If you look at the data on the Hodgdon load data site you will see the charges for Hodgdon and Winchester powders are quite a bit lower for the 125gr HAP bullets than the 124gr XTP bullets. (sometimes by a full grain) Be careful which data you use.
All load data should be considered nominal load data and work up carefully to a max load.
Like anyone else when Hodgdon works up a load with a particular bullet they are using a single lot of powder. If they got significantly different results with the 125 gr HAP and 124 gr XTP I suspect they worked the loads up at different times with different lots of powder.
In contrast, when a bullet manufacturer works up loads for its bullets it is more likely to use the same lot for all of the similar bullets when it is recommending the same data for all the bullets listed. If there is a bullet in the group that has more bearing surface and more "stickiness" in the bore, it's data will be the controlling data for the max load.
In either case, the load data needs to be taken with a grain of salt as while canister grade powder is more consistent than bulk powder used by ammo makers, there is still lot to lot variation.
For example, if you look at a manual like the Hornady manual, you'll see different max charge weights for powders that are identified by Hodgdon as being identical except for the label, such as H110 / Win 296, and HP 38 / Win 231.
The thing I see that is the most alarming is when hand loaders trying to duplicate military loads find what is literally a nominal charge weight and then take that charge weight as gospel. For example they might see nominal load data claiming 41.7 grains of IMR4895 for a match load, without realizing the acceptance criteria was based on measured muzzle velocity for the lot, a lot made with a 10,000 pound lot of powder for which a specific charge weight was developed for that powder lot.
It gets even worse when they see a nominal charge weight for a bulk powder like WC846 for an M80 ball load and again take that load as word, when the WC846 specification is extremely wide, and includes a narrower spec for WC844. WC844 and WC846 are regarded as more or less being equivalents to BLC-2 and H335, yet most handloaders wouldn't think of using them interchangeably.
