Bullets tumbling when larger sized.

[wv109323]

I am in pursuit of a load for USPSA in a CZ 75B Omega. The bore slugs to .3562 and is a 1:10 twist. The pistol was shot in a Ransom Rest at 20 yards.
Everything is the same except the bullet size in the two loads. The brass was miscellaneous. The powder was 4.4 g. of Bullseye by a Dillon 550 powder measure. Primers were Winchester small pistol. Bullet was a my cast from a Lee 6 cavity 120 TC. They were powder coated by the shake and bake method using Smoke's black pc. The diameter was .358 to .361 after powder coated. I crushed one in a vise and the powder coat did not break down. The first 10 rounds were sized to .3570 thru a Star machine. The next 10 rounds were sized to .3582.
The .3570 rounds grouped something like 4" in a slightly horizontal group of 10 rounds. Nothing to get excited about.
The .3582 bullets had 7 rounds in a 6" group. There were 3 flyers that keyholed some 12-15" from the group center.
So the boolits that were .0008 oversized were stable but the boolits that were .0019" larger keyholed and in a larger group.
What causes a slightly larger bullet to tumble?
I shot other groups with different powders ( blue dot and AA no.7)where the .3582" boolits group better or equal to the .3570 but with BE they tumbled. Explain

[alfadan]

I think the random cases may play into this. Some are thicker than others.

[Dusty Bannister]

Both the Lyman Cast Bullet Handbook and the RCBS cast bullet manual suggest the max charge is lower than what you are using with this bullet in 9MM. Perhaps the larger bullet is providing a better seal and the pressure is distorting the base of the bullet at exit and the groups open up. A recovered bullet might be helpful in determining if the bullet is damaged. Are the other powders used also in excess of recommended charges. Blue Dot and AA #7 are both slower powders so perhaps less pressure is a factor.

[jsizemore]

What's the dimension of a pulled bullet?

[243winxb]

diameter was .358 to .361 after powder coated. .003" difference? Very poor quality control, is my guess.

If the coating is left extra thick, are the lands cutting into lead or plastic coat? If the lands dont get a good grip on the lead, may the bullets skid as they leave the muzzle?

[chutesnreloads]

Is your barrel throated? My experience is CZ + factory barrel + cast bullets = poor results
Sure shoots great with j-words

[garandsrus]

Your barrel might be leaded

[358429]

Use fc brass, 5.1 power pistol, 1.095 oal. Mp 359-125 mold. For my cz p09 it's my pet load. Too bad I am out of power pistol!https://uploads.tapatalk-cdn.com/20210904/18afc42b351ac867370f8b676f68e5dc.jpghttps://uploads.tapatalk-cdn.com/20210904/0401ecd64146046059beac11d0abd0ab.jpghttps://uploads.tapatalk-cdn.com/20210904/b490f20476f9c1ac79070da1ab488639.jpg

Sent from my SM-G930T using Tapatalk

[robg]

might be worth trying a slower powder like unique to slow the pressure peak so less chance of boolit base damage

[wv109323]

The boolits are not being sized down when seated. I have a special powder funnel that neck sizes for cast. Pulled boolits are still as sized .3570 and .3582.
I shot some groups with 5 rounds of same headstamp(BHA) and 5 rounds misc. brass. This was with a 147 g. Bayou coated bullet. One group showed a slightly smaller group with same headstamp but two others were the same size using same brass headstamp versus misc. Powders were Blue Dot and AA7. I loaded five misc. Brass and fired them. I marked the bullet holes and then fired 5 same headstamp.
Loads may well be hotter than Lyman and Lee for a cast boolit. These were powder coated so I thought I could run them faster. I has trying to make the required power factor of 230 for USPSA. That requires a velocity of 1083 fps for a 120 g. boolit.
All loads were aimed to make the PF, so 147 were around 880 fps.
Loads with same 120g.at the same velocity with WST, AA7 and W231 did not tumble. Just the loads with BE Powder and .3582 boolits tumbled. Same loads with .3570 bullets did not tumble.
Difference of .0012" larger diameter caused the tumbling. I can' t get a grip on why. Fast powder may be to blame but the extra pressure of shoving a .0012 larger bullet caused the problem?

[wv109323]

Misprint in previous post. PF is suppose to be 130 not 230.

[wv109323]

The barrel is throated to accept larger longer rounds. Groups fired after the BE groups were normal and did not tumble so I can not assume barrel was leaded. All boolits were coated so less likely to lead barrel.

[charlie b]

Bullseye is just not the right powder for higher power loads like that, IMHO. I would stick with the AA7 and Blue Dot. I like both for heavier pistol loads in a several cartridges, including the 9mm.

Don't know what is happening to make them keyhole.

[popper]

BE too fast, get base damage. Larger dia. bullets keep pressure spiky before the bullet moves down the barrel.