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Posted: 5/8/2020 7:12:32 PM EDT
Built a 9mm AR Glock Magazine PCC with 16" barrel. Am running a heavy 9mm buffer and XP recoil spring. Its been running good except for a couple failure to feeds which only seems to happen on the first round when I dont let the bolt slam open full speed.
Well, I ended up changing the hammer spring to an XP hammer spring in an attempt to make the trigger pull heavier and figured it would help slow down the bolt even more. The reason I wanted to make the trigger pull heavier was because the gun was way to easy to bump-fire. It would do 2-3 round bursts if I wasnt careful about keeping the rifle firmly to my shoulder and/or firm trigger pulls. The XP hammer made the trigger pull heavier and im not getting the doubling but now I am getting some pierced primers on my cases, especially on the hotter +P and NATO rounds im shooting. It seems the firing pin is not hitting the primers straight on and actually hitting them at an angle which would exaggerate the firing pin protrusion. My buddy says he thinks my headspace is "too tight" but this is a blowback gun not a locked breech gun where headspace is more of an ambigeous term. Any ideas?  
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Posted: 5/8/2020 8:15:15 PM EDT
[#1]
Perhaps instead of an XP hammer spring you could try a heavier trigger spring? Wouldn't help with slowing the bolt, but you wouldn't be poking holes in primers.
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Posted: 5/8/2020 9:18:11 PM EDT
[#2]
It may just be the magnification of the first photo, but I would look at the firing pin hole in the bolt face a little closer. That firing pin hole looks over sized, which would also explain the primer protrusion I see on a couple of the fired rounds. Excessive flow back into the firing pin recess would allow the primer material to flow back into the recess and the point of the primer would penetrate deeper.
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Posted: 5/8/2020 10:47:46 PM EDT
[#3]
Looking at that firing pin hole, I'd say it's time for a new bcg. Way too much erosion.
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Posted: 5/8/2020 11:47:21 PM EDT
[#4]
Quote HistoryOriginally Posted By M90A1: Looking at that firing pin hole, I'd say it's time for a new bcg. Way too much erosion. Its a brand new BCG. Only 30 rounds through it. It was that way from the get-go. I think its a firing pin/bcg issue as well. The primer strikes on all of the casings ive picked up are hit unevenly like this...whether the primer is pierced or not. And the heavier hammer spring is probably exercerbating a problem that has already there by adding more force but isnt the problem necessarily. My friend thinks its headspacing and probably too short of a chamber. But, its a blowback gun and headspace is usually less of a topic with blowback unlike a locked breech gun. I mean it feeds and ejects/extracts fine. If I put a round in the chamber, only the grooved part of the round sticks out. Unfortunately, I dont have any 9mm headspace gauges. The good news is the heavy buffer setup I have, the breech is staying closed long enough like it should which I guess helps fully burn the powder more. I dont have very sooty casings and the gun isnt getting real dirty at the breech end like a lot of blowback ARs in 9mm. The firing pin must be barely piercing the primers....it didint blow much soot out. |
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Posted: 5/9/2020 10:07:06 AM EDT
[#5]
Quote HistoryOriginally Posted By asdaven: Its a brand new BCG. Only 30 rounds through it. It was that way from the get-go. I'd be having a serious talk with whoever made that bcg. That firing pin hole is messed up, and I'm not talking about the diameter of the hole. That hole should be straight through with a sharp edge and no beveling at that edge. |
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Posted: 5/9/2020 12:50:08 PM EDT
[#6]
To assist and add scale, can you possibly take another photo with the firing pin extended through the face of the BCG? That will give a little better approximation of the size of the hole in relation to the tip of firing pin.
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Posted: 5/9/2020 1:56:53 PM EDT
[#7]
  Firing pin tip def has a little side to side wiggle in the front of the hole. The firing pin has the slightest divot/dent in the tip of the firing pin. Dont know if that was there before. |
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Posted: 5/9/2020 3:12:26 PM EDT
[#8]
Ok, it looks like the firing pin protrudes quite a bit further than the one my Colt 9mm bolt, even with my firing pin bottomed out in the bolt. I've only got one 9mm AR so that may not be a fair comparison, the Colt bolt/firing pin has a spring in front of the firing pin. I know there are other bolt systems out there and it is difficult to just visually say it's too far. It really needs to be checked with a firing pin protrusion gauge . I still say it looks like the firing pin hole in the bolt face looks over sized. If possible, I would be contacting and/or e-mailing the BCG manufacturer with the pictures you have, including the fired brass and give them a chance to evaluate.
