Have been playing around with my low pressure launcher concept experimenting with large bore pvc pipe barrels of 25mm and nearly 30mm. Tested a variety of projectiles both skirted and with sabots. These work really well are stable and accurate in testing. Only downside are hand finishing is required to suit each individual barrel and at any decent speed are fragile and single use only.
Glued together a shortish barrel of 30 inches with 4 inches of porting to reduce noise levels at higher pressures. Decided to test 25mm steel balls weighing around 60 grams. By using double patching in the larger bore I had a pseudo sabot projectile. This worked very well, easy and ammo is reusable. Barrel is muzzle loaded with makeshift ramrod, then screwed onto launcher for firing. Shooting with around 120 psi of pressure showed great promise, accuracy was very good with plenty of power.
Will post chrony speed results soon
Test results far exceeded my expectations. Was only hoping for 250 fps ( 75 m / s ) and around 200 joules of energy with such a short barrel. Only took 140 psi of pressure to better this. Using my pump to it's limit got me close to 200 psi, a scary figure in a pvc vessel. The performance was outstanding. Speed was over 360 fps, and those big 60 gram balls were exceeding 350 joules ( 250 foot/pounds )of energy. Recoil was quite noticeable with a substantial kick.
Taped together a 38 inch barrel for comparison and limited myself to 120 psi pressure. This combination really showed potential topping 270 psi and 200 joules ( 150 foot/ pounds ) with ease. Almost did some penertration tests but the thought of those big balls richocheting back quickly killed that idea.