I bought a Mossberg ATR Youth model in 308 Winchester. This rifle will be used for hunting, so all the work involved in load development will be aimed at that goal.
The bullet I’m starting with is the Lyman 311467.
I have several 30 caliber molds to choose from, but I chose this one for a few reasons. At 188 grains after the gas check and lube, it should stop anything I’ll be shooting at around here. Assuming, that is, I do my job.
This bullet is a Loverin design. With the multiple bands and grooves, it should do well with Black Magic, the lube I’ll be using.
The profile of the driving bands is tapered. The front band drops at .300″ and the rear band drops at .314″. The length of the bearing surface is .750″. This enables the bullet to be seated such that the forward bands engage the riflings on chambering. This should help with axis alignment and accuracy.
The gas checks are .016″ aluminum and they fit the shank tight. They’re sized on by running the bullets through a Lee .309 sizer die that has been opened to .310″. I’ve tried to pry off a couple and had to ruin the bullet and the check to do so.
Because of the case capacity and the bullet weight, I’ve chosen IMR 7383 powder to start with.
No one can say for sure what results they might get with any caliber/bullet/powder combination being tried for the first time, but I’m confidant I can make it work.
I’ve been burning 7383 for 12 years. I’ve used it in 223, 243, 308, 30-06, 303 and 8MM, all bottleneck calibers. Like others that have experimented with this weird powder, I’ve learned it has a propensity to create pressure spikes as the charge density approaches 100%.
When I established the COL with the 311467, I set out to establish 100% charge density. I seated a bullet in an empty, unprimed case. I then drilled out the primer pocket with a 15/64″ bit. I filled the case by trickling the powder through the drilled out primer pocket until the powder level was up to the inside if the case web.
I poured the powder into my scale pan and found the charge to be 40 grains. This is the 100% charge density. Knowing that the best density to start with using 7383 is 95%, I calculated that and came up with a starting charge of 38 grains.
The next step in this parade is to find the top of the pressure window. I loaded one round with 38 grains, took it outside and fired it. No pressure signs at all. I loaded one at 39 grains and repeated. No pressure signs. I repeated this process until I finally got to 40 grains.
I was very surprised to find still no pressure signs at 100% charge density. In all the load development I’ve done with 7383, I’ve found the pressure starts to spike at 97 to 98% charge density.
I took some time to think this through and can only come to one conclusion. The only variable that is new in this is the Black Magic lube. I cannot say, absolutely, this is the reason I was able to go to 100% charge density with this load, but I cannot think of any other variable that would create such results. In all other testing I’ve done with 7383, I’ve never used Black Magic. And in all other testing, I’ve found the pressure starts to spike at the values I mentioned.
I have put together the first batch of test ammunition. I loaded three rounds each of 39.6 grains to 40.0 grains in .1 grain increments.
As soon as I get a decent day with a few hours of reasonable temperatures, I’ll shoot this ammo and report my findings. Be patient, I’m workin’ on it.