W.C.,
I looked up the 250 grain XTP. It is a .452" bullet intended for .45 Long Colt. The base may not be too long, but, even though .452" is a standard diameter for cast bullets in the .45 ACP, it will cause pressure increase over the standard .451" diameter jacketed bullets normally used in the ACP. I am not clear how much, so you will want to start low and work up carefully, whatever you use?
No, .01" won't matter. Note also that even the deep bullet I illustrated is still within +P+ pressure levels, so most guns will still run it just fine. Ones with generous chambers will see lower actual pressures. My data comes from a .45 ACP test barrel I had custom made for an Encore frame, and its chamber is tighter than most 1911 barrels, so the pressures read a little high. You will find, for example, that Alliant's web site lists a very short COL for 230 grain FMJ of only 1.19". Since that would be potentially dangerous in FMJ RN, I had some back and forth with one of their techs on the subject. It turns out the loads were developed with a truncated cone shape, like the Hornady, so it is not a good number for FMJ RN which is normally 1.275" maximum COL. You just get a bigger case bulge ahead of the extraction groove in unsupported chamber barrel designs than the standard pressure produces. Also, the faster the powder the more this is an issue. I just put it up as a general heads-up on seating depth considerations.
The bullet I illustrated is close to the time-honored 200 gr. H&G #68 style, that has been copied by just about every mold maker there is. The actual H&G #68 is a bit wider at the base of the ogive cone and a little more rounded at the corners of the meplat. The #68 is a very successful design going back at least to 1940, when it was written up in a couple of magazines. It was available in either plain of bevel base originally. It remains a mainstay target and practice bullet shape in the .45 ACP because of its accuracy.
In 2005, then retired, Wayne Gibbs made this comment about the design:
"When I first started at H&G (I was almost 13 years old) as "CEO" which stands for "Cleaning", "Egads, more blocks to polish?" and "O my gosh, more sprue cutters to drill?" I heard that #68 had been designed by a customer of ours that wanted a lighter bullet than the standard hardball 230 grain bullet, so figured that the nose could be flattened a might, then the nose tapered back with a tad of angle to end in a semiwadcutter shoulder, which would lighten the weight to 200 grains,yet the chamber wouldn't guess the bullet it was digesting was not a standard roundnose bullet. Probably to his great amazement,it was also especially accurate. I think it has always been the "bullet to beat" for accuracy. Such were the way that great advances were made in the "old days"--no computer modelling!"
-Wayne
At any rate, it is a good bullet shape to work with.
As to Unique vs. AA #2, I can give you QuickLOAD's estimates. Before using Unique, please check that your lot isn't part of the
recall from 2006.
In the computer model, Unique produced, at the same charge weight, equal velocity at slightly lower pressure than #2 does. #2 is therefore going to be more sensitive to the case volume issue. I would go with Unique. With a .451 diameter bullet, I would have said to start at 5 grains and work up, but with the fat bullet, I would actually fire one round down at 4 grains, just to play extra safe and to see what this is going to do? A .001" oversize bullet is of little concern in a rifle, and the old French MAB pistols would shoot jacketed .32's that were 0.003" over groove diameter without a hiccup, so this is not really a big deal. I just like to err on the side of extreme caution in these situations. If all goes well, you might get up as high as 5.5 to 6.0 grains of Unique, depending on the shape of your chamber. Just keep watching for pressure signs.