Another Cosby Mystery-Weak primer Strikes

[www.Prussia.us]

This issue is persisting here is a review of the background from my previous post:

Here is the problem, extremely weak (almost non-existent-weak) primer strikes on an SA Mg42.

The hammer is hitting the striker straight-on in the sweet spot,
the bolt slides up and down the rails when the recoil spring is removed w/o binding issues,
bolt locks into battery seemingly nice and tight,
bolt head is headspaced checked w/ barrel and passes with a go gauge,
dummy rounds cycle/eject all day long w/o issue,
Ammo is Winchester 8mm commercial.

Bolt: Pirate’s V2 semi-bolt
1) Checked firing pin, size is normal, no damage, or chips
2) Bolt locks into barrel extension, pops out when barrel is bounced off the floor (using the bushing of course against the floor).
3) Bolt headspaces with the barrel extension.
4) When bolt is out of gun and rollers pushed out (like when locked in the barrel extension) pressing the striker with moderate pressure activates the free-floating firing pin, protrusion looks good, the same as a regular bolt.

Gripstick/FCG: Thompson Machine grip that Richard did, the front area has been slightly milled so that the hammer range is GTG
1) Replaced standard Ar15 hammer spring with Wolf heavy spring.
2) Ground hammer down as per Rocco’s directions from many years ago (I miss his humor and contributions).
3) NO binding of the hammer anywhere and it has the full ability to move forward and ONLY make contact with the striker on the bolt, (furthermore Pirate’s bolt has the metal milled in a way whereby the hammer is very unlikely to ever hit the top/bottom of the rear area thus slowing the hammer down).

The Receiver:
1) Everything measured to be in check, it was re-welded by a reputable FFL07 who has done many semis and some Post may samples.

Question:
Is there something simple I am missing?

I almost wonder if the bolt somehow in battery is not actually “in battery” thus keeping the rollers from flaring out and allowing the firing pin full forward travel, however w/o the recoil spring the bolt will slide into the extension and lock requiring the charging handle to pop it out.

Any ideas, Jbaum, Blanksguy, Bob Naess, Bueller??????????????????

I was called in to help get it going, but I have exhausted all of my troubleshooting abilities.

[Blanksguy]

Just a couple quick questions:

1: When you checked "Headspace", was this with the barrel/bolt in or out of the gun (?). I ask as this would be a quick-check to see if the "assemblies" were allowed to move all the way forward.
The hard part on this (and nothing against the manufacturer of your SA42) is that if the relation of the cam-piece's "ramps" vs. the location of the barrel-stop riveted under the rear-sight is slightly off, it could (in theory) slightly hold the bolts rollers from full outward movement-?

2: Do both cam-pieces have the same "original-stamped" serial-numbers (?)........mismatched parts may again be holding the bolt's rollers from full outward movement.

3: Slightly bent feed-lever (?).....or top-cover not centered over top of receiver (?). This might not allow full forward movement of Bolt-assembly. Here you would try "hand-loading" a "Blank" at the range (or appropriate area) and try firing that one "Blank" to see of you get good primer "hits" with the top-cover and feed-tray removed.

4: Is the right-side cam-piece bent inward any (?)......this (again) will keep the bolt from moving all the way forward and/or stop outward movement of bolt-rollers. Could be something as simple as a "burr" on one of the pieces.

5: As this is a new SA42.....is the bolt hitting anything during the last of its forward movement that you are not seeing (?). Use a "Black-marker" and color those areas of the bolt-head and rear-roller that may hit something and try you movement again.......then remove these parts to inspect for "Black-marker' being removed.

6: Is the barrel-assembly going fully-forward against the barrel-stop under the rear-sight (?). Inspect the barrel-bearing/Flash-hider area if not.

There are several other things that can be checked on a new gun.......was your SA42 made from new parts-receiver or DEMILed receiver (?).
Anyway, this should keep you busy for a couple hours of inspections.....and please post back any findings on the negative-side.
Regards, RichardS
US Army, Retired
Blanksguy2001@outlook.com

[www.Prussia.us]

Thanks Richard, I have plenty here to work with. First my gun is in storage far away from me, it works well, Pirate did the internal work, a 3-cut that went together like a charm.

