I've been reading how some of you have converted your .40 cal to 9mm by swapping the barrel, however, you are still using the .40 cal mag for the 9mm round. How are you getting this to work? When I try and load my .40 cal mag with 9mm the first round won't even stay in the mag, it pops right out because the opening at the top of the .40 cal mag is slightly wider than the 9mm mag. By keeping my thumb on the top of the mag as I load it I suppose I could fill the .40 cal mag with 9mm but as soon as I took my thumb away I would have a little mini geyser of 9mm shooting up in the air. Are you guys able to load 9mm in .40 cal mags consistently without any problems?

I think some probably have bad information. It's not something I would personally do.

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Rod
M&P 22A, 40c, 15A, 15-22

It's not that I have bad information. It works on my pistol. I have had no problems with rounds jumping out. They are not tight. If you were to drop a loaded magazine the top round would either pop out or at least point up 90 degrees. However I have not had a problem getting them to stay in at least as far as loading them and then inserting the mag. I have 3 magazines and they all will hold and feed the 9mm's with no problems. I went out the other day and fired 150 rounds with one failure to feed which for me is acceptable for range work. I loaded 10 rounds at a time and loaded each mag 5 times and never had a round jump out. I didn't really have to be carefull loading them or anything. Have you tried another mag? The top round in the mag will sit at a slightly funny angle but they will function. Here is a thread I started when I got back from shooting. Just got back from trying out my 9mm barrel

I wouldn't do it myself just on general principle. Interesting that it even seems to kind of pretty much works most of the time and but I wouldn't want to bet my life on it and wouldn't even want to do it at the range!!

I had 9mm Mags from my full size when I converted my 40c. Just bought an x-grip to cover the mag.

Do yourself a favor and go ahead and buy a couple of 9mm17 round magazines and then you can safely fire your weapon here's over 100 in stock 44MAG.com - Smith & Wesson - Smith & Wesson M&P Magazine 9mm Fullsize 17 Round for$29.99 each plus a small shipping. They ship fast I have already bought 5 magazines from them!

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59,M&P9,40,40C,357,(2)45,G26

You can load .40 rounds into a 9mm mag and usually works fine, not the other way around however.

This is why I don't buy into the whole extra barrel/conversion thing.

If I need a 9mm I get a 9mm, same with a .40, etc. I've seen too many fellow competitors show up with the wrong ammo, wrong magazines or the wrong barrel.

Randy

I think you should use the proper equipment........period. These are guns, not Swiss Army Knives. SHOOT SAFELY!! We don't need another statistic trying to save a buck or re-invent the wheel. JMO

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Go big or stay home

I have had this discussion with others before. I find it interesting that I will say "I have done it. it works fine with my pistol". And I will still be told "No, it doesn't work". I agree that there is always the possibility of mixing ammo. However, the question wasn't "do you have to be carefull not to mix ammo" it was "will it function with .40 cal mags". No matter what else is said my answer is still ".40 cal mags work with 9mm ammo in my gun. Is this the absolute best option. No, of course not. Will it work, yes. At least it has for me.

OK, this is where y'all learn about manufacturing tolerances. Anything that's made has a nominal dimension and a tolerance above and/or below that nominal dimension that will still provide acceptable service.

There are some standards: holes can be oversize, but rarely undersize, things that go in holes can be undersize but rarely oversize. If the manufacturer doesn't provide specific guidance, there are established common practice tolerances that generally vary according to the size of the nominal dimension.

There is a nominal dimension for the width of feed lip opening on magazines and a range above and below that dimension that will still allow it to function as designed with the proper cartridge.

So, the distance between feed lips of a magazine for a specific cartridge may, in some cases be small enough for, say a .40 caliber magazine to hold 9mm cases in place for acceptable service. On the other hand the next mag you pick up may not. It has nothing to do with your particular weapon, it's the individual magazines that make the differences.

Do what you want on the range playing around. If you're doing something more serious, buy the correct magazines.

I agree 100%. I might have lucked out and got 3 mags that will feed 9mm. The next guy might not. Even though my magazines work with 9mm that does not mean I wouldn't pick up a 9mm mag. The fact is that I do intend to pick one up. The 9mm conversion using the S&W standard barrel seems to be working well for me and even with the .40 mags it is dependable enough to take out in the woods for practice. I would never advocate this combination for any serious work and if the mags don't seem to work for you that doesn't mean a guy can't pick up another mag of the correct size. Mine seems to be working and I'm happy for now.

Welocme to the world of tollerance stacking, each part is with-in some tollerance of so many thousanths +or- if you get lucky some parts when put with others will work perfectly, others will work on a some times fashiol and others will not.
I once built a 1911 for my nephew, just to find out how he liked 1911s
it was out of my junk parts drawer for the most part and no name parts. It came together like a bank vault and shot like a dream even with GI sights. 15 years later it is still in his safe next to his Kimber.
Says he is saving it for my great nephew.
Some days you get lucky.
Same is true of all mfgs, the specs for 40 must cross into 9mm area, some will work some won't.

As heard many time on the Rush Limbaugh Radio show Mega dittos! from this poster, great insight and guidance plus valuable information a gun is not something to play around with otherwise they would let children go and buy them like lollipops or tootsie rolls or some sort of candy!

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59,M&P9,40,40C,357,(2)45,G26

Whatever. It works and I'll continue doing it.

Thanks for the info everyone. Didn't mean to call anyone out in the process. From other posts it just seemed like it was supposed to work and it didn't for me. Will go the extra mag route personally. Besides, you can never have too many mags right

The best price I've been able to find on mags is at http://www.botachtactical.com/smwempma.html I may order one from them myself just to help keep things seperate. They're asking $22 with free shipping.

Thanks for the link. That's the best price i've seen!!!

I have never tried it with S&W 40 magazines. However, I had a Sig 229 Sport in 40 S&W for which I purchased an extra slide and 9mm barrel. The 10 shor Sig 40 S&W 229 Sport magazines fed the 9mm ammo very reliably.