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Discussion Starter · #1 ·
I have a 9mm Firestar that works perfectly.
I have installed a .40 S&W upper unit and use .40 factory mags.
I can't get it to work reliably. FTF and FTE. From all accounts, the 9mm and .40 frame are exactly the same, and all the parts interchange.
The recoil springs are the same.
I have spare 9mm and .40 ejectors, and they are identical.
Again, the slide barrel and all parts are .40
Anyone have any ideas what to try? It does seem like the rounds are just too long - It is impossible to cycle loaded .40 rounds, they stick on the barrel and don't want to come out. OF course, when shooting there are no bullets, but that may be a clue...
I got the best function with Ranger 135 Gr JHPs.
Anyone have any ideas? I would love to get this working.
 

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Well, as you say, the frames are in fact identical, and a complete .40 upper should be made to work reliably on any M43 or M40 frame. I have this combination working without issues (complete M43 pistol and additional complete M40 upper).

But you must note two things........... first of all, the recoil spring is NOT the same, being heavier the .40 one, check that if you don't want to damage the pistol.

Also, and this may be the clue, the slide stop is different. The one for the .40 is specific, and has more clearance for the bullet. Using a 9mm slide stop may cause the FTF you're getting. That's probably why the JHP ammo seems to work better for you than regular ball ammo. Are you using the same slide stop for both uppers???

Difficult cycling of complete live rounds is normal, it should work fine with just the empty cases.

Hope this helps.
 

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Discussion Starter · #3 ·
Well, as you say, the frames are in fact identical, and a complete .40 upper should be made to work reliably on any M43 or M40 frame. I have this combination working without issues (complete M43 pistol and additional complete M40 upper).

But you must note two things........... first of all, the recoil spring is NOT the same, being heavier the .40 one, check that if you don't want to damage the pistol.

Also, and this may be the clue, the slide stop is different. The one for the .40 is specific, and has more clearance for the bullet. Using a 9mm slide stop may cause the FTF you're getting. That's probably why the JHP ammo seems to work better for you than regular ball ammo. Are you using the same slide stop for both uppers???

Difficult cycling of complete live rounds is normal, it should work fine with just the empty cases.

Hope this helps.
I have several slide stops. One or two are for sure 9mm, the third came with the .40 upper (as did the recoil spring). How do I tell the difference? I am sure one of them is the .40, but not sure which one as I have two Starvel stops.
Thanks for your help! I knew there was an answer there someplace.
 

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Discussion Starter · #4 ·
To follow up, I have a blued slide stop that came with my 9mm gun. I have two Starvel stops, one came with the .40 upper. The two Starvel stops are identical and are marked with a "2". The only difference i see is that the blued (9mm) stop has a shorter part that grabs the slide. The Starvel ones have a longer piece which is cut at an angle. I have been using the Starvel stops in both 9mm and .40, no issue at all in 9mm with them. I wonder now if the blued 9mm stop would work with .40, or if there is still another version that I need to find someplace?
 

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Discussion Starter · #5 ·
Wolff list the standard recoil spring as 16# for both the 9mm and .40.
Jorge, you are the expert. What weight should I order for the .40?
I am using the one that came with the upper, but a new recoil spring never hurts. They also list packs with different weight striker springs, but I don't really want to do that if I don't have to.
 
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