06-10-2023, 12:33 PM
Hook Wrote:I have been loading for and shooting a Grendel upper for about a year. It has been a blast, but not without difficulties. When I first started, brass was unobtanium, so I reformed a batch of small primer 7.62X39 I had set aside and used it. It averaged about 15-20 grains heavier than the 4 pieces of Grendel brass I'd found, so I reduced the powder charge accordingly. Eventually I bought some Starline Grendel brass but am still shooting the reformed brass.
Got to thinking the other day about the overabundance of LR primer 7.62X39 brass I have available and wondered if it would perform as well as the SR primed brass. If it did, I could hoard the Starline brass I have for 'important' stuff and use the reformed for fun. My basic frugal nature would be tickled not to have to buy more expensive Grendel stuff. I just didn't know what the difference would be using the LR primers.
To try to get an idea, I loaded a stiff load using Starline brass and another load with 2 grains less using SR primer reformed brass. The velocities averaged within about 25 fps of each other. Then I tried the same reduced load in the LR primer reformed brass (BTW, it weighed the same as the SR primed reformed brass). It averaged almost 100 fps SLOWER. I was worried the LR primer would jack up pressures and I'd have to drop the powder charge more but then this happened....
Now, I only tested 3 of each of these loads but assume they are representative. How in the world can large primers produce less velocity than small primers? Am I missing something?
Hook.
Having loaded a bunch of 7.62 X 39 stuff when the only place making Grendel brass was Lapua and none of it was in the USA, all I can say is -- I don't know why.
I do know that with the same charge as real Grendel brass, the 7.62 X 39 normally got higher velocities but I could tell the pressure spike was severe. Also, the large primer pockets opened up in two or three shots. This is pretty much the result of the 7.62 X 39 brass being thicker so there was less powder space which no doubt spiked the pressures.
There is enough real Grendel brass about today that forming 7.62 X 39 is pretty much a waste of time. You get lower velocities and shorter brass life. Probably OK for throw away stuff but otherwise not as efficient as real Grendel brass. If I wanted some throw away brass I would buy some once fired, shoot it to make sure it functioned in my rifle, then load it up and keep it for those times when losing brass is expected.
LR-55