FTF and an Abusive Bolt

[Will486 7]

Right, well. I took the devotchka to the range today, and the first round failed to fire. So.. Tap, rack... Boom. It failed to fire intermittently for about the next hour while running through approximately 50 magnum rounds. Not to worry, I think I know what the problem here is. It is running a JTE 25% reduced power hammer spring, but I dont think thats it. I modified my Krebs retaining plate so it would be easier to install the axis pins. This was a brilliant idea until I found out that it no longer retained the front pin, and the hammer could rotate off axis when the pin popped out to the left. I believe this is what was causing the FTFs, as when I held my thumb against the pin, I experienced no problems and I could see the hammer hitting the firing pin after unloading it, but it could be striking just off to the left.. Ill work out some way of retaining it properly..

 

The other issue is puzzling me. I believe its a mag issue. When using SureFire 13 rounders, the bolt carrier travels about 80% of the way back before jamming itself on top of the brass of the next round in the mag. It does this every round with multiple 13 round mags. I did not experience this problem with the russian mag. I shot Remington 2 3/4" 9 pellet 00 buck, and 3" 15 pellet 00 today, so no shitty ammo. If you think it makes any difference, this is a 3 port, 19" gun. As the bolt gets stuck on this top round, it dents and scratches the brass severely. Obviously there is excess pressure on the bottom of the bolt carrier from the mag/top round. (I doubt highly that the bolt carrier is riding too low, the only thing Ive done to the rails is polish them). My first ideas included chopping the mag spring, or filing down the mag's rear locking tab until it sat low enough to properly cycle, but I thought Id run it by you guys first before screwing with anything else. So, any ideas?

 

Gotta find a new way to retain the front pin, and work out this bolt issue..

Edited January 10, 2010 by Will486

[gtnichols 51]

Was it having problems before? hence the reduced power hammer spring?

Put the stock spring back on it.

[Will486 7]

easier said than done. I have faith in the JTE spring and doubt that it caused the FTF. I think it was the pin causing the hammer to be out of alignment, which was my own damned fault.

[RRice 34]

I ran 400 rounds today between my 2 S12's.One has the JT spring in it and has about 1k rounds through it now.I had 2 light primer strikes today on some cheap wally world Remington bird shot.This has never happened before.

 

Just a thought,what gas setting were you using?Maybe the mag wasn't feeding the gun fast enough?I have seen guns with too high of a gas setting slam the carrier forward so quickly that it does what you are describing.Using full power loads like what you were using might cause this.

[Will486 7]

2nd setting, for birdshot. But, no, its not failing to feed rounds, its failing to set them off. All my failures to fire today all had a chambered, live round that had light or no indentations on the primers.

[hobbyshooter 59]

FTF typically means failure to feed. What you are experiencing is a light primer strike which is directly related to your lighter hammer spring.

[Will486 7]

Right, sorry. I did explain that it was failing to fire and feeding fine, but- doesnt matter. My point is that theres a thread floating around on the JTE reduced power hammer spring in which many users testify as to its reliability. The only time Ive ever heard of guys with reduced power hammer springs experiencing light strikes is when theyre using it in conjunction with a heavier Tromix firing pin and/or spring. I am sure that JTE would not sell a spring that did not fire. I am almost certain that the failure to fire was because the axis pin that the hammer rides on was out of alignment, and so the hammer could not contact the firing pin, or could only contact it partially.

 

That problem is simple to resolve, rip everything out and install a new retaining plate/spring. The real problem Im having is the bolt getting stuck on the top round's brass. I dont know whats causing it, though I assume its an over eager mag. I was hoping someone else might have had similar problems and know how to resolve it...?

[Cobra 76 two 2,677]

If I was getting light primer strikes I would swap the hammer spring back out. You obviously really want that thing in there but it could be causing some problems. Why don't you just take 2 minutes and pull the hammer out, then swap it and see what happens? You said it was out of alignment anyway. You could get some of those E clips from the hardware store, just til you can get another retainer plate. Then you could write that out of the equation. You might be surprised and find out the retaining plate is what's causing your bolt carrier to hang up when it comes back. They have to be modified or the bolt carrier drags across the top of them.

