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Saginaw Gear Conversion to 9MM

Printed From: The Carbine Collector's Club
Category: The Club
Forum Name: General Discussion
Forum Description: Carbine Related
Printed Date: Sep 23 2021 at 5:56pm
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Topic: Saginaw Gear Conversion to 9MM
Posted By: floydthecat
Subject: Saginaw Gear Conversion to 9MM
Date Posted: Oct 17 2020 at 5:45am

It walks like a duck, looks like a duck and quacks like a duck...must be a duck. It is an SG 3.3 USGI carbine converted to 9 x 19.

Over the past few months my partner-in-crime, 03manV and I have been working on a 9MM conversion. This project never would have happened without Don's help and expertise. The objective was to convert a stock 30-caliber USGI carbine to 9 x 19 without altering or destroying any valuable and rare USGI components. Prior to the current panics, 9MM could be had for around 14-15 cents a round, or about 1/2 the cost of 7.62 x 33. Not so attractive now, but hopefully 9MM cost and availability will return to pre-panic levels like the at-one-time very scarce 22LR.

We were not 100% successful in building prototypes that would digest and cycle just any 9MM ammo, but enough for me to call it a success. The pictured example runs on good quality ammo and reloads. No original USGI components were altered or destroyed in the process and the carbine will feed and cycle on stock 30-caliber magazines.

Of course, there is a lot more to the story. Most enthusiast won't show any interest in the conversion, but it has been an interesting journey. I can provide more information and details on the project to anyone interested for purpose, or simple curiosity. PM me for further information.

Posted By: 03manV
Date Posted: Oct 17 2020 at 9:56am
That's a nice looking "special" carbine.Smile

I really enjoyed working with you on this challenge!Thumbs Up


Posted By: floydthecat
Date Posted: Oct 17 2020 at 10:03am
Don, me and you know that you deserve the lion’s share of credit for  putting all this together. All I had was had the skills, tools and patience. If nothing had ever came from it, still would have been worth the trip.

Posted By: W5USMC
Date Posted: Oct 17 2020 at 10:24am
Great project, I think you should post the details here for all to see. I know that I am curious. 

USMC Retired
NRA Life Member

Posted By: floydthecat
Date Posted: Oct 17 2020 at 10:39am
Originally posted by W5USMC W5USMC wrote:

Great project, I think you should post the details here for all to see. I know that I am curious. 

I am rapidly reaching the same PM box has been lighting up all morning. Had no idea it might be this interesting. Think I will be adding some details, if nothing more than a broad overview. 03manV will have to help keep me honest. 

Posted By: GotSnlB28
Date Posted: Oct 17 2020 at 10:44am
+1 looks like a neat project I'm interested in the details.
Also in the accuracy you've observed at the range in comparison to the native chambering.

Posted By: floydthecat
Date Posted: Oct 17 2020 at 11:06am
If this gets too boring just pass it up. Feel free to ask specific questions. Don can chime-in and fill-in the blanks I leave.

I have been shooting a little Iver Johnson 9mm carbine for some years now. I hardened the carbine with GI parts and made alterations to things I never liked and made a great shooter out of it, but I never really got comfortable with it not being “pure USGI”. 03man and I crossed paths, one thing led to the next. He has the skills and tools to do what machining was required, which made it economically possible for us to attempt this conversion.

The only parts actually requiring machine work are the piston and piston-nut. We created what can be called a Type III nut by recessing the shelf in a Type II nut to facilitate additional piston travel and removed some material on the inside base of the piston as well. These changes lengthened the piston stroke. Don also opened the barrel gas-port slightly with the idea to provide more gas. There has been no further machining on any other component, other than the bolt, if a GI bolt is used.

A 9mm barrel must be obtained as well as a specific 9mm extractor. A GI bolt can be altered by opening the face to accept the 9mm base, or a specific 9mm bolt can be obtained. All other components are spec. USGI. 

The barrels are shot-out USGI barrels that have been over-bored to 9mm. Barrels are installed and head spaced to Luger chamber specs. using the bolt of choice.

This is a start....we will discuss magazines and tuning in the next post.

Posted By: floydthecat
Date Posted: Oct 17 2020 at 11:13am
Originally posted by GotSnlB28 GotSnlB28 wrote:

+1 looks like a neat project I'm interested in the details.
Also in the accuracy you've observed at the range in comparison to the native chambering.

Accuracy for me is...well, as good as I am with a 30-caliber. I don’t think either 03man or myself have done any long-range testing. At short feeling-out ranges, the groups seem to be as good as one can get with a 7.62x33. Remember this is a 9mm Carbine and shots much past 50-75 yards just don’t matter a great deal anyway.

Posted By: floydthecat
Date Posted: Oct 17 2020 at 11:18am
I need to mention that my round-count has gone past 400. I have found no evidence of gas system failures, such as a broken or cracked piston nut. Mine looks no-worse-for-the-wear than what one would see on a well-fired 30-caliber.

Posted By: floydthecat
Date Posted: Oct 17 2020 at 12:30pm
Before we get to magazines, we need to discuss tuning and try to discover what it can shoot. 30-caliber magazines are good enough for this. 3 rounds can be positioned in the magazine and will reliably feed enough to see if we go much farther.

Any semi-auto can be ammo-picky, even the 30-caliber and we are playing with the low end of the 7.62 x 33 pressure curve. It is going to be gun-dependent on what it may shoot. In general, it will not shoot the cheap standard power stuff. Standard power ammo is loaded down to around 1000fps. While velocity may not exactly correlate to actual pressures, it is a good indicator of how strong the ammo is. I have found S&B SB9A and Winchester NATO Target to work very well. I have not tried everything out there. If at first you don't succeed in cycling, adjust the hammer spring. I have ran springs of 1.965 and 1.977 in length with success. Do not clip the springs...heat and collapse coils on each end to reach a length that will still provide good primer strikes. I have also found strong reloads in just about any powder I use to be effective, both pistol and rifle powders. You can load-up the 9MM for use in the carbine. The brass is completely supported and there is much less chance of case ruptures.

