I am trying to load the Cast Performance 405gr LBT style bullets for my 45-70 Contender. The problem that I'm having is that I can't expand the case mouths large enough to accept the bullets. When I seat the bullet, the case bulges. The rounds still chamber and fire, but the accuracy is just not what I have come to expect from this barrel.
After I expand the case mouths, the inside measures .455". This is making me think that I just need a new expander plug. The dies that I'm using are from Lee, so I thought maybe I am just getting what I paid for. I have had excellent luck with Lee dies in the past though, so I don't know what to think. If anyone has any suggestions for me, I'd love to hear them. Thanks.
Andrew

You absolutely need a Lyman 'M' die.

I have a set of dies from CH4D that I think work on the same principal as the "M" die. It expands the case to bullet diameter and then puts a bell on the mouth. The bullet get seated straight with the case and not tilted as it might become if the bullet is having to expand the case to fit.

CH have a range of expander buttons and you can order any size you need. I use a .458 for my 45/70 to hold a .459 bullet.

I thought this would be too loose but you can't pull it out with fingers. there is about .0015 of spring in the brass after expanding so the neck still grips firm.

If your bulging case when you put put in bullet, the resize die is making the case smaller than needed. Then when you
use mouth belling die, brass springs back smaller, making it tight fit to get bullet in.A lot of resize dies do more than needed and overwork brass, thus shortening brass life. Ed.

Collegekidandy:

I've done a lot of work with cast bullets in .45-70 single shot rifles, both Sharps and Ballards. You didn't mention it but you do need to bell the mouth after sizing. This is done of course with the belling die. Also, cast bullets need to be treated a bit differently than jacketed, at least in my experience. Your cast bullet should be about 0.002" larger in diameter than your groove diamenter. Therefore, if groove dia. is 0.458", the bullets should be about 0.460" in diameter. Also, your expander plug should be about 0.002" less in diameter than your bullet (ie, you should have about 0.002" of neck tension). You should measure your bullet diameter & order a custom expander plug to the required dimensions. When belling, adjust the die so the mouth is expanded just enough for the base of the bullet to be inserted, no more. The idea of belling is to avoid shaving/deforming lead upon seating

My understanding is that the expander plugs provided by the manufacturers is basically a generic design intended for jacketed bullets. Cast bullets have to be treated differently. My advice is based on shooting a lot of BP cartridge rifles & info gleaned from BPC competition shooters. Take it for what you think it's worth. Bear in Fairbanks

Well, Hubel has it right for the most part. If you have the "snake-what-swallered-an-egg" look, your cases are being sized down too much in the first place, relative to your chamber and certainly your bullet size. A lot of .45-70 dies are made that way and others, too, so as to provide a death grip on jacketed bullets. Lead bullets seldom need this much grip, and this much grip can also deform the bullets and destroy accuracy.

I would buy the .45-70 sizer die that Redding makes, because it only sizes down the bullet holding portion to a large degree. That might even be too much for your situation. If so, I would call CH-4D and explain the problem and see if they would make you a custom die for a reasonable price. In any event, you only need 0.003" of grip on the bullet, so call CH-4D, or Dave Gullo at Buffalo Arms (Idaho, www.bullafloarms.com)==he is an old cartridge specialist), or Redding, or RCBS which sometimes has expander choices, for a custom inside expander of the correct diameter. The less you size your brass, the better off you are, in many ways.

Measure the throat of your rifle. Your bullet needs to match the diameter of the throat of your rifle, not necessarily the diameter of the grooves. Have that information before you talk to people and before you order bullets. Undersize bullets destroy accuracy. Remember, it is the throat diameter that you want. Being over-groove diameter is of no consequence here.

Thanks for all the help. It sounds like I at least need to get a different expander plug, maybe just an entirely new set of dies. I only paid $5 for the dies anyways, so I'm not really out anything. Thans again for all your help.
Andrew