Why The Switch From Slanted Gas Ports To 90 Degrees ON AKs.

[WAR FACE]

Why did the Russians switch to 90 degree gas ports on the AK74 from the slanted on the AK47? I think I read on here that the 545. guns experienced "bullet shear" which I assume meant that the jackets of the bullets would strip off wile passing over a slanted port. If this is true why doesn't it not seem to be a problem in Romy 545. guns that still have slanted ports? Or is it a problem?

[sua175]

I understood it as a part wear issue.

[fhk96]

Bullet shear on the gas port and simpler/more efficient to just drill 90 degrees into barrel from what I understand.

The Romanian '74s gas block is 90 degree as the opening of the gas port; 45 there after.

[black22rifle]

I think it also had to do with the shape of the hole. When you drill a hole at an angle it is oval shaped, I remember Jim Fuller talking about it but I forgot exactly what he said.

[Roc_Kor]

I believe the Romanians also avoid the problem in their gas blocks by ensuring the gas port is drilled in a groove, and not a land of the rifling.

[LtNovakUSA]

here's a good thread that discusses it:

https://www.m4carbine.net/showthread.php?87315-quot-Bullet-shear-quot

BLUF: It was indeed to cut down on bullet shear when they moved to 5.45.

[eodinert]

I don't understand why a 90 degree port would have less bullet shear than a 45... seems counter intuitive to me. If I made a cheese grater the same way, one would shred a lot more cheese than the other.

[montrala]

I don't understand why a 90 degree port would have less bullet shear than a 45... seems counter intuitive to me. If I made a cheese grater the same way, one would shred a lot more cheese than the other.

Remember that bullet not only moves forward it rotates. With 45dgr port elongated (oval) shape of gas port creates more contact against bullet jacket, that round gas port of 90dgr port. This longer side is at 90dgr to bullet jacket, so longer contact with bullet rotating against it create more shear.

[SteyrAUG]

I don't understand why a 90 degree port would have less bullet shear than a 45... seems counter intuitive to me. If I made a cheese grater the same way, one would shred a lot more cheese than the other.


I think it was specific to the 5.45mm round. All three types of AK-47s and the AKM used a 45 degree block. The early 5.45 74s used a 45 degree and that is when they started getting problems and for whatever reason a 90 degree block solved the issue.

From that point on it was just standardization of production and eventually the 7.62 rifles got a 90 degree block as well.

[zack991]

Mine still has a 45 degree gas block and it is a Ak74. I am wondering if that was just the parts they had with it.

[Roc_Kor]

zack911 is yours Romanian? SAR-2 and WASR-2 rifles should have 45-degree blocks, as do the Romanian military AK-74s

[zack991]

zack911 is yours Romanian? SAR-2 and WASR-2 rifles should have 45-degree blocks, as do the Romanian military AK-74s

It is a SAR-2

[WAR FACE]

Do gas ports on ARs have to be drilled in the groves also? Is this something a lot of sub par manufactures ARs or AKs neglect to do?

Edit: Ok I reread the old thread. Somebody said Krieger drills them partially on a land and groove how would doing ether or effect accuracy.

[Labayu]

Bullet shear on the gas port and simpler/more efficient to just drill 90 degrees into barrel from what I understand.

The Romanian '74s gas block is 90 degree as the opening of the gas port; 45 there after.


This is exactly what I was told by a retired Radom engineer who emigrated from Poland in the 90s.