How much over bore?

[Akheloce]

I just bought a KKM barrel in 10mm for my G20, which slugs .3983, and a Lymam 401638 which casts .4023 without sizing, BHN of 18 (with my 3/1 COWW/ Lino alloy).

Should I size them, or should this be ok?

Also, I had to taper crimp them I a tad bit more than usual to pass the "thunk" test in the chamber. Not a lot, but more than I'm used to with J-words in other calibers... Is this indicative of a boolit that needs sized?

Thanks in advance.

[petroid]

Pull a bullet and check it. If the crimp is squeezing it down its too much crimp. I size everything for consistency. Never know when you don't have the mold tightly closed and a fat one gets through

[pworley1]

As long as the loaded round will chamber and you are not getting leading, those should be just fine.

[Shiloh]

Load up a couple, close the bell on the case, and see if they chamber. Cycle a few rounds. If there are no issues, load some up using tried and true load development techniques.

Shiloh

[Akheloce]

Thanks for the advice.

The freezing rain let up enough that I could shoot some today. As mentioned, the loaded rounds passed the "thunk" test (dropped into the removed barrel, with proper headspacing).

I'm using a new KKM barrel which is giving me fit problems. It does not reliably return to battery, resulting in light primer strikes. At first I thought it was the fit of my loads, but it did the same thing with factory j-word rounds.

On a side note, after 50 rds, I got a fair amount of leading. The first 2" in front of the chamber is clean, but the rest is leaded. The dimensions are as per my OP, the boolits are lubed with 45-45-10 WL, and chrono at 1175 fps.

[Shiloh]

So there is no hanging up on the throat when you do the 'thunk' test right??
Is this pistol broke in?? A similar boolit works very well for me in a .40 with an aftermarket barrel.

Shiloh

[Akheloce]

So there is no hanging up on the throat when you do the 'thunk' test right??
Is this pistol broke in?? A similar boolit works very well for me in a .40 with an aftermarket barrel.

Shiloh

Right.

The pistol is nearly new. Perhaps 300 rounds through it. It functions flawlessly with the OEM barrel, I think I have a fit problem with the KKM. What happens is that it stops approx. 1/16" from battery- close enough to allow the striker to function, but a light primer strike. It takes very light pressure from by thumb on the rear of the slide to push it into battery. The type of push that it requires is the kind that makes it finally "click" into place, not the kind that is forcing the cartridge into the chamber. A stronger spring may help, but I think that is a band aid, not the source of the problem.

[shooter93]

I shoot a .401 in a Dan Wesson 1911. I had the same problem when taper crimping myself. It seemed like it was sort of like "camming" over to get it to chamber freely. The gun is very tight and I was beginning to think it was my dies so I had a fellow here at the site load some using his dies and my components and they worked fine so I crimp until they chamber easily and use that OD to check the rounds. It's simply a tight chambered gun and they shoot very well that way so that's how I load them. I load 45 acp using OD measurement with my bullets also.

[Shiloh]

Send KKM an E-mail. If it is a fit issue, they may need to look at it. See what they say.
http://www.kkmprecision.com/contact/

Shiloh

[popper]

size to 401, just remove the mouth belling & leading should go away.

[sigep1764]

So I recently changed my powder through expander to a custom one on my sdb. I was swaging down my boolits and this solved my problem with my 358 boolits. My Kahr cw9 did the same as yours, having to push the slide into battery ever so slightly. It continued for about a hundred rounds or so. I shot 400 rounds that day through the kahr. The first 100 were a little light on the charge. The 300 after were slightly heavier by .2 grains. No worries on those and absolutely no leading. I would look at your lube for leading. What inch barrel and is that tumble lube you're using?

[Akheloce]

6" barrel, using 45-45-10 tumble lube.
The leading is the last 4" of the barrel.