To get past that" Whoosh-bang" delay, use your vent pick in the TH to open a hole in the main charge. Then, Don't BANK the priming powder AGAINST that TH. Any blocking of the TH will delay the ignition in the barrel.
As to raising point of impact, first increase that powder charge by 5 grain increments to see if the POI raises. And, go back to 50 yds, now that you see you have no windage problems.
Use a "sighter" pasted to the top of the bullseye, so that the balls will stay on the paper, since you know that your shots are hitting low.
When you establish a " Most accurate load," Then, and only then, do you consider filing down the front sight to raise the POI.
You will also need to try different ball diameters, and patch thicknesses to see if that won't raise the POI. For instance, my first shots with my then new Fowler, a .62 caliber gun, involved using 75 grains of FFg Goex, and a .600" diameter lead ball wrapped in a denim patch that measured approx. .017" thick. The balls all hit low- very low, at 25 yds. We ran a couple of shots over a chronograph and found that velocity was only in the 800+ MV range- way too load for that powder charge and ball. So, we got out the calipers and measured the bore, finding its bore diameter was NOT .615", but instead, .626-27" ! :shocked2: The barrel actually was not a 20 gauge barrel, but closer to a 19 gauge barrel(.629" nominally) So, I have acquired some .610 balls to try, and much thicker mattress ticking for patches. Since my RB shooting with that gun is minimal- I already have a deer rifle---- I have been concentrating on working up shot loads for the gun. I will now be working on a good RB load- and if the larger ball diameter works better, I will consider ordering a mold in that diameter.
Only when I settle on my RB load in that gun, based on all the testing- changing to 19 gauge OP wads increased the velocity of that same 75 grains of FFg Goex by an increase of almost 250 fps, and Raised that POI by 6 inches, simply because of the better seal I got with that OP wad behind the PRB------ Will I begin to file down the front sight to "zero" those sights to that load.
Oh, BTW, I have long been in the habit of using a "6 O'clock" hold with my iron sighted guns, so I want my ball to be hitting above the POA. That means I file my front sights SHORTER to get the POI higher on target, than other shooters who use a "center-hold", when aiming their iron sights at targets.
By using a 6 O'clock hold at, say a 50 yd. zero, I can still shoot at game out at 60,70, and even 80 yards and be pretty confident that the ball will hit at or above my aiming point. That is about as far as I want to shoot at deer sized game with a smooth bore shooting RBs. By using that "lower" hold, I can see any movement of the animal as I am taking up slack on my trigger, and applying pressure to release the sear to fire the gun.
My shooting began with handguns, and I became used to using the 6 O'clock hold from hours of shooting handguns with iron sights. Others have only shot guns zeroed to allow "center -holds". Use what is comfortable for you. :surrender: