Hot water coil loop through boiler

I have mounted my stainless stel hot water coil horizontally about 1'-0" above the grate in my leisure line pioneer.
I black piped with 3/4" down to my boiler about 12'-0" away and am trying to temper my boiler water. The boiler is a 4 section weilmclain cast iron boiler. Al zones are off and valves off, and I have a recirculation pump running 24 7 from the coal stove to the boiler, I would assume total volume of 12 to 15 gallons. Temp on the coal stove loop doesn't get past 180 degrees. Boiler reads 160 degrees. I am surprised the loop is not getting hotter. 2.5 lnf of coil in the stove. I can even keep the water in the boiler at 180 degrees when the stove is at full bore. 95,000 btu stove should be able to keep the water in the boiler hot. Also the contact time does not matter. And restricting the flow. Any body have Any ideas.

Remember the burner is capable of 90,000 btuh input, the stove is generally 86% efficient or so with respect to output for hot air, which it is designed for, that provides a net output of 77,400 btuh. With your coil only getting part of that I would estimate the net to the coil is around 45,000 btuh at peak burn.
One idea is that you need the coil closer to the grate, also you didn't mention where it crosses the grate, is it in the sweet spot where it gets flames all the time?
One more idea, when trying to heat a boiler with a coal stove that is regulating output based on air temperature and has no idea what the boiler needs I would expect that the boiler would fire a fair amount of the time.
Not sure if I have been helpful but best wishes for a successful science project.

I would calculate the surface area of the pipe inside the stove and the the surface area of the combustion chamber. The heat radiating from the fire to the pipe and stove is not going to go to the water only because it is cooler than the sides of the stove. Boilers suround the fire with water backed metal. Also your fire comes on and off based on room temperature, not water temp.

The combined linear footage of my coils is either 9' or 12' - can't remember ... but even with that, I have just enough heat on a cold day to maintain 70° in a 13' x 13' TV room with cathedral ceilings, and crap windows. If the indirect boiler sees a DHW demand, the oil burner will kick on. When it's above 30°, then there's a little extra heat left to handle some DHW. In the 40° range, boiler water gets up over 220° if the fire is cranking good. I've seen it over 260° several times - that works wonders for DHW!

Bottom line is, there just isn't enough surface area in a coil to act like anything close to a boiler.

Thanks that helps