10mm load keyholing

[Rio Laxas]

I am having problems with keyholing out of my 10mm practice load. I use a Dillon 550B. It is a 180 grain TMJ with 7.7 grains of unique at an OAL of 1.25. It has worked great until recently. I think the problem is with the amount of bell on the case. I had a batch with quite a few keyholing rounds, so I checked my set up and added a little more bell at the second station.

I loaded 25 rounds yesterday, and it seemed like the amount of bell decreased with each successive round (though I made sure the die was snug). Today I went and shot them and only got 2 keyholes out of 25. This makes me think I may have solved the problem until the die "slipped". Does it seem like I am on the right track with this problem, or should I be looking at the amount of crimp (which was based on Dillon instructions)? I had considered that as an alternative source of the problem.

 

[steve4102]

No matter the amount of "bell" it should be completely removed during the crimping stage. The crimp should be just enough to remove the "bell" plus maybe a hair more, no more.

 

[rcmodel]

I can't think of any way the amount of case mouth bell could have any effect at all on TMJ bullets if you are not scraping off rings of jacket metal when you seat them. And that should be pretty obvious.

The bell should all be removed by the seating crimping die when the bullet is seated.

Not enough bell with lead bullets can shave the sides off them and ruin the bullet, but not so with TMJ bullets I would think.

Not enough taper crimp would not remove all the bell, and might cause chambering problems, but not accuracy problems.

Too much taper crimp might squeeze the bullets undersized, and cause a loose fit in the barrel, which could result in key-holing.

As for all the problems you seem to be having with the dies changing after you set them?
Don't they have lock rings you can tighten after you set them correctly?

rc

 

[Rio Laxas]

My thought was that it might be shaving a bit of the jacket off from not enough bell when the bullet is seated. In the problem batch it seemed like the bullet seating stage had a tad more resistance than I am used to. I still consider myself a novice, so I'm not sure if this is possible. I read in one of the loading manuals that you should only put in enough bell to be able to set the bullet on top, so that is what I was going for. The dillon dies are locked in place with a nut, but sometimes it seems like they get a bit loose. The instruction manual says to only hand tighten them, so that is what I have been doing.

 

[rcmodel]

You need to bell enough to hand start the bullet straight in the case before seating.
I like to be able to pick up a charged case by the unseated bullet without them falling apart.

Inside chamfering with a deburring tool will also help prevent shaving jackets.

But, if you are in fact shaving jackets, you should be finding all sorts of copper jacket shavings stuck to the finished rounds.
Or stuck in your finger when you run it around the case neck joint.
You should also be seeing the shavings falling out on your press shell plate.

That ain't something you can easily miss seeing, or feeling.

rc

 

[Rio Laxas]

Thanks, that helps a lot! I will adjust my bell settings as you describe and probably back off on the crimping a bit and see if that solves the problem.

 

[rcmodel]

Use your dial or digital caliper to measure the case mouth after taper crimping.

The 10mm should measure somewhere in the neighborhood of .421" when properly crimped. If it is larger then .423" you aren't getting all the bell out.

If it is smaller then about .421" you are over-crimping.

The object of the taper crimp is just to remove the bell and make the sidewall perfectly straight again. SO, lay a steel straight-edge on a loaded round and see if it is straight, or not.

rc

 

[[email protected]]

I noticed that you said you were using a tmj bullet. What brand is it? Is it a plated bullet or a traditional FMJ? I have had bullets that keyholed before. One loading was caused by too light of a powder charge. Which brings up my next question, what type of powder measure are you using and do you weigh each charge to eliminate the possiable short charge. Unique is a large flakeish powder and can bridge in the powder measure giving inconsistant charges. May need to give the measure a good cleaning. Did you notice any difference in the recoil while shooting?
My second expierence with keyholing is with plated and cast bullets. I used the lee fcd die and it actually swaged the bullet to a smaller diameter causing a poor fit in the barrel. You may pull a loaded bullet and measure it to check if your resizing the bullet. The bullet should be .400 if fmj and .401 if plated (my expierence). I am assuming you are using a glock. I was using the berrys in my glock 22 40 cal, bullets started keyholing, pulled bullet it measured too small, stopped using fcd die, no more keyholing. They just need enough crimp to remove the bell.
One more thing, what charge did you start with on load development, and where did info come from. Alliant shows 8gn for max charge for the GDHP bullet and lee manual shows 7.0gn for max charge on fmj bullet. Both list velocities around 1125fps. Just an idea and couldn't verify with out a chroney, but you may be at the max velocity that the bullet can handle if you are using plated bullets. for what ever reason you may have a small amount of rounds that produce higher velocity and they are unable to grip the rifling. there is emdless possiabilities but just try one at a time so you can pin down what the problem is. You may load a few with a lighter powder charge to try to duplicate the keyhole. weigh each charge and mark the case so you can identify. If you are not having signs of over pressure according to alliant you still have .3gn to play with, load some up at max (carefully) and see what happens. If they keyhole you proabally are exceeding the max velocity for the bullet. In my expierence though the only way flaring the case can cause your problem is if you are shaving the bullet.

 

[atblis]

What diameter are the bullets?

 

[Sunray]

New batch of bullets? Check their diameter.
The amount of belling has nothing to do with keyholing. Keyholing is caused by under-sized bullets or too slow a load. An over-sized barrel will too but that's not likely.
"...might squeeze the bullets undersized..." Won't cause the whole bullet to be undersized though. Just where the brass is crimped.
"...Inside chamfering..." Won't do squat to a handgun case. Brass is too thin and the flare replaces chamfering anyway.

 

[243winxb]

it seemed like the amount of bell decreased with each successive round

Trim your brass to all the same length. Then reset your bell & taper crimp dies.