Second this is another kettle of fish, it was a four-cut 1944 receiver. The head space was checked out of the gun and you gave me some great ideas to try, I hope to get back within a week to help with the project.

THANKS...........

[www.Prussia.us]

Okay had a chance with an afternoon off to try a few things with this project, ground a few spots that may have been problem areas until being absolutely sure that NOTHING could impede the hammer from hitting the striker:


1) Headspace with barrel in gun is good, checked with a no-go, go, and field, it all worked as it should (neat trick though trying it with everything together).

2) With clay filled into the primer cavity of a dummy round (as JBaum suggested many moons ago), I hand loaded the round into the bolt head, and slid the bolt into battery, pulled the trigger and a very nice deep dimple resulted, this would have easily fired had it been a real primer.

3) Okay I hand-loaded a live round into the bolt, carefully put the spring, buffer/buttstock, back on (feedtray and topcover were removed), put on my protective gear, pulled the trigger and "click" same thing,,,,,a real primer only offered another weak primer strike, same as before

The whole feeding system is ruled out (for the moment) b/c I handloaded, the headspace checked out, granted the cam is not a matching serial numbered set, they are both Berlin-Borsigwald, I hope given the clay dimple and good headspacing that the issue is not the un-matching cam.

I am utterly confused, granted it does not take much, any thoughts??

[Blanksguy]

Prussia,
We'll try to talk you through a couple ideas (items to check) taking everything that we talked about earlier out of the variables........only looking at the light primer hits in a new SA42 made from a 4-cut receiver.

Some ideas/thoughts are listed below :
Note: I have to take the ammo out of the equation as it should be "new" standard 8x57mm Mauser ammo.....correct (?)......not reloaded.....and that during your "clay-primer-trial" that you didn't inadvertently allow the bolt-head or firing-pin to move during installation into the chamber......correct (?).

1: At this point, with everything else out of the equation, we will have to look at the SA42-Bolt-Assembly and its contact by the hammer. Clay is softer than the metal of a real primer. We will have you check two areas next.......
First....with the SA42 set where you can install the bolt assembly slowly so that the firing-pin stays in the rear position.........check to see if there is any "drag" on the firing-pin and/or firing-pin-parts for 2-pcs. firing-pins as it/they move forward during a primer-strike. Maybe it drags.....or binds in a spring, etc..
Second......put some thin strips of clay on the rear of your Bolt-assembly where the hammer would hit the firing-pin's rear. With the bolt fully forward....see if the hammer hits the firing-pin "squarely" ......and not to one side nor above or below. Adjust if needed and try again.

2: The second item to check with light primer hits I will have to continue with my next posting to this thread as the MG42-Board doesn't give me enough space/letters to reply fully.
Regards, RichardS
US Army, Retired
Blanksguy2001@outlook.com

[Blanksguy]

"reply" continued..............
2: The next item with be a little more difficult to check.......as we are working inside the SA42-receiver.....
This next section has nothing to do with the builder of your SA42, nor of his/her abilities to do this things ......"but" sometimes things get welded and/or warp/bend during the heat of welding these together. This is especially noticeable in the area of the cam-section and receiver-half of the SA42.

With that said, we will have you check to insure that the bolt-head rides level in the rails and enter the cam-piece (trunnion) on the same level (IE: The bolt-head won't move upward/downward on either side and does not tilt any to the left nor to the right. Your barrel-assembly must be installed to check these things because if the receiver was welded/warped during welding in these areas it can make the bolt-head twist and/or tilt causing a binding of the firing-pin(s). Barrels are pretty much generic....and you can try different barrel-assemblies with the same results.).
If the bolt-head tilts or twists during its final movements, this may cause the binding and light Primer-hit. The only cure here is to correct the location of the offending parts.

As you go through this part.....you will need a good flash-light or bright-lights to see down inside the SA42 receiver when/where the Bolt-Head makes contact. Take your time and move the parts slowly...........then when the Bolt-Head is fixed to the barrel-extension........then recheck to see if you have any binding of the firing pin parts.

