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220grn MK’s louder then 180grn SST’s.
I loaded up some rounds using 11.2grns of 1680 with 220grn MK’s and 180grn SST’s. I seated the 220 MK’s to 2.089 OAL, which I read is the recommended OAL listed for the 300 Blk sub rounds. I then took the ogive length and used that to seat the 180’s.
Both ran fine in my 8.5” AR with adjustable gas block and Gemtech Sandstorm, but the 220’s were a lot louder then the 180’s. With the 180’s the bolt was the dominant noise and with the 220’s it sounded like they were close to being supersonic. I tried them at night and during the day so the temp ranged between low 60’s – mid 70’s. I also tried all three settings on the gas block and it didn’t make much of a difference on the 220’s.
When I pulled the 220’s that I had left over I noticed that the powder was packed solid in the case with an indention of the bullet in the middle. I had to use a wooden dowel to break up the powder before it would all dump from the case. I’m not sure if dropping a few .1’s of a grain would help make room in the case to prevent the powder from being packed when seating the 220’s. I know I can make the AOL longer to make room in the case, but wasn’t sure where to start so I went with the 300 Blk OAL.
Any recommendations?
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