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Old 03-19-2009, 09:18 PM   #1
skemler
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Default PPS-43 Build - Need Advice

Been looking into a PPs-43 build, but I need someone to help explain the complications.

A PPs-43 normally fires from an open bolt, correct ?
So are you not allowed to use the stock bolt and must it be modified to fire from a closed position ?

I see that a couple places sell trunnion kits (Gunthings and MGS). Is this trunnion needed for a build ? Does the stock trunnion not come with the kits ?

MGS also sells a reciever repair section (no FFL needed), what is this for ? Says that it has semi-auto features. Anyone know what those features are ?

Thanks for any help.
I couldn't resist since the kits are down to $79 w/ 4 mags at Sportsmansguide.

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Old 03-19-2009, 09:38 PM   #2
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The bolt is modified by removing the fixed firing pin and drilling it for a standard type moveable one. The face is modified by flattening the lower feed lip even with the casehead recess. The notch on the bottom that catches the sear to hold the bolt open is removed. This converts the bolt to closed bolt operation.

The trunnion is riveted into the receiver, when they were cut up the trunnion stayed with the removed section of receiver. You will need a replacement one, the rivets that hold it in, and a small bracket that fits underneath it and joins the upper and lower sections of the gun. Usually sold together as a trunnion kit.

The repair section is essentially the missing piece of the receiver that was cut off the original gun. It is welded in between the front and rear receiver sections that came with the kit. The top has a stamped in groove, this prevents an unmodified FA bolt from fitting as the bottom of the groove forms a rib inside the receiver. you have to grind a corresponding groove in the top of your semi auto bolt to clear it.

You will also have to fabricate a semi auto trigger group. Many people are modifying 870 shotgun groups to fit, you could also rig up a striker fired system similar to an Uzi.
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Old 03-19-2009, 09:48 PM   #3
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BTW, does the SG kit come with the original bbl? If not, you will also have to purchase one which will add to the cost.
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Old 03-19-2009, 10:06 PM   #4
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It is possible to use an AK style trigger group for your semi build as well. It will not throw off the authenticity as a remington group would.
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Old 03-20-2009, 05:47 AM   #5
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KernelKrink - thanks for the great info. I have a much better picture of what is going on now.

No, the SG kit does not come with a barrel. I found some for $35 at Omega. Will likely order one today.

I did see a trunnion kit with rivits, I will need to order that.

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Old 03-20-2009, 05:55 AM   #6
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I dont think a AK FCG will work. It sits very high and you would have to mill the bolt down. I am looking at a Cobray FCG.
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Old 03-20-2009, 07:09 AM   #7
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There is a very thorough KP44 tutorial using a Wise Lite on Weaponsguild (sorry - not trying to promote another forum) using a Remington 870 FCG. Here is the link:

KP44 Build
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Old 03-20-2009, 04:55 PM   #8
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You CAN build a Open Bolt PPS-43 (Or anything else) but it must be single shot.
It's actually quite easy compared to modifying stuff for closed bolt operation.
Lots of folks have found out the hard way that guns designed for open bolt but converted to closed bolt can be quite dangerous because the mass of the bolt has been reduced, the return spring is not powerful enough and the fact that open bolt guns fire from 'Advanced Primer Operation' which means the bolt is still going foreward when the gun fires. So DECREASING the mass of the bolt is the very LAST thing you want to do.
Heck, even an M-11/9mm COBRAY with the same mass bolt as a COBRAY SMG will very often rupture cases and blow primers.
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Old 03-20-2009, 05:25 PM   #9
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tell me about it...jeez.

this is Sellier and Bellot ammo, which I was told is safe to shoot in my pps-43 rifle which can't shoot milsurp ammo. notice the burnt powder on the top side of the glove...that's the residue left from holding the magwell when it blew up...







here's my pps-43 pistol which blew up on me before I knew to use a glove on the magwell hand to test the replaced rifle. MGS graciously replaced my pps-43 pistol with the carbine version..which unfortunately had the same problem as it was probably made around the same time as the pistol version...with the same SHIT COMPONENTS for a trigger group and an under weight bolt.





this actually hurt...but not as bad as when the diconector spring failed and it shot a 5 round burst and then blew up on me...that one really did hurt.

