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Old 07-26-2015, 09:44 PM   #1
ouroboros
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Default Saiga 7.62x39 90 Degree Gas Block to 45 Degree Gas Block Question

I know threads with similar titles have popped up before, but this is about something a little different.

This is regarding swapping a 90 degree gas block to a 45 degree on a Saiga 7.62x39 rifle in order to get a more classic AKM look.

Disclaimers:

I know it won't be completely authentic, etc.
I've heard most of the "why would you do that...?" questions, etc.

I'm not sure I'm going to do it, but IF I decide to do it, I know that welding the old gas port in the barrel and re-drilling a new one to accommodate the 45 degree gas block is the preferred method...

...but someone brought to my attention the idea of cutting a channel into the barrel... and I could potentially do this on my own.

I'm thinking a U-shaped channel, similar to the notch for the handguard retainer lever but going down the length of the barrel of course instead of across it, to connect the already-drilled port in the top of the barrel for the 90 degree gas block to the port in the bottom of the would-be 45 degree gas block further up the barrel.

Make sense?

I made a basic diagram to try to illustrate this. Read the key below the diagram to see what the various colors represent.

If the yellow text is hard to see, it says "path of gas flow."



Further questions:

Would cutting a channel allow enough gas to cycle the system correctly and reliably?

Would / Could it be over / under gassed?

Would carbon buildup / cleaning be a problem?

If I were to cut a channel, is there a certain width and depth that it ought to be?

Anything I'm missing? Good idea / bad idea?
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Old 07-26-2015, 10:02 PM   #2
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7.62x39 may require a larger channel than 5.45 or 223. A channel in the barrel may not be large enough. How far off are the holes? Maybe drill the hole in the gas block to a larger diameter.
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Old 07-26-2015, 10:05 PM   #3
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7.62x39 and I haven't removed the 90 degree gas block yet but by eyeballing it and putting a 45 degree block up next to it, and by going off of a diagram found in an article about converting a Saiga to an AKM which was written by a member here, it seems that the holes are about 6mm apart.

Here is a link to that article.
http://modernrifleman.net/2015/03/22...configuration/



Text taken from the article:

Quote:
AKMs have a 45-degree port that is drilled just behind the bayonet lug. This means that the two holes are a little over half a centimeter apart. Measure approximately 6 millimeters forward of the original gas port and drill a new one using a 1/8″ cobalt drill bit. I recommend countersinking this hole somewhat to allow for some flexibility in gas block placement. Also note that it is not necessary to drill the gas port at 45-degrees like original AKM barrels, a 90-degree gas port will work fine with the 45-degree gas block.
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Old 07-27-2015, 05:20 PM   #4
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Weld up old hole, drill new hole. The channel method may very well work though. Def worth a try.
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Old 07-27-2015, 05:34 PM   #5
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The AKM gas port is 26 degrees. Don't weld on the Saiga barrel. There aren't going to be any more of them. If you have to, just use another barrel.
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Old 07-27-2015, 05:46 PM   #6
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Alright, next question... and thanks for the responses... if I decided to try the channel and it doesn't cycle reliably with the 45 degree block, do any of you foresee any problems with putting the 90 degree block back on there? It would cover up the channel.
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Old 07-27-2015, 05:57 PM   #7
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Has anyone ever though of making a "short" version of the classic style gas block thats compatible with the 90degree gas hole placement?

It wouldnt be authentic, but it would be neat for projects like this where some one wants the look.
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Old 07-27-2015, 06:23 PM   #8
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You could drill the AKM gas block straight up from the bottom just like the Saiga gas block is drilled.
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Old 07-28-2015, 08:03 PM   #9
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That picture above makes it look like you can drill straight up from the bottom, but I don't think the two rifles are exactly in line in that picture. I checked it in person by holding a 45 degree block right next to my 90 degree block on my saiga and if I were to drill the AKM 45 degree block straight up and use the 90 degree port, I would have to cut off a good portion of the gas tube and piston to get it to fit... looks like attempting a channel is still my only DIY option...

