25 pdr. Technical description / comparison with 105/155

Discussion in 'Gunners' started by EX_STAB, May 25, 2008.

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  1. Could someone give a technical comparison between the 25pdr and modern guns/rounds?

    Did the modern rounds evolve from the 25pdr or are they all new?
    Are the cases similar at all or are all post 25pdrs bag charge only?

    If there is an online document summarising this please just link it if it is authoritative - I wouldn't trust wiki etc.

    Thanks.

    ES.
     
  2. 105mm uses Cart Case.

    155mm Uses (mostly) incremental bag charges.
     
  3. Modern rds (ie 105mm Fd and 155mm L15) are both 'new' ie post WW2 designs, although their ballistic shapes are similar to 25 pr and other designs of that period (in WW2 orgive curvature was defined by 'circular radius head', this was not used in post war designs so exact comparisons are difficult.

    The main difference is that 25 pr used relatively low grade steel (for ease of production in wartime). This meant that the proportion of HE to steel was quite low, which in turn meant significantly less lethality. Modern shells user higher grade steel with thinner walls which means more HE. Rough calcs are 25 pr - 8% HE, 105mm Fd 15.5% HE, 155mm L15 26% HE.
     
  4. How accurate is light gun in direct fire? What would the "group" size be at, say, 800m?
     
  5. On the YOs course I attended in 1979 the technical types did a comparison.

    The L118 105mm Light gun weighs about the same as a 25 Pdr and is about as easy to handle.

    It fires a shell that is C 40% heavier and 50% more lethal 50% further. It does it because the ammunition, gun and trail are all made from modern materials compared to the 25 Pdr.

    The development history is on Wikipedia http://en.wikipedia.org/wiki/L118_Light_Gun Its a replacement for the 105mm Pack Howitzer using the same ammunition as developed for the Abbot SP gun.

    However, if the trail of the L118 is damaged it needs to go back to ROF Nottingham (if it still exists). It can only be manufactured by specialist manufacturers so if there was ever a need to wage industrial war we would have a problem!

    I don't think there is much difference in the grouping between a 25Pdr firing AP charge Super,Abbot firing HESH charge Super and L118 firing HESH charge 5 in the anti-tank role.
     
  6. As a means of comparing artillery I think 'grouping' at 800m is pretty meaningless. It's also nothing to do with 'accuracy'.

    Assuming the sights are correctly aligned with the ordnance, then artillery accuracy is determined by the quality of the ballistic data and the quality of the mathamatical models used to compute this data and firing data. 25-pr was before the age of computers (yes I know there was a FACE tape 25-pr but its data was derived fromn the old stuff). The old manual methods and calibrating sights were nowhere near as accurate as digitally computed firing data using up to date MVs.

    Assuming accurate laying, 'grouping' in the horizontal plane reflects the probable error (ie consistency/dispersion as given by Probable Error (PE) in the FT (or RT if you're old enough)), and this in turn is mostly determined by round to round variation in MV.

    At shortest ranges there was very little difference between 25-pr and Abbot/L118 when you compare the most consistent charges. But once you get to about 5km the 105s start to show noticably smaller PEs. Originally Abbot and L118 RTs showed very similar PEs, as you'd expect because they fired the same ammo. However, in 1985 an amendment to the L118 FT significantly reduced its PEs, but IIRC there was no similar change to Abbot (perhaps because it was due for replacement). This revealed L118 as much more consistent than 25-pr (assuming 25-pr data were accurate).

    For direct fire anti-tank grouping is in the vertical plane, and for this the flatter trajectory is always better at a particular range. Higher MV gives a flatter trajectory (which is why tank guns have higher MVs than arty)Keeping it simple to compare like ammo with like (ie not getting mixed up with AP (3 different MVs for 25-pr and HESH) then max HE MVs were 520 m/s for 25-pr and something like 710 m/s for Abbot/L118. Therefore Abbot/L118 would show better vertical grouping but it probably wouldn't be very noticeable at 800m.

    The original requirement for L118 anti-tank shooting was a 65% probability of a first round hit up to 1500m and a 90% probability of a second round hit. 25-pr trials in WW2 showed the probabilities of hitting a 6x6 ft vertical target (with AP) were 80% at 1000 yds and 45% at 2000 yds.
     
  7. ugly

    ugly LE Moderator

    I didnt think you grouped with guns, however according to the Father in Law, his dad commanded a troop of 25 pounders before Dunkirk and they reckoned on direct fire HE killing any tank available then!