New STG58 Build Function Problem

[Regal Beagal]

Goodmorning Folks!

Well, took the new STG58 carbine build to the range yesterday to check her out for functioning (Enterprise receiver with an un/MB 18 " barrel). Started the gas setting at 7 and cranked off a round. Shell didn't extract and the carrier and bolt was pushed back about an inch. Kept adjusting gas setting and samething all the way up to 1. On 1 it kicked like a mule but same outcome. :redface: What could be causing this? I used an Enterprise receiver that I had to do some metal work on to get everything to fit and manually function. I also cut the barrel back to 18" but didn't open the gas port. I can't tell if the extractor is getting hung or if I need to open the gas port to get enough pressure to push the gas piston back. The barrel is TDC and the gas piston moved freely and didn't seem to bind. I figured that even with the barrel cut back to 18" that the rifle would cycle enough to eject the case. HELP! RB

[TinMan99]

Could be your gasport needs to be enlarged slightly, especially if this was a full length barrel that was cut down to carbine length. More gas is needed faster because backpressure is lost sooner.

Check your bolt carrier for free movement, lubricate your carrier rails with light gun oil and examine the rattail to make sure it's perfectly straight.

Could be your extractor relief cut isn't large enough, might need to be enlarged slightly.

Check headspace. Sometimes too tight a headspace makes the bolt disengage with difficulty, leaving no inertia to cycle the bolt. Perhaps a slightly smaller locking shoulder is in order.

TinMan99

[mosbysmen]

is it on the grenade setting instead of the rifle setting ? that happen to me one time when i put it back in upside down .

[Regal Beagal]

Nope, after the first round I checked to make sure that I hadn't inadvertently set it on the grenade setting. I have a feeling it's either the extractor hanging up, the rat tail is bent which when I assembled it did look slightly bent or the headspace is a little tight. I'm going to check all of these areas. The headspace may be a little to tight since I had some problems in this area from the get go. Enterprise when machining out the locking shoulder area didn't take out enough metal and the holes were slightly missed aligned. I will never buy an Enterprise receiver again.....! RB

[aleph_beth]

rb,
what does your gas tube have in it. could be some crud or kinks
is it a short one soldered on? old style full length? is there any gas carbon blowby on the gas block threads? first thing i would do is check the old gas tube,(if its the removable kind) it doesn't take much abuse to cause the threaded end to deform and cause problems.

[mrbonecrusher]

Had a similar problem. Fixed by polishing the bolt, carrier and receiver contact ares with a green Scoth pad. Then removed the front sight and cleaned out the gas port with an abrasive pipe cleaner and the cleaned the rest of the rifle up. Had to replace the extractor and the BHO. Then all was good. I had been thinking of opening up the gas port but others steered me away from that. Check all operating parts for smooth function before drilling and save a barrel. Maybe check gas piston for size and smooth operation. I did this by removing the bolt and the gas piston spring then put gas rod back in clean gas tube. Raised up rifle barrel and piston should fall all the way thru to bottom out.
Good luck.

[acr]

I recently took an STG that I had assembled on an Enterprise receiver to the range and had a simular outcome. With the gas set at 1, the rifle would move the carrier almost all the way back to complete the ejection cycle. Some times it would eject, but most of the time it would just crush the case. I looked it over last night and found that the gas port was very clogged. A .096 drill bit would not pass through the port. I cleaned the port out and then checked the gas tube. The last person who worked on this rifle in Austria had put the tube in 180' off! I turned that around and now things should be fine. I would check these items as well as the piston diameter before doing anything more involved. I have an 18 inch STG that functions as it should with the gas set at 5, with no gas port size increase. Some times these things go together and work perfectly and some times you have to tweak them a little. In the end you will have a great rifle and a better understanding of how it works from all your labor. :D

[orca]

Hi Beagle......I'm sure from the symptoms that your chamber and extractor or functiong:

Not quite reaching ejection and re chambering the spent case.

I would expect something restricting full ejection position of the bolt (such as a recoil 'buffer' or rat tail probs) or????) keep looking before you get too heavy on the panic button. orca

PS: does it eject easily during hand operation?

[Regal Beagal]

Well, I didn't get a chance to work on her today due to a 13 year old Lawn Boy mower acting up and totally pissing me off. I can't complain, I got 13 years out of it and now that I have a dust bowl for a yard what should I expect. These mowers weren't meant to be abused and sucking in dust like my commercial mowers. The carb. is getting blocked from very fine dust entering in threw the air filter. Unlike my commercial mowers the air filter compartment doesn't have a gasket around it to seal it off and the filter is just a piece of foam, were as on the commercials are actual paper filters with their own top gasket for an additional seal.

I did use a Tapco gas piston for this build. I plan on checking it also. It is one of the kits with the soldered on short gas tube, which shouldn't be the culperate. The gas piston does slide all the way threw when dropped so it's not binding. I'll check the gas piston diameter with an original to see if it may be undersized and allowing gases to escape rearward. I still have a feeling that the headspace may be a liitle to tight since I had problems with this area from the get go. Either that or the locking shoulder pin may still be up a little on the left. On my other builds the top of the LS are pretty level with the receiver floor. On this build the LS is raised above the receiver floor about 2/32". Could this be a problem? Thanks! RB

OMG.... Orca is in the house and alive. Good to see your handle again :biggrin: