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Posted: 9/15/2025 2:44:13 PM EDT
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My new (to me) Type 56 SKS won't cycle. The bolt only goes back maybe an inch or so and then feeds the fired round back into the chamber. The gun has been taken apart and thoroughly clean, oiled/greased, and does not seem to be missing any parts or springs. The gun feels smooth and it works fine as a manual straight-pull. The distance the bolt goes back is consistent when firing. Manually extracting a fired case by pulling the bolt back feels smooth. This gun came from the recent Atlantic batch, which some think came out of Albania. The gun looks pretty good, as if it was used but not too harshly (or is refurbished, which seems more likely). Nothing seemed loose or looked odd when I took the gun apart for the thorough cleaning, but I'm not experienced with the SKS and could be missing something obvious. Ammo used was "AAC "Soviet Arms" 7.62x39mm 122 Grain FMJ SSSC 20rd Box Ammunition" from PSA. I'll grab some PPU or similarly well-known 7.62x39mm next time I go to the gun shop to test, and chrono both the new ammo and the old ammo, but it doesn't look (from a quick search on google) like the AAC 7.62x39mm is known to have low pressures or anything. Any ideas what the cause could be? |
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I think I understand. you can fire a round but there's not enough gas to cycle the action? you can cycle the action manually, completely , (over the hammer) and all the way to the back of the rifle? the gas port is clean and unobstructed? you have an op rod in the gas tube and a littler piston extension rod that goes through/ under the rear sight leaf? it sounds like you're not getting gas. Use the gas port cleaning tool. google: Gas system issues This is the most common cause of cycling problems, also known as "short-stroking," where the bolt does not travel far enough rearward to fully eject the spent casing and load a new round. Cosmoline or carbon buildup: Older surplus SKS rifles can have a significant amount of dried cosmoline or accumulated carbon in the gas system, which blocks the flow of gas that operates the action. Fix: Fully disassemble the gas system, including the handguard and both gas pistons. Use a cleaning solvent and a bristle brush to remove all gunk from the gas tube, the gas block, and the pistons. Misaligned or obstructed gas port: After cleaning, use a pipe cleaner or a paperclip to ensure the small gas port in the barrel is completely clear of obstructions. Incorrectly installed pistons: The SKS has two gas pistons, which must be installed correctly for the rifle to cycle. The "knob" or thicker end of both pistons should face forward. |
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| Corrosive ammo without a thorough hosing down can gunk up moving parts but you'd see rust. If you have another SKS maybe swap the recoil springs and shoot them. See if issue moves to the other rifle. Also, check the gas port. If partially blocked you'd experience weak cycling. |
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Lock the bolt back, insert a cartridge in the chamber, hold it in place with your finger, then blow compressed air down the muzzle and confirm that the gas piston/op rod is extending outward 3/4". See pic. It should make an audible "thunk" when the piston hits full extended travel. As soon as you let off the air, it should immediately retract/snap back. Tony  |
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Originally Posted By Bounce19712: I think I understand. you can fire a round but there's not enough gas to cycle the action? you can cycle the action manually, completely , (over the hammer) and all the way to the back of the rifle? the gas port is clean and unobstructed? you have an op rod in the gas tube and a littler piston extension rod that goes through/ under the rear sight leaf? it sounds like you're not getting gas. Use the gas port cleaning tool. google: Gas system issues This is the most common cause of cycling problems, also known as "short-stroking," where the bolt does not travel far enough rearward to fully eject the spent casing and load a new round. Cosmoline or carbon buildup: Older surplus SKS rifles can have a significant amount of dried cosmoline or accumulated carbon in the gas system, which blocks the flow of gas that operates the action. Fix: Fully disassemble the gas system, including the handguard and both gas pistons. Use a cleaning solvent and a bristle brush to remove all gunk from the gas tube, the gas block, and the pistons. Misaligned or obstructed gas port: After cleaning, use a pipe cleaner or a paperclip to ensure the small gas port in the barrel is completely clear of obstructions. Incorrectly installed pistons: The SKS has two gas pistons, which must be installed correctly for the rifle to cycle. The "knob" or thicker end of both pistons should face forward. I'll order an SKS cleaning kit, which is certainly cheap enough and has all the tools including the gas port cleaning tool |
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Originally Posted By D00m: Corrosive ammo without a thorough hosing down can gunk up moving parts but you'd see rust. If you have another SKS maybe swap the recoil springs and shoot them. See if issue moves to the other rifle. Also, check the gas port. If partially blocked you'd experience weak cycling. Originally Posted By TonyRumore: Lock the bolt back, insert a cartridge in the chamber, hold it in place with your finger, then blow compressed air down the muzzle and confirm that the gas piston/op rod is extending outward 3/4". See pic. It should make an audible "thunk" when the piston hits full extended travel. As soon as you let off the air, it should immediately retract/snap back. Tony https://i.imgur.com/VWUMiMb.jpeg Thanks all, I'll try the suggestions above and see if that fixes it |
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@TonyRumore Tried the air compressor test. My air compressor is cheap and crappy, so it might not be providing enough pressure, but the gas piston doesn't move at all. All the air comes out the gas escape hole in the piston housing, or pushes against the round my finger is holding into the chamber. Does this test require a ton of pressure? I disassembled the gas system to make sure nothing was stuck, and the main piston moves fine and if I manually press on the piston extension under the rear sight it moves smoothly. Reassembled with no change in result. Since all the air is escaping out the gas escape hole, I'm wondering if the fit between the piston and the housing is too loose to provide enough of a gas seal. ETA: I can stick a paperclip into the barrel from the gas bock, so it does not appear to be blocked by gunk. I'll give it a more thorough scraping when the sks cleaning kit I ordered arrives. ETA2: there is a bit of what I assume is some carbon buildup in the gas tube. Are SKS rifles tolerant of some carbon in there, or does it need to be brushed completely clean to function? I'll clean it anyway, but I'm curious. It certainly doesn't stop the piston from moving freely with the tube off the gun. |
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After doing some more testing with the air compressor, it seems pretty likely that the air is just going around the gas piston due to too loose of a tube/piston fit. No amount of pressure with the air compressor moves the piston at all, all the air goes right out of the gas tube vent hole. I contacted Atlantic and asked to return it. |
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Originally Posted By backbencher: Just buy another piston. |
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Originally Posted By TonyRumore: The test worked fine on my gun with 125psi. Tony |
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Originally Posted By CFletch: I don't want to spend more money and try to play mix and match with pistons and tubes. I'll just send it back and let the seller deal with it since they offered to do so when I told them of my issues. Originally Posted By CFletch: Originally Posted By backbencher: Just buy another piston. I don't want to spend more money and try to play mix and match with pistons and tubes. I'll just send it back and let the seller deal with it since they offered to do so when I told them of my issues. Fair enough. |
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