RPK Yugo

[wonderwolf]

I got a RPK Yugo kit from the creek from copes dist. It was by far the best in the lot (barrel was really good IMHO). I took it back to the truck and looked the kit over. the guys parked next to us came over to have a look at what I got and the one guy turned out to be very knowledgeable about the kits. He pointed out a odd mark on the forward trunnion where the receiver is. It looks like a spot weld of some sort. I don't have the kit here with me as it went with my dad to be stored until I come home for Winter break to build it.

Has anybody else seen this on a RPK or variant?

[nalioth]

None of my parts had spot welds on 'em. The kit I got had been previously built on a homemade-from-a-flat receiver (seller cut it up before sending it to me), if that might make any difference.

[kevin]

i had some yugo underfolder kits that had some very tiny welds on the receiver/trunnion, made getting the receiver scrap off just a little harder but not bad

[wandering_ronin]

My fixed stock Yugo AK kit had the receiver stub tack welded onto the trunnion. Read elsewhere that this was done for strength in regards to grenade launching.

[k98k792]

Yep, there is often a spot weld in that area.

[wonderwolf]

Ok thanks...now the next obvious Q?.....whats the best way to get it torn apart?

[Otis61]

You grind the spot off. On a bench grinder, a die grinder, or a milling machine. very carfully, of course.

[k98k792]

Remove the rivet heads with a cold chisel or grind them off.I clamp the rear of the front receiver stub in a vice,good and tight. Then I bend it away from the trunnion till I can get a cold chisel between the trunnion and the receiver stub. Sometimes you have to grind down the remaining weld left on the trunnion in that area.

[Simon]

Using a milling machine makes this really easy. You can simply look up or measure the thickness of the receiver (.060" ?) and use a plunge cut endmill to plunge 5 or 10 thousandths of an inch less than that distance (say, .050"). Be sure to use the fine feed on your machine. With only the 5 or 10 thousandths of the weld left you can peel it off with vice grip pliers like it was nothing.

[k98k792]

It's an AK, not a freakin Weatherby !

[nalioth]

My fixed stock Yugo AK kit had the receiver stub tack welded onto the trunnion. Read elsewhere that this was done for strength in regards to grenade launching. RPKs weren't used for launching grenades, which is puzzling in wonderwolfs case.

I've got a bunch of Yugo kits and I don't think I've seen a weld on any of them. Anyone got a pic or can photoshop a circle around where the welds are supposed to be (if they're present) ?

[k98k792]

Here is the aftermath of the first one I did in April 2005. There was a good thread about the subject on the old Gunboards.

[wonderwolf]

Dang....My mom is in town for a meeting and I should have had her bring my kit so I could post a pic (gonna go have dinner with her).

Its in a odd spot for "added strenth" isn't it? the above pic in k98k792 post shows where it is. Could it be a simple tack weld if they had problems with the receiver and trunion moving around during manufacture while riviting???

k98k792 does it hinder assembly at all?

[wandering_ronin]

Its in a odd spot for "added strenth" isn't it? the above pic in k98k792 post shows where it is. Could it be a simple tack weld if they had problems with the receiver and trunion moving around during manufacture while riviting???

Seems like it would cut down on any shearing force on the rivets due to stronger forces being placed on the trunnion during grenade launching. Just my thoughts. My fixed AK kit actually had a couple of spotwelds per side. Maybe since the RPK was a SAW type weapon (meaning more of a "sustained" fire kind of weapon) there was some issue there...again, just kinda thinking out loud.

[k98k792]

I don't know if this is true or not,but I had heard that this was done by unit armorers because they were having the riveting loosen up.

Also that they started doing this later in the war.
From what I hear,it seems to be done a lot less frequently in the RPKs.

Wonder,it made no difference in the current build, or performance of the weapon.

Just remove the weld from the trunnion,and you are good to go.

[nalioth]

Seems like it would cut down on any shearing force on the rivets due to stronger forces being placed on the trunnion during grenade launching. The Yugos use a bulged trunnion in a 1.6mm steel receiver shell. I doubt you'd even need rivets in it, to hold up to launch a grenade.


Your theory makes sense if a non-bulged trunnion is used (like the Polish rifles).

