Posted: 5/13/2008 7:08:32 AM EDT
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i tried in the armory section but no dice... anyhow, anyone own a Military Gun Supply PPS-43? If so have any pics of it? Reviews? I just bought one from them and its inbound to my dealer. 
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With the current costs of ammo, and the current costs of parts kits, I've taken to building nearly ALL of my own guns. The AK kits have all pretty much dried up, and with the upcoming election, importers don't want to bring in any more parts kits because they're afraid of new legislation passing and being stuck with a massive inventory of shit they can't legally sell anymore! So, I've been working on homebuild projects, parts kit projects, and a bunch of other things this year. One build in progress is a Semi-Auto belt-fed MG-47 hybrid similar to this MG-47 build by Sharps Shooter:  It uses an AK-47 or RPK-47 parts kit, MG-42 / MG-1 / MG-3 top cover & feed tray with heavy modifications to fire 7.62x39mm in a semi-auto rifle. Total cost is around ~$550, weighs about 14 lbs. Requires a sizable amount of work (I'm estimating mine will take ~6 months). Another one of my build projects in progress is my PPS-43 semi-auto...    The bolt and fire control group modifications are pretty heavy, and until I get to head down to a friend's place with a mill & lathe, I've got to put that build on hold. I need to do the bolt mods before I can order the receiver repair section. Don't want to be in possession of a receiver section when you've still got the full auto bolt! That'd be Possession with Intent to Manufacture. I've not yet decided whether or not I'll build it as a 'Carbine' with the goofy 16" barrel or use an original 10" barrel, and weld the folding stock in the upper position to build it as a 'Pistol'. Another thing to consider is this: If you're intending to build one, better hurry up, from what I've heard, the ATF is putting LOTS of heat on the ONE and only company making trunions, brackets, and rivets for these... When I get my trunion & brackets I'll measure them, and then if the manufacturer of US parts has to shut down PPS-43 operations due to ATF pressure I'll post the dims/drawings online so someone else can pick up the ball where it was dropped. If you're going to get one, BUY ONE COMPLETE, or you run the risk of not completing the build. I heard the ATF is pressuring companies about these PPS-43 kits because all you really need is an original barrel for $35, a repair section for ~$60, the US Trunion, Bracket, and Rivets, and a little welding & grinding to recreate the original full-auto SMG. The ATF frowns upon this (how stupid easy it would be to make it auto). It's as if the PPS-43 is the next STEN fiasco to the ATF.  Also, the COMPLETED PPS-43 kits are having issues with cracked casings, erratic ejection/extraction, and other small things with surplus ammo. The COMBLOCK countries made their 7.62x25mm Tokarev surplus ammo EXTREMELY HOT to compensate for cartridge shortcomings - basically trying to make the pistol caliber SMG into a 'assault rifle' cartridge with higher velocities. So there's pretty frequent cracked casings. Don't expect to be able to reload surplus ammo because it's gonna have issues. Some are converting them to use Remington Shotgun fire control groups to deal with US parts compliance issues too. That's my take on the PPS-43. It's a decent gun, pretty accurate, but surplus ammo may cause some issues... |
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Their PPSH has had a couple of kabooms. With shitty MGS customer service. I was going to buy one of each, but not now.  www.akfiles.com/forums/showthread.php?t=28748 |
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The guy on AKfiles was one of the first owners of the Semi-Auto PPS-43 guns on the market, and subsequently was the first to experience problems. As I previously mentioned... 