Last edited by bounce19712; 03-20-2009 at 06:46 PM.
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Old 03-20-2009, 06:03 PM   #10
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Bounce, it looks like your rifle has an issue with pierced primers, and the pistol has bad headspacing/firing out-of-battery. Maybe I'm pointing out the obvious. Just my .02.

Try this for a good primer on the PPS-43 build:

http://www.pirate4x4.com/forum/showthread.php?t=663044

and

http://www.thompsonmachine.net/pps43.htm

I've never built before, and as my luck would have it, the bug hits me now. AK kit prices are thru the roof.


Receiver:

http://stenparts.com/Tubes/tubes.html

I picked up the trunion set from GB for $58. Seems to be of good quality. My plan for the trigger is to use a Tapco G2 double hook trigger group. For the firing pin, drill the bolt for an AR firing pin, but I'll have to use a 2-piece pin set-up to get the proper length. I still need to come up with a spring for the firing pin.
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Old 03-20-2009, 06:43 PM   #11
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it's hard to say if your 100% correct on the pierced primer thing... I think it only happened on the S&B ammo...by that time It was being shot out of the pistol version after I had sent it back for repairs....I got it back with a letter saying don't shoot milsurp in it...so I went out and bought a few boxes of wolf and S&B ammo to test the repaired pistol.

that's when the primer was pierced on that one S&B casing...also at that point the retainer bushing holding the firing pin on the bolt face was coming out or walking out of it's location....

also the rear of the firing pin where the hammer strikes it sheared off....

that along with the disconector spring failing to stay in place has led me to go with a rebuild attempt in the future consisting of an 870 trigger group and a bolt modded BY A PROFESSIONAL.

PHuque SMG manufacturing out of Decatur, TX. assHAT.
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Old 03-20-2009, 07:46 PM   #12
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Thanks all for the great links and advice.

Ok, I kind of jumped into this one. I've ordered everything I need for the build except the barrel. Will order the barrel tomorrow.

I have a bunch trigger parts and firing pins from AKs, FALs and ARs. I'll see what seems to work the best after I get the kit.

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Old 03-20-2009, 08:07 PM   #13
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Your funeral.
Just wear face armor, hand armor and safety glasses.
No face armor? Take a pic now so we know what you used to look like.
Seriously, watch your hands or face anywhere near the ejection port.
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Old 03-20-2009, 08:19 PM   #14
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heheh...there's some good heads over at that website that someone already mentioned....their pps-43s shoot fine.

I wonder if I'll ever be confident about holding the magwell without a glove on and cringing at the same time....

nitegunner's tutorial is good and Rocco1911 is a great resource...don't miss out!
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Old 03-20-2009, 08:56 PM   #15
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I've heard rumours of "don't shoot milsurp in this firearm" before, but don't understand it.
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Old 03-20-2009, 09:29 PM   #16
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Thanks for the warnings Etek, seriously.

I agree with your previous post that bolt mass if very critical...along with recoil spring pre-load and rate.

I haven't actually had my hands on any parts yet, but my thinking is to initially keep the bolt as massive as possible (adding mass is an option) and adding more pre-load and spring rate to the recoil spring/s.

Do this initially so that the thing fires single shot, then start reducing spring rate / pre-load and bolt mass until it cycles reliably without blowing up....basically start from the safe direction and work back.

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Old 03-20-2009, 11:56 PM   #17
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with the addition of the swiss charging handle thingy....you'll re-add two ounces...I think the necessary weight is 18 something ozs.
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Old 03-21-2009, 08:59 AM   #18
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Good info bounce19712 on the bolt mass. You stated that one of the units that blew up on you had an under weight bolt, any idea how much that was or how much the updated bolt is ?

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Old 03-21-2009, 01:02 PM   #19
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I weighed 2 bolt assemblies, 1lb 3.4 oz (19.4oz) exact on both.

I took the third bolt apart to check the AR pin size in the bolt face firing pin opening. Either a firing pin sleeve is in order, or find a larger size diameter firing pin. I'm thinking weld a sleeve in the current hole.
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Old 03-21-2009, 02:06 PM   #20
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both of my bolts from the rifle and pistol were in the 18 oz range..I foget what...I can find the numbers somewhere...

and then you must figure in the inertial weight of the open bolt config into the final weighht on ignition of the primer...lol...good luck with that one...it's gotta be alot more than 20 oz. huh?

the weight of my to be modded bolt should be around 20oz. with the swiss charging "barrel" addition to the charging handle.



here's what the blowback did to the end of my spring rod retainer...plus the sheared firing pin rear.