Hopefully, you will only find a bent firing-pin-section......or binding firing-pin rebound-spring.....or that the hammer does not hit the end of the firing-pin squarely.

On your "Cam-Set"....they are machined at the factory as "SETS", and then serial-numbered as a set.......this may still be an issue to keep in the back of your mind as you check that bolt-movement (?).

Let us know what you find........or what your thoughts are on all of this (?).
Regards, RichardS
US Army, Retired
Blanksguy2001@outlook.com

[www.Prussia.us]

RichardS, I AM MUCH OBLIGED, for your guidance and help.

Really quick, yes I delicately removed the bolt after the clay test, however I should have noted that with a free-floating firing pin on Pirate's bolt it would retreat w/o any further insertion to the clay.

The firing pin on the bolt slides smoothly fully out and fully in, however this weekend I will be checking it again w/ a closer look for any slight binding.

Yes I ONLY shoot quality reloads or commercial ammunition in these guns, I would rather spend more, shoot less, and not beat the gun up w/ military (especially corrosive) ammo, the testing on this gun has been with new commercial Winchester ammunition.

Good idea regarding the bolt-tilt that will be checked for sure, with your insight I think the issue may be the hammer I wonder if too much was milled off the top to round it for bolt clearance,,,,,,,,,,if only doctors were as smart as gunsmiths and could diagnose problems from afar w/o physically seeing them-you are doing an amazing job for not even having the chance to inspect the patient.............I will report back, THANK YOU

[Blanksguy]

Prussia,
Another way to check alignment on the two major bolt parts (bolt-head and carrier) is to remove the firing-pin-parts and insert the bolt-assembly back into the gun with the barrel-installed.........then using a "Flash-Light" at the muzzle end, slowly slide the bolt into the receiver (looking at the light through the firing-pin-channel) until it seats into the barrel-extension to see if the light changes.

Another item you should have already checked is to see if the firing pin is being hit "squarely" by the hammer.......try a small piece of "masking-tape" over that rear-area of the bolt-carrier that the firing-pin protrudes from...........while doing this, also inspect to insure that the hammer does not contact the inside of the bolt-carrier, such as the top-sides of the hammer, or its "tail" behind the head.
Sometimes this will cause the firing-pin to only be lightly hit.

Last, insure that your firing-pin-assembly has enough length, check firing-pin-protrusion....remember, clay is soft and will show a deep-hit by hammer even though your firing-pin is not long enough.
To measure, try removing the extractor-parts....then with the bolt/bolt-carrier attached to the barrel-extension.......try to measure the firing-pin-protrusion with a slight rearward pressure on only the bolt-head (not pulling on the bolt-carrier as this will lengthen the assemblies.).

If you have any questions on how to measure this, please post some questions........and photos may help soon.
Regards, RichardS
US Army, Retired
Blanksguy2001@outlook.com

[DARIVS ARCHITECTVS]

As a variation to what Blanksguy said regarding using clay as an indicator of firing pin protrusion, you may try this, since clay is very soft.

Take an unfired 8mm shell casing which has no primer. Fill the primer pocket with melted candle wax, which is a tad harder than clay, and shave the excess flush to the case base surface. You may want to press a bullet into the case to ensure that you replicate every aspect of the mechanical behavior of your gun. Chamber this test round and fire the firing group, eject the round and see what the firing pin is doing as far as protrusion. The wax may provide you a better picture of pin impression than clay because it offers more resistance to deformation. Using something even harder, like a soft plastic, will probably have too much resistance to deformation. You may even try using an active primer in an empty case. You should be able to determine if it fired or not. The downside is that you waste a perfectly good primer...

Just my wee little $0.02.

