Lee 309-230-5r 300 blackout stability

[nhyrum]

Took my blackout pistol to the range today to Chrono my subsonic load with the Lee 230. Shooting from 7 to 10 yards out of an 8.5 inch 1:8 twist barrel at a cardboard uspsa torso style target, I noticed about 5 out of 30 shots the cardboard was torn, indicating the bullets not fully stabilized. A ran the numbers in the jbm calculator say they should be stable at around 2.6 with today's conditions. The muzzle velocity is just about spot on 1000 fps. I used a MV of 950 in the calculator

These I do plan on running suppressed, so really don't want to risk baffle strikes. The way the cardboard was torn it was hard to tell if they were in fact not fully stable or just the way the cardboard tore from being hit.

How should I proceed? Shoot at unbacked printer paper?

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[358429]

Shoot at paper plates stapled to fresh cardboard.

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[badwolf]

Shoot farther

[GhostHawk]

If it is in doubt at 10 yards try 5 rounds at 20.

I suspect you will see shotgun pattern and keyholing.

Now I don't know about AR's, but every gun I ever had keyhole, it went away with a larger bullet.

To the point that I shoot as cast .38 special bullets in all my 9mm's.
.3575 to .3595. Key holing was gone like a bad dream and groups were tight.

[GregLaROCHE]

I cast some 320s for a friend who was trying to get an M1A1 to shoot subsonic. Before he could get down to subsonic, the Boolits started to tumble. I think rifle twist has a lot to do with stabilizing those boolits at lower speeds. That’s a rabbit hole I didn’t choose to go down. They did preform well loaded in 30.06 at higher velocities for me.

[Multra]

Machine out the boat tail with a 7.9mm reamer.

[jcren]

Before you take out the boat tail, might try crimping gas checks on them (yes, a 30 cal check will crimp firmly on the boattail) and size them a bit bigger.