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Occasional tumbling bullets...What's causing it


MilkMyDuds

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I recently started noticing a small number of my shoots are keyholeing on hard cardboard targets. Usually 10 yards or more, 2 out of 10-20 rounds. This did not happen before, and I have not changed anything...

Barrel - KKM 5'' (about 10,000 rounds through it) on MP9 Pro

Bullets - Bayou 147gr FP

Powder - Titegroup

PF - 130

OAL - 1.140''

Dillon 650 - Lee 4 die set (size, seat and crimp) with MBF (doing the belling)

Some possible causes I have found on the web:

1. Barrel twist rate - KKM has 1:20 twist rate thus should be more than enough to stablize the 147gr

2. Lead fouling in bore - I cannot visually see any leading in the bore. The rifling looks in a very good shape

3. Bullets undersized - I have been using Bayou 147 FP for a long time. I measured the latest batch I got and they are in 0.357/8'' range

4. Too much crimping - I pulled some of my loads, and do not see any visible crimp line

What could be causing this? Could it be the barrel already worn out at 10,000 rounds, maybe oversized by the usage somehow?

I have some minor coat shaving issue but very minor. Some of the pulled bullets show the coating gone in a very small areas with lead exposed, but no lead loss. Could this be causing the occasional tumbling?

Do the thickness of the brass matter? Different headstamps feel differently when they load, harder vs. easier, etc. I always suspect some headstamps make bad quality ammo, but I have not done any tests to prove it. I mainly load RP, FC, PMC, Blazer, Speer and Win headstamps.

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S&W went to the 1:10 twist barrel to stabilize heavier 9mm rounds, If you still have your stock barrel, give that a try (if your barrel is the 1:10)

If you're shaving bullets, that could definitely cause tumbling.

Edited by Bkreutz
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I have the stock barrel (with 1 dimple) and a BarSto barrel. I will be trying them soon.

The other interesting discovery today - I was pulling 30 bullets to investigate the cause of tumbling, and realized that some specific headstamp would give out the bullets really really easily (I was using a kinetic puller), at most 2 swings, while most others would hold until 5 swings. Because I run mixed headstamps, I suspect some got just enough crimp while others got none, due to the differences in brass wall thickness. After pulling all of the 30 rounds, I did not see any crimp line on any of them, but some do have coating shaved off a bit, exposing lead.

Would too little neck tension cause tumbling? I wound not think so, but I will do some experiments focusing on specific headstamps.

The other interesting thing with the Lee 4-die set, the stand-alone seating die appears to be removing the bell too. I know this because some of my loaded ammo could pass chamber gauge without going through the FCD. I thought only the seat+crimp die would seat and crimp? I do get enough belling because I run Mr. Bullet Feeder bullet seater, and I adjust the expander die to provide enough belling (about 5mm or so down the mouth) such that the bullet seater works flawless.

Any ideas?

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S&W went to the 1:10 twist barrel to stabilize heavier 9mm rounds, If you still have your stock barrel, give that a try (if your barrel is the 1:10)

If you're shaving bullets, that could definitely cause tumbling.

I thought the bare minimal to stabilize 147gr is 1:16? Some google results say the MP stock barrel with 1 dimple is 1:18 twist rate.

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S&W went to the 1:10 twist barrel to stabilize heavier 9mm rounds, If you still have your stock barrel, give that a try (if your barrel is the 1:10)

If you're shaving bullets, that could definitely cause tumbling.

I thought the bare minimal to stabilize 147gr is 1:16? Some google results say the MP stock barrel with 1 dimple is 1:18 twist rate.

The "dimple" doesn't indicate twist rate, it's for identifying the machine that made it for QC purposes. Twist rate is easy to tell by looking into the barrel. On a 1:10 twist barrel, any one of the lands will travel half the circumference of the bore in a 5" barrel, a 1:18 will only go approximately 1/4 the circumference. This is not exact but close enough to tell the difference. You need a faster twist with heavier bullets. A 1:16 is a slower twist than a 1:10.

