2 Blanks boom, then nothing, nothing, nothing

[HKARAK]

New semi build using BRP second gen bolt set up and BRP AR trigger set up. First two pulls successful and then nothing on next 8. Perfect primer hits on first two, then very light hits thereafter. Cannot figure out what changed. Any suggestions? Thanks.

[42rocker]

Talk to Brian at brp first and get his thoughts. Myself clean and double check everything and what type of blank ammo were you using?
Good to hear about the first two bangs that worked. Good Luck.

Later 42rocker

[Blanksguy]

Last would be after you clear up the issues with the gun's firing-mechanism..........if you have "Blank-related" challanges........post questions of that nature in the "Blank-Adapting the MG42/SA42/M53" Thread located in the MG42-Section.

Regards, RichardS
US Army, Retired.

[42rocker]

Here is the thread on blank firing.

viewtopic.php?f=9&t=1827

Later 42rocker

[usmc8488]

Had the same issues on my home build using the same parts, first use the heavy hammer spring provided, second I used an AR-10 hammer it is heavier. It fixed the problem.

[HKARAK]

Thanks for replies, link, etc.!!! Using German green plastic 7.62x51 blanks with German BFA. I have re-inspected all parts and will give a good cleaning hopefully this weekend.

Medium strength spring came with trigger/ hammer set up, so went ahead and ordered heavy one from BRP. Should have an update in a few days.

Thanks again.

[Blanksguy]

HKARAK,

Could it be possible that the Blanks were the problem (?)......such as the first two Blanks were loaded with enough powder to cycle the SA42 "System"........but the last two did not recoil the semi-only bolt system back far enough for the disconnector to catch the bolt (?).....this would allow the bolt to move forward with the hammer following it allowing a light primer hit.

The other issue may be as others have suggested with the firing-pin protruding from the bolt-face as it moves forward.

Regards, RichardS
US Army, Retired.

[HKARAK]

Update: To clarify- not a blank firing issue as when the blanks gets a sound strike they go bang and gun cycles. New heavy spring utilized and no change. Then determined the fa catch at the top of the AR hammer was possibly snagging on recoil spring, so ground that down. Now bang, bang, no bang, no bang, bang, no bang, bang................ Just not consistent. On all the "no bangs", there is very light primer strike. Buuuummmmmmmmmmmmmmmed.

[42rocker]

On some ammo that has been talked about there has been different primer depth. Something else you might want to check. On this blank ammo is it all from the same company and batch or ??
Good Luck

Later 42rocker

[HKARAK]

Good thought, but all blanks are same make, batch & even box.

It's a new day, so will give it a fresh look :-)

Thanks for pondering!!

[cptdarling506]

How old are the blanks?
Are you able to measure the length of the rounds and width of the neck and bases?
Here it was discovered that the old plastic blank (DAG) had shrunk over time
with tiny splits in the plastic where it joins the alloy base.
So you may have a headspace problem where some of the blank moves forward on hammer strike and
the not so shrunk/short blank still goes bang.

[blckwlfny]

I have those exact blanks
the primers are pretty consistent, so is the cartridge length. the powder charge is inconsistent, but that wouldn't cause your problem. They also work flawlessly in my semi mg13
in my '42 Im using the BRP trigger setup with a heavy spring.
Mine did something like that for a while,,,
With one exception,Im putting heavy money on the internals of the bolt assembly
it sounds like something is sucking the energy out of the hammer strike and inconsistent results means that its happening only when the components are in a certain orientation
I can think of 4 possibilities that can cause a weak strike
1) if the bolt is not fully in battery, this takes the zap out of the pin because the hammer moves the whole bolt
...hows your extractor?
2) or something is binding inside the bolt...maybe the ejector spoon is obstructing the pin.
...check the design is there a lip it might catch on?
3) or the pin is binding in the bolt wedge
...is there a burr on one side, or the wedge drilled slightly off center?
4) sometimes the 2-piece firing pin pieces can bounce off each other and actually absorb the energy just like a spring causing exactly what you are experiencing. the bolt starts with the pieces touching against each other and work fine, but then the recoil makes a small gap between them and they bounce causing the problem.

[HKARAK]

Using same blanks in Wiselite with absolutely no issues, so very confident it's not the ammo. #1- I am using the semi spring and wondered same about bolt body not being completely forward. Cant see/feel anything in regards to #2 or 3 and #4 -it is a one piece pin design. I'll try a cut down MG3 spring that seems to have more umph behind it. I really appreciate all the suggestions/ thoughts!! Thanks

[blckwlfny]

has it fired since then?
are you using a 2-piece barrel?

also some suggestions:
see if it works/doesn't work with the gun in different orientations fire it vertically upward and then downward. see if you can get the problem to happen consistently in one orientation, and then consider how the components are sitting based upon the position of the gun
(....it turned out that mine wouldn't fire when pointing upward b/c of the firing pin thing.) I know that yours is a one piece but these steps can help you eliminate a lot of guesswork to help diagnose what your guns particular "thing" is
I know it can be frustrating

Good luck.
let me know

[marknct]

The hammer might need to look like this, there can be a lot of conflicts in there. The primer will have a good looking hit but no ignition from the hammer dragging. The hammer might not reset sometimes which is the bottom of the bolt head hitting the hammer. The BC needs some clearancing and watch the firing pin for mushrooming. Clean up the pin and add a small chamfer. Heat to just red and then slow room temp. air cool.

[42rocker]

Thanks for sharing that nice info on the ar-15 hammer and what to do with the firing pin.

Later 42rocker

[HKARAK]

Happy Friday!!

Marknct= Thanks for your post and pics! What will that hammer shape do differently?

I put cut down MG3 spring in and now running about 80% booms, so some very good improvement :-). But still puzzled on that 20% Worth swapping out bolt head or barrel?

Thanks

[HKARAK]

Oh- its a one piece standard 7.62 x 51 barrel vs two piece. Thanks

[marknct]

What will that hammer shape do differently? Swing freely
top/back for BC clearance
top/front ejector rod
front/lower bolt head
You need to watch the BC when you pull the trigger (empty chamber of course) and see if the BC moves. Depending on where your pak mtg pin is located the hammer can hold the BC back enough that the rollers aren't at full lock. Bad thing.
Having at least 2 colors of Dykem here really helps. It tends to transfer more reliably in oily situations. The BC hammer slot doesn't have a lot of clearance either if the pak mtg bracket wasn't fixture located.
It will take multiple trips to the range to find all the conflicts, it's a 20 gallon in a 5 gal hat scenario.
I'd go back to the BRP spring and find the conflicts. I can see where the hammer is holding the BC back sometimes and releasing the hammer lets it slide past the back of the BC. The larger spring might shove the BC forward faster 80% of the time as the hammer chases it.

[blckwlfny]

are you sure that the hammer is hitting the top inside of the extension?
If that is a BRP FCG, then it is dropped about 0.125" and should eliminate that problem and a few others
I looked at the design, and I'm wondering if it might be obstructing the hammer slightly on the SIDES as it rises through that narrow opening. It looks like all you need to have that happen is to have the grip or bolt SLIGHTLY off center which can easily happen and still be within the tolerances of a stamped receiver like this.

if you haven't already done so, test the potential rubbing points it by coating the inside of the bolt with soot from a candle and look to see if/where it was rubbed away
...if nowhwere, next try it on the hammer and try to consider if it is rubbing on something other than it should during the normal cocking process.