Estimate chamber pressure and muzzle velocity for the 257 Roberts with the free,
in-browser MyLoads internal ballistics simulator. The figures below are illustrative
estimates from a physics model — not a recommended load. Always cross-check a current
published loading manual.
257 Roberts reference
Maximum average pressure (MAP)
54,000 psi
Nominal case capacity
56.0 gr H₂O
Groove / bullet diameter
0.257 in (6.53 mm)
Example simulation illustrative
Bullet
Hornady 0.257 117 gr SST
Powder
IMR 4350
Charge
37.4 gr
Barrel
22 in
Muzzle velocity
2,545 fps
Peak chamber pressure (interval, ±10% burn rate)
34,600 – 42,383 – 50,932 psi
nominal is 78% MAP (54,000 psi)
Illustrative example — every figure is an estimate; always confirm your load against a current published manual before loading.
Popular 257 Roberts powders
Powders and bullets handloaders commonly use for the 257 Roberts, drawn from public discussion and listed most common first. They appear as the Popular group in the calculator's pickers. This is not a load recommendation — always check your load against a current published manual.
IMR 4831
Hodgdon Varget
Alliant RL-19
Hodgdon H4350
IMR 4350
Hodgdon H4831
IMR 4895
Hodgdon H414
IMR 4064
Hodgdon Hybrid 100V
Alliant RL-22
Alliant RL-17
Popular 257 Roberts bullets
Nosler Partition 25 Cal 100 gr Spitzer
Nosler Partition 25 Cal 120 gr Spitzer
Nosler Ballistic Tip Hunting 25 Cal 100 gr Spitzer (Blue Tip)
Nosler AccuBond 25 Cal 110 gr Spitzer
Hornady 0.257 100 gr InterLock SP
Hornady 0.257 117 gr InterLock BTSP
Nosler Ballistic Tip Hunting 25 Cal 115 gr Spitzer (Blue Tip)
Nosler Partition 25 Cal 115 gr Spitzer
Sierra 25 Caliber (.257) 100 gr SBT GameKing
Speer Hot-Cor Spitzer SP .257 100 gr
Hornady 0.257 110 gr InterBond
Barnes .257 100 gr TTSX BT
Sierra 25 Caliber (.257) 90 gr BlitzKing
Use MyLoads as a 257 Roberts velocity and pressure calculator: it estimates
muzzle velocity, muzzle energy and the full chamber-pressure curve for your own powder,
charge and barrel length, compared against the reference facts above.