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Old 03-21-2009, 02:16 PM   #21
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thread jacking!!! humor photo

here's how my wife tried to open a can based on my phone explanation on how to open with a swiss army knife can opener..you know the one that looks like a bottle opener but sharpened edge?? she got it right in the end though...and open....I'm saving it.

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Old 03-21-2009, 03:56 PM   #22
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Underweight bolt is why I am thinking a striker fired system is the way to go, the weight of the striker is essentially added to the weight of the bolt when it is fired and the extra spring should help as well. Alternatively, making a bolt extension that could be welded to the rear of the bolt would both add weight and shroud the firing pin so it wouldn't contact the buffer.
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Old 03-21-2009, 04:37 PM   #23
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Okay, I'll try to put my thoughts down here so they make sense to someome else, not just the "other voices".

My plan:

Drill through the bolt. Use AR firing pin. Spring load the firing pin ( I found a spring at the local auto parts place that fits perfect). Using the large part of the AR pin as a stop to set up pin protrusion in the bolt face. Part 2: just a piece of rod the same size as the large part of the AR pin. Grind a small flat on the side of part 2. Drill a cross hole in the bolt to insert a spring catch/cotter key to hold the entire assembly in place. Entire 2 piece firing pin is now spring loaded and held in place by key/pin holding in part 2. Length of part 2 to be adjusted so no extra protrusion from back of bolt with pin depressed from behind. Should be nothing to beat up the spring rod retainer.

I plan on using an AK FCG.

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Old 03-21-2009, 07:03 PM   #24
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KernelKrink - isn't a striker fired system basically a spring loaded firing pin that is released by the trigger ? I guess I'm not 100% familiar with the system to understand why that would add mass to the bolt assembly.
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Old 03-21-2009, 07:29 PM   #25
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Best way to add mass to a bolt is to drill a hole or holes and fill with a heavy metal such as lead or tungsten alloy as used in crankshaft balancing.
A buddy has a M-11 SMG and the cyclic rate was horrendously high. A machinist (Ex crank grinder) drilled two long blind holes and added the Tungsten alloy which slowed the MAC down considerably.

My own M-11 Semi would blow every other CCI aluminum hull into pieces, blow out primers or crack the cases. Brass stuff was bulged and blew many a primer unless it was Mil-Spec ammo with swaged primers so we swapped in my buddy's M-11 bolt (After changing the firing pin) and VOILA!
No more problems.
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Old 03-21-2009, 08:48 PM   #26
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Quote:
Originally Posted by skemler
KernelKrink - isn't a striker fired system basically a spring loaded firing pin that is released by the trigger ? I guess I'm not 100% familiar with the system to understand why that would add mass to the bolt assembly.
On a bolt action rifle, the striker is basically just a spring loaded firing pin. On a semi auto subgun copy it is a chunk of springloaded metal that rides behind the bolt. When the gun is fired and the bolt cycles, the striker is held to the rear by the sear mechanism while the bolt returns forward. When the trigger is reset and pulled again the striker is released so it can slam forward and fire the gun. The firing pin can be mounted in the bolt and the striker is merely a "hammer" if you will, or like the Uzi it can have the firing pin mounted to the striker. Regardless, once the striker is fully forward the weight of it is now added to the mass that must be moved by the blowback action, along with the extra spring pressure from the striker spring.

Imagine the PPS bolt is cut in two right in front of the notch that catches the sear to hold it rearward. The forward section is always free to move forward whether it is cocked or not. Closed bolt operation. The rear section remains at the rear whenever it is cocked. Since the rear section has no spring loading from the recoil spring, let's add one to the right side of the striker and now it will slam forward when the trigger is pulled. If a normal firing pin is installed in the bolt it will hit the rear end of it and fire the gun. The bolt is now "whole" again until it cycles and the rear section stays rearward. That's the basic mechanics of it.