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I've had mixed results with the FCD using coated/lead bullets. Did you measure the bases of the pulled bullets and see if the FCD was swaging them down with thick brass?

This is a very interesting aspect that I have not thought of.

I did took measurements, see attached pic. It could well be that the base of the bullets getting undersized by the FCD, causing the rifling unable to engage fully when the bullets go through the bore. Why would FCD crimp more than just the mouth of the case? I already have the FCD die adjusted to as high as possible, e.g. it should only touch the mouth of the case. Maybe the seating die, on the upstroke, is pressing and undersizing the bullets?

My next experiments:

1. Check the same pulled bullet base right after seating but before FCD - I always suspect the Lee seating die actually does some amount of crimping

2. Reduce OAL to 1.125'' but keep the same crimping setting - theoretically this helps to restrict the crimping only to the mouth of the case

post-56818-0-96966200-1440944568_thumb.j

Edited by MilkMyDuds
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I didn't see how much powder your throwing, but at 130 pf I'd suspect around 3.0 gr.

With that twist rate it might be over powering the round. Maybe dropping down to 2.8 gr. might help stabilize the bullet.

I shot those bayous thru an XDm with no issues. OAL was 1.155 with anywhere from 2.7 to 3.2 gr of Titegroup. So I suspect barrel twist is the culprit.

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The seating die will crimp as it is the same one as in the 3 die set. I personally would not use an FCD as it will size down some bullets and the case will spring back some, while the bullet won't. This can lead to bullet set back in some cases.

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The seating die will crimp as it is the same one as in the 3 die set. I personally would not use an FCD as it will size down some bullets and the case will spring back some, while the bullet won't. This can lead to bullet set back in some cases.

Steve, do all 9mm seating dies size + crimp at the same time? When I was still using SDB, I don't remember Dillon ones did that. Maybe I should switch to a dedicated seating die.

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No, they do vary. Lots of 4 die sets break up the seat/crimp operations. But if you work at getting them adjusted properly the three die sets will work quite well.

You just have to read all the advertising literature to see which ones do what. :roflol::roflol::roflol:

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The FCD came in the 4-die set. I don't understand why did Lee include a seater that could crimp with the FCD in one set? Maybe they imply the FCD is not truly a crimp die because essentially what it does is to resize the finished round?

Anyway, I did measure pulled bullets before they go to FCD. It looks like the bullets are already slightly sized down just by going through the Lee seating die, 0.355'' on the base. Then once they run through FCD, they are further sized down to 0.354'' on the base.

I find myself learning all these even though I have loaded probably 20k 9mm.

I tried different headstamps, trying to determine their brass wall thickness. It appears with Blazer, FC brass the rounds pass case gauge 100% right after seating without ever going to FCD. Others such as RP, PMC won't gauge after seating and require crimping.

In short, it appears to me:

1. The seating die in the Lee deluxe 4-die set actually crimps a little bit in addition to seating the bullets

2. Both the Lee seating die and FCD will squeeze the coated bullets into a new dimension, e.g. smaller base diameter. This is with a crimp setting that does not show any crimp line.

My next step is going to try Dillon and Redding seating die, and some taper crimp die. Will grab some from Cabelas and try them today. Does it matter what brand taper crimp die I buy? RCBS, Hornady or Dillon?

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I believe the Lee seating die (in the four-die set) also crimps, but by backing out the die in the turret and screwing down the seating adjuster, you stop crimping and just use it as a seating die (it's in the directions).

I did that; my seating die seats, and I bought a standard Lee taper crimp to replace the Factory Crimp Die (FCD), which many people suggested was a poor choice for my slightly oversized coated lead bullets.

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Try checking the loaded rounds in your chamber, all the gauges are not the same and you aren't going to shoot from them anyway.

As mentioned above, you can just use two of the Lee seat/crimp dies and just seat with the first and remove bell with the second.

You don't want to crimp unless you are loading for revolver with bullets with a cannelure. For a semi-auto you just want the case wall straight when all is said and done.

