Yes, it felt a little hotter. As for the A6-4, one of them seemed to have more punch and noise and the other seemed weaker. It is also very interesting to hear that two C6's can give such different results. I know there is a range of total impulse, but I figured two motors with the same thrust would basically give very similar flights.
Not necessarily-- it depends on the thrust-time curve...
Equal amounts of identical propellant should give identical amounts of TOTAL IMPULSE, BUT, changing the DURATION of the burn will give radically different performance parameters--
Say you have two motors burning identical propellant loads, and both producing say 20 newton/seconds of total impulse (total impulse is basically force (thrust in newtons) times duration (seconds of burn time)-- it's a bit more complicated than that because burn force (thrust) varies due to motor grain design (propellant dimple/core shape/depth) and propellant characteristics (how fast it burns, specific impulse of the propellant, etc). Say one of the motors burns all the propellant in 1 second and the other motor has a duration of 2 seconds... the motor with a 1 second duration will produce TWICE the thrust of the 2 second duration motor, but for only HALF THE TIME. BOTH have "identical" total impulses, but they will produce DRAMATICALLY different flights in the same rocket... The 1 second duration motor will lift off VERY fast and just be a blur-- it will build up speed VERY quickly (and drag along with it, since drag squares with the increasing speed) which might cause the rocket to shred if it's poorly constructed). This will cause it to probably reach a lower altitude as well, as more of the energy from the motor is wasted as air drag. The 2 second duration motor will produce a much more gradual liftoff, building speed more slowly but building it up over a longer period of time, and experience much less gee force and drag than the faster burning motor... it should coast longer and farther, therefore usually will get to a higher altitude...
Now say you take the same two motors and put them in a heavier rocket-- say a payloader... the 1 second duration motor will "kick it in the pants" and get it up and moving more quickly, gaining flying speed much more quickly and coming off the launch rod straight and stable-- the additional weight will slow the flight down, so it won't just 'disappear' off the pad like the 1 second motor did with the lightweight streamlined rocket... the 2 second duration motor, with its lower thrust over a longer time period, will lift off SLOWLY and the rocket will sort of 'lumber' into the air... it won't be moving very fast when it leaves the launch rod, and might be prone to rod tip-off and if the breeze is blowing fairly good, will be VERY susceptible to severe weathercocking-- it'll be flying at a much greater angle into the wind, so will not get anywhere near as high, since it's flying much more uprange due to the weathercocking-- in short, the heavy rocket with the long-burn motor will probably not perform very well and may crash, even though it has IDENTICAL total impulse!
Make sense?? This is kind of a simplified explanation-- it's a bit more complex than this, but it's important to understand the effects of thrust duration (burn time of the motor) versus the thrust force in newtons, and where that fits with total impulse of the motor (its letter class). Changes in the motor design (core burners versus end burners, depth and size of the core "dimple", nozzle size, motor operating pressure, propellant grain length/diameter ratio, propellant chemical formulation and specific impulse, etc) all play significant roles in the shape of the thrust-time curve and can radically change the performance of the motor compared to a different motor in the same impulse class (motor letter classification). Additionally, just because a motor is a "B" or a "C" or a "D" DOES NOT mean that it will have identical total impulse with a different motor by another manufacturer in the same impulse class-- the impulse classes are a RANGE and some motors are usually at the high end of the range (usually called a "full B,C,D,etc" motor) while others are just somewhere in the middle or even at the low end of that range, which will make them perform more like the next smaller letter-size motor or seem much 'weaker' compared to "full size" motors in the same letter class-- for instance, the Estes D-12, IIRC (going from memory so forgive if I'm misremembering) only has 17 newton/seconds out of a maximum of 20 for the D size range-- so the Estes D motor is not a "full D" motor and would look rather "wimpy" next to a BP motor with a full 20 N-S of total impulse... (when you throw in the lower propellant weight due to greater ISP, and therefore lower motor weight of an APCP 20 N-S "D" motor the effect is even MORE pronounced!) But say you stick a D12 into a big heavy rocket and fly it-- it scoots off the pad, really gets up there, and deploys its chute... then stick an E9 (which theoretically has up to TWICE the total impulse of a "D" motor!) into the same rocket-- it will take off very SLOWLY and wallow around in the sky, arc over, and may well hit the ground before deploying its chute... all because of the lower initial thrust force at liftoff, despite the longer burn time of the E9 and the fact that the E9 has higher total impulse! Stick a Quest D5 motor in the rocket-- again, slow liftoff and a lumbering, wallowing flight, and probably a prang before the chute comes out...
Hope this helps! OL JR