10mm problem

[Jevyod]

I am pretty new to the casting for handgun scene. Have used cast successfully in several rifles. I recently acquired a M&P 2.0 chambered in 10mm. I cast some bullets from the Lee 175 TC mold, and powder coated them with Smokes clear. Sized to .4015. Loaded some up with Unique and was getting around 1100 fps which is great for simple practice. The problem I am having is they will not all chamber correctly. When the slide comes forward , there is a slight overhang in the back indicating the slide is not fully forward. Sometimes I can just push it forward, sometimes I need to pull back and release the slide. Yes, all these passes the test where I dropped them into the barrel, they all seemed to drop in just fine. For comparison the factory ammo I shot functioned perfectly.

So I dod a bit of comparison between my loads and factory, and found 2 main differences. First, when measuring the case right behind the bullet, my hand loads measure .422, factory is .419. I tried getting mine down further, but I am already applying a pretty good crimp. Crimp is being applied with the Hornady taper crimp a separate step from bullet seating.
The 2nd main difference I can tell is factory ammo has a COAL of 1.250. Originally mine were 1.260, loaded a few more at 1.255. I had fewer failures with the 1.255 than the 1.26. I am a bit hesitant to go all the way to 1.25 because according to manuals, that can drastically increase pressures.

The other thing that I thought may be causing this is I was not trimming my cases. I measured some, and they were all within.008 of each other. The brass came from a friend of mine, he picked it up at a range for me. Headstamp is mixed.

So with what I described, where should I start? I should also note that my powder coating process adds about .0025-.003 thickness. Is there a chance the nose of the bullet is too large?

I am tempted to increase seating depth to 1.250, back off a bit on the powder charge, and see what happens.

As an aside, the primers are a bit proud of the base of the brass, so measuring the COAL can be a bit challenging.

[justindad]

As an aside, the primers are a bit proud of the base of the brass, so measuring the COAL can be a bit challenging.

Fix that.

[36g]

How many rounds have been fired through the M&P? If a new gun break it in. If still basically new clear the gun, leave the mag out and cycle the slide while you are watching TV. Run 500 or so rounds of factory through it...

[Cast10]

Cowboy M die; expands the case further down (longer) so the case does not stretch so much as to cause a stoppage. In RCBS it would be a 38-40 expander die. I have a carbine that did it, and the M die fixed it. My Glock 20 has a larger chamber, but it still showed improvement, especially the amount of crimp it was taking……

[Walks]

Not familiar with your pistol, but
Maybe polish the feed ramp ?

[dondiego]

Seat the bullets to the factory specs........reduce your powder charge by 10%. Once you find the problem it is an easy fix. No high primers.

[Tall]

The Lee Factory Crimp die will crimp the rounds like the factory does. Aside from that the other problems mentioned need to be fixed too.

[44Blam]

Make sure to seat your primers properly - they should be just set in fully and should be under the base of the case by a thousandth or so. A proud primer can cause minor issues like not chambering properly or getting 'light strikes' (that actually seat the primer) to major issues like detonations when loading.

[rockshooter]

find a mold that is designed for powder-coating. You need one that has the nose portion .001 smaller than the sized diameter. The problem is that PC adds .001 or so to the whole bullet and you only size down the part that normally engages the rifling but some barrels don't have much of a throat and the nose portion, fatter because of the PC, hangs up on the leade. This is a common issue since PC came around. I like NOE molds because of the rebated nose portion and they show it clearly on their drawings.
Loren

[justindad]

Where did you get your load data? Was it for this exact bullet mfg & part #?
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What OAL is listed in your load data?

[cwlongshot]

Something that has cured many hiccups with cartridges in tighter chambers for me has been the LEE BULGE BUSTER. ESPECIALLY useful with range pick up /no your own fired cases.

Oh and for goodness sake SEAT PRIMERS PROPERLY!!

Give that a try.

[TD1886]

Kind of off topic, but we know the 40 S&W is a shorter version of the 10mm. With that said many pistol competition shooters load 49's to shoot in their 10mm's for practice to save money because you use less powder in them. I can tell you that the 1911 and the Glock are kind of like a control feed Mauser action. Those of you that build 1911's will know this, but I will explain for those that don't. While the breech face is stripping a round out of the magazine the rim of that cartridge slips up under the extractor. So does the Glock. With that said the extractor holds the case against the breech face firmly that you don't have to worry about the shorter 40 head spacing. I've shot these from my long slide Glock 10mm and my 1911 longslide 10mm with zero problems and interesting enough they shot pretty darn accurate.

[mdi]

Any time there is a fit problem, measure. Measure the "bad" handload in several places, OD at case mouth, mid body and just in front of the extractor groove, etc.. Check if the bullet is hitting the throat or rifling (mark the bullet, chamber cartridge, inspect bullet.). I find out why my handload doesn't fit then fix the problem. I do not cover it up with an FCD or "Bulge buster". I do not "crimp" any semi-auto handload, I just deflare with a deflaring die (aka "taper crimp die"). This has worked for me for many years for my 32 ACP through 45 ACP handloads

First though, fix priming method. Seat every primer all the way to the bottom of the primer pocket, below flush, and disregard "below flush measurement". I seat the primer until I feel it bottom out, then add a bit more pressure to "sensitize" or "preload" the primer. I have not had a FTF because of seating incorrectly that I can remember (35 years?) using this method...

[Jevyod]

Thanks for the help! Will try the things mentioned, along with lubing some with traditional lube instead of PC. Honestly if this were too easy it wouldn't be as fun!!

[fredj338]

Its likely your OAL, bullets hitting the lands. If shortening them 0.005" helped, certainly going to 1.250" would show if that is the issue. No, at 0.010" diff in OAL isnt really affecting pressures much, especially with medium & slow powders. Put that on your calipers & see how small that is. Nothing really gets interesting until you are 0.050" shorter. Bullets into the rifling increases pressures far sooner than bullets seated deeper. BTW, OAL in any data is almost useless. The bullet must fir YOUYR barrel. So all data is just a guide, not a bible.

[Jevyod]

So tested some more, seated primers flush, trimmed to 1.082, did minimal case flaring, and seated to 1.250 COAL. Loaded 15 in my magazine, 14 out of the 15 cycled and fires fine. The one that didn't indicated primer strike, loaded it back in and it went off.

[mehavey]

...they will not all chamber correctly. When the slide comes forward , there is
a slight overhang in the back indicating the slide is not fully forward.

And they all passed the plunk test where they (PC'd and all) would rotate freely while in your gun's actual barrel?

postscript: Another 5-thou seating depth isn't going to do anything dramatic pressurewise.

[justindad]

So tested some more, seated primers flush, trimmed to 1.082, did minimal case flaring, and seated to 1.250 COAL. Loaded 15 in my magazine, 14 out of the 15 cycled and fires fine. The one that didn't indicated primer strike, loaded it back in and it went off.

Your primer should be 0.002”-0.008” sub flush.
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Here’s how I do it with a ram primer: seat primers until I can just barely see a witness mark from the ram on the primer, then I back it off about 0.001” so that the witness mark is gone. This generally puts them 0.005” subflush, but it varies with different cases & calibers. I hand ground off the lathe nipple on my ram, so YMMV.

[Jevyod]

I use a RCBS hand primer. Not sure how to adjust that....

[mehavey]

I use a RCBS hand primer....

Simply bottom them out solidly (just don't gorilla to the point of crushing things)