Soft primer strikes

[rockyboy]

First, Thanks guys. I put the build of this gun in the wrong place. Sorry. Now that it's doing something different, I hope it's ok to start a new thread. I've attached pic's of the puzzle. I was having feeding issues when You folks help me with a different buffer spring and weight as well as an adjustable gas block. This was exciting to watch the feeding as I adjusted the gas block. I started from almost closed and slowly opened it. Then I started to get really light primer strikes. I've switched out parts from a Black Rain one by one. Different, trigger for a heavier hit, buffer spring then weight. Bolt and pin. The only part that will not change out is the BC. In one of the pics you can see a sliver nick where the black rain's BC hits the green upper. The last thing I tried was to put a patch of duct tape on the end of the pin. It worked just great. I doubt this fix is in the Gunsmith's Handbook of Acceptable Repairs. If you have a moment, I'd sure like for you to look at the pics and/or have an idea of what's happening, or not happening. I also tried the black rain pin. It also required the "duct tape" fix. Thanks for your time. 

[jtallen83]

32 minutes ago, rockyboy said:

In one of the pics you can see a sliver nick where the black rain's BC hits the green upper.

A quarter in the bottom of the buffer tube might stop that contact.

[rockyboy]

Thanks, That BCG of black rain just stops right there. I was lathing up some spacers for the buffer tube in some 6000 grade aluminum when people smarter than I said stop that. I built around 15? AR15's so I mistakenly thought I knew something about 10's. Haha.

[98Z5V]

There's some tolerance-stacking issues somewhere with the recoil system parts that you're using, or else something is blatantly out of spec.  Quarters are 0.069" thick.  Goes into the extension first, then you insert the spring and buffer.

Love to see the exact specs and dimensions of what you're running for the recoil system.

P.S.  Always start an adjustable gas block WIDE OPEN, and ratchet it down a notch at a time, until it doesn't lock back on one-round-in-a-mag.  Then you go back that one setting, or two, and you're done.  You burn less ammo that way, and it's a much more effecient way of setting an adjustable gas block.

Edited April 11, 2021 by 98Z5V

[rockyboy]

13 hours ago, 98Z5V said:

There's some tolerance-stacking issues somewhere with the recoil system parts that you're using, or else something is blatantly out of spec.  Quarters are 0.069" thick.  Goes into the extension first, then you insert the spring and buffer.

Love to see the exact specs and dimensions of what you're running for the recoil system.

P.S.  Always start an adjustable gas block WIDE OPEN, and ratchet it down a notch at a time, until it doesn't lock back on one-round-in-a-mag.  Then you go back that one setting, or two, and you're done.  You burn less ammo that way, and it's a much more effecient way of setting an adjustable gas block.

Thanks, This all makes sense. Right now I'm just trying to set off a primer. This gun did shoot. Now this. I'm putting a factory loaded cartridge that I've pulled apart for shell and primer only. Manually putting charging the gun and seeing if the primer goes off. I did try different springs and weights and got the same response. However, to say thanks, I do lathe and mill work. I would be happy to make you would like a series of spacers made of 6k or 7k grade aluminum, I'd be happy to send you a few on me. I'd make them fit the buffer on one end and accept the spring on the other. Size's per your request. I think once I get the gun to shoot again, I'll need to re-visit your thinking.

[shooterrex]

How long is your firing pin? Is there crud or something in the BCG keeping the firing pin from traveling all the way forward?  If the gun did shoot and now doesn't this is the first place I would investigate.

[rockyboy]

I changed out the FP with the one from BR. No good, then I butchered one by putting it on my lathe and re-cutting it just to see if a longer pin made any changes. I seriously doubt this is an acceptable method of gunsmithing. It is "slightly" longer than the BR's FP and still does not work.

[98Z5V]

9 hours ago, rockyboy said:

I changed out the FP with the one from BR. No good, then I butchered one by putting it on my lathe and re-cutting it just to see if a longer pin made any changes. I seriously doubt this is an acceptable method of gunsmithing. It is "slightly" longer than the BR's FP and still does not work.

