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Old December 31, 2012, 04:03 PM   #1
mlcompound
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M&p9c shallow chamber

I have been trying to reload for my m&p and I have found that the chamber is very shallow compared to other 9s I have seen. For example, my brother's cm9 chamber is 0.06 deeper. I have to stuff boolits so deep in the case I worry about pressure spikes. I do start the load very light and work up. Is this something that s&wesson would fix or should I take it to the gunsmith to have it cut deeper?

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Old December 31, 2012, 05:00 PM   #2
Unclenick
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Is it the whole chamber or just the throat? If stuffing bullets deeper into cases allows feeding, it sounds like the cases fit into it fine, which would mean the chamber is deep enough, but the bullets are stopping prematurely in the throat. I suppose it is conceivable you got a chamber that was roughed but did not get the final finishing reamer applied. Roughing reamers typically have no throat portion. It is also possible the manufacturer just had a reamer design that has a short throat or was using a normal reamer that had been resharpened one time too many.

If you drop a finished round with normal seating depth in rather than feeding it, does the head of the case fall in flush with the back of the barrel? Does that happen with commercial ammo? If so, then its not necessarily the chamber or the throat that's out of spec, but some other aspect of feeding that's the issue. The chamber being too narrow from using a worn reamer or improperly contoured chamber mouth or any of the various timing issues that cause feed problems could be involved. That would need a gunsmith's skills to check.

You ought to be able to send the barrel to S&W for inspection. You could also have a gunsmith apply a match throating reamer to it. Indeed, if you have a local gunsmith with a standard 9 mm reamer, just touching the chamber with that may fix the throat without deepening the case portion.
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Old January 1, 2013, 09:28 PM   #3
mlcompound
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Okay. I need some schooling on this. I guess the better way to explain it would be that the throat is less deep (or something, hehe). For example, I have a 124g 0.356 round nose loaded to a coal of 1.250. I drop it into my m&p9c barrel and the first band on the bullet makes contact with the throat and the bullet still has 0.06 left to seat flush. I drop the same bullet into the barrel of a kahr cm9 and it passes the plunk test. I used a test bullet 38 special and measured the amount above the barrel chamber and the m&p9c is 0.06 shallower than the cm9 when seated on the throat.

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Old January 1, 2013, 10:33 PM   #4
exnodak
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I have noticed exactly the same situation with my full size M&P9. Reloads using a 125 grain lead round nose bullet easily pass the plunk test in my Ruger SR9c, but will hang up on the lands in the S&W. The 125 grain lead cone bullet does better, so I switched to those as I want to use the same setup for both pistols.
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Old January 3, 2013, 06:18 PM   #5
Unclenick
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Again, a throating reamer would fix that by elongating the throat but leaving the rest of the chamber alone, if properly used. Page 6, here. A carefully used chamber reamer with the configuration you desire will work, too. Doing either will probably void the warranty, though.

In loading .45 Auto, the rule of thumb has always been that the front band of a bullet's bearing surface not stick out of the case by more than about 0.020 or so unless I know I have a chamber that's satisfactory for it. The thickness of a thumbnail is often cited. though that obviously varies with the individual hand.
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