WAAAAAAY ABOVE SAAMI SPEC for the cartridge! As mentioned on the AKfiles thread, the bolt DOES need to be lightened to convert it to semi-automatic. The fact that it fires from an inertial open-bolt mechanism means this: IN OPEN BOLT FULL-AUTO FIRING, IT DOESN'T NEED A BUFFER!!! In open bolt firing, the sheer weight of the bolt, and the pressure of the spring are capable of closing the bolt long enough for the chambered round to fire with relative safety! If that bolt looses weight by having material removed for the semi-auto conversion, the topstrap milled to fit the semi-receiver, and the firing pin channel drilled out... It's not going to have sufficient mass to hold the bolt closed! Even if it DID have enough mass, firing in SEMI-AUTO from a CLOSED BOLT format requires what's called a 'BUFFER'. This is the same free-floating weight in the AR-15 buffer. When the recoil spring pushes the bolt closed, that (now lighter weight) bolt will slam up against the barrel/trunion to 'Close', but since it is lighter weight, there's a possibility the bolt can bounce rearward a little too! A buffer, as found in the AR-15, has a free-floating weight which, when the bolt first slams home, the weight slides forward, and hits the rear of the bolt (carrier in the AR's case) giving it a second little 'nudge' to make sure the bolt STAYS seated all the way forward instead of bouncing rearward slightly! MOST COMBLOCK WEAPONS DO NOT HAVE A 'BUFFER' PER SE - Including the AK-47, the AK-74, the RPK, as well as their open-bolt SMGs. It's just a simple strong spring and a very heavy bolt / carrier! As such, some semi-PPS43 owners have reported they have to occasionally push the bolt forward after every chambering to ensure it's 100% closed. The newer bolt conversion method does account for the weight issue by trying to remove as little mass as possible from the bolt... However, that STILL does not account for the INCREDIBLY HOT SURPLUS AMMO on the market... There is so much powder in the Romanian, Hungarian, and Bulgarian surplus 7.62x25mm ammo that it's highly unlikely to ALL be burned up before the blowback operated bolt starts travelling rearward! As a direct result, there are bulged, cracked, and ruptured casings in nearly all PPS-43 semi guns firing the surplus ammo... The PPS-43 was built to withstand pressures a little above the original russian spec loaded ammo for safety in its slam-fire open bolt mode. So after WWII, RUSSIA got the AK-47's issued to their army, but COMBLOCK allies and Conscript nations were armed mostly with the SKS, PPS-41 and PPS-43 guns until AK-47 production could catch up with demand. The PPS-43 was typically used in Guard / Military Police duty, and to compensate for performance of a PISTOL round, the comblock nations made most of their 7.62x25mm Tok ammo VERY HOT to get higher velocity and better 'performance' out of their open-bolt automatics to give their performance a boost to a de facto 'Assault Rifle' cartridge. That is why some CZ-52's have reported issues with some of the hot surplus ammo too... With a semi-auto converted PPS-43, unless you add more weight (and perhaps a buffer assembly) to the rear of that bolt, you'll likely have these issues with most HOT surplus ammo. |
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Is the Romanian hotter than the Bulgarian? Is it safer to shoot than it? Would really suck to buy a $750 rifle and find out I am limited to crappy commercial ammo that costs 3x as much. Any way to design a "buffer" and install one? Why doesnt MGS produce one if they are aware of this issue? What is the instance rate of the cracked/split/bulged cases from milsurp ammo in the 43s? |
S&B, US Mfg to SAAMI SPEC, and maybe other 'light' loads would be okay though.