...does anyone think, if for some reason the channel doesn't work, that there would be a problem with re-installing the 90 degree block which would cover up the channel?
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Old 07-28-2015, 08:13 PM   #10
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http://www.akfiles.com/forums/showthread.php?t=223636
Someone just asked same question in another thread; post 35# has a real nice cad drawing made by Rforbus.
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Old 07-28-2015, 08:14 PM   #11
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Quote:
Originally Posted by ouroboros View Post
That picture above makes it look like you can drill straight up from the bottom, but I don't think the two rifles are exactly in line in that picture. I checked it in person by holding a 45 degree block right next to my 90 degree block on my saiga and if I were to drill the AKM 45 degree block straight up and use the 90 degree port, I would have to cut off a good portion of the gas tube and piston to get it to fit... looks like attempting a channel is still my only DIY option...

...does anyone think, if for some reason the channel doesn't work, that there would be a problem with re-installing the 90 degree block which would cover up the channel?
No, you don't modify the top. Drill from the bottom into the 26 degree gas port channel that is above the barrel in the gas block. The vertical hole will be far back in the bottom of the gas lock but there is just enough material to work with.
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Old 07-28-2015, 08:17 PM   #12
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Would you lose the second pin by drilling through it?
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Old 07-28-2015, 08:23 PM   #13
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Quote:
Originally Posted by Unit28 View Post
Would you lose the second pin by drilling through it?
The gas port doesn't go all the way across the gas block. if it intersects the pin hole it won't matter. There is no gas on the BOTTOM of the barrel.

Some Vepr gas blocks only have one retaining pin.

If the gas port does go through the pin hole, the pin can still be used anyway.

You can also use a little fudge factor and move the gas block back slightly and shorten the gas tube slightly but leaving everything long enough for the gas piston.
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Old 07-28-2015, 08:37 PM   #14
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Once you locate the correct position of the gas port, you can drill the gas block with an 1/8" drill.
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Old 07-28-2015, 08:52 PM   #15
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Quote:
Originally Posted by allesennogwat View Post
No, you don't modify the top. Drill from the bottom into the 26 degree gas port channel that is above the barrel in the gas block. The vertical hole will be far back in the bottom of the gas lock but there is just enough material to work with.
You were right, when I eyeballed it, I didn't account for the few millimeters of the gas block that disappear underneath the gas tube... so there does seem to be just enough room to drill a vertical hole.

I will very likely try this option within the next few days, thanks.
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Old 07-28-2015, 10:01 PM   #16
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Ok just wondering if it would have been enough metal to still use the pin.
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Old 07-28-2015, 11:05 PM   #17
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Quote:
Originally Posted by Unit28 View Post
Ok just wondering if it would have been enough metal to still use the pin.
Even if the 1/8" hole passed through the pin hole there would still be pin holes on both sides of the barrel in the gas block.
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Old 07-31-2015, 10:10 PM   #18
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UPDATE:

Thanks to ncthorn for writing the article I linked to earlier in this thread and thanks to allesennogwat's suggestion of drilling a 90 degree port through the bottom of the gas block with a 1/8" bit, I now have this...



...the ports line up fine, I checked it a bunch of times with water and compressed air and it flows freely.

I was able to reuse the front pin location but had to drill for the rear pin location.

I had to shorten the gas tube slightly but it locks up snug, not overly tight, and the piston moves very smoothly with no hangups.

Bayonets attach correctly and everything is straight, no cants (other than the fact that I'm pretty sure my RSB is canted very, very slightly).

I still need to touch up the paint and of course shoot it to make sure it cycles correctly (the most important part) but I'm fairly confident that it's good to go.

I'll post an update after I shoot it. I'll be doing that soon.
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Old 08-01-2015, 12:44 PM   #19
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Looks good.
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Old 08-02-2015, 06:04 PM   #20
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ANOTHER UPDATE:

Put 60rds of Tula hollow point through it today and it ran flawlessly.
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Old 08-02-2015, 10:49 PM   #21
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Here it is cleaned up.




Last edited by ouroboros; 08-02-2015 at 11:08 PM.
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