[Spartacus 1,619]

The real problem Im having is the bolt getting stuck on the top round's brass. I dont know whats causing it, though I assume its an over eager mag. I was hoping someone else might have had similar problems and know how to resolve it...?

 

I think if the mag spring were too strong, it would really be a problem for the people who have cut down the 12 rounder to 10 or 8 and have kept the spring intact. I have not seen any reported problems.

 

Maybe take some spent shells or dummy rounds and manually cycle them slowly and watch what is going on to see if you can find the problem.

Edited January 10, 2010 by Spartacus

[Will486 7]

Alright, thanks for the advice guys. I didnt even think about the retaining plate contacting the bolt, that certainly couldve caused the carrier to jam. Doesnt explain the scratching/denting on the rounds, but... I guess Ill work that out another day. For now Ill go through ripping the FCG out again and replacing or further modifying the retaining plate.

[Paulyski 2,227]

Just 2 ideas to keep in the back of your head....

 

1. Is your gas puc moving freely? I had som issues because I had been using Hopps #9 solvent & it's not too strong. I didn't spend enough time on it & got an accumulation of hard buildup. I hit it with Tipton Bore Solvent & the puck freed up.

 

2 The surefire mags you speak of are 12 rounders. 13 could weaken the spring. you may give it a little streach

 

3. Disassemble the Surefire & with the follower removed, check if the walls of the top fo the mag are dragging on shells.

There should be no drag from the top of the mag, on the side of the shells.

As I boiled my ProMag, I also did the same to my Sure fires. They weren't nearly as fucked as the ProMag, but failed to feed a few times never the less. Maybe they had a bad batch?

Day before yesterday, I did a rather extensive test, including the surefires (which I cut down to 8) & everything ran flawlessly.

Edited January 10, 2010 by Paulyski

[gpqueen 545]

You can add tension to the spring to make it hit harder by bending the saddle the hammer sits in forward. Look at the primers to see if they were dented.

[Cobra 76 two 2,677]

Alright, thanks for the advice guys. I didnt even think about the retaining plate contacting the bolt, that certainly couldve caused the carrier to jam. Doesnt explain the scratching/denting on the rounds, but... I guess Ill work that out another day. For now Ill go through ripping the FCG out again and replacing or further modifying the retaining plate.

 

I'm pretty sure you will find the plate was your main problem. Look at the top of it, over where the selector locks it in place. It will be scratched or worn there. People keep buying these plates made for the AK-47 and sticking them in their S-12s. They are not designed to work there. The rails sit lower on the S-12 and there's not enough room there for the plate. That's just one place I modify the plates I sell for the S-12, after test fitting them in an S-12 to be sure they function. If you have already modified it somehow so it's not holding the hammer pin in good, then it's trashed now. For $12, I can send you a new one made by RSA, that is guaranteed to work if you are interested. Just let me know.

[negev5021 25]

The real problem Im having is the bolt getting stuck on the top round's brass. I dont know whats causing it, though I assume its an over eager mag. I was hoping someone else might have had similar problems and know how to resolve it...?

 

I have the same problem. Load 12. The 13th round is not supposed to be there...

 

Edit: sorry, its EVERY round? Thought it was overloaded mag. Mine would FTE when I had 1 in the chamber and reloaded a 12 rounder with 13 rounds in it, then fired, and there was too much upward pressure, or perhaps abosolutly no downward room, and the bolt hung up on the 1st round from the full mag.

Edited January 10, 2010 by negev5021

[Will486 7]

You can add tension to the spring to make it hit harder by bending the saddle the hammer sits in forward. Look at the primers to see if they were dented.

 

An excellent idea, very simple. As far as retaining the pins go, Ill get around to opening it up sometime this week and ill swap out that plate. I dont think it was actually what caused the carrier to jam back, as the carrier slides freely when I manually cycle it. Ill also compare how high the Russian mag and the SureFires sit in the magwell to see if the rear locking tabs are just too tall, and are just forcing the mag and top round into the bolt.