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Posted: 5/9/2020 6:27:01 PM EDT
[#9]
This is exactly where measurements and gauges come into play..........firing pin protrusion should be measured to see if in specification, head space should be checked with gauges as well..........
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Posted: 5/9/2020 7:18:51 PM EDT
[#10]
Headspace isn't going to cause pierced primers, but firing pin protrusion could.
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Posted: 5/9/2020 11:45:37 PM EDT
[#11]
Your pics are not working for me. But does the bolt have a firing pin spring? That can cause exactly what you are having.
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Posted: 5/10/2020 1:14:53 AM EDT
[#12]
Quote HistoryOriginally Posted By M90A1: Headspace isn't going to cause pierced primers, but firing pin protrusion could. I realize that, my point is folks are putting together rifles, carbines etc....without measuring tolerances...........over pressure ammunition will pierce primers too .Headspace should be checked after performing any action work such as chambering a barrel, changing a barrel, or changing the bolt. You should also check it on any used gun you purchase at a gun show, a store, or from a friend - before you fire it. |
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Posted: 5/10/2020 8:32:28 AM EDT
[#13]
FP hole is cattywampus'd as mentioned. And the FP protrusion is to much.
That will leave the primer blow unsupported and stretched enough to pierce primers. I would return the Bolt to the manufacturer, after explaining your issues. |
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Posted: 5/10/2020 10:13:43 AM EDT
[#14]
Quote HistoryOriginally Posted By catcatcher1:Headspace should be checked after performing any action work such as chambering a barrel(how many owners can chamber a barrel?), changing a barrel, or changing the bolt. You should also check it on any used gun you purchase at a gun show, a store, or from a friend - before you fire it. Not worth the trouble or expense for most builds, or builders. 99-44/100% of the time, everything will be within tolerance. Modern CNC machining is pretty amazing. True match-grade builds might be the only exception, but even then, most of them will be fine, also. Your advice is admirable, but not practical in the real world. |
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Posted: 5/10/2020 11:38:36 AM EDT
[#15]
Quote HistoryOriginally Posted By M90A1: Not worth the trouble or expense for most builds, or builders. 99-44/100% of the time, everything will be within tolerance. Modern CNC machining is pretty amazing. True match-grade builds might be the only exception, but even then, most of them will be fine, also. Your advice is admirable, but not practical in the real world. He's right, you know...... ^^^ |
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Posted: 5/10/2020 9:40:10 PM EDT
[#16]
can you email the the pics...not showing for me
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Posted: 5/11/2020 9:57:55 AM EDT
[#17]
I dont have any of the gauges for firing pin protrusion or headspace but eyeballing it the firing pin does protrude more than I think it should as it seems to be hitting the primers pretty deep. I do know pistol primers are softer than rifle primers.
As far as headspacing, the cases fully chamber except for the edge of the extractor groove back which is about the depth of the pocket in the bolt. No bulges in the brass at all. Some flattened primer on the hotter loads ive shot though. Probably the +P is as hot as I should go in this rifle. I changed the XP hammer spring back to the normal hammer spring, didint get any double tapping this time and the primers were not pierced. I feel the bolt is still a QC issue. But the heavier hammer spring was magnifying the problem with the firing pin. And yes, it does have a firing pin spring being a blowback. Macon Armory- I will try to send pictures to you later today. |
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Posted: 5/11/2020 1:25:43 PM EDT
[#18]
Quote HistoryOriginally Posted By M90A1: Not worth the trouble or expense for most builds, or builders. 99-44/100% of the time, everything will be within tolerance. Modern CNC machining is pretty amazing. True match-grade builds might be the only exception, but even then, most of them will be fine, also. Your advice is admirable, but not practical in the real world. Wrong......Ive got a brand new and unfired upper assembly from Delton inc and guess what, it closes on a no-go gauge.....bought a brand new Ruger Mini 30 and the fired cases were blown out so much it was scary......Pick up any US Military service and read about checking headspace on M16's......failure to do so could result in death and serious injury to the operator. No sir, im using the gauges. |
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Posted: 5/11/2020 1:50:51 PM EDT
[#19]