[www.Prussia.us]

Hey DA, THANKS for chiming in, that is excellent advice, so far RichardS has also offered much sage guidance as well,

I think I may have found at least one problem, not sure how to fix. As suggested, except I had to use Prussian blue (you know the Prussian thing)-just a tiny bit, at the tip of the stricker where the hammer contacts it, and noticed a smudge indicating this situation (see below at me pathetic quick photoshop sketch, yes a kindergartner could have done better, graphic art is not my strong point ) Please note, the hammer face actually extends above the stricker-so that if it hit perfectly horizontal there would be some material above the stricker-again poor sketch, showing the angle of the hit is the main point of the sketch.

It appears the hammer is not able to strike the the sticker with the blunt face, it is catching the bottom 40% (and is obstructed by nothing else but the stricker), since the hammer cannot be adjusted, I gather the only option is to shave off some of the stricker ?

This is why I stuck with all of Pirates internals on mine, once you blend (this one having Pirate bolt and Thompson Grip), you start to have to play doctor, and I am more like Mengle than Pirate, gunsmithing is not my strong point either

[DARIVS ARCHITECTVS]

Despite the incredibly crappy etch-a-sketch MS FingerPaint drawing , we do understand what's going on with your hammer/striker situation. If the striker in this gun design is able to rotate, then slightly rounding off the edge of the end of the striker will allow the hammer to hit the very center of the end of the striker, no matter what position the striker is rotated in. If the strike is prohibited from rotating by design, then the end of it may be rounded to a simple radius in the transverse vertical plane only. Just make sure not to take any meat off the center area of the end of the striker, or that will shorten it, which may change things a bit in terms of protrusion (assuming this strike is integral with the firing pin farther forward.

In the configuration as it presently is, the hammer contacting low on the striker may have a tad less force, and may even result in some force pushing the end of the striker upwards instead of all the force applied in a direction along the center axis of the striker. This is really a simple exercise in geometry and force vectors. Ensure that the striker is polished very smooth, even mirror, along with all other parts that slide, so you reduce friction to a minimum. If corrosion is an issue, blue the parts after polishing them mirror smooth, so you form a magnetic (oxide) layer that holds oil, hence no steel will be in contact with air (and thus moisture) and rust orange on you.
The problems with ALL semi-auto conversion I have seen are:

1) a reduction in recoil spring strength from cut/downsized recoil spring, resulting in much weaker feeding force to push the round out of the tight belt links and into chamber,
2) increase friction due to more surface area of sliding parts in the modified design, and
3) heavier firing pin/striker mass requiring strong hammer force so military hard primers are struck hard enough to fire reliably. A solution may be a combination of a heavier hammer spring with a heavier hammer. AR-15 guts don't seem adequate to solve the problem. Also, the AR-15 parts can break after a time. (easily replaced).

A legal full auto MG-42 is much more simple and reliable, but as we all know, they are ridiculously expensive and really eat your wallet in ammo costs, even though the sound they make is FRIGGIN' AWESOME.

I dinked with my buddy's semi auto M-53 enough to get it fairly reliable, but it still doesn't slam that bolt forward with the speed and force of an original MG-42, which makes me cross my fingers every time we run it.

[Blanksguy]

DA,
You are correct in several of the points that you bring up about troubleshooting SA42s.
Prussia's current issue of light-primer-hits with live ammo in a newly made SA42 has a few challenges....and we could be seeing several things going on.

The rounding of the firing-pin's-rear-tip may only correct part of the issue if the hammer-axis-pin was located too far forward. (IE: If 4-cut receiver was welded together where the trigger-group now sits slightly forward.....or that the location for the hammer-axis-pin was made too far forward in the grip.).

The second issue is that the hammer may have been located correctly in all of this...."but" the inside rear-stop-point for the hammer against the firing-pin-rear may not have been machined enough to where "it" now sits too far to the rear when the bolt-assembly is fully forward. The correctly located hammer now tries to hit the rear of the firing-pin but is unable due to being blocked ........ and possibly requiring the machining of the inside of the bolt-carrier or the undercutting of the hammer just below the Firing-pin contact-point. We don't know if the firing-pin is too long.......and all of this may just require a slight trimming of the length of the firing-pin-rear-section (IE: New SA42 just welded together.).
We've asked that he check all of these areas in/around the bolt-carrier and hammer-contact......and to insure that the bolt-assembly moves forward without binding of the firing-pin-parts (bolt-head-tilt off center axis).

