Hello to those in the KP-44 community. Below is a pic of a test gun build. This gun will incorporate an experimental striker FCG and show a first effort at building a semi accurate receiver using my drawings reverse engineered from a rare and expensive old kit which has an intact trunnion/magwell area. I have these drawings in a package currently at auction on Gunbroker (parts kits, Suomi) under my handle b-17f405.

New: This drawing package is now available to Weaponeer members and guests at $28 in a new WTS post in the FOR SALE/TRADE OR WANT TO BUY forum. If you are new here like me, This forum can be found by clicking the Forum button at the top of the page and scrolling waaay down the list of forums to DIRECT EXCHANGE (DX).

 I say semi accurate because I'm using a MGS repair section which isn't fully accurate to the original. The first job was to cut the section in two in the rear sight area. This was to insert the sight piece as it comes in the kit. More on this later. Next, was cutting the extractor slot and this is shown in the pic. Wasn't looking forward to this job but turned out easier than expected. The section was mounted on a 45 deg fixture (50 deg would be more accurate but not a big deal). My Chinese lath/ mill is great but not as rigid as what the pro's use, so I started by milling a 3/16 slot full length and working up 1/16 or 1/8 at a time to 3/4 inch. Turned out quite nice, though not fully authentic because the Finns put the hole in the flat.

In my previous post I failed to note that the 50 deg angle I mentioned is from the horizontal (making the hole closer to the top.

 Here are pics of the next step: building a barrel alignment tool. This is a 1.125 x 12" piece of bar stock (McMaster Carr) drilled to take a piece of 7/16 rd to insert into the barrel.  This barrel mandrell was turned to  .345 dia for a snug fit in the  barrel, with a .380 dia x 5/8" lg section to go into the chamber. That last isn't necessary but adds some rigidity. This barrel mandrell extends 6" and was was epoxied into the big piece after a lot of trouble trying to weld and braze it. For those wanting to build one of these tools I recommend fabbing the barrel mandrel with a 5/16 thread at the base to screw into the big bar. This mandrell should have a shoulder  to tighten up to. This would be a much handier design.

Here are a couple more pics. The first is the trunnion and barrel installed on the tool and the other is a sketch of a threaded barrel mandrel design. The shoulder prevents the large section butting up to the barrel but that's not necessary.

Now for the trunnion instl. The original trunnion design was a removable barrel concept with the barrel trunnion assy held by 6 rivets and a pressed in dowell pin on top. This pin holds the barrel in the proper extractor clocking as well as bracing everything else. The barrel fit in the trunnion is unknown. I haven't pressed out the pin in my special kit  to see but suspect it is a light press fit ala AK-47.  First picture is the new trunnion assy. This is a MGS trunnion milled on the bottom to weld to a new bracket, fabbed of .073 1020. This assy is close to the original Suomi design even though the MGS receiver repair piece is not quite the correct shape in front. The next pic is this assy bolted into the MGS piece. The screws will eventually be replaced by rivets but for now I want it easily removable. The 6 holes were drilled in the repair piece and then the barrel alignment tool, barrel, and trunnion assy were clamped in the repair piece and the 6 holes were match drilled into the bracket. The 6 screws locate the barrel and it hardly touches the repair piece anywhere. The MGS trunnion is 1.125" dia and fits with .015" or more total clearance. This implies that there could be considerable error without an alignment tool. The original Suomi trunnion fits  tighter and in fact has no clearance at the aft end. It seems to use some kind of bedding compound. Anyone know what that might have been in 1944?  

As you can see the barrel/trunnion is easily removable, though with rivets in place of the screws, not so easy. Would that meet the BATF requirement for carbine barrel unremovability?

"Would that meet the BATF requirement for carbine barrel unremovability?"

I'm not really sure. 

While I'm not fond of them, there are a lot of AK screw builds out there, and I have not heard anything about them as not being ok as long as the barrel is pinned.

Looking at the screws made me think about a good way to retain them, and thought it would be nicer if you made a steel block that would fit in there, with threaded screw holes.  take it a bit farther and rivet the shroud to a steel block, and have that be the block the screws attach to.  easy take down model..

 Drilling of the upper pin hole started with mounting the assembly with a barrel on a milling/drilling fixture and laying a bolt in the receiver in it's firing position (the extractor  nosed into the barrel cutout). The first pic shows this. The assembly was checked for vertical and the bolt handle leveled, and the bolt clamped in place. A U-clamp was put on the barrel and tacked to the receiver. The barrel was rocked back and forth to find a center position of the extractor cutout and the U-clamp tightened. This holds the barrel in position for drilling. The hole (3/16") was started in the mill (second pic) and taken down to the limit of the cutter, about halfway. This was easy enough but my mill and fixture were not rigid enough. The hole was wallowed out by several thou's. Not a problem though. The pin will be a taper pin, so the hole will be reamed larger. The other half of the hole was drilled (3rd Pic) with no problem and came out much tighter.  Next - the taper pin instl.

Okie

Looking good! Thanks for sharing! I look forward to MORE!

