300 BLK subsonic mould for PC

Ian

Ian

Notorious member
Ok, range report is in. A few key points:
  1. 7" rate of twist will stabilize these at 100 yards, but barely.
  2. A ding on the nose makes them wobble and fall out of the group.
  3. The bullet is quite accurate when the stars align.
  4. The bullet nose is not going to feed on an AR-15, even through Lancer 300 BLK mags. Had to single feed these after the first one made a banana out of the second one.
  5. [Edit] I can't count. That's 2-8, then 9, then 10. I loaded 11 and one was crushed when the bolt went over the rim.
20201029_171124.jpg

Cold dirty bore shot went high, then 8 into 7/8" between swirling wind gusts, no idea why #10 yawed and dropped, #11 I dropped on the ground and it hit a rock, mangling the nose (soft wheelweight alloy) so it has good reason to yaw and miss the group, I thought it interesting how much it mattered.
 
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Spindrift

Spindrift

Well-Known Member
Interesting report, Ian!
You can actually see how hole #11 is less round than the others. The accuracy potential seems to be excellent. But it seems to be a very volatile/sensitive system with (as you said) borderline stability.

Where these checkless PC? If so, I would try to add a GC. This would slightly increase drag, which might «calm down» the bullet and make the groups less sensitive to minimal inconsistencies. Just a thought. Thanks for the report!
 
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Will

Will

Well-Known Member
Definitely looks like the 1st and 11th shots the bullet yawed some. Hard to tell for sure but the pic appears that way. I would think that 1-7” twist would stabilize that bullet though.
 
Ian

Ian

Notorious member
One in the upper left of the group also yawed. I agree a gas check would both add base weight and move the CP forward and would help stability, but I don't want to do that. The shank was to improve BC slightly and offer the option of a check if wanted for pushing the bullet much faster.

Now that I'm convinced the bullet is marginally stable in flight, (plus it won't feed), I'm proceeding with the redesign which will lose some weight, thin the nose, and shorten it about .085". I really like how clean the base band is after coating and shooting, so I think I'll leave the check shank alone. Flat base bullets get dinged too easily when coating via shake/bake and BB bullets are easily made "unsquare" by the slightest error in mould handle pressure.
 
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