Frank, now wouldn’t barrel diameter effect pressure or even bullet diameter? Let’s say Hornady vs Berger Vs Sierra vs solids? A load that is safe in one barrel may show signs of early pressure in the next. I have seen factory ammo pressure out early and show signs of pressure.
I think your talking about the actual bore diameter (bore and groove size) correct? Not the outside diameter of the barrel?
If your talking about actual bore and groove size…then the answer is yes! Actual bore and groove size can and will have a big impact on pressures and velocity.
As will the actual chamber reamer spec used as well.
As well as actual type of bullet and bullet diameter will effect it as well. Not just conventional lead core bullets but solid bullets as well. Solid bullets can be a whole other topic and I feel they can be even more temperamental when it comes to the actual bore and groove spec as well as the type of solid bullet it is. I feel the solids are not as forgiving as a conventional lead core bullet.
Lets stick with actual bore and groove size of the barrel. Anytime you tighten up the overall bore size of the barrel lets say both the bore and groove…you will drive up pressures!!!! I’ve seen actual pressure test barrels where the bore was .0005” undersize and the groove was also a .0005” undersize. So let’s say a min spec. 30 cal is .3000” x .3080”. By making the bore and groove size both a .0005” undersize that will drive up pressures right around 10k psi! Making the bore and groove size bigger…..it will drop pressures faster as well as you can lose velocity.
That’s why I tell guys…unless you know actual bore and groove size of a barrel to the 4th decimal place and you know what actual chamber reamer spec was used to cut the chamber….you cannot compare or say a barrel from maker X‘s barrels produce faster velocities than barrels from barrel maker Z! Unless you know the actual sizes…you are not comparing apples and apples!
I’ve also seen where the throat freebore was .0001” to .0002” under min spec. Then you stuff a bullet in it that ends up being right at the min spec…that .0001” or .0002” tighter freebore can drive up pressures around 6k psi and drive up velocities as well.
Tighter isn’t necessarily better! Too loose isn’t good either!