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The KKM and BarSto barrel wont chamber if the rounds don't pass gauge. BarSto sometimes wont even chamber the rounds that pass gauge. It looks like taper crimp is still needed, because with just seating no crimping, a lot of headstamps won't pass case gauge.

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I've got a new Kart barrel in a 1911 and I had it reamed, mostly to lengthen the throat and to also make sure that it would work with any of my reloads. A lot of the replacement barrels will have a rather short throat and/or chamber. Better to have it run all the time than attempt to make a bench rest rifle out of it.

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The FCD is not, technically, a sizing die. It has a carbide ring that will "size" the case down to just under the minimum chamber dimension--which is larger than the upper limit of the case size. Thus, if using 0.355" bullets in 9x19 cases that have correct wall thickness, the carbide ring will not touch the case mouth (other than the case mouth flare, of course). If you used a sizing die in place of the FCD, it would size the case down to or below the lowest case size and the bullet would be about 0.010" smaller and really rattle down the bore.

The FCD is very good for crimping and fixing problems that can be cured by properly setting up the dies--with jacketed bullets of nominal dimensions. However, I find that it will often swage my cast bullets down and I will lose accuracy and sometimes get leading. Thus, if I was to use a Lee crimp die, it would a Lee Taper Crimp die and not the FCD. So, why not buy a Lee Taper Crimp die and see what happens ( just $12.79 at MidwayUSA)?

From my experience, tumbling is almost always caused by one of two things: the bullet is too small for the actual groove diameter or the muzzle has serious damage and is "blasting" the bullet into a tumble. I am sure there are other reasons, but those are the ones I have seen.

Any time you have a bullet problem, you should always pull the bullet from at least one round and inspect and measure it against a new bullet that has not be loaded to be sure it wasn't damaged during loading (of course, for lead and plated, I also recommend measuring a few random bullets before you even load them).

Edited by noylj
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I had similar problems as you with cast lead boolits but the problems went away after I switched to Dillon dies. The FCD is fine for copper plated or jacked bullets but will cause nightmares with lead. I also had a custom powder funnel made a few thou larger than a std funnel and that helped a lot too.

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Wall thickness will vary from headstamp to headstamp. The thicker walled brass can cause swaging issues with lead or plated projectiles, The FCD usually works well with the thinner walled stuff. It only stands to reason that if the outside of the case is sized the same when comparing thick vs. thin that when run threw the carbide sizing ring on the FCD that that something has to give and that is the bullet in the thick walled case is swaged down to a smaller diameter, so you get the smaller bullet rattling down the barrel and tumbling. And for the record I use PC'd lead bullets and the FCD in my Hornaday AP in 9mm, 38 cal. and 45acp with no tumbling and no leading, with some 9mm fps at 1180 and 357 at 1350 with no issues.

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I got a Redding taper crimp die here, but yesterday I tried some rounds loaded with backed off FCD, no tumbling. I am not exactly sure how FCD's resizing work on the loaded case, but it appears to me the trick is to back the FCD die all the way up, then turn the crimp knob all the way down till it touches an empty case mouth. That seems to do the trick.

I will run this setup until I see tumbling again, then swap the taper crimp die on.

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I obviously spoke too soon... Just loaded 200 rounds and 2 of them came out of the FCD into the finished ammo bin with bullets separated from the case, spilling powder all over in the bin. This happened before about 3 or 4 times but I never thought much. But I know better now.

I measured the base of the bullets on those 2 rounds, 0.352 and 0.353. I pulled some other finished rounds and measured. 0.356 all of them. What's unique about the 2 that got pulled by FCD is that they are both CBC headstamp.

I pulled more finished rounds, and found these patterns:

1. CBC - 0.352/3/4

2. JAG - 0.354

3. RP/PMC/Win/etc - 0.356

So I could either keep the current setting and not run any CBC or JAG headstamps, or switch in taper crimp die and try. My guess is that the thickness on CBC and JAG is causing the bullets to be squeezed undersized.

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