Delayed firing pin ignition, Huge SD and ES

[Rtheurer]

I am at a loss. My 1000 yard Prone Rifle has been giving me fits. A once tack driver has been slowly giving me issues at Major events like State Championships, and Nationals.
Rifle is a Very Early Stiller Predator long action with a 3 digit SN. It sits in a Master Class FIberglass Prone ( Robertson) Stock, CG Jackson Trigger, Satern 20 MOA Rail. It has seen several 6.5x284 barrels over the years since the Early 2000's when i built it. Recently i chambered it up with two 6mm Creed barrels and a Straight 284 barrel. It slowly has been giving me flyers way out of the group at 1000yds and has been getting steadily worse. I changed the firing pin to a Tubb duel spring a couple weeks ago.

I can feel a every so slight delay in the firing pin fall once the sear lets go of the cocking piece. So i took off the CG Trigger and cleaned it up real good. Reinstalled it and it kept doing it. I noticed on the E target i had an ES of 120FPS. Well that aint good. So next step was to change the Firing pin spring, I also pulled the CG trigger and put on a TImney i had in the drawer. Still same issue and the ES went up to 578fps ES at 600 yards.
During bore scope inspection I noticed that the Raceway that was cut for the M16 extractor was cut deep and through the bolt body leaving an opening into the Firing pin opening inside the bolt body. the spring on the M16 Style extractor was down inside the firing pin race way ever so slightly.
I have another Long action Predetor that is my Back up Palma Rifle so I pulled the bolt out of it and looked at the Extractor cut along the body. It is not to deep and does not go into the firing pin raceway like the early one does. So i put the other bolt from my Palma rifle in the gun, This with its new bolt, Firing pin, Cocking piece and Timney trigger.
Still the same issue. Looked good for five rounds then a ten shot string showed a ES of 130fps ES with flyers again at 600 yards. I can still feel an ever so slight delay during the firing pin fall even on a completely different bolt out of another rifle.

So now as i write this, Action screw in the back to tight and causing some Bending of the rear Tang causing the Cocking Piece to Drag? Or something else causing the cocking piece to Drag? A bur?

Any ideas?

 

[clowdis]

I'd look for a drag between the firing pin cocking piece and trigger sear. If the mounting for the trigger is off a little bit (too high) it could cause this condition even with different triggers. I'd start by stoning the cocking piece on the old firing pin to give a little more clearance over the trigger sear.

 

[Will Henry]

I would also adjust the trigger for a little more overtravel. WH

 

[One Eye Pete]

If the gun once shot well look for what changed shortly before the problem started.
Since the problem occurs with two different triggers and two different bolts I would start by removing the action from the stock and clean the bottom of the action and the bedding area then reinstall it and torque the front bolt first then the rear bolt. I don't know the suggested torque values for that action but I would go with a fairly low value (especially on the rear bolt) to avoid any bending force on the action. Try the gun with the re-torqued action and see if it makes a difference.
I don't doubt there is an action or trigger problem as all indications are that something is causing the firing pin to drag but I wouldn't rely too heavily on E target chrono data. Try to use a standard chrono to get actual muzzle velocities when further diagnosing the problem.

 

[Pawnee Bill]

Did you take the firing pin out to see if it was gummed up?

 

[Rtheurer]

Chrono Data from E target or not. I can feel an ever so slight delay. So there is something aw fowl. When a shot lands low on the 7 ring and has a 100fps different velocity on target...

Thank you Blair and Pete. I will look at those two items.

 

[One Eye Pete]

I do not for a minute doubt you have a real problem. The only reason I mentioned the E target chrono readings is that when you do find the source of the problem (and you will) you want to make sure you completely eliminate it and get the ES and SD numbers as low as possible. This will be easier done with a standard chrono.
Now that I think of it you tried the bolt from your backup Palma rifle in your F class gun and still had the problem. (I assume that the Palma bolt in the Palma rifle has no problem) Provided the headspace is correct, why not try the F class bolt in your Palma rifle and see what happens. If this works well with no delay then it will help eliminate the possibility of an internal bolt issue with the F class bolt.
Please keep us posted on your progress.
Good luck!!
Pete

 

[Dusty Stevens]

I have fixed a ton of guns that quit shooting by taking those firing pins and springs out and putting the originals back in.

 

[Walt Krafft]

How is the firing pin protrusion? Could something be stuck in the inside of the bolt?

 

[STS]

It seem to me that the key clue is the dramatic increase in ES when you went from your CG trigger to the Timney. 120 fps ES up to 578 fps. You cleaned your CG and that didn't help. That would suggest to me that there is a mechanical drag somewhere in the cocking piece and sear or possibly the trigger plates. More so with one trigger than the other. I think I would disassemble and color up the parts with a Sharpie marker and try to identify the contact area that shouldn't be there.