Something is stopping that hammer from slamming the hell out of that pin.  I'm betting it's a blown primer, stuck down there in the trigger mechanism.  Check that trigger close, remove it for inspection if you have to.   Be honest, if you find a blown out primer down there...  

[rockyboy]

Yeah, I thought about the trigger. "A heavier hammer" as one friend suggested. I've tried three different triggers. Two are pretty darn nice. Or cost enough to be. Anyway, Thanks for the brain effort. I really appreciate you spending a bit of time with my problem. But no foreign objects in or around the trigger. It's like the triggers need to "go more forward". I just don't get it. But when I put that patch of duct tape on the end of the FP, it worked.      

[jtallen83]

Have you double checked the firing pin channel for debris or burrs? Loose tolerances there let crap in. A little soak in a copper solvent will help if there is any brass build up, these things make some brass shavings.

[98Z5V]

Measure the firing pin protrusion into the bolt face.  Just take the BCG out of the gun, push the bolt into the BCG, all the way back, then push your finger on the end of the firing pin, push it forward - measure how much the firing pin protrudes through the bolt face.  

Like Jim said above - let's eliminate the hardware first, piece by piece.  If that FP protrusion isn't good, rip the whole BCG apart and see if there's anything in there, and clean the hell out of it, and try that test again. 

Edited April 14, 2021 by 98Z5V

[rockyboy]

Hey guys thanks for info. Here's where I am. But first, everything is clean as far as all the parts in the upper and lower. This is a new build and has less than 15 rounds through it. I've changed each part on the build with a working Black Rain. With no results. Yesterday I wondered about something I'd read years ago, bolt bounce. Placed a empty round with only a primer. Put in an empty mag. Locked the bolt back and then let it go by the release. Nothing. So I tried pulling the bolt back until I thought it was enough to just put the bolt into battery. Pulled the trigger and "BANG!" My guess is that I've got way to much forward energy and now have bolt bounce? Plan is to try different springs and weights. Yes? 

[jtallen83]

No marks on the lugs, inside the upper, anywhere in the carrier, cam pin? 

[98Z5V]

14 hours ago, rockyboy said:

 My guess is that I've got way to much forward energy and now have bolt bounce? Plan is to try different springs and weights. Yes? 

If you think bolt bounce is the issue, then the only cure for that is heavier buffers.  Springs alone won't fix that.  Just heavier buffers.

[Tack14]

Hope this works out for you rockyboy. Concerns like these are why I am very skittish about messing with the firing pin I got on BCG#1 I opened up or the rest of the BCG either.

Edited April 17, 2021 by Tack14

[mtrmn]

20 hours ago, 98Z5V said:

If you think bolt bounce is the issue, then the only cure for that is heavier buffers.  Springs alone won't fix that.  Just heavier buffers.

If I may add something: shake the buffer to make sure the internal weights move freely. This is supposed to give the BCG a sort of "double tap" when it slams home. Sorry if this has already been stated I haven't had time to go through the whole thread.

[rockyboy]

On 4/16/2021 at 11:43 AM, jtallen83 said:

No marks on the lugs, inside the upper, anywhere in the carrier, cam pin? 

Yes there are. Two places. I can see the bolt camming over but know don't know if it's all the way. Plan now is to get some gauges. Then perhaps I'm going to try a bit of milling. Then sell it for scrap and dive into my 12Y/O+ scotch collection. I have tried numerous combinations of springs and weights. When I thought of bolt bounce it was when I tapped the BCG forward and it fired. It won't do this anymore. Thanks guys.  

[mtrmn]

+1 on the scotch🙂

[rockyboy]

On 4/16/2021 at 11:43 AM, jtallen83 said:

No marks on the lugs, inside the upper, anywhere in the carrier, cam pin? 

On 4/16/2021 at 11:43 AM, jtallen83 said:

No marks on the lugs, inside the upper, anywhere in the carrier, cam pin? 

Yes there are. Two places. I can see the bolt camming over but know don't know if it's all the way. Plan now is to get some gauges. Then perhaps I'm going to try a bit of milling. Then sell it for scrap and dive into my 12Y/O+ scotch collection. I have tried numerous combinations of springs and weights. When I thought of bolt bounce it was when I tapped the BCG forward and it fired. It won't do this anymore. Thanks guys.  