***NOT*** meaning <10% KaBoomed. That's not too common, but I mean the pressure of the cartridges beats the hell out of the cases. Large 'Dings' from hard/fast extraction/ejection, cracked casings (high pressures), and gouges in the rim where the extractor claw jerked it out upon ejection. That lightened bolt flies straight backward EXTREMELY FAST with the high pressure loads. Primers that bulged out a little rearward, cracked/bulged/ruptured cases, and I'd bet if you measured the spent casings, you'd find the case neck would likely need trimming. It probably lengthens pretty good considering how hot the surplus ammo is... What I'm saying is MGS is likely right, and there's not much of anything wrong with the guns, it's the ***HOT*** surplus ammo on the market now that is loaded to pretty far over spec pressures. Another possible alternative is to modify the bolt and receiver slightly so it's not a STRAIGHT BLOWBACK, but a DELAYED BLOWBACK operation. This would likely require heat treating the receiver a fair bit. The bolt should be around 30 to 45 on the Rockwell Hardness scale so it's not too difficult to machine (like some other bolts), but the receiver repair sections used to make them are not what I'd call 'hardened' in any way. To make a delayed blowback will require hardening. Likewise, the reason not many machinists are willing to weld on a weighted extension on the rear of the bolt is because it WILL affect the hardening of the bolt. Some could argue that hardening of a bolt is negligible on a blowback operated firearm (as opposed to a locking breech like an AR/AK bolt) but nonetheless it may be a safety issue some people aren't willing to compromise on... Then again NOT adding weight or a buffer to the bolt might be ANOTHER safety issue when using crappy surplus ammo. Another option is to buy a parts kit, and scrap out the parts for a one-of-a-kind homebuilt gun... That way you can do whatever you want with it rather than trying to keep the 'original' appearance of the PPS-43. Though I can understand why so many people want to do that just for historical appearance sake... Your Mileage May Vary, and it probably will. -inuhbad |
how is the milsurp on the market out of spec supposidly if it was made for the SMG and MG's chambered in 7.62tok? Would they really produce ammo to blow their own guns up? Doesnt make sense. Also whats all the milsurp 7.62tok on the market CAPABLE of running in without blowing up? ETA: what about making a plastic buffer seated in the rear of the bolt, similar to say a AK blackjack buffer? |
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++ Most open bolt blowback weapons are based on Advanced Primer Inginition.The primer is ignited before the round is fully seated in the chamber.As a result part of the cartridge impulse is expended to decelerate the bolt and the remaining to accelerate it backwards.This arrangement allows for a lighter bolt and an increased rate of fire with milder vibrations and increased gun life since only the remaining impulse drives the bolt backwards.In smgs the inginition is acheived by the friction that develops between the case and the surface of the chamber and the fixed striker being the first point to push the round after it aligns itself with the chamber (even chambering a round by hand and firing it is damaging for API systems).In larger calibers the firing pin is controled by a lever on the bolt that times the inginition (oerlikon autocannons). Modifying an open bolt design into a closed bolt system using the same bolt mass will definitely lead to increased recoil velocities of the bolt and damaged cases since there is no initial bolt momentum to counter part of the cartridge impulse and cases are exposed to atmospheric pressures while the chamber pressure is still high.Increasing the bolt mass is the best solution. |
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It was loaded to be fired from a fully-automatic, open-bolt firing SMG. Not a semi-automatic, closed-bolt firing carbine. The open-bolt mechanism has a fixed firing pin. The bolt is held rearward until the trigger is pulled. It moves forward under spring pressure, strips the top round from the mag, and the moment the cartridge is centered in the chamber, and resists the bolt, the gun will fire (the moment it's in battery). Meaning it fires the round so fast the bolt doesn't usually have enough TIME to bounce back like it would on a closed-bolt gun. The higher pressure ammo probably isperfectly safe to shoot in an unmodified full-auto open-bolt form. But when you have to lighten the bolt significantly to make it legally semi-automatic (Mill off lower Feed Lip, Mill off Open-Bolt FCG Catch, Mill a top channel to fit into semi-auto receiver, drill firing pin channel through bolt & recoil spring lug, recess breech face for firing pin bushing - that's a lot of modifications that will reduce the weight of the bolt), and change it so it fires from a closed bolt instead of the way it was intended to be fired... By doing all that you're potentially creating some safety issues with ammo that was once safe to fire in the same gun. Not to mention the 16" carbine versions will have have a longer duration in which there will be gasses in the barrel as opposed to the 10" original barrel. |
this is the route ill be going i think.. time to contact Wolff to have some springs made me thinks... and time to order up some ammo! |
As for the belt fed, the example pics are a build done by Sharps Shooter. Mine is modeling his build pretty closely though. Same style receiver, (Made from 1/8" steel flat), and it will also have an RPK front-end, and FN style buttstock. My own build has a looooooooong way to go (but it is in progress). That kind of belt-fed homebuild takes several months and TONS of pre-planning before you really can start making some progress. 
