Too hot, it tumbles?

[redruns]

Working on a new load and the accuracy is terrible and even a couple of elongated holes in the paper from tumbling bullets. I'm trying to track down the cause so I can start to work in the right direction to solve this issue.

Bullet is cast from Lee mold 124 grain truncated cone tumble lube design (TL 356-124-TC).

Slugged bore and it reads .354. Sized bullets to .356. Wheel weight lead.

Cartridge overall length 1.065 +/- .005

High load of 4.5 gn w-231. I had good results with this charge with 125gn lead round nose. No pressure signs.

Will the hot load contribute to the keyholeing I saw tonight? Or is this just a bad bullet design and I'm stuck with 1800 pieces of remelt?

 

[DMT]

Depending on design, bullets can become unstable and then tumble as they go through the sonic barrier. Check if your velocity is around the sonic barrier of about 1100 fps. This varies depending on temperature and pressure/altitude.

 

[redruns]

So I've worked up 10 rounds each with powder charges of 4.1,4.2,4.3,4.4 and 4.5. Everything else stays the same. My hypothesis is that 4.3 and above will have decreasing accuracy.

 

[just having some fun]

if this is for 9mm is not 4.5g a bit hot ??

Pull and measure a loaded round -- undersized ???

 

[Seagull]

Are you getting more leading in the barrel than with the round nose ones you used? Also what were the round nosed one sized to?

 

[redruns]

if this is for 9mm is not 4.5g a bit hot ??

Pull and measure a loaded round -- undersized ???

Yeah, 4.5 grain W-231 is hot, and I think that this is the culprit.
Good suggestion about pulling a loaded round. Pulled 5 and measured as best I could at the front thin driving band. 3 of them were nuts on .356 and two were .355 and .354.

Are you getting more leading in the barrel than with the round nose ones you used? Also what were the round nosed one sized to?

Pulled the barrel and had a good look. There is some smearing in the first 1/3 of the barrel, but nothing past 1/2 way. I think that the load is not engaging the rifling fully until half way. The RN after 500 rounds showed lead smears at the edge of the rifling grooves at the end of the barrel, but only the thinnest sliver. Leading present but not enough to concern me.



I was using a factory crimp die. I wondered if that was contributing to undersizing the front drive band, so for the test rounds I removed it. I was putting the tiniest crimp with the FCD but was unnecessary. The FCD was to ensure consistancy, but it is not too likely that there was a problem there.

This tumble lube truncated cone design doesn't have a wide driving band, but a thin band and a few lube grooves to engage rifling. From what I have been reading, a bullet will tumble if too hot or undersized or a combination of both. Therefore a little hot and a little undersized would add up.

 

[fingers284]

Where the 125 lead RN a hard cast commercial bullet or the same WW that you used in the 124 gr?

I ask this because I had an accuracy problem with a 30-30 I was shooting WW cast in last winter. I had the same problem you describe in your second post. You say you are finding some bullets that measure smaller than before seating (356 down to 354) ,I discovered the same thing with that 30-30...that being that the expander ball wasn't expanding the brass enough for the larger lead slugs and the brass was swaging some of the soft WW lead bullets down to their size instead of expanding enough to accommodate the .311 size I wanted. A slightly larger expander plug for the die solved my problem anyways.

I suspect the ones you are finding sized down to .354 are the ones that are key holing.

 

[Auggie Doggie]

Try some without running them through the FCD. If they still chamber ok, you may not need it. I stopped using an FCD when I found it caused leading issues in my guns. I believe it was swaging my cast bullets down enough to cause the problem.

Auggie D.

 

[tjhaile]

Hot loads of fast-burning powder will sometimes cause keyholing with lead bullets in 9mm. I would try reducing the powder charge and I would use a regular crimp die without the carbide sizing insert.

If those two steps don't work, I suggest sizing instead to .357". A slower-burning powder might help if you have some on hand.

 

[tigrr]

I never size my TL bullets. Lube reload and shoot. Try some without the sizing process.
I also use 231 as my 9mm powder.

 

[kg]

Some of LEE's molds are not cut properly and will drop conical bullets, undersized towards the front band.

 

[redruns]

Thanks for the interest. In case someone else ever searches for a similar problem, here are my solutions.

Reduced powder charge stopped the tumbling and increased accuracy. A charge of 4.1 grains w-231 with a cartridge OAL of 1.065 was satisfactory. At 15m it was able to produce a 10 shot 2" group. OK for what I need. The only concern I have is that I need this load to reach 1050 fps. I don't have a chronograph, so I'm guessing at this point.

Factory crimp die did not improve performance, and is found to be redundant with the Lee bullet seating die. May have been undersizing the front driving band with the slight roll crimp

Here is my target. clockwise from top left is 4.4 grains, 4.3, 4.2 and 4.1 in the lower left. Note the really tight grouping at 4.4 grains EXCEPT for the 3 tumbling flyers. 4.3 was a disaster, 4.2 is better and 4.1 has the minimum 2" grouping.

 

[ted_dent]

Both a friend and I both tried that bullet design with minimal success. Poor accuracy and tumbling were common. We tried different loads, different sizing diameters, etc. but it still never worked well. I had slightly better luck seating the bullet out further but it never could come close to the Lee 125 gr. round nose non-TL bullet for accuracy so I went with that one instead. Some bullet designs just inherently aren't that good.