.308 TEXAN Hammer length question

I have made a .308 barrel for my .457 Texan but just get "tank dumps" each time. The possibility is that the hammer /spring tension is too heavy for the smaller calibre & lighter 130gn to 220gn cast lead slugs regardless of tank pressures under 3,000psi. My only course is to make a set of lighter/shorter length hammers to see if the dumps stop. Has anyone measured or weighed the hammer on their .308 barrelled Texan? I do not think the top hat holes are too large or the spring tension even on the lightest wheel setting with pressures between 1,500 & 2,500psi. Tank dumps every time. After replacing the .457 barrel things go back to normal regardless of pressures. Luckily it only takes a few minutes to swap barrels.

Questions like that are more likely answered on a forum like GTA (gateway to air guns)
Lots of technical info, and engineers who build and modify air guns there.

Just to let any members playing with smaller calibre barrel swaps on a texan .457 that if a eg. 308 barrel is replaced & that a lighter hammer or/and a lighter spring they still will no work to stop tank dumps. The only method I have found is to reduce the top hat holes from 5/32 to smaller holes (a lot of machining) OR reduce the valve inlet tube before the poppet with screw in reducing plugs of different diameters holes. The latter is the better method. From what I have researched no one has posted this info before so I had to try it.