220 Grain Subsonic casting for 300BLK

[Danimal45]

I searched around the web a little and could not find any info. I am looking at making some subsonic .30 caliber boolits for use in an AR-15 chambered in 300BLK. I want to push them as close as I can get to 1000 fps.

I am not dead set on 220 grain, that is just the industry standard that will cycle the bolt reliably, but I will use the best molds for this type of application even if they are 200 grain or close to it.

I am fairly new to casting and have only cast for pistols so I am going to need the full rundown on the differences, including alloy, what molds to use, gaschecks, the whole nine yards. For this application there is a lot that I need to look into because once I get the load worked up, I am going to put the suppressor back on and have some silent fun.

[bld451]

Don't know if you've checked out the active group buys section, but there is a 247 gr. whisper-specific mold by NOE that is almost closed now. If you get in, it will be a fast turnaround. He's notified the group that payment is due, so time is short if there's any left, but it's a very popular design. Check it out. Get the mold, then you can work out the casting details.

http://castboolits.gunloads.com/showthread.php?t=133407

[Tonto]

The NOE mould is terrific but you will be modifying your magazines to feed it semi-auto in an AR. Not a giant chore but a factor. 1680 powder is the one to try for load development. Sierra has load data for jacketed bullets that provides great guidance for cast loads for the 300 whisper. Be nice to see a cast design that gets the subsonic out of heavies that doesn't require super deep seating or mag mods. The new LEE design gets closer but not quite. Regardless, this is a round you can shoot almost for nothing once you are in gear and it is wonderful. Enjoy......

[Danimal45]

Thanks for the tip, I think that I will jump on that.