Just bought a 28-30 Stevens. Breech seating the bullet - how to load with black powder without causing a pressure bulge Ine the chamber throat?

Card wads?

Thanks John.

That was going to be my next question.

Thanks

droptube the case full of powder such that the wad is level with the top of the neck.
ldpe or card wads are the best because with the airgap you lose some bumpup, and a harder wad will maximize this.
start shooting groups with the bullet base touching the wad, and incrementally  breech seat further until groups tighten.
38/55 will often shoot best at about 1/16 airgap, and 40 and 45 cal about 1/8".
there are no hard and fast rules about airgaps, you have to find what works in your gun and calibre, but it will be obvious when you find it.
good on you for having a go.
keep safe,
bruce.

Congratulations on your purchase it should provide you several years of enjoyment.

JLouis

George
There has been good info offered on this thread.
Here are some other ideas you might consider.
- Instead of leaving a 1/16th inch (approximate) void between case mouth and bullet base, try filling that void with a 1/16th inch felt wad. It seems to reduce the number of flyers in my groups (your results may vary).
- Swiss is good powder but also consider Olde Eynsford 1.5. It burns a little cleaner than Swiss plus delivers a bit more energy.
- Consider a duplex load. For your 28-30, about 3.0 grains of IMR 4227 with the remainder of the case full of either Swiss 1.5 or Olde Eynsford should produce good accuracy and burn cleaner than straight black (important given that small 28 cal hole through your barrel).
- Use a drop tube to load black powder in cartridge case and a try a primer pocket wad of newspaper.
- Whether straight black or duplex, fill the cartridge case to the mouth and press an over powder wad in the case until flush with mouth. This will give some powder compression. Try card wads of about .060 and .030 to see which gives best accuracy.
- Another presented the importance of fouling mitigation, heed that advice.
The included illustration might make it easier to understand my description.
If your rifle is on a Stevens 44 action, you probably should not use duplex loads.

a good post by randy.
the only comment I would make is that you need to be very careful of case necks and compression dies.
a possible way to avoid this issue would be to droptube to a level 0.030 below the case mouth, compress 0.030 without a wad, leaving a 0.060 void, into which a 0.060 wad can then be placed.
the suggestion of a wad under the primer is an excellent one.
another paper well suited to this is computer printer paper.
pistol primers are often worth trying, federal being the best for me for some reason or other.
getting a load by breech seating is a bit of effort, but the rewards are well worth it in terms of interest and satisfaction.
I would say good luck, but it is not about luck, rather doing the yards. the journey is what it is all about.
keep safe, 
bruce.

LES38
Theories differ but in essence, it prevents small kernels of powder from getting through the flash hole and resting against the primer. This might happen on some cartridges but not others and could cause inconsistent powder ignition.
Others claim it slightly lessens primer brisance (flash intensity) as most of today's primers give more flash than is needed to ignite black powder. 
Illustration shows how to seat primer pocket wad.