Browning HP 9mm to 357 sig

[MICHAEL B YORMARK]

hello everyone,
I’m posting this to gain advice and learn from anyone’s experiences about converting a 9mm BHP to 357 Sig. I’m looking to do this with an Israeli hi power in 9mm. I know about the BHP 357 sig KKM barrels but from what I’ve read on other forums not many people have converted the 9mm to 357 sig. In fact the only instance of this I found was with Novak’s in the 1980s and it was for FBI’s HRT, before they went to 1911s. So it can be done! But how?!

I’ve read the slide on the 40 slide doesn’t fit the 9mm, so a slide switch is out.

So how do I make this happen? What needs to be done in order to make the 9mm into a 357 sig?... and one that won’t self destruct on me.

 

[Schlegel]

I didn't try firing with the slides switched, but I fit my 40 slide on my 9 frame just now and it seemed to fit appropriately, mag cutoff worked, slide release worked, trigger dropped the hammer as usual. I thought the thicker slide on the 40 was the big change as the 9mm slides were beat up too fast originally? I can't try firing the 40 on my nine as it's an alloy frame so I know it isn't built to take the stress. My 40 came with an aftermarket 357 Sig barrel. I have't used it, it was just an extra thrown in by the previous owner. All it requires in a 40 slide is changing the barrel, the 40 magazines work for it.

 

[MICHAEL B YORMARK]

Very interesting!... anyone know when the Israeli contract hi powers were used and how frames were made?

Also, anyone know a place where I can find a good BHP slide?

 

[Schlegel]

I believe the Israeli BHP's are from the forged frame era. If you look at the magazine well is the bottom of the handle smooth or does it have ridged lines? nearly all the cast frames have the ridges.

 

[boom boom]

I won't say that you cannot do so in a safe fashion. I have no idea about your talents nor experiences. However, as someone who has a relatively educated opinion, imho, your best bet unless you are an experienced gunsmith is to hire such a conversion to be done rather than simply rely on putting an aftermarket barrel and a new recoil spring on it. An experienced gunsmith familiar with the High Power is likely to tell you whether it is possible, possible problems with it, and some measure of accountability if things go South on the conversion.

Pistols are designed as a system so you would need some determination of recoil spring strength, feeding, etc. which are based on the size and weight of the slide and its resistance to the force generated when you fire the round. You might also have problems with extraction.

For example, the .357 sig generates about 500-600 ft lbs in recoil while the 9mm generates about 350-400 ft lbs. This is leaving aside the +p or +p+ type rounds. The sig round also is rated quite a bit higher in chamber pressure. Given the pressures involved, I suspect that parts wear would be accelerated to something like that of a 9mm +p or higher pressure 9mm round. Thus, if it worked very well at all, it would probably lead to accelerated wear and given that High Power production is no more, might very well cost you on the appreciated value of the Israeli High Power in the future but also the expense of having it done in the first place. One off conversions, generally do not have a very good resale value.

FWIW,
Novaks used to do quite a bit of High Power gunsmithing and I know that Cylinder and Slide did and does too. This does not discount that others don't exist that do good work on high powers.

 

[Schlegel]

I personally wouldn't want to do it unless using the later era stronger slides. Recoil may be comparable to or even less than a hot 40, but pressure will be higher. To my knowledge the aftermarket barrels are all 3 lug and meant to go in the 40S&W slide, anyway.

 

[NIGHTLORD40K]

Very interesting!... anyone know when the Israeli contract hi powers were used and how frames were made?

Also, anyone know a place where I can find a good BHP slide?

Some of the Israeli Hi-powers were actually bootleg Hungarian FEGs marked as FNs. That may explain some issues with parts not being 100$ interchangeable as well.

Personally, I wouldnt try to turn an old, worn, surplus 9mm into a .357. The .40s were built stouter for a reason......

 

[BBBBill]

I’ve read the slide on the 40 slide doesn’t fit the 9mm, so a slide switch is out.

Incorrect. The Mark II and earlier 9mm frame differs from the later Mark III 40 S&W frame in some small details. I don't have a Mark III 9mm handy to check if those changes are present on those. I imagine that they are. No reason for them to be different. I modified (minor frame mods) an old Israeli FN/Browning to 40 with a Mark III 40 top half very briefly as an experiment. It worked and will still work with 9mm after the mods. I very strongly do NOT recommend it as FN specifically stated that the older frames would not hold up to the increased pounding from 40 and the 357 SIG will pound at least that much if not more. I am still holding that top half while searching for a candidate Mark III to have a two or three caliber gun.

It absolutely will not work with a 9mm slide without major mods to the slide. If you went that route you will end up with a gun that will break in very short order. If you use a forged frame the lifespan will be greatly shortened.

So a 40 cal slide is required along with a Mark III cast frame if you want the gun to last.

 

[#1buck]

Convert a .40 S&W Hi-Power with a drop in barrel and heavier recoil spring. You can change between .40 and .357 by changing out the barrels and recoil springs. The .40 mags will work as well. What you're doing will stress the older components that weren't built to handle the recoil and pressure of those hotter cartridges. The .40 version is much beefier for a reason.

 

[rodinal220]

Forged frame on the left and cast frame on the right. I believe the cast frame came out some time in the early 1990s due to the 40 S&W MKIII version.

 

[Texas10mm]

How could Novak have converted HPs to .357 Sig in the '80's when the round didn't come out till 1994?

 

[BBBBill]

How could Novak have converted HPs to .357 Sig in the '80's when the round didn't come out till 1994?

They didn't. They did convert some 9mm Hi Powers to 40S&W. The 40 conversions had modified slide breech faces and proved to be not durable at all. I don't recall any details on the outcome of the 41AE experiments. I do see an occasional 41AE conversion kit for sale on GunBroker. Bottom line - Stick to the factory Mk III 40S&W (or at least use a Mk III frame and 40 slide) for conversion to 357SIG.