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Thread: SGN-9

  1. #281
    Gunco Rookie tommerr's Avatar
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    Drawing down the hardness: wrap the bolt in a stainless steel bag to keep down the oxidation. Heat the bolt at 900F for 1.5 hours and cool. You end up with a tough bolt that is machineable. I did a lot of experimenting to find this out. All Rc measurements were done on a calibrated machine. Some people are thoroughly softening these bolts and then trying to reharden them. That carries the risk of cracking from thermal shock if the temperature and the quench medium are improper.

  2. #282
    gunco irregular moleman's Avatar
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    Thanks Tommer. I've seen the stainless foil in the fastenal catalog, I'll give it a try. Is it going to be soft enough to tap at 40/45 rc and are you using hss or carbide bits?

  3. #283
    gunco irregular moleman's Avatar
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    Well after pretty much letting this sit all summer I pulled the parts back out their box and worked on them again. I had scratched the ar15 fire control lower and decided to make one that used a remington 552 trigger group I got for $25 shipped. While I was at it I roughed out a suomi type rear filler sized for the 1.25" tube out of some angle iron and a .3"x.5" shim for the mag catch slot. Earlier this summer I had messed up the ejector slot on a suomi barrel bushing/front trunion when I had a bit walk. I decided to just turn the bushing down and use it for this build and make a new one for the suomi. The bolt is done, but I need to find what I did with the bolt handle or it might be faster to just make a new one. Here's what I've got done so far.
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  4. #284
    gunco irregular moleman's Avatar
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    While working on my 17hmr ar15 bolt and looking at a ruger MKII bolt extractor, I had one of those slap your forehead I can't believe you didn't think of this earlier moments. Part of the reason the suomi isn't as reliable with the lower section of the feed lip removed is that the case can slide down the bolt face and off the extractor before it gets to the ejector. Its really noticable when you're extracting a live round. The epiphany I had was to mill the front 5/8" or so of the extractor slot down .025" and deepen the extractor retaing pin hole accordingly. I tested it out on a sgn-9 bolt and the extractor now holds a dummy round through light shaking where as before it wouldn't. here's some picts. It will be a while before I can try it out, but it seems to work much better now.
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  5. #285
    gunco irregular moleman's Avatar
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    I got a little more done. I cut a 3/16" ejector slot centered behind the left side barrel jacket lug. I want to make a screwed on ejector so I will make a 1/4" cut in the receiver tube above the slot in the barrel bushing. I cleaned out the inside of the receiver tube by honing it with a brake cylinder hone, making sure to keep at least a .001" press fit between it and the barrel bushing. I then made the 1/4" bolt slot about 7" long with a 3/8" back end to remove the bolt handle. Then I pressed in the barrel bushing and centered the ejector slot in the barrel bushing with the ejector slot in the bolt while the bolt handle held the bolt in its correct position. There may be a little bit of tweeking of the ejector slot as I just eyeballed that the .080" (IIRC) ejector slot in the bolt was centered in the .188" slot in the barrel bushing. I figured when it is time to make the ejector I'd just make the ejector full sized and color the top of it with a sharpie marker. Then I'd hold the ejector in the receiver and then work the bolt to wear off the sharpie marker except where the ejector slot is in the bolt. Then just mill off the shiney spots for a perfectly positioned ejector. Thats the plan anyway.
    I also pressed in the barrel bushing (so that there is less than a .4" gap between the back of the jacket lug on the barrel bushing and the front of the receiver ring) until the barrel jacket fit snugly on the receiver. I then drilled a 3/8" plug weld to hold the parts together for final machining of the mag and ejection ports.
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  6. #286
    Gunco Veteran muttman's Avatar
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    looks like you have a plan. I finley have a 10.5mm end mill on order. when it comes in I can start in on a bolt and get the " crap, I did that" out of the way. BTW have you ever given a thought of using a fal firing pin? I was working on my fal and was looking in the parts box and eye balled the pin and spring and have let my two brain cells work on fitting one in a bolt. they are cheep right now and should work. muttman

  7. #287
    gunco irregular moleman's Avatar
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    Muttman, looking forword to seeing your build. The method that ViperDude suggested about using a standard end mill as a boring bar in a lathe to make the bolt face does work well. I ended up using that method to make the bolt face in my 17hmr ar15 bolt. I had originally looked at the fal, and g3 firing pins as possible pins to use for the suomi bolt modification. I ended up figuring out how to make the ar15 pin fit relatively easy so I just stuck with that. I buy the pins 5-6 at a time from midway for $5.85 ish. Its been 5 years or so since I owned a fal and looked at a fal firing pin, but IIRC the firing pin tip sized section is quite a bit longer (1/2" ish) and would give you an easier time fitting the firing pin over that of the ar15 pin. If you end up with too much firing pin protrusion you could just simply trim off the excess. On the ar15 on the other hand if you have too much firing pin tip protrusion you have to wonder if you drilled too close to the bolt face with the first step in the firing pin channel and the area around the firing pin hole is now paper thin.

  8. #288
    gunco irregular moleman's Avatar
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    I cut the magwell and ejection port openings as well as welded a total of 6 3/8" plug welds to secure the barrel bushing. 3 welds behind the magwell and 3 in front of it. I turned down the welds in the lathe to remove the majority of them. The suomi magwell is cut at a 45 degree angle and slightly tapered to the front. I still cut the sides of my magwell at 45 degrees, but I didn't taper them. To lay out the magwell I covered the entire lower section where the opening would be in black sharpie marker. Then I scratched two lines .7" and 2.2" back from the front of the receiver tube. Then I squared up the receiver in the mill vise by using a dial indicator to make sure the flat surface on the right and left barrel jacket lug were within .001" of being flat. The mags I measured were around .975" wide and the receiver tube is 1.25". I set a dial caliper at .135" and scratched a line on the receiver tube using both sides of the mill vise as a guide. I had now laid out where my magwell needed to be. In order to get the 45 degree angle cuts I rotated the receiver and set a level on the corners of the bottem and left or right barrel jacket lugs as seen in the photo. In the photo I'm setting up to cut the left side of the magwell. The bottem of the end mill cuts the sides of the opening and the side of the end mill cuts the front and back of the magwell. I cut the one side, rotated the receiver, leveled it up again and cut the other side. It turned out perfect. I them cut the ejection port which I got a little low for my liking, but its in line with what was on the suomi. I also welded the rear filler to the trigger housing and drilled the mag catch pin hole. Here's some pic's.
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  9. #289
    gunco irregular moleman's Avatar
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    I got a little bit more done on the build. I got the front filler attached and the trigger housing finished and tack welded on. If you're using suomi drums and mags you will need to put a 1/8" spacer at the top of the rear filler mag tab channel because of the smaller diameter receiver tube. I still need to make an ejector but the gun will feed from drums and stick mags, it just won't eject rounds yet. I'm debating either using a screw on, weld on or rivet on ejector. I haven't settled on the buttplate or buffer style yet. I have popped the primers on several primed cases and it seems to be fine as far as that goes. I still need to clean up the welds and finish welding the trigger housing on before I take it out for a test fire. The stock sights will not work as is and I think I'll end up putting a red dot sight on it.
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  10. #290
    Gunco Veteran muttman's Avatar
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    moleman,
    the more I look at the photos the more Im thinking key stock on the tube with some holes and a M4 buttstock and a riser (ar rear sight ) hint hint,,,,,, muttman

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