Ammo manufacturers don't use canister powder. They buy bulk quantities of powders that meet some specification, and then, if need be, blend it with other bulk powders to get the pressure curve and mv they want. That is one of the variables that makes for different lot numbers on the end flaps of cartridge boxes. That, and differing lots of brass, bullets, primers, new tooling...
Why are factory loads a lot hotter than max reloading published data
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Both barrels would be produced on the same production line, so should have identical bores/rifling. The bull barreled one is just not sent out for fluting. It is about 10% heavier, so I'm guessing it alters the timing of the rotating barrel lockup. I can definitely see that the spent brass from my bull barreled X-Calibur does not eject as far away as when shot from my fluted barreled X-Calibur.
View attachment 48293
View attachment 48293
VanMan, about that ~20 FPS difference, were those barrels rifled to the same twist rate? Same number of lands/grooves? Heck, same exact inside diameter and length? Shot on the same day at the same temperature and air pressure?
OP: I've just finished sacrificing 10 rounds of 9mm Fed Am Eagle RN 115gr so I could use them as spare parts/dummies to set up my dies. Aside from finding out that those bullets usually weight 114gr, I found that they use 4.7gr of some powder (flakes shape). That would be overload with Bullseye or Titegroup or Hodgdon 700X but underload with most slower burning powders like Power Pistol, Blue Dot, VV N350 or 3N37, Hodgdon HS-6 or Accurate #5 or #7.
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Any reference for this I'd like to see it?
All depends on powder you're using. When using a powder like Longshot in 45ACP or 40S&W my max loads kick the #### out of your average factory loads. Find powders like clays, HS6, HP38 , etc. are great for softer more manageable loads. That's the joy of reloading, custom ammo tweaked and refined to ones needs.
In the case of superformance, the powder used in factory ammo is not always the same as the superformance powder available in a can. There is a "blend" of powders used in the factory ammo that changes by chambering/calibre.
RE: Brass variations...I find some variation is spent brass, so it would stand to reason it was produced that way.
I have purchased match barrels made from the same lot # of steel, consecutively drilled and rifled. They were not identical.
In rifles each barrel needed a unique load for best accuracy and velocity with the same ammo was over 100 fps different.
I have worked in an ammo factory (CIL) and seen how powder is chosen. Factory ammo is loaded to a specific velocity.
In most calibers, it is not difficult to reach that velocity, so there are a number of powders that would work.
The choice is often made on the basis of what has been used traditionally. If it is on hand, the usual powder is used. If there is not enough on hand when the line is ready to switch over to the new caliber, they use something else that will work that is available.
The commercial powders are often similar to a canister powder. The 4895 they use by the ton is similar to what you use, except it does not have to meet a specific speed specification. It could be faster or slower than what we buy by the pound. The factory just adjusts the load to get the target velocity for that caliber.
The 4895 I am using at this time is quite a bit slower than canister 4895. I need 46 gr for a load that would usually use 44 gr of canister powder.
You just can't beat actual experience. Thanks for sharing yours Ganderite 
Now that I've got a good reliable load worked up for my bull barreled X-Calibur, I'm thinking of converting the other one to a bull barrel as well. Will be interesting to see if there is a similar difference in FPS.
Now that I've got a good reliable load worked up for my bull barreled X-Calibur, I'm thinking of converting the other one to a bull barrel as well. Will be interesting to see if there is a similar difference in FPS. 
