Ok here's one quick set of data using the spring. I did NOT weigh powder charges here, I just ran about 20 rounds through, checked multiple times that the weight was 4.8 gr of BE86, and then loaded 20. I will say that each of the few I had measured before I ran this 20 was within half a grain of 4.8, so the scale range was like 4.75-4.85. (I have that high precision scale from UniqueTek).
BE86 using a 124 gr plated round nose from Berrys, all in fps. All new starline brass with WIN SPP. 1.115"
I ran the Mark 7 at 2100 per hour, with bottom dwell of 1, index speed no reduction. I use the little rubber discs on the locator pins to reduce wobble, so there is no spillage influencing these figures, and I cleaned and watched each round. This is WITH a return spring on the powder bar.
I did NOT weigh all these drops, however. I just loaded and chrono'd with my LabRadar.
16 shots
max 1079
min 1015
ES 64
Average 1048
SD 20
Concordant with Wobbly's comments about the value of the spring, I have long noticed that if the system sits still for awhile (meaning more than a few minutes) the next charge is often higher than it is during continuous run. I assumed it was because powder was settling in the bar from the hopper, and that was the reason the return spring helps, but maximally settling things so it can't settle (fill the powder bar) any more?
Still not impressed with this SD and ES.
C
PS here's the individual shot data. V0 is muzzle, V10 is 10 feet, using the LabRadar indoor range, about 70 degrees, dry, no wind.
V0 V10
1022 1015
1059 1051
1063 1054
1067 1057
1082 1072
1081 1070
1072 1062
1087 1076
1050 1040
1089 1079
1045 1035
1047 1040
1050 1041
1036 1028
1038 1029
1027 1020