Use a modified whole bolt for the front section and a cutoff second bolt for the rear striker, modify the trigger group to semi auto only with a disconnector and you have a striker fired semi auto closed bolt subgun clone. Because the feed lip on the front of the bolt was removed any attempt to modify the trigger group to FA will simply let the striker ride forward with the bolt, keeping the nose of the firing pin extended. When the round tries to feed it will slide up the smooth breechface surface on the bolt until it jams under the extended firing pin and the gun refuses to feed.
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Old 03-22-2009, 09:42 AM   #27
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Now I'm with you KernelKrink.

I really like the idea. Have you ever seen it done, or is this a new idea from you ?

I like the idea so much I'm going to order a second bolt to play with.

The only thing I was wondering about -- is if you get the total bolt assy too long so that the rearward travel is not sufficient to properly eject and strip new rounds off the mag...basically a short cycle. Will have to see after I get some parts to play with.

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Old 03-22-2009, 01:34 PM   #28
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The bolt travel on a PPs43 is extremely long, there is plenty of room in there to add a striker.

I had the idea to use a striker on the PPs43 to solve some inherent problems, but striker fire itself is not my idea. Similar striker fire systems have been in use for decades at least. The semi auto Uzi uses a lightweight striker with a firing pin attached. The current STEN conversions are using a heavier chunk of steel as a striker similar to what is needed in a PPs43. If you can dig down to the basic operating principles you can redesign to work with almost anything.
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Old 03-22-2009, 07:52 PM   #29
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Anyone know where to buy extra PPs-43 recoil springs ?
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Old 03-22-2009, 10:28 PM   #30
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You might try a want to buy ad here for the extra parts you want. Back when the kits were cheap people were cutting off the magwells and folder stocks for other projects.
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Old 03-25-2009, 05:52 PM   #31
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Quote:
Originally Posted by avgrant
I dont think a AK FCG will work. It sits very high and you would have to mill the bolt down. I am looking at a Cobray FCG.
Not exactly AK style, SCALED DOWN.


Just don't use the Remington group, it really detracts from the originality.
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Old 03-28-2009, 06:27 PM   #32
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What's the purpose of removing the lower feed lip ? I don't understand why this is necessary.
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Old 03-28-2009, 06:51 PM   #33
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Quote:
Originally Posted by skemler
What's the purpose of removing the lower feed lip ? I don't understand why this is necessary.

Not that it's needed but removing the lower lip of the bolt face will cause the weapon to to jam with the rim of the cartridge stuck on the firing pin in a striker fired system where the striker is allowed to ride forward if it's not held back by the trigger / disconnector. With the feed lip on the bolt face if the striker is allowed to ride the bolt forward instead of being held by the trigger the weapon can fire full auto. It is more reliable with the feed lip though even i semi auto and removing it requires care in how much is removed, or rather how high up the bolt face it's removed. Most semi auto Uzi's have the lower half of the lip removed but other semi auto sub guns have the full bolt face lip.
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Old 03-28-2009, 06:54 PM   #34
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On a FA open bolt gun the firing pin is fixed in the firing position, this sets off the primer when the round is chambered. Since the pin is sticking out in front of the breechface of the bolt, if the feed lip was not there to keep the cartridge ahead of the firing pin point it would slide up the flat breechface until it contacted the underside of the firing pin and jam during feeding.

On a semi auto this is desireable in that if the firing pin were ever to get jammed in the forward firing position (either by malfunction or intent) the gun would jam instead of becoming a runaway full auto.

Most semi auto copies of open bolt SMGs have the feed lip removed for this reason, safety as well as making it harder to convert to FA.
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Old 04-02-2009, 05:34 PM   #35
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Ok, makes sense now about the bolt face.

Two more questions:
(1) anyone know why the MGS receiver section has the round cut-outs where the pivot pin is supposed to go ? I don't understand why this is. Seems like there should be material there so that the pivot pin can go through the receiver, then through the trunnion bracket on both sides.

http://www.militarygunsupply.com/sho...roducts_id=314

(2) Are you supposed to weld the trunnion bracket to the trunnion ? Seems like there isn't much holding all this stuff together if you just have the one rivet connecting the trunnion to the receiver, then two rivets connecting the bracket to the receiver.

SK
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