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Sigma 40 Mags Converted to M357 and M40

11132 Views 50 Replies 14 Participants Last post by  ThaiBoxer
Howdy All :)

I don't know if there is any interest on the forum for this conversion, but I have converted 2 S&W Sigma 40 15-round hicaps to 15-round hicaps for my M357A-1. The Sigma mags actually load much easier and there is no problem feeding or dropping free. It should be an easy conversion for the M40's, as well. If there isn't any interest in this conversion, I'll be glad to shut my trap. Anyway, hava great weekend.


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Wulf, I would love to hear how you did this, and if you have pics of the mag loaded and unloaded, in the gun I mean. Thanks!
hey man, if you know some steyr crap, this is the place to let it all out. i'd love to have a 15 rounder as a spare for the s40.

so away.
With some pics and discriptions we could put it in the tutorial section.

"I'll make you famous"
My tool/die maker friend is cutting lockup hole in Sigma 17rounder mag for me. I tested the fit and lock up to slide and it works so far. I'd like to know the specific model # of the S&W mag for 40 cal. I may have to raddle the cage and get that mag back sooner and test fire it...
.......Stainless, very well made....but they aren't cheap either.....base plate is a little different, but workable.
Howdy :)

I did post a pic in the photo gallarie, Steyr Pistols #6 I guess. It shows the magazine and how it drops a bit lower than the factory 12 rounder. I contacted Deluxe247 about getting a grip plug for it, but I guess they aren't available for the A-1's yet. <shrug> I'm not sure how to add an image to a post, but I'll fig'r it out soon enough, I expect. Til then, if you email me, I can send pics of the factory mag next to the converted mag and pics of the 15 round Sigma hicap in the M357A-1. My email addy is [email protected] and I check my email often so, fire away. If there is enough interest, I'll put together a few pics and some additional info to make the conversion better understood. Heck, its easy! Even I can do it. Hava great weekend.




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I was considering this, but the f9cking Sigma mags are more expensive than the 12rd Steyrs! How this is possible I have no clue.. but best price I found on Sigma mags was 35 bucks.
Interesting idea for range use. For defensive purposes I'll stick with factory
Howdy :)

I did upload another picture of the factory Steyr M357 12 round mag and the Sigma 40 15 round mag, side by side. The mag lock window of the Sigma mag has to be cutout to accommodate the mag lock/release function on the Steyr. I disassembled both mags to better index the cutout. A Dremel tool with a cutoff wheel worked nicely, but there is a bit of filing that should be done, as well, to make the window clean and tidy. The last little bit of filing to the top of the window is the most critical part and the final strokes were made sliding the magazine into place and allowing the mag catch to lock up. Reassemble the magazine and make sure that when the buttplate is installed that the window cut is still enough for the mag release to function properly. You don't want to cut this window too much or there will be some slop to the magazine fit. You can always file a bit more, but too much and its too late. The slop will be there to stay. This was easily checked with the slide removed so the mag well was clearly seen as the magazine was slid into position. Take your time...there's no rush and the result will be dependent upon your careful efforts. I suppose I could use my digital micrometer to measure the changes I made to the Sigma mag, but most of what I did, I did by small increments of cutting and filing. The Sigma mag butts that I had to deal with were quite a bit larger than the factory Steyr mags use and I used the cutoff wheel on the Dremel to cut away the big bits, then finished up with a file and then some fine emery cloth. I did polish them a bit more and actually hand lapped the finish to better mate the inserted mag in the pistol. You'll understand much better when you are sitting in front of the TV honing your way to a perfect feel. ;) The uploaded picture should become available when its approved by an administrator. It should be in the Pistol/Other album of the photo gallery. Sorry to be so long-winded. I find that it is much easier to actually do the work than to instruct others to do the work. If you have any questions, I'll be happy to help however I can. Oh well, good luck and enjoy the Zen-like energy flowing between you and your newly enhanced steyrarm. :)

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this was done soon after the AWB sunset when all the leo marked 12 and 14 round steyr mags were gone in like two days.

Please note that while the sygma .40 mag is the same body as any steyr mag (except the location of the catch hole as noted above) the sygma 9mm mags are skinnier and will not fit. If you need to make an 18 round mag for your M9s then use the sygma mags in .40 NOT in 9mm and bend the feedlips in a tad to accomodate 9mm.

both mags are made by Mecgar in Italy.
Hiya Chef :)

Thanx for your valuable input. The mag conversion of Sigma 40 S&W mags to M Series mags that I've done twice now with very favorable results has nothing to do with the M9 or M9A-1 models. This applies only to M40's and M357's. Sorry for any confusion to the forum. It does look like there is the same increased capacity advantage for the M9's, though using Sigma 40 S&W mags and it seems that FlaChef has the info for that Sigma hicap conversion. Good call. :)

LoneWulf, that pic looks great. I haven't found anything lower then 35$ for sigma mags either......Chef, bummer to hear my efforts on the 9 will be fruitless, but sounds like fun to try the 40 retrofit. And it seems more of an advantage to have a few more 40's .......