[k98k792]

In the films I have seen of Serb units launching grenades,though they were equipped with Aks, they had soldiers with SKS's launching with the weapons butt on the ground,braced by they're foot.

Recoil looked STOUT.

The soldiers with the SKS were the only one launching grenades in the films,though at least one of the other soldiers had the launching muzzle attachment on their AK.

There has to be a reason for the spot weld.

Nalioth,what would your guess be?

[nalioth]

In the films I have seen of Serb units launching grenades,though they were equipped with Aks, they had soldiers with SKS's launching with the weapons butt on the ground,braced by they're foot.

Recoil looked STOUT.

The soldiers with the SKS were the only one launching grenades in the films,though at least one of the other soldiers had the launching muzzle attachment on their AK.

There has to be a reason for the spot weld.

Nalioth,what would your guess be? You have to remember that forces that will break human bones will not even bend the steel in these rifles, especially at the angles of force involved. The Yugo bulged receiver cradles the bulged trunnion against those forces. The 'put the buttstock on the ground or against a tree' firing method was taught by all countries that fielded the 'over-the-muzzle' rifle grenades. The recoil from a 2lb grenade and a 2x strong grenade blank would injure you if you weren't careful.

As far as the weld, I have no freakin' clue. I've looked at all my kits and none of them have any.

[k98k792]

You have to remember that forces that will break human bones will not even bend the steel in these rifles, especially at the angles of force involved. The Yugo bulged receiver cradles the bulged trunnion against those forces. The 'put the buttstock on the ground or against a tree' firing method was taught by all countries that fielded the 'over-the-muzzle' rifle grenades. The recoil from a 2lb grenade and a 2x strong grenade blank would injure you if you weren't careful.

As far as the weld, I have no freakin' clue. I've looked at all my kits and none of them have any.

I understand about the firing method and the forces involved. I have a feeling the Yugo Aks might not of stood up to these forces as well as one might think.I think the welds are, if you will a expedient to beef up the rifles,even though they are pretty beefy already.

I have noticed that the Yugo trunnions seem softer then other countries. I was talking about this to Ken Kubin and he concurred. I wonder if this might have something to do with the welds?

We talked about this at great length back on the old Gunboards.
I believe it was Mike Riddick who first suggested it was for grenade launching.

Also it seemed much more common in the first batches of Yugos then in the later batches.The trunnion shown was from the very first batch CFS had.

[drine]

It's an AK, not a freakin Weatherby !

Well here's another fine comment I'll have to copy and paste on my tool box. (ralmao) Back on topic, it must be similar to the spots on the cetme trunnion. I peeled what I could and used a die grinder to clean what was left.

[wonderwolf]

Could it have been a factory oops?.....Got a batch of receivers in...they have 1 misslocated hole or 1 hole to many?? Fill with weld and grind down...easy fix for them...Maybe it was for a prototype receiver that was made for a extra rivet but instead they simply welded it.

Can we trace the manufactures of the RPK's that have this? Mine has a mfg stamp but since its not here and I didn't write it down or take pics. I dunno what it is....

I look at the picture posted and it looks like it would be in the right place for a "opps"....I'm thinking this because the heat treat or blueing covers the weld (on mine)...and that would have to been done at the factory unless you had a armorer who was really specific.

If it was a unit armorer wouln't he have to drill the receiver then weld it? Wouldnt it just make more sense to weld the top of the trunnion instead? But then it would be a PITA to take apart for our needs.

just a few thoughts...I have nothing really to base these off of.

[k98k792]

They were not filled in holes.They are spot welds.

[okie shooter]

Wonderwolf, if you are trying to recreate spot welds on sheetmetal parts with a wire feed, you useally drill a hole and fill in and kinda of make a weld like a spot welder does. If you had a spot welder you could do a easy weld build on a ak by just opening the jaws wide, makeing sure the trunion is in position then welding a couple of spots together on different places on the trunion/receiver. The spot welder makes a bright "cherry' and fuses the metal together there.

[wonderwolf]

Nah...I'm not worried about duplicating the spot weld...Just curious as to why it is there.

[k98k792]

Well it has to be as an reinforcement. The question no one has ever been able to answer is, why?

[k98k792]

Just sent off an Email to Zastava. They have been good at replying to my questions in the past. Let's hope we get a response,and answer this once and for all.

[wonderwolf]

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