rich636 Posted October 7, 2015 Share Posted October 7, 2015 (edited) Hi all, I recently started using my STI Trojan 9mm CRP purchased from Dawson Precision in some IDPA matches and have an issue where the has two live rounds trying to enter the barrel causing a jam. It appears as the slide returns, stripping a new round from the magazine, there is already a live round waiting part way in the barrel. So the stripped round push up under the round sitting partly in the chamber and becomes stuck. The gun is equipped with the Dawson ICE magwell and I use Dawson Supreme Tactical magazines. Ammuntion is reloads with 3.7gr of Win 231 behind a 147 RN Berry's bullet, OAL is 1.115. I contacted Dawson thinking it was a magazine issue. They responded asking for measurements of the magazine body and feed lips and they were within spec. So their guess was that my thumb is likely dragging on the slide causing this issue. I sent them a video (below) showing my grip and a jam, conceding that I do ride the slide closely and asked two questions they did not answer in the reply, and so I'm hoping you all be able to with your collective expertise: 1) How does the friction of my offhand thumb facilitate the feeding of two live rounds towards the chamber? 2) Where should my offhand thumb be? I used to hold it lower but I had issues of it interfering with slide lock. Edited to add frequency: this jam happened once to twice a match (approx 100 rounds) for the three matches I've competed with it. Thanks in advance for any insight, Rich Edited October 7, 2015 by rich636 Link to comment Share on other sites More sharing options...
andrewtac Posted October 7, 2015 Share Posted October 7, 2015 Does it normally happen when you are resting on a wall? In the video (when the jam occurs), prior to ignition it looks like you are applying more side force with the left thumb to push the gun against the wall. It looked like most of the time your thumb was floating off the slide to slightly touching, except at the jam. Link to comment Share on other sites More sharing options...
andrewtac Posted October 7, 2015 Share Posted October 7, 2015 I had put a piece of grip tape right under the slide for a while. It was to reference where my thumb needed to be, mainly for dry fire to work on the grip (after switching from a cz). Link to comment Share on other sites More sharing options...
rich636 Posted October 7, 2015 Author Share Posted October 7, 2015 Hi Andrew, I don't recall if they've all happened while posting up like that but I will certainly test that next time I'm at the range. The grip tape on the frame for a tactile reference point is a great idea. I don't think it's IDPA legal but I can definitely practice with it on until I get in the habit. Link to comment Share on other sites More sharing options...
andrewtac Posted October 8, 2015 Share Posted October 8, 2015 Yep, not sure on legality but it was mainly for dry fire. I took it off and have no issues now. I never had dual feeds but tended to have my thumb higher than. I wanted. Link to comment Share on other sites More sharing options...
wmetzler01 Posted October 8, 2015 Share Posted October 8, 2015 (edited) I'd shoot two mags with the gun rested on a bag or bench to see if the jam occurs. Said another way, shoot with your strong hand thumb no where near the left safety. If no jam, then it could be your thumb so install a thumb guard on your left safety. There's tons of YouTube videos out there that will illustrate what's happening. Edited October 8, 2015 by wmetzler01 Link to comment Share on other sites More sharing options...
rich636 Posted October 8, 2015 Author Share Posted October 8, 2015 Thanks, isolating to one hand is a good idea. I'm still curious about the physics of slide resistance causing 2 live rounds to feed. I can see it impeding ejection or feeding of 1 round from the mag. Link to comment Share on other sites More sharing options...
PatJones Posted October 8, 2015 Share Posted October 8, 2015 Touching the slide with either thumb is asking for trouble. That said, I don't see how drag on the slide would cause it to turn around and go back for another cartridge. I'd like to see a close up picture of what the jam looks like before you clear it. Link to comment Share on other sites More sharing options...
choppe Posted October 8, 2015 Share Posted October 8, 2015 In my experience, the majority of double feeds are caused by a weak recoil spring combined with a weak mag spring. With a weak or under-powered recoil spring the slide comes back too fast/hard and rattles a round free. Then when the slide goes forward it grabs another round. When the mag spring is weak its easier for jar a round loose accidentally. Not sure how slowing the slide down with your thumb would play into this? Crazy. Link to comment Share on other sites More sharing options...
PatJones Posted October 8, 2015 Share Posted October 8, 2015 2) Where should my offhand thumb be? I used to hold it lower but I had issues of it interfering with slide lock. I don't see any need for the weak hand thumb to touch the gun. Grip tape on the frame is unnecessary, just let your thumb float next to the gun. Many of the malfunctions I see at my work are caused by customers touching the slide. Link to comment Share on other sites More sharing options...
wmetzler01 Posted October 8, 2015 Share Posted October 8, 2015 In my experience, the majority of double feeds are caused by a weak recoil spring combined with a weak mag spring. With a weak or under-powered recoil spring the slide comes back too fast/hard and rattles a round free. Then when the slide goes forward it grabs another round. When the mag spring is weak its easier for jar a round loose accidentally. Not sure how slowing the slide down with your thumb would play into this? Crazy. Your thumb dragging on the slide as it cycles can mimic a weak spring as it limits the action just like a weak spring would do. Another possible cause, aside from the mag spring listed above which is a good observation, could be your feed ramp not having the right radius - it may be fine with most loads but a hollow point or more squared bullet could be causing the issue, still another could be the chamber not being correctly shaped. It's very hard to guess without being physically present to view the gun. Wasn't trying to sound like a dick when I suggested looking at a few videos, but it can be helpful. Link to comment Share on other sites More sharing options...
