Has anyone else found pressure versus velocity discrepancies with Vihtavouri's listed loads for N135?
I have been working on loads for Barnes 130TTSX and 175LRX (a bit heavy, but I had a good number on hand). I don't have a chronograph at the moment, but I have chrono'd a bunch of those bullets with other powders and have parameters in Gordon's Reloading Tool dialed so it consistently predicts my rifle's velocities and nodes within 10-25 fps.
Burn rate charts list N135 next to H4895/IMR4895 and just a bit slower than Varget, so a great zone to fill a 308 case and achieve 100% burn. However, the max loads in Vihtavouri's manual are all listed with charges weights 2-4 graines less than, velocities well below, equivalent powders in other manuals (e.g., ~200fps less than 4895 and Varget in the Barnes and Hodgdon manuals, etc.). That makes it look like Vihtavouri was just very, very conservative on pressure.
But then I plugged those loads in Gordon's Reloading Tool, and using default values for cartridge, bullets, and powder, it predicts VV's listed max loads would produce velocities exceeding 4895 and Varget, but with pressure exceeding SAAMI by several thousand PSI--despite being a lot lower charge weights! That could make it look like N135 has a much faster burn rate than burn rate charts suggest. However...
When I adjusted the bullets' Initial Pressure to the same value that consistently trues up velocities yielded by other powders (750psi), GRT predicts N135 velocities in between: ~100fps above VV's manual and 100fps below velocities listed (and shot) with equivalent powders. When I used OBT function to adjust the powder's values to produce book velocities, GRT predicts that VV's listed max loads will produce pressures in the mid-40k's.
So, is VV's manual just hyper-conservative with pressure, staying 25% below max when they could safely top out 200fps higher? Or do VV's max charge weights reflect pressures nearing 60000psi, indicating N135's burn rate is faster than generally thought?
For those who have used N135, did VV's manual reasonably predict the velocities you got (after adjusting for barrel length)?
I have been working on loads for Barnes 130TTSX and 175LRX (a bit heavy, but I had a good number on hand). I don't have a chronograph at the moment, but I have chrono'd a bunch of those bullets with other powders and have parameters in Gordon's Reloading Tool dialed so it consistently predicts my rifle's velocities and nodes within 10-25 fps.
Burn rate charts list N135 next to H4895/IMR4895 and just a bit slower than Varget, so a great zone to fill a 308 case and achieve 100% burn. However, the max loads in Vihtavouri's manual are all listed with charges weights 2-4 graines less than, velocities well below, equivalent powders in other manuals (e.g., ~200fps less than 4895 and Varget in the Barnes and Hodgdon manuals, etc.). That makes it look like Vihtavouri was just very, very conservative on pressure.
But then I plugged those loads in Gordon's Reloading Tool, and using default values for cartridge, bullets, and powder, it predicts VV's listed max loads would produce velocities exceeding 4895 and Varget, but with pressure exceeding SAAMI by several thousand PSI--despite being a lot lower charge weights! That could make it look like N135 has a much faster burn rate than burn rate charts suggest. However...
When I adjusted the bullets' Initial Pressure to the same value that consistently trues up velocities yielded by other powders (750psi), GRT predicts N135 velocities in between: ~100fps above VV's manual and 100fps below velocities listed (and shot) with equivalent powders. When I used OBT function to adjust the powder's values to produce book velocities, GRT predicts that VV's listed max loads will produce pressures in the mid-40k's.
So, is VV's manual just hyper-conservative with pressure, staying 25% below max when they could safely top out 200fps higher? Or do VV's max charge weights reflect pressures nearing 60000psi, indicating N135's burn rate is faster than generally thought?
For those who have used N135, did VV's manual reasonably predict the velocities you got (after adjusting for barrel length)?