Once you have tuned the action and discovered what it will shoot, you can entertain magazine options. The most economical choice is just to keep using downloaded 30-caliber magazines. Another good choice is the Universal style polymer 4-round magazines. These work with three rounds with hardly any effort needed to modify them and they can still be used in 30-caliber carbines.

If magazine capacity is an issue, the most obvious choice is the Iver Johnson BHP conversion. This will allow the use of any BHP magazine in any capacity. The components are not that expensive and are available. The down side is the necessary modification of a trigger housing mag-well to accept a polymer adapter and BHP magazine. When you reach the point of making a trigger housing a dedicated 9mm component, 3-round magazines that fit the unmolested GI trigger housing might be more practical. I have experience with both. I do not plan to take this carbine to war, so 4-rounds at a time are good enough for me. Effort continues to find a non destructive method to modify a 30-caliber carbine magazine.

In the end result, if for some reason one cannot get the carbine to cycle at all and are not a re-loader, the worst thing you can wind up with is a straight pull 9mm carbine. Some countries are restricted to that anyway. The carbine is a re-loaders delight. If commercial ammo is problematic, you can comfortably develop loads that will cycle the action.

Posted By: 03manV
Date Posted: Oct 17 2020 at 2:24pm
BHP = Browning High Power or Hi Power = the 13 round 9mm Browning pistol magazine

There are also 30 round mags available.

The BHP mags need a "new" notch for the mag catch on the IJ carbine type trigger housing/magazine insert, on the left side. This must be in the exact, correct position.

Numrich still have these inserts available.
The 9mm barrel came from a cache in Texas that were rebored, being sold on ebay from time to time.

When I was shooting the prototype that Floyd has now, I could shoot up to 6 or 8 rounds from the HP magazines; never loaded past that level.

Accuracy- as good as the .30 and as good as I can shoot. ;)


Posted By: floydthecat
Date Posted: Oct 17 2020 at 3:39pm
Thanks for the chime-in 03. I think there is no doubt that the Iver Johnson BHP system is superior to anything else tried. One might have to live with limited capacity mags, or make the decision to go ahead and modify the TH to accept those components. A compromise choice might be to sacrifice a commercial TH for that purpose. Even the stronger aluminum versions can be modified.

If a round can be manually chambered, fire, extract and eject, gas is not the problem, round placement in the magazine is more likely the problem. The IJ carbines were designed and operated as a short-action. The slide only retreated enough to cock the hammer. The BHP magazine positioned the round well forward in the mag-well. Trying to duplicate that with what we have has been a chore. If greater capacity and likely a broader range of ammo that works is desired, the IJ system is the preferred path.

Posted By: New2brass
Date Posted: Oct 17 2020 at 5:26pm
Sounds like you should do an article with lots of pictures!Big smile
that way it is there for the future

-------------" rel="nofollow - Club Survey Saginaw Receivers

Posted By: floydthecat
Date Posted: Oct 17 2020 at 5:57pm
Got it all on paper Dan...looking for a “publisher”😁.

Never thought there could be this much interest. A shame me and 03 could not get this done when 9mm Luger was so cheap. I am sure that Don will agree, as I will, to provide more specific details (before the book comes out) to those wishing to advance a winter project.

Posted By: floydthecat
Date Posted: Oct 17 2020 at 7:23pm

I wanted to show what 03 came up with for a 30-caliber magazine modification. The kit contains a spacer for the back of the mag, a spring and a follower that even has a built-in bolt stop after the last round. The limiter is the flimsy construction of the carbine magazines and they are not all created equal. You can't load more than 3-4 rounds or the body is bulged outward so severely that you cannot insert the magazine. This is a RUGG and it's the strongest magazine I have in my stash, it works with 4-rounds loaded. The spacer forces the short 9MM round forward, which allows the shooting of some standard pressure ammo. I am firing White Box with this set-up and that's pretty standard pressure stuff.

Notice how he painted arrows on the parts so even a dummy like me can assemble it. Still playing with springs and feed-lips, but this seems to be a winner if using a stock TH and 30-caliber magazine.

This also complies with our self-imposed rule not to destroy any USGI rare or expensive component.

Posted By: floydthecat
Date Posted: Oct 20 2020 at 7:46am
Just to sort-of wrap this up for those that have shown an interest, you only need three things to create a 9MM convertible carbine, the barrel, a modified bolt and gas piston/nut. If you have a buddy with a mill or lathe, the machining cost might be next to nothing. The only component you might destroy and make 9MM specific is the piston and nut, which are relatively inexpensive and plentiful. 30-caliber magazines can be non-destructively modified for 9MM operation, or used as-is. It is a fun-gun to shoot and up until recently, at 1/2 the cost of 7.62 x 33.

The carbine has been converted in various calibers, some successful and some not. Hopefully, the craziness going on at the moment driving-up the cost of anything 9MM will subside and the gun will be that much more fun to shoot. The barrel could also be chambered in anything within the 9MM family, such as 38-Super, 9MM Winchester Magnum, 9 x 21 or 9 x 23 and most of these should feed from a stock 30-caliber magazine. Possibilities seem endless.

I love all my USGI 30-caliber carbines and would never do a thing to modify or destroy one, or one of it's components. Commercial components can be used to create this conversion. You will never come anywhere close to damaging the carbine action shooting 9MM.

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