NEW Firing pin spring and tune change?

[Stumpy1]

Hi All, I am looking for advice and opinions (some of you guys are pretty darned smart).

Situation; 223 Rem, Palma rifle, launching 85.5 grain bullets, CCI 450 primers. This past weekend, had 16 rounds not go off in a 60 shot match. This level is something new, but I have had the occasional misfire over the past year. The rounds that did go off shot well, with good X-count. I thought it might be the firing pin spring. Borden tube gun action (short action clone), properly set up. So, I took the firing pin apart and found a broken in half cross pin (first time I saw that happen).

Swapped out the firing pin spring, installing a 28 pound spring in place of what should have been a 24, in an attempt to eliminate the occasional misfire if had been seeing (good pin fall >0.260"). New cross pin of course. Pin fall 'sounds' good -nice and crisp.

Go to the range; all but one of the misfired rounds now go boom -Yay! BUT. You knew that there was a but. In shooting some fresh ammo of the same load, I have now picked up about 80 feet per second of velocity from a couple of weeks ago with the old spring, and the rifle clearly needs re-tuning as is has definitely opened up. Or does it? Am I finally getting good ignition with the heavier spring, and need to tune to the new reality of proper ignition.

FINALLY, the question -is there any downside to having the 28 pound spring in there relative to the theoretical 24 pounder? I am a sling shooter, so no rifle disturbance in bags, or anything like that. Mostly wondering why I picked up all that velocity, and wondering if changing the spring back to 24# would bring the rifle back in tune.

Thanks in advance for helping me understand!

Frank

 

[dminn1]

I would be concerned about the broken cross pin. Does the cocking piece bottom out on the bolt when in the fired position?

 

[LVLAaron]

Yep - you've changed your ignition a great deal, so you'll need to tune.


28lb spring wont do any harm, other than a heavier bolt lift. If your 24lb spring was so weak it gives you misfires, a new 24lb spring will probably will effect your tune.


My general recommendation is "new barrel, new spring"

 

[Stumpy1]

I would be concerned about the broken cross pin. Does the cocking piece bottom out on the bolt when in the fired position?

Yes, all is good there. I checked that first thing. One thing I found interesting (you can call it weird), is that the old cross pin is a rolled spring pin (like a tightly would flat spring), and the cross pins I recently got from Borden are split pin design, and are touted as an 'upgraded' part, so there may have been issues with the coiled roll pin. https://bordenrifles.com/product/borden-cocking-piece-roll-pin-upgraded/

I am just surprised that my ignition was apparently that poor previously -perhaps a result of the broken coiled roll pin (though it still held cock and fired, oddly enough) as it was broken in two really, really close to equal halves.

Just an odd situation (well, maybe not odd to others, but sure new to me...).

Hoping that Alex Wheeler can chime in as he is certainly an ignition guru.

Frank

 

[AlNyhus]

If it was on my work bench, I'd reinstall the original spring and check the pressure....it may or may not be 'weak'.

Unless you know where you started, it's hard to know where you're at, now.

My 2 cents worth............. -Al

 

[Stumpy1]

If it was on my work bench, I'd reinstall the original spring and check the pressure....it may or may not be 'weak'.

Unless you know where you started, it's hard to know where you're at, now.

My 2 cents worth............. -Al

That's kinda what I was thinking too, Al.
Information, understanding, and knowledge is what I am after.

Who knows, it might help someone else out at some point.

Frank

 

[urbanrifleman]

I have now picked up about 80 feet per second of velocity from a couple of weeks ago with the old spring

That's almost a grain of powder.

 

[SKWERLZ]

Yep - you've changed your ignition a great deal, so you'll need to tune.


28lb spring wont do any harm, other than a heavier bolt lift. If your 24lb spring was so weak it gives you misfires, a new 24lb spring will probably will effect your tune.


My general recommendation is "new barrel, new spring"

It’s amazing what a worn spring can do.

 

[Stumpy1]

Hi Again, All,

I went back to the range and got some numbers with the old 24# spring, a new 28# spring, and, of course a fixed cross pin in the firing pin assembly.

All brass was match prepped and weight matched, same lot of powder, primers, and bullets as before the misfires started. I have numbers from about 60 shots before the misfires really started, and a string of 30 shots with the old 24# spring after testing the 28 and 24 pound springs.

The good news is that the cross pin fixed the misfire problem -about 60 shots with no issues. Keeping fingers crossed. It also looks like ignition energy is sufficient with the old 24# spring.
The velocity pickup after fixing the cross pin looks to be just over 40 FPS. Though I swear right after installing the new 28#, I had velocities with older ammo that were over 2930... Anyway...

It looks like I need to re-visit tune, but all else looks good to me. I welcome anyone else's thoughts on the matter, and thanks for listening and offering opinions earlier.

Frank

 

[swd]

Just drop the charge back down to your 2830 average and it should come back into tune.