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anyhow, got any pics of PPSH43s? I think ill be safe with Romy ammo. 
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Dieter122, I bought one of the KP-44 semi-auto pistols from MGS. They are also made by the same company (SMG Firearms) that make the PPSh and have a very similar design. I don't want to hijack your thread, but I've had some issues with my pistol. I posted these pictures in the Ammo Forum a while ago. I shot a full stick magazine (36 rounds) and a full drum magazine (71 rounds). I ended up with two FTF (fail-to-fire) due to light primer strikes. They occurred after 30-something rounds in the stick mag and maybe half-way through the drum mag. The cartridges had very interesting markings on them, as though they had been 'crimped' by the chamber. The following picture shows the two FTF rounds #1 and #4, left to right. Round #2 was chambered but not fired. Round #3 was a fresh round. All the ammunition I have fired was Winchester White Box 9mm ammo. I have not shot any surplus or otherwise 'hot' ammunition:  These are the same rounds but a headstamp picture. Note the light primer strikes on #1 and #4:  This is a headstamp shot of spent shells:  I was very concerned about the 'crimping' of the cartridges and so I shipped the KP-44 pistol back to the manufacturer. They changed out the bolt, videotaped them test-firing it and shipped it back. I took it out and fired two stick mags worth of ammo. Again, I only used WWB. No problems. I took it out again and I had a couple of FTF but wasn't worried because it is a new gun and needs to be 'broken in'. Unfortunately, the 'crimping' on the FTF cartridges was still there. I don't know what is causing them and I don't think it is normal or safe. My sense is that it is a chamber issue. I took it out again this past Sunday and brought a Fiocchi cartridge to see if maybe it was an ammo issue. I chambered it from the magazine and ejected it. It had the same 'crimping' on the cartridge. I loaded a WWB cartridge, but this time put the cartridge in the chamber to see if the 'crimping' was caused by the chamber or because the cartridge was hanging up on the magazine or feed ramp. It left the same 'crimping', so it had to be a chamber issue. My sense was that the chamber is too short and is 'buckling' the case, but I am a complete novice when it comes to firearms. I then loaded a magazine of WWB and started shooting. First round was fine and the second one KaBoomed!     Again, the only ammo that has ever touched this KP-44 has been WWB except for the one Fiocchi round that I chambered but did not fire (Fiocchi is factory ammo anyway and while it may be slightly hotter than WWB it is quality ammo). I saw the first round hit the dirt so I know it wasn't a squib, but I checked the barrel anyway and it was completely clear. This was not a squib and the second round must have fired out-of-battery. I haven't had a chance to get back to the manufacturer and saw this thread today so I thought I'd post this to see if anyone has any ideas as to what is causing the 'crimping' of the cartridges. I think that the lighter bolt means this gun could use a heavier spring, but this doesn't solve the 'crimping' issue. Any and all advice is appreciated.  |
AFAIK, the internal designs of the PPSh-43 and KP-44 are very similar, so I'm not sure how that would solve the problems. Although it would be useful to define what all the problems are to begin with. The 'crimping' is not normal and someone must know what is causing it. |
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For the PPS-43, it was designed to fire a higher pressured 7.62x25mm Tokarev cartridge. The semi-auto bolt SHOULD need little or no modifications to convert it to 9mm Parabellum. You will just need a different 9mm barrel that is machined (profiled) to fit the original PPS-43 Trunion, and is chambered to the proper depth for the 9mm cartridge fitting in your bolt! As for the KP-44, they're a GREAT firearm in their original full-auto form! However, semi-automatic conversions of *ANY* of this type of SMG (open bolt, slam-firing) firearm can be seriously problematic! If not done PROPERLY, or PRECISELY, they can be very dangerous or merely prone to frequent malfunctions.  