I'm currently loading a Cast Performance 405 gr. WLNGC bullet for my Marlin Guide Gun. I would have prefered to use Beartooth bullets from the git-go but (can't remeber why) couldn't get them as quickly as I needed. After seating the bullets, I notice a slight bulge on about half the circumference of the brass on the outside of the case, which is an outline of the base of the bullet. I'm using new, re-sized Remington brass and the bullet diameter measures .459 - .460. Any ideas? These loads are extremely accurate and I haven't had any problems with chambering or ejection.

Completely normal. What you are seeing is just as you suspected, the base of the bullet. When you size then expand, the expander only goes down so far. With longer bullets like the 405 gr. the base of bullet goes below the end of the expander and then it expands the case. This is almost always seen with long bullets in the straight walled cases, handgun and rifle but especially so in the rifle.
The reason it only goes half way around is because the bullet and the case are not in perfect alignment. If you had a match set of dies that held the bullet perfectly straight and the case perfectly straight and then both in perfect alignment while seating, then you would see the bulge go all the way around, but in tapered rounds like the .45-70 that will seldom be the case.

The bullet diameter is slightly larger than the case after being sized. You need the smaller case to get some tension on the bullet - not relying on the crimp alone. This is fairly common, as 45-70 brass is not as thick as most bottleneck cartridges.

If you have no problems chambering or extracting, nothing to worry about. Mine will show this slight wrinkle, or bulge, also. You can find the same occurrance with thin walled handgun cases, too.

Thanks for the help, guys! I guess the 45-70 is the only staight walled case I load long bullets for. This puts my mind at ease. I shoot IDPA matches and load thousands of rounds a year on my Dillon for .45 ACP and .40 S&W and have never seen this, apparently the expander travels behond where the base of the bullet rests in those cases.

After seating the bullets, I notice a slight bulge on about half the circumference of the brass on the outside of the case, which is an outline of the base of the bullet.To get better aligned bullets, make sure the rim of the case is fully in the shellholder then place the bullet as straight as possible in the casemouth before raising the loading tool ram. GENTLY raise the ram until you feel the bullet LIGHTLY touch the seater plug, then finish seating the bullet with normal force. That gives the bullet a chance to center itself in the plug before being seated into the casemouth. I too, like to see the the base of my bullet all around the case and not just on one side. :)

To get better aligned bullets, make sure the rim of the case is fully in the shellholder then place the bullet as straight as possible in the casemouth before raising the loading tool ram. GENTLY raise the ram until you feel the bullet LIGHTLY touch the seater plug, then finish seating the bullet with normal force. That gives the bullet a chance to center itself in the plug before being seated into the casemouth. I too, like to see the the base of my bullet all around the case and not just on one side. :)

Thanks for the advice, I'm going to give your method a try.

To get better aligned bullets, make sure the rim of the case is fully in the shellholder then place the bullet as straight as possible in the casemouth before raising the loading tool ram. GENTLY raise the ram until you feel the bullet LIGHTLY touch the seater plug, then finish seating the bullet with normal force. That gives the bullet a chance to center itself in the plug before being seated into the casemouth. I too, like to see the the base of my bullet all around the case and not just on one side. :)

You might also pay attention to the depth you expand the case when you use your expander die. If you allow the bullet to find its own way to the maximum seat depth by self expanding the case during the seat step you might get uneven seating (thus the bulge on one side). Running your expander die a little deeper will reduce friction and drag on the bullet during the seat step and may provide a more even seat. I ran into the same situation when loading up some 500 grain bullets. Those puppies were long but I did get a uniform seating.

..... and load thousands of rounds a year on my Dillon for .45 ACP and .40 S&W .....

In addition to everyone elses input, my $.02 as follows:

I used to load .45acp on a Dillon SDB, & would occasionally notice the same one sided bulge that you describe on 45/70.

The Dillon cust. service rep suggested what should have been a no brainer - When adjusting bullet seating depth, "center" the seating die on the case, by raising the ram (& cartridge) to full height, & only then cinching the die lock ring.

This solved the "problem" w/ my SDB, so when upgrading to my current 550B, I carried the practice across, & use it when adjusting dies at all four stations.

On my 550, I load .45acp, .44mag, .308, & 45/70. I use a mix of dillon, rcbs, forster, & redding dies.

I length trim ALL caliber brass as required, to assure uniform bell & crimp. The handgun calibers get loaded full progressive - w/ a 550 powder die & measure. For the rifle calibers, I utilize a 450 powder die set up - & hand measure all charges.

Maybe not the speediest set up for mass production, but the results are..... satisfying.

Sorry for the extended reply, but hope it helps in some way.