Quote HistoryOriginally Posted By catcatcher1: Wrong......Ive got a brand new and unfired upper assembly from Delton inc and guess what, it closes on a no-go gauge.....bought a brand new Ruger Mini 30 and the fired cases were blown out so much it was scary......Pick up any US Military service and read about checking headspace on M16's......failure to do so could result in death and serious injury to the operator. No sir, im using the gauges. Well, that is partially correct. It is not unusual to find military spec type rifles that commonly use military spec type ammo that will close on a "No Go" gauge due to the desire for functionality under adverse field conditions. Is it preferable in the civilian world? Probably not, but it is not uncommon. However, actions should not close or lock on a "FIELD" gauge and if they do then they should be removed from service. Also in order to properly check headspace the chamber needs to be as clean as possible and the ejector and extractor should be removed from the bolt to prevent getting false readings. Applies to bolt action rifles such as K98 Mausers, US 1917's, Garand or AR type actions. |
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Posted: 5/11/2020 2:46:01 PM EDT
[#20]
Quote HistoryOriginally Posted By catcatcher1: Wrong......Ive got a brand new and unfired upper assembly from Delton inc and guess what, it closes on a no-go gauge.....bought a brand new Ruger Mini 30 and the fired cases were blown out so much it was scary......Pick up any US Military service and read about checking headspace on M16's......failure to do so could result in death and serious injury to the operator. No sir, im using the gauges. You're welcome to waste as much of your time and your money as you wish. Most people aren't going to invest the money in buying the tools you recommend, nor the time to learn to use them. And, they're not going to spend the money to have a gunsmith do it for them. As I stated, thank goodness manufacturing methods are as good as they are. If there were as many problems as you intimate, there would be a lot of guns blowing up, but there aren't. Carry on!! |
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Posted: 5/11/2020 4:27:19 PM EDT
[#21]
Quote HistoryOriginally Posted By Mad-Machinist: can you email the the pics...not showing for me Could you PM me your email address? This website does not allow me to upload pictures. |
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Posted: 5/11/2020 5:33:31 PM EDT
[#22]
Quote HistoryOriginally Posted By M90A1: You're welcome to waste as much of your time and your money as you wish. Most people aren't going to invest the money in buying the tools you recommend, nor the time to learn to use them. And, they're not going to spend the money to have a gunsmith do it for them. As I stated, thank goodness manufacturing methods are as good as they are. If there were as many problems as you intimate, there would be a lot of guns blowing up, but there aren't. Carry on!! you are welcome to give as much unsafe information out here as you wish.........No gunsmith would not even think of doing a rebarrel without checking headspace. To tell folks that it is okay NOT to check headspace after assembling a collection of parts is ignorant........carry on? FAIL |
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Posted: 5/11/2020 8:28:11 PM EDT
[#23]
Quote HistoryOriginally Posted By asdaven: Could you PM me your email address? This website does not allow me to upload pictures. Let me post your pictures for you: Picture 1 of 4:  Picture 2 of 4:  Picture 3 of 4:  Picture 4 of 4: Not posted as it looks very similar to picture #3 Hope this helps. |
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Posted: 5/11/2020 8:47:36 PM EDT
[#24]
Rudy...what you think?
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Posted: 5/12/2020 9:36:02 PM EDT
[#25]
Fire pin has too much nose to it.. Quick check with surface micrometer...
Headspace on a 9mm AR-15,, you dont need gauges,, surface-depth mic is all you need,, set it using a 0.743/.744 sized case for reference You looking for 0.135" case sticking out of end of barrel,, pocket of bolt face should measure 0.125" Closed on the case, this will ideally leave you with a 0.010" gap between bolt face and barrel face with cartridge sandwich in between... only time bolt slap barrel be empty chamber |
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Posted: 5/12/2020 11:51:02 PM EDT
[#26]
Quote HistoryOriginally Posted By SBR7_11: Fire pin has too much nose to it.. Quick check with surface micrometer... Headspace on a 9mm AR-15,, you dont need gauges,, surface-depth mic is all you need,, set it using a 0.743/.744 sized case for reference You looking for 0.135" case sticking out of end of barrel,, pocket of bolt face should measure 0.125" Closed on the case, this will ideally leave you with a 0.010" gap between bolt face and barrel face with cartridge sandwich in between... only time bolt slap barrel be empty chamber agree 100%.......first thing I see is a LOT of firing pin......how are you pushing forward....it is an inertia pin.....have you checked to see if the spring is broken? see if you can get a pic with the tail of the firing pin flush whith where the hammer rests on the bolt....everything else is spot on in above quote |
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Posted: 5/13/2020 1:15:05 AM EDT
[#27]
Quote HistoryOriginally Posted By Mad-Machinist: agree 100%.......first thing I see is a LOT of firing pin......how are you pushing forward....it is an inertia pin.....have you checked to see if the spring is broken? see if you can get a pic with the tail of the firing pin flush whith where the hammer rests on the bolt....everything else is spot on in above quote It is an inertia firing pin with a spring. Spring is fine. Removed spring and threw the firing pin back in just for that picture. |
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