Joined: January 20 2011 Location: United States Posts: 65
Posted: August 24 2012 at 6:50pm | IP Logged
I started a new thread on this subject as I didn't want to clutter my build thread with another FCG design which might reach a dead end. Last month it finally became clear that The striker system, which I have been working on for far too long, is not practical. I know! Some of you warned me! It works fine but I can't keep it legal. I don't know what the legalities are but I can't sell a system that will revert to it's old ways and go FA at the first opportunity. This means passing a failed disconnector test. Have others done this? I don't know. I've noted that my AK-47 passed such a test that I did, but it also fired 2 rounds FA once. Lightening the striker enough to pass this test resulted in a built-up weldment that was too fragile to take the considerable loads involved. Not the first time in my career as a Mechanical "Engereer" that I engineered myself into a corner. Time to concede defeat and go hammer and this I have been frantically working on to get back on track.
The original motivation for a striker was to get a system that would use as many of the original components as possible for authenticity and for ease of installation. The goal was to be able to install with out machine tools. Looking at the surgery required for other hammer systems convinced me that this wasn't possible going that route. Maybe I was wrong! The system shown in Pic 1 is what I came up with. This shows my test lower with the new hammer system installed in comparison with an original lower. Note that all the old system is still there on the test gun except the sear. Pic 2 shows a closer view of the FCG. The old sear has been replaced with a actuator bar/frame that's buried in a complicated looking little box affair with a hammer. Pic 3 shows the ugly box sitting on the table.
Status: Offline
okie75
Sgt
Joined: January 20 2011 Location: United States Posts: 65
Posted: August 25 2012 at 9:03am | IP Logged
The 1st pic below shows the components of the FCG including the firing pin. I sprayed some primer on some of the parts not to make them prettier but to get a better look at what they actually look like. These parts have led a tortured existence. The original trigger is pinned to the actuator bar in front of it. This bar is pivoted in the box below it at the same station where the old sear pivoted so it describes the same movements as the old sear. This actuator has 2 cross pins which actuate the disconnector and sear. The hammer and it's springs turn on a pin at the front of the box. Above the actuator are the hammer and 2 funny looking pieces of sheet metal. The piece sticking into the hook of the hammer is the disconnector pawl. The one waiting to it's right is the sear pawl. Their springs are above.
Pic 2 is a closer up view of these parts. Both these pawls and their springs pivot on a pin at the top of the box. These pawls are modeled on the rachet and pawl mechanism - one of the oldest and most reliable mechanisms known to man. S&W revolver FCGs feature a pawl as a disconnector of sorts and that was my inspiration. Thank you S&W. I owe you one!
The light springs push both pawls into the hammer hook at all times such that both pawls are trying to grab the hammer. When the bolt flies back, after firing, with the trigger pulled - which is normal, the hammer is pressed down and hooked by the disconnector. The sear is being held aft by the forward pin through the actuator bar pressing on the front surface of the sear. The bolt goes back home
and the hammer is still held down. When the trigger is released the original trigger spring lifts the actuator bar same as it used to lift the old sear. The disconnector is rotated aft now by the aft actuator pin pushing up against the aft extension of the disconnector pawl. The disconnector is pulled out of the hammer hook while at the same time the sear pawl is released by it's actuator pin moving up. This allows the sear to move into the hook. The sear is slightly shorter than the disconnector so that when the disconnector comes free the hammer moves up only to be caught by the sear. When the trigger is pulled again the actuator again pushes the sear out of the hook . The disconnector is trying to get back in at the same time but it's too long now and is held back by the edge of the hook. If the bolt is racked with the trigger released the disconnector is being held aft by the actuator so it doesn't come into play and the hammer presses down until it's hooked by the sear and the gun is ready to fire. The beauty of the pawls is that they allow a one hook hammer simply by being different lengths.
Pic 3 shows the assembly minus the trigger. The trigger is pinned to the actuator using the original pin. This pin rides in the slot in the original safety which is retained and works as before. In fact the safety is used to help lift the FCG assembly out of the lower.
The assembly will be a "drop in" box held in by a screw in the front bottom and the aft left side which is the block on the side with a threaded hole. Why a screw in the side? Because the old sear pivot block riveted in thru the trigger guard is "hard as the hubs of hell" and I couldn't drill thru it for a mounting screw. The installation requires drilling the screw holes and some dremel work on the old sear pivot block and the left hand bolt guide rail. The FCG assembly will hopefully be a fully tuned box ready for instl. Next post - firing tests.
