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Light primer strikes and failures to feed |
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Matt_X
Hard Corps Joined: Nov 10 2020 Location: Phila, Penn Status: Offline Points: 766 |
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Posted: Oct 29 2021 at 9:14am |
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Yesterday at the range with the new-to-me Midway Underwood had two
rounds that failed to fire. Also had some failures to feed. I don't
think they are related, but I could be wrong.
First can we confirm these are light primer strikes? I made a second attempt to fire one but it still didn't. Brought this one home and lined up next to ones that fired. I can see two impressions but, seems to me they are not as deep as on the others. Casing measures about 1.285" (On the left are spent shells fired from a different carbine.) |
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Smokpole
Hard Corps Joined: Oct 21 2019 Location: Madison ohio Status: Offline Points: 1052 |
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They do look a bit light. But I think they were probably a problem with the primers. remember, primer indents from fired rounds are always going to look deeper since the primer molds itself around the tip of the firing pin and at least a couple of those fired rounds have backed out primers. In both cases, I would suspect ammo to be at fault. But as to the FFTF problem, it could be the shape of the bullet nose or a minor mag problem.
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floydthecat
Hard Corps Joined: Oct 13 2016 Location: Mississippi Status: Offline Points: 1996 |
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I know we work this subject over a lot, but it always needs to be considered. I am sure you have checked head space, but if it’s too long, even spec length brass might not ignite and backed out primers are another indication. Of course, could be primers or even firing pin protrusion issues. I agree they look a little light, but mine usually fire with that much indent.
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GotSnlB28
Hard Corps Joined: Jan 01 2016 Location: WI Status: Offline Points: 892 |
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For sure check headspace on all your rifles, but having slight primer backout on PSD has been observed before. One can of 84 I've since shot up had a few like that and my headspace is good. I also recall another thread where a member had some PSD duds and from memory that was 86.
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Matt_X
Hard Corps Joined: Nov 10 2020 Location: Phila, Penn Status: Offline Points: 766 |
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I do recall a thread not too long ago with some PSD not firing. I've now shot 440 rounds from that box. These two are the first two that didn't go bang on the first hit. I didn't have the other carbine with me at the range or I would have tried it in that gun. Headspace is 1.296" - tight. 1.297" no go. Firing pin protusion when all the way forward is .065". (Figured using the back of the vernier caliper as a depth gage and then subtracting.) The firing pin movement was sticky and gritty. With the bolt standing face down it wouldn't drop from its own weight. Took the bolt apart and cleaned it and its moving freely now. Overall length of the FP is 2.955", inside of the triangular section to the tip is about 2.628" (the shortest acceptable according Kuhnhausen.) Bolt rear, before cleaning. Hammer spring 2.245" Ejector spring 1.065" Extractor spring 0.394" Operating spring 10.32" Long, 0.183" I.D., 0.258" O.D. That ID is large according to Kuhnhausen. Maybe this spring is a replacement made of smaller diameter wire. |
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Matt_X
Hard Corps Joined: Nov 10 2020 Location: Phila, Penn Status: Offline Points: 766 |
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No failures this morning. Only fired 40 rounds compared to 60plus but should have been enough to shake out problems. So it would seem the magazine tweakes fixed the misfeeds and perhaps the bolt cleaning helped with the failure to fire - or I just got unlucky with the dud last time. Seems like a alot of red residue but maybe I just never noticed before. Is that primer sealer? |
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GotSnlB28
Hard Corps Joined: Jan 01 2016 Location: WI Status: Offline Points: 892 |
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Correct, nothing to worry about there. |
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Matt_X
Hard Corps Joined: Nov 10 2020 Location: Phila, Penn Status: Offline Points: 766 |
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Another apparent dud today during the match. :( Fortunately it happened during prone slow fire, so there was plenty of time to give it second chance and then switch to an extra I put in the box. I'll try both this one and the previous failure in the Saginaw some time soon, but unfortunately think its the primers.
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David Milisock
On Point Joined: Aug 03 2019 Location: USA Status: Offline Points: 334 |
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Looking at the fired case heads it appears you're getting pressure variations. Surplus ammo? It looks as the dud has a deeply seated primer. You might try a replacement spring kit for the firing group.