Postal Bob Posted October 8, 2015 Share Posted October 8, 2015 Had this exact same issue with the same gun for months. What is happening is that as the slide hits the back end of its travel, the jolt causes the top round in the magazine to pop out and sit within the chamber. Then the slide coming back strips the next round off the mag, and you end up with 2 rounds trying to feed into the chamber. I only realized what was happening when a live round popped out of the mag, and actually out of the gun before the next round was stripped off the mag. Kept thinking it was bad magazines that had the feed lips spread too far apart, or weak mag springs. Some of the feed lips were wider than others, but not really too wide. And they were new, so the mag springs were not weak. The problem ended up being the recoil spring. I was using a 9 or 10 lb spring, which seemed to be what everyone was using. And it seems the lighter the spring, the faster they wear out. But even new 9 lb springs gave me the problem. So I tried an experiment. I went to the range with recoil springs from 9 to 14 lbs. I shot several mags using each spring weight starting with the 9lb. What I ended up finding is the double feeds completely stopped when I used the 12 lb spring. And not only did the double feeds stop, but my double taps were more tighter on target. Now I have smaller hands, so any recoil is greater for me. But with 12 lb spring, not only is my gun shooting flawless, but my double taps are now tighter. So try a heavier recoil spring if you're using a 9 or 10 lb spring. Link to comment Share on other sites More sharing options...
Postal Bob Posted October 8, 2015 Share Posted October 8, 2015 (edited) Btw, I too at first thought it had something to do with my thumb dragging along the slide. So I would try exerting more pressure against the slide, to see if I could duplicate the problem. Didn't seem to cause the double feeds. Again, go to a heavier recoil spring, and your problems should disappear. Edited October 8, 2015 by Postal Bob Link to comment Share on other sites More sharing options...
incorrigible Posted October 8, 2015 Share Posted October 8, 2015 Great insight Bob. I think you nailed it. Link to comment Share on other sites More sharing options...
rich636 Posted October 8, 2015 Author Share Posted October 8, 2015 Thanks everyone! I will name my next born son "Postal Bob"! That info is so valuable. My recoil spring is super mushy and in retrospect this problem started when I went from a softer loading to a more potent one which would exacerbate the problem. I will order the 12lber and report back to hopefully close this thing out! Link to comment Share on other sites More sharing options...
choppe Posted October 8, 2015 Share Posted October 8, 2015 My open Glock will double feed after I get 1500 rounds on the recoil spring. The hot 9mm major rounds wear them out so fast. I put a new spring in and the double feed goes away. Link to comment Share on other sites More sharing options...
ChuckS Posted October 8, 2015 Share Posted October 8, 2015 Btw, I too at first thought it had something to do with my thumb dragging along the slide. So I would try exerting more pressure against the slide, to see if I could duplicate the problem. Didn't seem to cause the double feeds. Again, go to a heavier recoil spring, and your problems should disappear. Actually, the thumb dragging along the slide would simulate a stronger recoil spring to some degree. If the root cause is a weak recoil spring, that would mean that too little recoil energy is being transferred to compressing the spring and too much being transferred to the frame. Dragging the thumb would be absorbing some energy that would of been dumped into the frame. The thumb, in this case, would likely mask the problem. Good thread, thanks for the info! Link to comment Share on other sites More sharing options...
rich636 Posted October 9, 2015 Author Share Posted October 9, 2015 Hi Chuck, that same thought occurred to me on my drive home today. I think my thumb has a reputation problem, it's not thaaaat draggy The gun appears to throw the empty out in a brisk fashion and it hasn't failed to lock back on the last shot. Also I've never had this issue with my RIA 9mm 1911 which I hold the same way, or my 1911s in .45. I'm eager to test some springs and get back to you all. Thanks again for the comments. Link to comment Share on other sites More sharing options...
Postal Bob Posted October 9, 2015 Share Posted October 9, 2015 Part of the reason the lighter 9 and 10 lb springs didn't work for me, was that I slicked up all contact parts of the slide, bottom of breechface, bottom of the firing pin stop, underside of slide, etc. So all that resistance that is normally there combine with the recoil spring was now reduced. So I had to go to a heavier recoil spring to compensate. Link to comment Share on other sites More sharing options...
rich636 Posted October 12, 2015 Author Share Posted October 12, 2015 A quick update. My buddy had an 11lb Wolff spring that I swapped in before a range trip today. I put 100rds through the STI with no issue of any kind and the slide did feel less sluggish between shots. I didn't change my grip at all. About 200 more uneventful rounds and I think I can assume this issue is behind me. Thanks - Rich Link to comment Share on other sites More sharing options...
Absocold Posted October 12, 2015 Share Posted October 12, 2015 Most double feeds are an empty case in the chamber and a live round trying to feed in after it. They probably thought this is what he meant so after making sure the extractor and ejector were good they gave another common cause for this type of failure: thumb drag. What he has is a double feed of two live rounds. Causes are: weak recoil spring, weak/binding magazine spring, follower bind, follower tilt/cant, feed lips too wide, lip angle too steep and probably a couple more I can't think of right away (it's late here). Installing a shokbuff often helps too. Link to comment Share on other sites More sharing options...
whoflungdo Posted October 27, 2015 Share Posted October 27, 2015 I had exact same thing with a Tanfo. It had a thumb rest so no dragging. It was a weak recoil spring. Went up 2lbs. Problem solved Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now