School me on AK rivets

[powderedtoastman]

So I've been poking around the web and have got info. telling me two different things. Tapco says that the two forwardmost rivets of the trunion are swell necks, so the receiver would need dimpling. I.E., here:http://www.tapco.com/pdfs/instructions/ZAK0664.pdf Other videos I've seen have only the rear rivet getting dimpled for a swell neck. 4 questions:

1. Which rivets need dimpling/swell necks?
2. What is the purpose of swell necks?
3. Why aren't all rivets on the trunion swell necks?
4. Why do I sit on the internet for hours looking for answers getting tunnel vision when I should just ask knowledgeable calgunners?

[Wyseguy]

On a Romy G kit
1) the two rear rivets are swellnecks, and the two rear rivets on the front trunnion are swellnecks.
2) to hold it together
3) they don't need to be
4) You're addicted to the internet

[SJgunguy24]

So I've been poking around the web and have got info. telling me two different things. Tapco says that the two forwardmost rivets of the trunion are swell necks, so the receiver would need dimpling. I.E., here:http://www.tapco.com/pdfs/instructions/ZAK0664.pdf Other videos I've seen have only the rear rivet getting dimpled for a swell neck. 3 questions:

1. Which rivets need dimpling/swell necks?
2. What is the purpose of swell necks?
3. Why aren't all rivets on the trunion swell necks?
4. Why do I sit on the internet for hours looking for answers getting tunnel vision when I should just ask knowledgeable calgunners?

1. Depends on the kit, some are 2 4mm swell and 2 4mm non swell rivets. Some use 2 4mm non swelled and 2 4.5mm swelled. The mag well rivets are always swell rivets of the 4mm type but I have seen some that are 4.5mm. Then you have the Yugos, the bulged trunnions use IIRC 2 4mm non swell and 2 4.5mm swell and 1 4.5mm long rivet. Those are also spot welded as well on both trunnions. The rear trunnions can be confusing as hell too.

2. The swell neck rivet locks the sheetmetal into the trunnion, it spreads the shearing forces to the trunnions and increases the strength and helps keep everything in place. (IMO that's a huge reason what a fully heat treated receiver is a must if you want your gun to last, that anneled metal is really soft.)

3. Not sure 100% but the load can only be spread out so much. 2 swell necks too close can lead to the metal tearing.


4. Normally I don't just give out answers, because lazy people deserve exactly what they put in. You put in nothing then you deserve nothing. I put in the hours and I worked to get what I know.

My back round is sheet metal, welding, and some machining also. This is what I was taught in school when I asked about solid rivets. We normally don't use solid rivets much but I also used to build race cars and the cars I built used an aluminum monocoque and that is were I learned the most about rivets.
Never use Tapco rivets, they are too soft and anybody who says they are not is mis informed.

[Roccobro]

I can answer 1 and 4 (kinda)
1- For a Romy G: the little ones closest to magwell, and rear trunion. SJGG has answered this question much more in depth.

4- Because you don't want to abuse a good thing...? Once you've done your due diligence in searching for information, THEN your allowed to ask the experts (not me!) with a clear conscience.

and 6- So you can (and will!) pass on this information accurately whenever the opportunity arises.

Justin

ETA: What the heck is Tapco trying to represent in that diagram??? FUBAR'd!

[Trench Broom]

Easy way to remember is: beveled trunnion holes = swellneck rivits, non-beveled holes = regular rivits.

[SJgunguy24]

Easy way to remember is: beveled trunnion holes = swellneck rivits, non-beveled holes = regular rivits.

Well yeah, but the OP is asking the purpose of the types of rivets and how important is it to use the correct rivets.

[powderedtoastman]

Thanks for the info. guys. The K-Var list is a big help too. Just figuring out exactly what I'll need and gathering info. for my Romanian build on my NDS-3. Much obliged, gents.

[valleyrat]

Another little known factoid:

Bulgarian and Russian AK74 barrel trunnion swell necks are 4.5mm shaft dia.

[SJgunguy24]

Another little known factoid:

Bulgarian and Russian AK74 barrel trunnion swell necks are 4.5mm shaft dia.

Covered that in my first post, and the welded Yugo trunnions too.

[valleyrat]

Covered that in my first post, and the welded Yugo trunnions too.

Not specifically. There are 4 swell neck 4.5mm rivets on the Bulgarian and Russian 74 types, the two front and the two magwell locations. The center rivets are standard 4mm.

[powderedtoastman]

Easy way to remember is: beveled trunnion holes = swellneck rivits, non-beveled holes = regular rivits.

This kind of has me a bit confused. The front trunnion has individual rivets on either side of it, but the rear trunion has 1 long rivet for each hole. I inspected my romanian rear trunnion and BOTH sides are beveled. The rivets are flat on one end.

[valleyrat]

This kind of has me a bit confused. The front trunnion has individual rivets on either side of it, but the rear trunion has 1 long rivet for each hole. I inspected my romanian rear trunnion and BOTH sides are beveled. The rivets are flat on one end.

You dimple both sides of the receiver, the side of the rivet that you crush expands and fills the dimple.

[bigbob76]

This kind of has me a bit confused. The front trunnion has individual rivets on either side of it, but the rear trunion has 1 long rivet for each hole. I inspected my romanian rear trunnion and BOTH sides are beveled. The rivets are flat on one end.

Where did you get your long rivets?

[SJgunguy24]

Where did you get your long rivets?

Tapco, DO NOT USE TAPCO RIVETS!!!!

[valleyrat]

Tapco, DO NOT USE TAPCO RIVETS!!!!

+1, AKbuilder all the way.