Have a Interarms Mark X that was a 30-06 and I had it rebored to .35 Whelen and misfires about 1 in 5 shots. Been to three gunsmiths and still same problem. I do not know if it did this as a 30-06, never fired it as 06. Called fella I bought it from and he does not remember selling it to me. So may have always had this problem.
So anyone have any ideas on a fix??? Trigger been reworked new firing pin and spring installed.

I'm guessing there is evidence of a light firing pin strike???

Improper amount firing fin extended from bolt face?

Headspace?

Head space been checked.

Handload or factory?

factory

If it fired before and it doesn't now, it has to be the
ammo to chamber fit; it might pass headspace gauge, bot realize that there is a huge allowance between chambers and ammo. You will have to load your own, and form the brass to fit the chamber. Now, tell me what the firing pin protrusion is; any of those gunsmiths should have checked that first.
Fix?, sure, but I have to have it to fix it, or, back to theory #1. In which case, you have to fix it with the correct ammo.
New firing pin and spring? What is the FP protrusion? And spring weight? So many variables to diagnose over the internet.

Do not if it fired before. Will load some and try that.

Normally a CRF will catch the rim and provide enough resistance to forward movement to all the shell to fire.

I've seen people blow the shoulder forward using the extractor to hold the case against the bolt.

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I'm not sure if the Mark X applies. But there were a couple of Mauser trigger variants that could be adjusted in such a way that the main sear would place to much upward pressure on the cocking peice and slow it down just enough to cause intermittent misfires.

The Mark X are using a speed loc spring and a short fall with the firing pin. I would first check the amount of firing pin protrusion in the fired position. Should be .058 to .060 and the original bolt will have a recess cut for the cocking piece to about ,100 depth. This make the speed lock and a stiff firing pin spring necessary. I have seen the same problem with the mini Mauser failing to fire. I made a sleeve to place between the firing pin spring and the bolt shroud, ,200 length to give more spring tension and it would stop miss firing. Headspace should be checked first to be safe to fire and maybe question the person who made the conversion to the new caliber. Just some of the problems with action change overs.

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The Mark X are using a speed loc spring and a short fall with the firing pin

Les, Some of the Mark X had the speed loc. I've owned more Mark X without the speed loc.

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Originally posted by tractorred:
Have a Interarms Mark X that was a 30-06 and I had it rebored to .35 Whelen and misfires about 1 in 5 shots. Been to three gunsmiths and still same problem. I do not know if it did this as a 30-06, never fired it as 06. Called fella I bought it from and he does not remember selling it to me. So may have always had this problem.
So anyone have any ideas on a fix??? Trigger been reworked new firing pin and spring installed.

You've been given some good advice. If a new firing pin and spring were installed then I would first check to see if there is any internal interference. If You have the old FP and spring try installing them and check. Another oddball reason I have experienced is sloppy bolt shroud to bolt tolerance when screwed in. If it is loose then the cocking piece strikes the internal surface of the bolt shroud prematurely, driving it forward. This reducing FP momentum. Take the bolt down and just screw the BS in the bolt to it's proper assembly position. Push the bolt shroud back and forth. It should have little if any perceptible play.