofors design (indigenous cartridge and all), however when the Brits gave the green light for the 105 L7 (ca 1959) it was obvious to construct the S-tank gun for that cartridge.

Thank you once again blockhaj, very interesting and perceptive.

Regards
Pioneer

Is that a 20mm autocannon for the commander on those early designs?

Colonial-Marine said:

Is that a 20mm autocannon for the commander on those early designs?

Click to expand...

View: https://www.youtube.com/watch?v=q_ml4dhopUs

Trials showed problematic accuracy but the idea stayed until the mid 1960s. The S1 and S2 prototype, plus the strv 103-0 pre-series featured the 20 mm cupola but majoirty of the time without the 20 mm gun. Images below from some old War Thunder post i made.

blockhaj said:

View: https://www.youtube.com/watch?v=q_ml4dhopUs

Trials showed problematic accuracy but the idea stayed until the mid 1960s. The S1 and S2 prototype, plus the strv 103-0 pre-series featured the 20 mm cupola but majoirty of the time without the 20 mm gun. Images below from some old War Thunder post i made.

Click to expand...

Majority of the time? Does that mean the S1, S2 and 103-0 sometimes did have a 20mm?

Are there any documentations about that?

Les_Bien_Pain said:

Majority of the time? Does that mean the S1, S2 and 103-0 sometimes did have a 20mm?

Are there any documentations about that?

Click to expand...

The S2 in the above photo has it mounted but no image of the 0 series with it have emerged. A document from 1965 still mentions the 20 mm next to the final solution of the FN-mag cupola.

Even if you could just stick the L62 barrel into the L7/M68 ordnance, you'd need to rebalance the gun.

10 calibers is 1050mm, barrel walls are on the order of 25mm thick at the muzzle so the overall barrel diameter is ~155mm. (7.75^2-5.25^2)*pi*105cm=10,720cc, so roughly 75kg heavier forward of the trunnions at the end of the barrel. I'd want to avoid bolting weights onto the recoiling part of the gun, but if the fixed recoil rails could take a good 375kg of ballast the gun would balance naturally.