Bull’s range improvements came at a huge loss of accuracy. As in “oops, dropped a shell on our guys” loss of accuracy.
Bull was working on increasing velocity, and on a very low budget. He was about a year from putting a projectile into orbit when the US pulled his funding to avoid the embarrassment of someone actually agenting to orbit on a shoestring before our very expensive rocket program.
There was no attempt to maintain accuracy, and he was working with a very poorly constructed gun. Read the HARP* final report. The gun was made by welding two naval rifles together end-to-end and stiffening the assembly with guy wires. A purpose built tube could have done much, much better.
And his sabots were made of plywood. Constructed in a carpentry shop. Now I know that a "sabot" was originally a wooden shoe, but this was a quick & dirty expedient. A sabot made of modern aerospace materials would have a lot more uniformity and better accuracy.
If he had not been murdered, I think his guns would have produce astonishing results.
* This HARP is not the same as Obama's refinance program with the same acronym. It stood for High Altitude Research Project.
Effectively, his factory straddled the US-Canadian border, and he simply moved "product" from one end to the other, before shipping...
His 155 artillery piece had increased range (maybe around 20%) and accuracy. Might have had to use his shell shape design, too.