I recently bought a couple of pounds of Vectan from Grafs to try out in a pistol. After some research I bought a bottle of GM3 and one of A1. The GM3 was first up.
Its burn rate on the chart is right next to Unique so after going to several forums overseas and reading posts from guys that have used it I surmised that a starting load of 3.0gr in a 38sp under a 358140 would be well within safety bounds and was, in fact, under the min suggested loading for GM3 using this round. I did have to extrapolate a little between a 158gr and a 125gr Lead Boolit to get there.
First off, about GM3.
Attachment 136054
It is described as a single based granulated powder. It is composed of random sized grains and is grey in color. It has an odd smell, in fact it was odd enough that I poured some out to make sure it was alright and it looked fine so I decided to begin testing with it.
I used my trusty 50th Anniversary 357 Mag Blackhawk as I always do when I start testing unknown powder as it is strong enough to take about anything on an initial loading. I used 6rds of 3 starting loads 3.0gr, 3.2gr and 3.4gr checking for pressure signs and leading. The day is 70 and sunny.
First load:
3.0gr GM3
358140 SWC
38 sp Brass
Fiocchi SPP
60/40 lube
Unsized but dropped .359 and 141-142gr average with BHN 10-10.5. The rounds were all in the black at 10 paces and showed no signs of pressure. Recoil was light as expected from the BH. Very little leading and a clean barrel. With these results showing the pressure was fine I decided to trade the BH for a SW 14-4 I just acquired and had not fired yet.
Attachment 136042
Next was 3.2gr GM3 in the SW 14-4:
Attachment 136049
Still little recoil but the hits were spread a little. Still a small amount of leading at the start of the rifling but the barrel was clean indicating the Bens 60/40 was doing its job.
Next was 3.4gr GM3
Attachment 136043
Hard to believe but from 10 paces that center hole was 3 rounds. I'm not that good but this pistol appears to be. Still little leading, the barrel was crystal clean and no signs of pressure. The recoil was easy to manage and I would have no problem shooting 100rds without cleaning the gun with this load.
The brass looked like it was unfired:
Attachment 136044
GM3 appears to be a big winner. I don't have a chrony yet it seemed to me that it was a mid range load. The felt recoil did not vary that I could tell but that is subjective. The full sized grip on this pistol kept it very manageable.
Nice recoil, no signs of pressure, very clean. What's not to like?