These are the areas I'm considering milling.

The blue marker seems to be from the shoulder of the BCG. But is this not allowing the cam to fully engage? The yellow is because I took a BCG with bolt and pin and put a case with only the primer in it. Then I put this into the barrel. When I tapped the FP it fired. After three BCG's, bolts and pins. Four different buffer springs and as many weights. All of these in as many combinations as I can figure and it seems to only work without the upper? The green arrow? I have no idea.

[jtallen83]

Did the upper come with those dings in the threads? Marks around the cam pin cutout aren't totally unusual, I have a Sig that has some, made them new but it hasn't progressed since. The mark at the front of the ejection port must be from brass getting caught? Don't be milling the front of the upper unless you are positive that it is out of spec, I lap mine till they are uniform/square but that isn't taking much off.

[rockyboy]

16 hours ago, jtallen83 said:

Did the upper come with those dings in the threads? Marks around the cam pin cutout aren't totally unusual, I have a Sig that has some, made them new but it hasn't progressed since. The mark at the front of the ejection port must be from brass getting caught? Don't be milling the front of the upper unless you are positive that it is out of spec, I lap mine till they are uniform/square but that isn't taking much off.

On 4/16/2021 at 11:43 AM, jtallen83 said:

No marks on the lugs, inside the upper, anywhere in the carrier, cam pin? 

16 hours ago, jtallen83 said:

Did the upper come with those dings in the threads? Marks around the cam pin cutout aren't totally unusual, I have a Sig that has some, made them new but it hasn't progressed since. The mark at the front of the ejection port must be from brass getting caught? Don't be milling the front of the upper unless you are positive that it is out of spec, I lap mine till they are uniform/square but that isn't taking much off.

All the marks came from taking shots or trying different parts. If I mill the front of the upper. Can't I shim it back?

On 4/16/2021 at 11:43 AM, jtallen83 said:

No marks on the lugs, inside the upper, anywhere in the carrier, cam pin? 

Yes there are. Two places. I can see the bolt camming over but know don't know if it's all the way. Plan now is to get some gauges. Then perhaps I'm going to try a bit of milling. Then sell it for scrap and dive into my 12Y/O+ scotch collection. I have tried numerous combinations of springs and weights. When I thought of bolt bounce it was when I tapped the BCG forward and it fired. It won't do this anymore. Thanks guys.  

These are the areas I'm considering milling.

The blue marker seems to be from the shoulder of the BCG. But is this not allowing the cam to fully engage? The yellow is because I took a BCG with bolt and pin and put a case with only the primer in it. Then I put this into the barrel. When I tapped the FP it fired. After three BCG's, bolts and pins. Four different buffer springs and as many weights. All of these in as many combinations as I can figure and it seems to only work without the upper? The green arrow? I have no idea.

[392heminut]

On 4/18/2021 at 11:46 AM, rockyboy said:

Yes there are. Two places. I can see the bolt camming over but know don't know if it's all the way. Plan now is to get some gauges. Then perhaps I'm going to try a bit of milling. Then sell it for scrap and dive into my 12Y/O+ scotch collection. I have tried numerous combinations of springs and weights. When I thought of bolt bounce it was when I tapped the BCG forward and it fired. It won't do this anymore. Thanks guys.  

You've managed to post this^^^^^ three times now! Just go ahead and sell it and get into the scotch!

[mtrmn]

😆

[98Z5V]

I had an upper one time that had the cam pin cutout machined too far rearward - that stopped the BCG from even fully closing in the upper receiver.  No way was it gonna fire.

I cut the cam pin journal further forward, on the forward side of it, and it fixed the problem.  Mine was severe, off by alot.  This might be the issue you're seeing, but it's only off by a few thou.

Look into the designs and prints out there, on the positioning of the cam pin cutout.  Shouldn't matter is it's an Armalite print or a DPMS LR-308 print - those two should be in the same place, or we wouldn't be able to cross over some of those parts and make them work.