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They both use swell-necked rivets as well as non. Diameter and material is the same. PSL rivets are a little larger in some areas.
 

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Bulgarian 74 rivet sets that K-Var sells contain 4 larger than normal swell neck rivets that match the 4 larger than normal barrel trunnion holes.

Many build Bulgy 74s with standard rivets and have no problems. IMO there is too much play for the normal rivets to perform as intended by design. When I built mine I used factory Bulgarian rivet sets because of this issue.
 

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The front trunnion on a 74 uses 4 swell neck rivets as opposed to two on an AKM. The AKM (excepts some late Russian) tang uses 2 long rivets, whereas the rear tang on a 74 uses one long rivet and two short for the forked rear tang (except really early kits).
 

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m0ondoggy said:
The front trunnion on a 74 uses 4 swell neck rivets as opposed to two on an AKM. The AKM (excepts some late Russian) tang uses 2 long rivets, whereas the rear tang on a 74 uses one long rivet and two short for the forked rear tang (except really early kits).
Just wanted to add that the short rivets for the forked rear, at least for a Bulgy fixed stock, are actually a little longer than a standard short rivet. AK Builder includes this size with the fixed stock 74 rivets he sells.

As for the two swell neck rivets for the front trunion that need to be thicker, couldn't one just cut most of the shaft off the long rear rivets and use that? Haven't tried it myself... just curious.
 

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I'm pretty sure that when I crushed my rivets into the larger than normal 74 trunnion holes, the rivets expanded to fit the holes. I mean they do expand when you crush them, so what's the issue?
 

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I'm pretty sure that when I crushed my rivets into the larger than normal 74 trunnion holes, the rivets expanded to fit the holes. I mean they do expand when you crush them, so what's the issue?
I am not saying what you did would be wrong, they should be fine.

The Polish 74 tantal uses 6 standard swell neck rivets for its barrel trunnion. They designed it differently from their AKMs for some reason. Possibly the more violent, higher pressures associated from the 5.45x39mm round. I would assume the Bulgarians developed their rifles with the change to compensate for the different pressures associated with 74s too. They went with a larger sized rivet for 4 of the 6 rivets. Has anybody seen a Russian 74 trunnion with rivets removed, what are the hole sizes? Add to the mix why are the more modern Russian and Bulgys using two rivet bullet guides over the previous one rivet?

The available factory Bulgarian rivets are 4 larger swell necks and it includes the flat head rivet for the Arsenal FCG anti-trigger slap feature too. That would be what Arsenal in Bulgaria would use for assembling their 74s.

Rivets by design are supposed to be expanded only so much to maintain designed specifications.

I found some pics I did before covering the same topic.

Romy G uses 4 standards, 2 standard swell necks.
Bulgy 74s uses 4 larger swell necks, 2 standards.
Polish Tantal 74 uses 6 standard swell necks.
Top to bottom Romy, Bulgy and Polish Tantal

Left to Right Romy, Bulgy, and Polish Tantal


I hope you can see the difference in the pictures. :smile:
 

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The bulagarian AK-74 front trunnion uses four swell neck rivets, 4.5mm in diameter and two regular 4mm rivets.
 

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what about the Akbuilder rivet size? I am used to order their AK74 and AKM rivets back when I was still building my own. Are they the correct size for the front trunnion swell necked holes?
 

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Vashthestanbeto said:
what about the Akbuilder rivet size? I am used to order their AK74 and AKM rivets back when I was still building my own. Are they the correct size for the front trunnion swell necked holes?
I have built several Ak-74's with his rivets. They work great.
 

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Attention to detail is what keeps the trunion from flying off the reciever and hitting you between the peepers when you reach that 9,999 round count from a screw build or using the wrong rivets . :reaper: Good job Tango ! Keep paying attention to detail !
 

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In one occassion I discussed this rivet issue with Jimmy Streetman , owner of Armory USA, he told me that Ivan, who used to be his head enginner and held the same occupation in former Bulgaria State Arsenal, told him the usage of swell neck and specific size rivet being a great feature but isn't really necessary. From what he told jimmy, when they run out of swell necked rivets they just use normal flat rivet for all applications, and yet never had a problem, trunnion shifting or else with guns assembled this way in their service life.And those are even full auto "real deals" so I think our semi replica rifle will fare better.

Another approach comes from a book"testing the War weapons", somewhere in there was a record of rivets coming loose in M2 machinesguns after approximately 250,000 rounds. Thats a hell lot of shooting. with a fraction of recoil compared to .50BMG,It is very reasonable to believe that the rivet structure will most likely outlive the barrel longvility wise.

Just something I think is related to this topic and intesesting.

BTW m0ondoggy Thanks for your reply, I built 5 guns with their rivets and love them to every bit.
 

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Vashthestanbeto said:
In one occassion I discussed this rivet issue with Jimmy Streetman , owner of Armory USA, he told me that Ivan, who used to be his head enginner and held the same occupation in former Bulgaria State Arsenal, told him the usage of swell neck and specific size rivet being a great feature but isn't really necessary. From what he told jimmy, when they run out of swell necked rivets they just use normal flat rivet for all applications, and yet never had a problem, trunnion shifting or else with guns assembled this way in their service life.And those are even full auto "real deals" so I think our semi replica rifle will fare better.

Another approach comes from a book"testing the War weapons", somewhere in there was a record of rivets coming loose in M2 machinesguns after approximately 250,000 rounds. Thats a hell lot of shooting. with a fraction of recoil compared to .50BMG,It is very reasonable to believe that the rivet structure will most likely outlive the barrel longvility wise.

Just something I think is related to this topic and interesting.

BTW m0ondoggy Thanks for your reply, I built 5 guns with their rivets and love them to every bit.
I really can't see the difference, specially considering that these rifles are never fired full-auto. I dumped the entire "swell-neck" thing about 25 builds ago, and one of the Tantals I built afterwards has about five cases of rounds through it, and it has had no problems. The swell-necked thing is really not necessary for what we do.
 
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