Welded the receiver back together. The first pic shows after welding. The sight section is welded in but note an extra section aft of the sight. This was an unfortunate consequence of grinding out the accursed blocking bar, which meant filling the exterior groove with weld. After making a mess of this I had to use the extra section I cut out for the sight. The other pics show after grinding. Though this scheme gives a pristine sight and has the advantage that forming 2 flat pieces would be easier than 1, the body comes out somewhat wavy because of weld distortion and the fact that the original sight section doesn't exactly match the repair section in thickness and shape..  A more skilled welder might not have this problem so much. The interior looks better than the exterior because the welding was done with the barrel alignment tool in place to align the sections.

top notch work

Okie,

That was some dang fine welding! That looks VERY straight!

I have eyed the KP for a long time... you are making it look too simple!

Once again, I look forward to more!

Another fussy (but not difficult) job - installing the guide rails. The 1st pic shows the rails. These conform to my prints - original Suomi design, except for material thickness: .065 4130 vs .104 on the original. The original was hell for stout but it supported 650 rpm. For installation, the receiver was clamped upside down in a vise and a bolt placed in the firing position. The bolt was shimmed with a piece of brown paper (.005) at the front and a .006 feeler at the back to give the operating clearance to the inside top of the receiver. The receiver was checked for verticality with a level and the bolt for horizontal on the handle. The guides were placed in the correct fore and aft position resting on the bolt and clamped and tack welded as shown in pic 2. The guides will be spot welded as per the original after everything else in this area is fitted.  Pic 3 shows the tops of the guides. I milled these a few thou for flatness. The rear edges of the guides are rounded on top to guide the bolt on as it comes forward. Next : feed ramp and magwell fit up.

It's getting late, I'll be hearing from my wife any minute now so tomorrow: Feedramps 101.

WOW! Nice job!

I wanna let you know... you have made this look so easy... I have ordered an 80% plate, and a kit!

I like your idea on how you shimmed the bolt and rails in place... this technique will come in handy for my next build! Thanks for the inspiration!

I like the use of the spot welder. It is amazing the tools that "us modern" folk have...

Keep going!

Thanks for the reply MM. Actually I used spot welds because the Finns did. 5 spots per rail. Some of us are anal about such things. For today I promised feed ramps 101 and here we go - as if I know anything about it. Get ready for a lot of pics. First one shows my forming die set built during the snowstorm this week. My wife says: It's official, I don't have anything to do! The bottom (female) die holds the 2 flat ramp plates in place, the plates nose up to a stop pin (2nd pic). In operation, the ramp plates are torch heated in the bend area to a red heat, the top (male die is quickly slipped onto the pin and hammered down. The 3rd pic shows the results. After days of work on the die set these first 2 parts were done in a couple of minutes and came out nicely and a reasonable facsimilie of the original Suomi design. The 4th pic shows a side view of a ramp. The front part of the ramp is to be milled or ground off flat back to the uppermost point . I tried to mill the first one but the 4130 was too hard locally and ruined my 1/4" end mill - an all too common occurence. I didn't think the plates were hot enough or cooled guick enough to harden. Wrong. They have some unknown degree of hardening in the bend, probably mostly near the edge, which was hottest. I will post all this now, then on to Rampology.

I'm no expert on feed ramp design and operation ( or anything else concerning guns) but I know that some are having feeding issues with current builds especially with stick magazines. I suspect that ramp design is critical. The Finns (and I suppose the Russians before them) went to a lot of trouble in tooling for their curving feed ramps and I can attest to this, having done it crudely myself. The male die wasn't too hard to free hand, on the lath, to a template but the female die was another matter. Aren't females always? This involved a graph and a table of carriage and crossfeed movements. Even with .005" depth movements it still came out not very smooth, though smoothness is not required on this side of the plate.

Now look at the 1st pic of the Suomi style curved ramp and the Wiselite/MGS type straight ramp. The new ramp is spot welded (6 spots) to tabs which simulate the bent tabs of the original. The right hand cartridge in the stick mag is the critical one because it has to climb about 3/8" to get into the chamber. The left cartridge only has to climb about 3/16" though both have to move about 3/16" laterally. The RH bullet touches about 3/16" down from the end of the ramp and meets a wall at an angle of 60 deg or so above the horizontal. On the straight ramp, it touches at about the same angle but this angle remains constant while the curved ramp angle rapidly decreases down to 30 deg or so as the bullet starts entering.

But this is only half the picture. With the stick mag the bullet has to move 3/16" inward laterally. With the curved ramp it meets an angled surface and the angle rapidly decreases. Not so with the straight ramp. It meets a 90 deg flat surface and doesn't see an angle until it is starting into the hole and this point depends on the vertical position of the ramp. As if this weren't enough most current builds don't have the lateral stop at the front of the mag. For stick mags which have lateral forces as the rounds are forced to the center this is a potential problem. The original had a slot, in the forward magwell, which mated with a protrusion on the front of the stick mag. The next pic shows the new ramp pressed against a stick mag. Note the engagement.

Drum mags don't have the protrusion. They don't need it. All rounds are centered with no lateral movements or forces. This is one reason drums have been working better - the rounds enjoy a nearly straight shot into the hole.

So what's the upshot of all this learned discussion?  Not to criticise the suppliers but I go with original. It worked at 650 rounds per minute, sticks or drums, and I don't buy the idea that the Finns had to mix and match to find mags that would work, even if they did have serial numbers that matched the gun. No army would have tolerated that.

I will speak to admin about offering ramps for the members to purchase. Most of you will have better things to do than making forming dies. Post again, then ramp instl.