We don't have a clear picture yet of what is happening inside the SA42......nor of the length of the firing-pin at the rear of the assembly once seated........and don't know if the firing pin is too short (light-hit)......being hit by the hammer from the underside (as drawing-shows, and again would be a light-hit).......or if hammer is obstructed by the bottom of the bolt-carrier (partial-hit). At this point, just trying to sort out the easiest way for "Prussia" to get past this small challenge.
Note: After the above is corrected so that the gun fires.....he will have to check semi-automatic-fire and operation of the feed-mechanism and belts.........making adjustments, etc. where needed.

Regards, RichardS
US Army, Retired
Blanksguy2001@outlook.com

[DARIVS ARCHITECTVS]

I agree about the hammer angle issue. The hammer should be 90 degrees with respect to the striker axis with the firing pin fully extended. Anything other than that means less impact force. You are right in saying there are many other factors.

The gun should be analyzed for each and every factor and corrected methodically.

The next step as you mentioned is to see if the firing pin is actually capable of full extension forward without interference.

[www.Prussia.us]

Hey DA and RichardS,

Much obliged, first I just noticed that my dearth of sleep last night compelled me to consistently misspell "striker," anyway, it seems my spelling is as bad as my, sketching , and gunsmithing

Okay, b/c this project is not in a place I can physically get to everyday, I have maybe a few hours a week, so bear with me.

The issue of the cut re-welding resulting in a hammer too far forward is indeed an intriguing and scary thought that I have considered, and more likely than being the fault of Richard's/Thompson grip, if that is the issue.

The hammer when dry-fired w/o the bolt in the gun has full forward travel well past the point where the striker stops it-when in the gun, Pirate's bolt has milled channels in its rear that prevent the hammer from binding on anything in the rear of the bolt except the striker.

I have to try and get to it tomorrow, check the bolt head for possible tilt issues like RochradS stated, and open the bolt and see if that striker mechanism up close again.

You guys are the best, THANKS for your patience, and help, ALL advice is appreciated

[Blanksguy]

Prussia,
....as I posted earlier......."if" the "challenge" turns out to be that the hammer can not make full 90-degree contact with the rear-tip of the striker (firing-pin-assembly), it may only require either a slight re-shaping/undercutting of the hammer-face. This may not be the best option due to mass/weight loss for hammer to hit firing-pin-assembly/"striker"....(but cheaper, and you can get spare hammers ? ). The other option at that point would be to slightly machine the inside area where the "striker" (firing-pin-assembly) sticks out of the inside-rear of the bolt-carrier. If you do not have a milling-machine or lathe, this may be slightly more expensive "but" once corrected will end "this-issue".

Neither of the above will correct a misaligned REWELDed SA42 as it may only eliminate the issue of the hammer contacting the firing-pin-rear-tip at 90-degrees. It will also not correct other issues such as (but not limited too) firing-pin-assembly binding on a "re-bound-spring" inside the bolt-assembly, a burr or piece of metal binding the firing-pin-assembly, mismatched cam-pieces tilting bolt and/or rollers out-of-time with each other, etc.. All of these items you must check for one-at-a-time. Clear photos may show up these and other areas/items/issues that you have not brought to our attention.

Regards, RichardS
US Army, Retired
Blanksguy2001@outlook.com

[www.Prussia.us]

Well, here is where I am at, I think RichardS nailed it.

First thank your for your patience, this project is located a fair distance away, in a location without power, so I have to parachute in with whatever tools and limited knowledge to work with that I possess.

