Can it dump the tank?

I had came across a Talon barrel which measured 5.35mm at lands & the pellets he wants to shoot are having heads of 5.40 & skirts of 5.80mm. The pellets are causing tank dump & not moving from breech at all. The same pellets are flying at approx 750-800 after resizing them to 5.50 at skirts. Tank pressure is 2700 psi

Very often I read here that many types of heavy pellets are very tight fit in barrel yet they are shooting it without tank dump then why this perticular airgun is not being able to shoot above mentioned pellet? Does it need to have stronger valve spring or the barrel id should be more to have easier fit?

Masters please suggest me the best remedy.