Take the barrels out of the stock. On the underside, there will be an indication whether each barrel is choked. It may be in letters, or in numbers, and probably in millimeters, if its in numbers.YOu will have to use conversion tables to figure out how much choke those numbers represent.
To be sure about any gun, ALWAYS measure the bores with calipers. Get the EXACT bore diameter to the thousandth of an inch.
Yes, you can shoot Round balls out of that 10 gauge, but the question is normally, will the two barrels shoot balls to the same Point of Impact(POI)? The answer to that question is usually NO, since the guns were made for shooting shot, and not round balls.
What size Ball? Well a 10 gauge is NOMINALLY.775" in caliber. However, don't be surprised if your gun is different. And if it has choke in the barrels, that will affect the ball choice further, depending on how much choke is in each barrel.
General rule with smoothbores is to find a ball size that is at last .010" smaller in diameter than the most narrow portion of the bore( choke), but some people find that using an even smaller ball -- as much as .020" smaller-- works better in the larger smoothbores. They use thick patches, often denim that measures .022"-.26" in thickness to surround the balls.
Powder charges. Start low and work up by 5 grain increments. I recommend beginning at 75 grains( 2 3/4 drams) and work up from there. Shoot just one barrel at a time. Only when you find a load that shoots well with one barrel should you then begin working on the other barrel.
With Single Barrel 10 gauge guns, powder charges using FFg powder in the range of 80-90 grains are the norm. You MAY find that using less powder in that double will give you better groups, or it may do as well with those loads. I hear of people using more than 100 grains of powder in heavy built single barrel 10 gauge guns, but the recoil becomes brutal, and I don't recommend them for hunting deer. Its just not necessary, given the range limitations and the thin skin and light bones of the animal. The heavy powder charges also near, or cross that sound barrier, where all kinds of bad things happen to move a ball around in the air. so that accuracy suffers.
Remember that you are going to lose 25% of the MV at 50 yards, shooting a RB, and at 100 yds, you will have lost 45% of the MV. Put that heavy ball into the heart/lung area of a deer and you have a dead deer. More Velocity is not the key to hunting success.
You may find that one barrel shoots RBs better than the other, and that your DB shotgun is better used with only the one barrel loaded for deer. Of course, you can load the second barrel for a coup d grace shot if you put a deer down, but it is still moving when you get to it. At that close range, you are not likely to miss, no matter how badly the second barrel groups at 50 yards. Don't be surprised to find that each barrel likes a different powder/patch/ball combination for best accuracy. If you can find loads for both barrels that shoot to the same POA, that is fantastic luck!
You can buy 10 gauge OS cards from Circle Fly, but your gun may require even larger diameter cards, if the bore is oversized. The Advantage of using OS card is that they are thin enough to be able to bend slightly to push through the choke at the muzzle sideways, then turn them in the barrel to seal the bore. You can use 4 of them between the powder and the PRB to seal the gases, and use 2 OS cards on top of the PRB to keep the balls in place when the other barrel is fired. One OS card normally is not going to provide enough friction to keep the ball from pushing it forward, in recoil from the first barrel, but 2 cards do provide that stability.
Use an awl to poke an off center hole in the OS cards. Put them in the barrel so that the holes don't align with each other. 12, 3, 6, % 9 o'clock positions for the first 4 cards over the powder; 12 & 6 o'clock positions for the 2 OS cards on top of the PRB. The holes let you load the wads into the gun without turning the edges and losing the gas seal you want. Without the holes, air is caught under the card, and you get a " dieseling " effect, with the air pushing the card back towards the muzzle as you try to push it down. The holes also allow air to go through the cards and separate them as soon as they leave the muzzle, so they drop out of the line of travel of the PRB.
With such a heavy RB, I don't think you have much to worry about the OS cards bumping the RB enough to make if veer off POA, but I am just now working with this same issue with a 20 gauge fowler, and am hoping over time to find out just how well the OS cards work, and if I see an improvement in group size.
I also find that running a greased cleaning patch down the barrel after those OS cards are seated helps to increase the velocity of the ball, while reducing the SDV more.
Don't be looking for a lot of velocity. This is still a 50-65 yard gun for deer, even with the huge ball that is going to drop any deer at that range. The problem is hitting the deer, with the poor sights, and the " knuckle ball " flight path of that Round ball. You will find that keeping the velocity at the muzzle under the speed of sound( sound barrier= 1100fps. nominally) will help you get better groups.
Just because it throwing a huge ball that will kill at over 200 yards if it hits something does not make your shotgun a 200 yard gun. Its a 50 yard gun, and if truth would be told, probably more likely a 35 yard and under gun. Lots of deer are killed with shotguns shooting round balls or slugs, from zero to 50 yards, every year.
When I checked Deer back in 1968-69, Most of the hunters were shooting their bird guns with no rear sights. The extensive interviews I was required to do of the hunters then- we don't even have check stations anymore--- indicated that most of the deer were killed at under 25 yards! in very thick ravines and wooded areas. Rear sights on shotguns was a novel idea. I only had One hunter out of 200 who had mounted a scope on his gun. Times have changed, but the guns haven't.
THANKS to everone for your replies,this will help me get it rite and safe at the same time