Wulf, do you have the exact # of the sigma mag??? When I look at the SW list there seems to be a bunch of different listings.......
Hiya Shooter :)

You're in luck! Fortunately, I'm a bit slow to empty my trash and I have the clear plastic pkg that the 2nd mag I bought came in. I bought this particular mag NIB at Ross's Sporting Goods in Farmington, NM for $37.97 and has the Smith&Wesson Accessories #'s and barcode. The factory sticker reads 193540000 SW40F MAG ASSY 15RD. This is at the top of the pkg. Just above the barcode is 975-CLIPS AND MAGAZINES SW SIGMA 40HICAP. Just below the barcode is Q129-13600. There is a phone # (1-800-331-0852) and an invitation to "VISIT US ONLINE AT". That's all the info that it has in the pkg. The other Sigma mag I bought was in Amarillo, TX at a Gander Mtn a few months ago. It had the same pkg info, I believe, but I don't have the pkg anymore and didn't think to copy it down. It seems that I paid $39.99 for that one. I suppose, if you were to find a used one at a gunshow or some sporting event and the mag wasn't pkgd, you may recognize it since it is clearly stamped 40 S&W on the front of the mag and the S&W logo on the right side at the bottom, just above the plastic butt plate. Also, the # of rounds view holes on the right side are 5-7-9-11-13 and 15. The left side is 6-8-10-12 and 14. On both of these mags, the plastic followers are orange. I was fairly vigilant about these mags and bought when I found them and could afford them at the time. I've checked and they are usually around $40 +S&H. use to have more of them available but they were always $25 used and $45 "new in wax" +S&H, with the $25 listings no more. Cheaper than Dirt usually keeps them in stock, but they were around $40 at the store near Ft. Worth, TX and more if you get them online because of the S&H. I can remember when I was actively trying to acquire one of these Sigma mags, thinking, "God that's a lot of money if I don't make the correct modifications and it doesn't work. I'll be out 50 bux!". After having converted the mags, however, I'm quite pleased. I now have 2 15-round hicaps for my 357 SIG, the 2 12-round factory hicaps and a lot more knowledge of what they are truly worth to me. The converted mags load easier, have an increased capacity (15 +1) and feed flawlessly. The only detriment is the 3/16" length added to the pistol for imprinting. The pressure is off for me to try and find another Sigma Hicap but given the opportunity to buy right, I wouldn't hesitate to do so again. If there are any members who know of a good source for these mags, please share that info with the forum. Hope this helps.

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Thanks for the info wulf, I've used clips & mags before. I'll leave the work to my machinist takes months, but he's modified Berreta mags for me to fit my Taurus (older model with single action trigger, cock and lock feature), and he's a perfectionist........
At first I was moderately interested in this issue, because I hadn't quite got it yet. Now that the little light bulb in my head has gone off, I am really interested in this.

So if S&W can deliver mags that hold significantly more rounds from the same mag body, why can't Steyr? If they won't or can't, I'm all for using converts, even for carry, provided they have been function tested by me.

The Sigma mags may cost more, but you get a substantial increase in capacity. If it were 1 or 2 rounds it probably wouldn't be worth it.

I wonder how many rounds a Sigma mag would hold if it were shortened to fit flush in an S40? How cool would a flush fit 12 or 13 round S40 maga be.
I just got two mags from Cheaper then Dirt for 28$ each......not bad for stainless 15rounders..........if they are 9's that probably 17.......
Wulf, I am curious, the Sigma mag does not seem to really be that much longer than the Steyr mag, is it just the butt-plate that is longer? Or is the mag body actually longer? If it is the same length, is the spring shorter than the Steyr? I am really interested to know this, cause if all it is is the spring, why not just get a sigma spring and replace the steyr one for a 15 round cappacity. Please let me know if I am just in error. Thanks!
Sound25 said:
Wulf, I am curious, the Sigma mag does not seem to really be that much longer than the Steyr mag, is it just the butt-plate that is longer? Or is the mag body actually longer? If it is the same length, is the spring shorter than the Steyr? I am really interested to know this, cause if all it is is the spring, why not just get a sigma spring and replace the steyr one for a 15 round cappacity. Please let me know if I am just in error. Thanks!

Now that's interesting. Maybe the Sigma base plate has a hollow in the bottom, adding to the internal volume.
If the spring is indeed shorter but fits the M series magazine body and follower I wonder if it would work to add capacity.
Good point, maybe getting a Sigma spring from Wolfe springs would solve the problem cheaply, although I like the idea of stainless steel mags.........
From the picture you can see that the Sigma mag body is just a bit longer than the Steyr mag, but not enough so to account for the round increase. I think you guys are onto something with the spring and follower.
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