Bishop liner

I got a bishop liner back in June and have been finding my needles go blunt / ink flow stops very quickly. At first I thought it was the brand, so I changed a few times but experienced the same thing. Even had the same issue with da Vinci cartridges which are made for bishop machines. I have tried slowing my voltage down which works to some extent, however it feels unnatural for my hand speed to be going so slow. Can anyone offer advice? Thank you!