Status: Offline
okie75
Sgt
Joined: January 20 2011 Location: United States Posts: 65
Posted: August 25 2012 at 9:13am | IP Logged
A series of firing tests was completed yesterday 8/23/12. "Lions 50, christians 1"!. After some tweaks on hammer width, pawl length, etc the system has worked quite reliably. Some early disconnector failures turned out not to be any such thing. What they were was slam fires! With a light firing pin spring the one piece firing pin was too heavy and the gun fired any time the bolt hit hard regardless what the FCG was doing. Then came a series of lighter and lighter firing pins and heavier and heavier firing pin springs (and hammer springs). Note the size of that firing pin spring in the pic of the previous post. Finally after the slam fires stopped it was time for the dreaded failed disconnector tests. Heavier firing pin springs yet and a lightened hammer. Finally passed the test but only marginally. The only problem with the FCG mechanism was a sticky disconnector because of the heavy hammer springs. The trigger needed a nudge to release. I expect the original trigger spring to be enough after some refinements. I plan to experiment with a 2 pc firing pin to get an effectively lighter firing pin. Some of you can give me some pointers on this and the whole problem of firing pins, hammers, and springs. Next comes productiion design and testing. I think I have an integrated FCG that will work for the KP-44 and by extension for the PPS-43 - but then I thought that before. We've all been waiting too long for the answer to the FCG problem.
Status: Offline
okie75
Sgt
Joined: January 20 2011 Location: United States Posts: 65
Posted: September 23 2012 at 2:11pm | IP Logged
An update on progress: Below is a pic of the new production prototype box frame installed in a lower. The rear attach point has migrated further aft to a point behind the old sear pivot plate where a screw hole can be drilled in the bottom of the lower. This is the 3rd iteration of this part. When you have 1.2 cubic inches to work with, along with several obstructions, it's a puzzle.
Next comes new stuff in the frame and then another test firing session.
Status: Offline
Karl_T
Cpl
Joined: August 23 2011 Posts: 32
Posted: September 23 2012 at 5:52pm | IP Logged
Thanks for the update. I just got bit by the KP44 bug and bought three kits with barrels today.
Karl
Status: Offline
okie75
Sgt
Joined: January 20 2011 Location: United States Posts: 65
Posted: September 28 2012 at 9:35pm | IP Logged
Test fired the production prototype box assembly today. Worked! See pics below: First is the assy installed, 2nd shows the mounting fasteners just fwd of the safety and inside the top front notch in the grip. 3rd shows the assy on the bench. This one has had a tortured history too. Next job is drawings for the laser cutter, a new firing pin, and a new modded bolt. At this point it looks like it's going to work but the definitive failed disconnector tests will come with a new lighter firing pin and the new bolt which will be considerably heavier. The bolt in use now has been cut for this and that until it's quite a bit lighter than original which makes for faster cycling and more difficulty in passing the test.
Status: Offline
okie75
Sgt
Joined: January 20 2011 Location: United States Posts: 65
Posted: October 02 2012 at 12:08pm | IP Logged
I checked a Russian PPS-43 kit against the KP-44 and found them nearly identical as far as the FCG is concerned. It says a lot for the people who designed the PPS that the Finns copied it so completely. The only real change they made was the safety. The Finns centered the thumb bar - which made it harder for me since part of the thumb bar was in the way of my assembly box. The box had to sit above the bar as the bar moved back and forth. On the PPS the safety is completely out of the way. Looks like the FCG will fit the PPS with little or no changes.
Back to the KP, I made 2 changes to make the old safety work. The pic below shows the forward curved slot dremeled out. The original design featured a bolt blocking system. When the safety was pushed back (On) the safety bar rode up in front because of the curved slot. This blocked the bolt which was in the aft position being an open bolt gun. This caused interference with my assembly as the thumb bar moved up too, so that feature had to be eliminated. The new cut out allows the bar to move straight aft. The safety now works much easier and the bolt blocking is supurflous anyway because the bolt is now closed and forward of any blocking means. This mod may not be necessary on the PPS since it's safety is out of the way. The other change was a new trigger pin shown near the slot it rides in. the head of the pin is larger than the original so as to nearly fill the slot. This is needed because the new sear is more sensitive than the original and if the pin fits too loosley in the slot it may not prevent firing. More later.
Status: Offline
Mech warrior
Admin Group
Joined: October 22 2011 Location: United States Posts: 1384
Posted: October 02 2012 at 11:45pm | IP Logged
okie75, the finns copied the pps42! That was the original design. The pps43 was redesigned to make production easier and faster. Not sure why they choose the centered safety.
__________________ Measure, think about it, measure again, think about it some more, measure again, then cut......."Oh S***!!!!"
"Courage is contagious. When a brave man takes a stand, the spines of others are often stiffened." Billy Gram
Status: Offline
okie75
Sgt
Joined: January 20 2011 Location: United States Posts: 65
Posted: October 03 2012 at 1:05pm | IP Logged
Yes I know Mech. The Russians did the '42 in the freezing, bombed out factories of Leningrad, all while starving, and they came up with what some consider the best SMG of the war. I have a lot of respect.
You cannot post new topics in this forum You cannot reply to topics in this forum You cannot delete your posts in this forum You cannot edit your posts in this forum You cannot create polls in this forum You cannot vote in polls in this forum