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David Milisock
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Matt_X
Hard Corps Joined: Nov 10 2020 Location: Phila, Penn Status: Offline Points: 766 |
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Yes PSD 86 Korean Surplus. I appreciate the observations. If the primary cup is a little deeper than spec, then in combination with the firing pin protrusion that is just at minimum spec, that might be just over the margin for ignition. I bought two FP from Numrich, one of which is appears new so that will be the next test. If the pressures are varying considerably, that certainly not helping my match scores. My thinking has been that I'm the biggest factor in shot to shot differences, more than even say 100 fps difference in muzzle velocity.
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David Milisock
On Point Joined: Aug 03 2019 Location: USA Status: Offline Points: 334 |
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I've said this many times, in consideration of the time period, the length of time for development and the quality of the final result, the M1 Carbine and its variants, the M1A1 and M2, especially when configured as the A1 are some of the finest defence rifles ever made. With that said it is a minimalist design only operating at 40,000 PSI. I have 2 that are used as working rifles, they are in their 70's. I replaced all the springs and any dubious parts. They work wonderfully well with quality factory and my reloaded ammo but they needed care to get them there. They are not anywhere as accurate as my AR15 A2 in 5.56 nor my AR15 M4E in 6MM ARC. However my carbines were 40 years old and 77 years old when those rifles were built. With that said with the carbines within 300 yards you're in trouble, within 200 it's too late.
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David Milisock
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Rebel92
Grunt Joined: Jul 20 2021 Location: Hattiesburg, MS Status: Offline Points: 541 |
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With that said with the carbines within 300 yards you're in trouble, within 200 it's too late. [/QUOTE]
I like that, may have to borrow that saying when people try to speak ill of the handy little carbine.
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Matt_X
Hard Corps Joined: Nov 10 2020 Location: Phila, Penn Status: Offline Points: 766 |
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My goal and initial question was to get some insight into clues on the cartridge. I like isolating and solving problems. The three possibilities are: Something primer related Firing pin related Combination In my estimation, I'm not yet at a point of consistancy in my bullseye shooting to be too concerned about cartridge consistancy to be costing me points. On the other other hand, if it doesn't go bang, that can cost me points. First of all its a mental distraction when it seems likely to happen at least once in the 35 round course. Second, it eats up time doing a manual reload in the rapid fire. Fortunately this match allows 80 seconds - I assume to accomodate the bolt guns. In a true carbine match it will be 60 seconds. Anyway that's my project and that's why I'm using this ammo at this time. I have some IMI JSP but that's a limited resource best reserved for when SP is most appropriate. |
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David Milisock
On Point Joined: Aug 03 2019 Location: USA Status: Offline Points: 334 |
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Enjoy your project, in my experience you're correct the duds will cost you points but also in my experience in a 30 Carbine even the best ammo in the world at any cost won't gain you many points either.
With that said the cartridge and rifle was designed for 1 purpose and I'll be damned 80 years later it's still really good at it.
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David Milisock
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Matt_X
Hard Corps Joined: Nov 10 2020 Location: Phila, Penn Status: Offline Points: 766 |
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Took my SG to the indoor range today because I really wanted to answer the question about the primers. Both cartridges fired fine. So seems likely there was a lack of sufficient impact with the Underwood. I've changed the bolt and the hammer spring. So next time out I'll see it can get through 50 or 60 rounds without a failure to fire. While I was at the indoor range, I worked on my offhand. That went OK. I really do prefer the Irwin stock over the Winchester. Only hiccups were a couple feeding issues. Might be the new to me magazines, although the very last shot the empty didn't fly and it got caught in the bolt closing. :(
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David Milisock
On Point Joined: Aug 03 2019 Location: USA Status: Offline Points: 334 |
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The primers my be hard, the strikes seems lighter. If you've got a decent smith available pull the firing pin make sure it's in spec, replace all your springs with a new spring kit, (I use Wolf Springs kits).
Judging from the fired primers it appears the ammo may be producing quite a bit of variation in pressure.
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David Milisock
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Matt_X
Hard Corps Joined: Nov 10 2020 Location: Phila, Penn Status: Offline Points: 766 |
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The bolt and hammer spring change worked. 65 rounds this morning and not one hiccup. No pierced primers either. I think my interpretation of the firing pin protusion measurement is correct.
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