my 1886 win in 4570 is 150 to 170 fps slower than a ported guide gun? i have 22 inch br,

Sorry every gun, chamber and barrel is different. My guess is you are simply not building as much pressure. Chamber a touch larger, longer bullet jump bore dia is a touch larger. Two rifles as close to twins as you can build them will often vary by that much.

Yep; what ramrod said; you are trying to compare a Winchester barrel made in japan to a Marlin barrel made in the US. Any similarity is a coincidence.

I have always said the best way to ruin your sure bang them dead killer is to chronograph it

I can tell how fast my 45-70 bullets are going by how much the rifle kicks. Elmer said he wanted his rifles to kill at both ends. me too.
Don't fret over it.