.260 Rem velocity question

[mrjdasr]

hogdon load is 39.5 benchmark w 120 bullet for 2935 fps
chrono refused to work as usual
5 shot group at 100 yds is dead on point of aim at 200yds is 1.9 inches low, same point of aim
at 300 yds , 5 shot group is 7.5 inches below point of aim
using JBM ballistics , this indicates a velocity of 3250 fps
is this possible with a bartlein 30 inch 5r 1-8 twist barrel to get that much more fps over a generic 24 inch used by hogdon for data??
fired in damp cloudy 500 foot altitude new York state

 

[Bart B.]

Yes.

Unless your barrel and ammo components are exact duplicates (same chamber & bore dimensions as well as component lots) of what any published load produces, yours can be off up to 100 fps in velocity. Sometimes more. Unequal amounts of case neck grip on bullets can cause a 50 fps difference.

Normally, a given barrel looses about 25 fps per inch cut from the muzzle for cartridges in the 2500 to 3000 fps range. Reverse that adding inches to barrel lengths. Your extra 6 inches adds 150 fps on average. Your difference is probably caused by barrel and ammo variables.

 

[Sniper338]

mine runs 2850ish in a 28 inch barrel with 140gr bergers

 

[sbhooper]

I think that is pretty close. My 24-inch sends 129 interlocks at 3010, with a max load of Re17.