 

[Dusty Stevens]

It seem to me that the key clue is the dramatic increase in ES when you went from your CG trigger to the Timney. 120 fps ES up to 578 fps. You cleaned your CG and that didn't help. That would suggest to me that there is a mechanical drag somewhere in the cocking piece and sear or possibly the trigger plates. More so with one trigger than the other. I think I would disassemble and color up the parts with a Sharpie marker and try to identify the contact area that shouldn't be there.

It seemed to me that it happened when he installed that firing pin spring. Cleaning his trigger didnt fix it. Those pins and springs have been known to wreck groups if you do some searching around here

 

[BoydAllen]

Dry fire it out of the stock.

 

[STS]

It seemed to me that it happened when he installed that firing pin spring. Cleaning his trigger didnt fix it. Those pins and springs have been known to wreck groups if you do some searching around here

Pretty sure he stated that the groups had been getting worse before he changed the spring, which motivated the spring change. Agree that spring changes, trigger changes, firing pin changes etc. can certainly cause problems. I made it a policy a long time ago to check all the ignition parameters if ANY of those parts have been replaced. There's definitely something dragging in the mechanism. Just need to isolate and eliminate the problem. Blanked primer disc(s) in the bolt bore??
Gotta go shoot a few hundred gophers and will check back later.

 

[Alex Wheeler]

Ever blow a primer?

 

[Bob3700]

Alex beat me to it. I wonder if the pin has a burr on it where it passes thru the bolt face.
Might try a 10X magnifier on It and see if there are any issues u can see. Might also run an .062 drill bit shank thru the holl and see if the hole could be an issue.
worth a try.

 

[Rtheurer]

I really looked it over well with the Bore scope, But the symptoms did not go away with a completely different Bolt ( had to push the brass shoulders back another .001 to adjust for Headspace differences) which includes the Firing pin, Spring and Cocking piece. So this leads me to believe something is causing the Cocking piece to drag on both Bolt assemblies.
Right now I thinking maybe its the Bedding. I snug them up, but tighten the front Action screw first then the back one. I wonder if if the rear action screw is pulling the Tang down putting a little spring in the action?
Thats what I am leaning toward now. Going to try a third trigger as well.

 

[STS]

You can get a rough idea about your bedding by standing the rifle on its butt and loosen and tighten the front guard screw while holding an index finger at the junction of the forend and the barrel. With as much stress in the bedding to do what you are describing, the barrel will move significantly away from the stock when you relax the front screw. If it moves more than a few thousands at the most I'd be looking for a crack in the stock. You said the rifle was a great shooter in the past which would lead me to believe that the bedding was good at some point.

 

[BoydAllen]

Have you dry fired out of the stock? Let us know the result. Also, assemble the bolt without a spring. Starting with the bolt head up, turn the bolt over so that it is vertical with the head down and see if the pin assembly drops freely, repeat several times while pushing up down and sideways on the shroud ( not touching the cocking piece). You can even do this with the action in the stock to check for interference with the cocking piece. There is a method for checking bedding with a dial indicator to see if it is correct. It is the only way that I know to properly check. It can look good and not be. Alex wheeler, and Mike Bryant have mentioned the method. When you install a trigger the side place can be driven out of place when the pins are installed, causing it to catch the corner of the cocking piece as it falls. You fix this by pushing the side plate back in its proper place while the trigger is in the action.

 

[Alex Wheeler]

I really looked it over well with the Bore scope, But the symptoms did not go away with a completely different Bolt ( had to push the brass shoulders back another .001 to adjust for Headspace differences) which includes the Firing pin, Spring and Cocking piece. So this leads me to believe something is causing the Cocking piece to drag on both Bolt assemblies.
Right now I thinking maybe its the Bedding. I snug them up, but tighten the front Action screw first then the back one. I wonder if if the rear action screw is pulling the Tang down putting a little spring in the action?
Thats what I am leaning toward now. Going to try a third trigger as well.

I missed the part about you trying another bolt. Im having a hard time thinking a light strike could could give 500 fps es. Thats extreme. Not saying impossible though. Have you tried any other primers? Dry firing should sound "snappy" like a hammer on an anvil, not a thunk sound. Post a picture of a fired primer if you can. Looking to see the indent.

 

[X Count]

Had a similar issue several years ago. Swapped, polished and cleaned everything imaginable and it turned out it be a batch of CCI primers.

Extremely minute hang fire maybe 1 or 2 in 10 at its worst. Gun would hold X ring then pop a shot into the 9. Shot wasn't always low as you would expect from poor ignition.