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Discussion Starter · #1 · (Edited)
Hey all,

I was looking for some magazines for my H&K USP .40 full size I bought back in 1995. I have a custom ported JARVIS barrel for it (.357 SIG) but have had some feeding issues (needs different follower?) using the original polymer 13 rd magazines when loading more than 10-11 Rds. I know they are bottle necked cases so different than intended.
Anyone have experience with a reliable .357 SIG magazine for the USP? I guess it is a gen 1

Thanks

Semper Fi
 

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I’ve read on the RCM website (RCM makes conversion barrels for the .40 to .357 Sig) that what’s needed for this conversion to work is a 17 round 9mm Jet funnel mag. Apparently this mag will resolve all the feeding issues. I’m betting this will work for your barrel as well.

Taken from the RCM website:

RCM RECOMMENDS THE JET FUNNEL USP 9MM 17 ROUND MAGAZINES. THEY WILL HOLD 15 ROUNDS OF THE 357 SIG AND PERFORM 100%. THE DESIGN OF THE MAG LIPS IS WHAT MAKES IT FEED CORRECTLY.

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Discussion Starter · #3 · (Edited)
I’ve read on the RCM website (RCM makes conversion barrels for the .40 to .357 Sig) that what’s needed for this conversion to work is a 17 round 9mm Jet funnel mag. Apparently this mag will resolve all the feeding issues. I’m betting this will work for your barrel as well.

Taken from the RCM website:

RCM RECOMMENDS THE JET FUNNEL USP 9MM 17 ROUND MAGAZINES. THEY WILL HOLD 15 ROUNDS OF THE 357 SIG AND PERFORM 100%. THE DESIGN OF THE MAG LIPS IS WHAT MAKES IT FEED CORRECTLY.

Sent from my iPhone using Tapatalk Pro
Awesome, thanks I will check it out, although 17 rds might be hard to conceal if it sticks out like a bat!
 

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In case you want to try, use the full size usp 9mm mag. The 357sig round will not dive.
 
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Here is a picture out 375 sig in both 9mm and 40sw. Please note, the usp 9mm and 40sw are interchangeable.
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After 2 rounds, the round will catch on the front of the mag like this and fail to load in 40sw mag. Sometime it will nose dive into the magazine body. Don’t have a picture.
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Discussion Starter · #8 ·
Thank you for this information, greatly appreciated. That is exactly what is happening when I am using .357 Sig. I will be buying a couple of 9mm magazines for my USP .40, now to find the best price.

Semper Fi
 

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Btw, round caught on the lip is easily fixed by filling/dermal down the front lip a little. It is the diving is the major issue.
 
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