C-4, you're certainly having an INTERESTING problem!!!I must admit, that I can only SPECULATE as to what's causing the KaBoom, but I DO know what is causing the crimping issue! ...There are very CLEAR signs of machining marks on the breech face. This is because there originally was a wider, fixed firing pin that was held in place by the extractor (a design copy of the PPS bolt). One thing to note though... The KP-44, PPS-43, and PPS-41 bolts are ***NOT PERFECTLY CIRCULAR*** so if you were to lock them into a lathe based upon this assumption, you're going to be cutting/drilling the bolt slightly off-center. That's evident in the slightly off-center machining marks. Those machining marks are from when the breech face was drilled with a 'shoulder' recess, and they then fit a machined 'bushing' into the breech face, usually silver soldered or press fit, and then the breech is re-machined somewhat smoothly. This removes a hair of material from the breech face, or else you may have a rough breech face as is seen on your bolt. Either one (being rough, or too much material removal) is a bad thing! As a result of the bolt not being perfectly circular, the firing pin channel, shoulder, breech bushing, - all of that will likely be slightly off-center. That's why your primer strikes are also not centered in the primer (if you look). The ORIGINAL fixed firing pin WAS in the center of the breech face. The thing that is causing your bullet crimping problems is this... Your KP-44 uses an ORIGINAL military SMG barrel. It was designed to be slam-fired from an open bolt with the fixed firing pin! On the PPS-41/43 SMG's, they're a 'necked' case, and they are headspaced on the shoulder of the case. However, typical straight wall cartridges for 'automatic' firearms all have chambers that are headspaced on the CASE WALL CRIMP POINT. 9mm, .40s&w, 45acp, 10mm, etc... ALL OF THEM headspace on the crimp point of the case wall, typically using a 'taper crimp'. It's easy for a 'necked' case to be fired in a slam-fire manner because it headspaces on the shoulder, and the crimp is unaffected! However, on a straight-walled cartridge like the 9mm, it's a little different... Here's a couple diagrams to help my descriptions... Forgive the crudity, they're not completely accurate & to scale, and are modeled more after the PPS-43...  In the above diagram, you can see two bolts.. The one on TOP is the side section (not showing firing pin channel & bushing) of a properly converted bolt. The one on BOTTOM is the original Full-Auto bolt which has a very visible lower 'Feed Lip'. This is of CRITICAL importance in understanding the functional differences between the Semi-Auto conversion bolts, and the original fully-automatic bolts (and the way various parts were designed). This understanding will help diagnose your problems with the 'crimp' issues.  Anyway, as the bolt moves forward, and starts to chamber a round, you can see in the above diagram how on the SEMI bolt, the rear of the cartridge rides up against the breech face, sliding up under the extractor as the round moves into the barrel. On the AUTO BOLT, the cartridge rides the lower FEED LIP as it's entering the chamber, this keeps the rear of the cartridge from striking or hanging up on the Fixed FIRING PIN which constantly protrudes from the breech face...  As the bolt continues forward, the cartridges become more aligned with the barrel/chamber, and after a point, it becomes fully centered...  When fully centered in the chamber, the bolt will continue forward until the top front of the bolt contacts the rear of the barrel! Regardless of whether or not the cartridge wall / taper crimp has already contacted the end of the chamber... Remember, these original SMG barrels were designed to have a slightly shallow chamber - so the cartridge reaches the end of the chamber before the bolt is fully closed - in order for the open-bolt fixed firing pin to slam-fire the primer & ignite! This is where your problem occurs... On the top bolt, if the machining of the bolt face was done improperly (or left in its original form), the bolt may continue forward a little before contacting the rear of the barrel and stopping - even though the cartridge has already butted up against the end of the chamber. This will damage the crimp on a straight walled cartridge, causing the 'wavy' pattern in your casings. If the waves aren't too pronounced, it should be okay... HOWEVER, if they are pretty significant (as they appear to be in your examples), it could increase the chamber pressures dramatically upon firing! That's bad. In the case of the full-auto bolt, this is the first point when the cartridge has stopped and is fully seated in the chamber, but the bolt hasn't fully closed yet. The fixed firing pin first comes into contact with the primer, but hasn't yet fired in this moment...  