After close analysis it appears Thompson’s/PanaceaBeachBum’s grip, which is like the early WLA gripstick, sits further forward than the hammer on the FAL/fcg gripstcik box, this is where RichardS intuitively picked up on the distance issue regarding the receiver-which cannot be totally ruled out but currently does not seem to be as overt an issue as the hammer angle, it is my assessment that the options are either:

1) Obtain an FAL/fcg grip from Project Guns and perform the necessary alterations to the receiver and recoup to fit,

2) Contact Thompson and hope he responds after all these years and either see if he still is making semi-bolts (I doubt) but maybe he will have the amount of space the firing pin protruded behind the rear of the bolt for the hammer to hit (Thompson’s bolt did not have a striker if I recall) and then experiment and remove that material from the striker and hope that the striker will still get enough force to activate the firing pin,

3) Buy a BRP bolt and hope it is compatible with the grip,

4) Or, as RichardS stated, shave the hammer to fit---good theory $20 hammer is cheaper than a $200 BRP bolt


I checked the bolt head tilt—no issues, checked for burrs or damage to the cam pieces internally-no obvious issues, used bee’s wax in the primer cavity of a dummy round to check the FP protrusion same--as the clay, checked to be doubly sure the sail on the bolt was not hitting the charging handle keeping it from full battery, despite passing the headspace tests—no issue, also triple checked to make sure the AR15 hammer spring was not installed backwards, clearly the bolt functions, and the hammer is too far forward to make a hard 90 degree contact.

QUESTION: Is there any such tool to test the strength of the hammer velocity? Also who sells the cheapest AR15 hammers??

If I had a cell phone to get pictures of this it would have helped but I eschew cell phones so we had to do it the old fashioned way, and a most impressive diagnostic run down put forth from RichardS, and thanks DA for your input it was also helpful.

I need to get more information about either removing the striker’s rear material, hammer material, or obtaining a BRP bolt, after such time, if the issue persists, this thread and the nightmare will continue

[Blanksguy]

Prussia,
To answer your question about "Tools to Test AR15/M16-series Hammer-Springs"......the manufacturers probably have them but due to costs, it will be way cheaper to buy spare new springs.....and "Wolf-Springs" will probably have a good selection of standard and stronger springs.

On the question as to who has the cheapest Hammer.....(?).......prices from all of these "Vendors" will change from weeks to months to even days.........doing a quick check - search on the web will bring up several vendors selling these.......and all will be about the same prices.
I do believe that either a heavy-hammer, or even an M16-series FA Hammer will be more heavy than a standard AR15 hammer.

More later..........
Regards, RichardS
US Army, Retired
Blanksguy2001@outlook.com

[Blanksguy]

Prussia,
(More-information..................).

On your quest for more information on your hammer location vs. where it strikes the firing-pin ("striker") .....
1: Regardless of who made the firing-grip-housing...........the location is relative to the location of the inside-rear-edge/ledge of the Bolt-Carrier where the rear of the firing-pin-assembly sticks out for the Hammer to strike it. (IE: The Hammer rotates on the Hammer-Axis-Pin directly under the Bolt-Carrier-Assembly.).

2: If the Hammer-Axis-Pin is located too far forward, the standard hammer hits the firing-pin-rear-tip from a slightly lower point/direction.....and where "DA" was saying that it could lose force due to some of the force used in pushing upward on the rear of the firing-pin-rear-tip.

3: If the Hammer-Axis-Pin is located too far rearward, the standard Hammer hits the firing-pin-rear-tip from a slightly higher/downward-point/direction..........and could lose force due to loss of hitting-force being use to push/hit the firing-pin-rear-tip downward and not directly towards the cartridge-case-"Primer".

There are several "fixes" to chose from on correcting this challenge/issue.......and the owner will first have to figure what their SA42 id doing "before" they can decide which way they want to correct the issue. Each SA42 is different and will depend on what receiver (and/or receiver-pieces) was used to make their new SA42. Some issues are a quick "fix" by adjusting a part....other cost more due to the owner choosing to machine/correct a part so that they can continue to use standard-parts such as standard AR15/M16-series Hammers vs. modified hammers.

Keep us informed as you walk this path and we will try to assist you in other challenges as they present themselves.
Regards, RichardS
US Army, Retired
Blanksguy2001@outlook.com

[42rocker]

Richard and DA Thanks for sharing a lot of great info.

All folks that are starting off should look at and review this list of what if's??

Thanks for sharing everyone.

Later 42rocker