In the above diagram, you can see, that the semi-auto bolt is closed (likely having damaged the crimp), and ready for you to pull the trigger... In the lower automatic bolt, the bolt has finally, fully slammed home, and the fixed firing pin has fully struck the primer, and started to fire the gun... However, one thing to note here is that on the Full-Auto bolt, the lower feed lips provide the remaining reinforcement needed to fully support the cartridge in the chamber... On the SEMI-bolt, when fully seated, the bolt does not provide full support of the chamber, and part of the cartridge's brass side-wall is exposed!!! This is known as a 'Partially Unsupported Chamber' - the same design flaw inherent in Glock pistol barrels. Typically with 9mm this is not an issue of much concern, but with an original open-bolt Submachinegun barrel, the chambers are not always cut in far enough to seat the bullet deep enough. Depending on the ammo, it might cause a KaBoom, or might be a contributing factor. If there are additional imperfections in the bolt, there might be other problems as well... These problems are pretty common on these old Submachinegun kits... And they typically are only an issue when the machinist doing the conversion either cuts corners, or does a sloppy job by not properly fitting the newly converted semi-auto bolt's breech face, and upper bolt face to the rear of the barrel, and taking the chamber's variation of seating depth into account (and re-machining the rear face of the barrel, re-checking and reaming the chamber if necessary, and fitting the bolt & breech face to the barrel). Often these are steps overlooked when many do 'quick & dirty' SMG kit builds. Just because it was designed to fire full-auto from an open bolt doesn't mean you can just convert the bolt only, and have it work properly... We're talking thousandths of an inch here, but in some cases, those thousandths of an inch might be CRITICAL in determining whether or not a firearm is safe to operate. In my opinion, unless the manufacturer re-fits the bolt face & breech face to better fit the original SMG barrel (which will fix your 'crimping' issue), or rechecks the depth of the chamber, and any corresponding exposure of any portion of the case's side wall (to address safety of possible 'KaBoom' issues or case ruptures), I'd return the firearm, and ask for a full refund of my money. The machining marks on the breech face indicate to me that whoever did this bolt conversion was trying to do it QUICKLY (probably for production quantity sake), and as a result did a somewhat poor job. Another thing to consider, is that in order to re-ream or do any work on the chamber, the manufacturer would need to remove the bracket and trunion from the receiver (which could be damaged upon removal), and remove the barrel from the trunion... The potential to damage the receiver is too great, and I doubt any manufacturer would go to that length to do repair work anyway. They'd likely just clean up & recheck the bolt face and send it back to you. Does this address some of the issues? Maybe... Will they do a better job of machining the 2nd time around? Maybe... Who knows. Your safest bet is likely to return it for a full refund... That's why I prefer to do my own SGM kit build. I can build mine with a chambered barrel blank (rather than a .mil surplus one) and ensure the barrel is profiled to fit the PPS-43 trunion, and that the bolt doesn't cause any issues with seating depth or other concerns... With the PPS-43, I can buy a 9mm barrel blank, have it chambered to a specific depth (to fit the bolt face & Breech depth), and then contoured to fit the original trunion. Since 9mm is lower pressured, and the new barrel will provide full support, I'd not have to worry about any of the issues you've encountered. I might not even finish mine in the 'original' format. I might just buy a 7.62x25mm blank, and a 9mm blank, and make mine a dual-caliber carbine with quick-change barrels - But proper chamber depth is important to account for. As to others doing this type of build... Your mileage may vary, and it probably will! What works for one person's kit might not work for another's... Hope this helps. -inuhbad |
Thank you for that detailed and thorough explanation.  I'm not sure what I'm going to do at this point. 
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You don't want to. It'll blow up in your hands! And people complain about Glocks. |