I made up a youth model rifle for my 6 yr old using a Remington 510. I had a new barrel installed and cut back. The problem is we are getting misfires even with CCI. Always fires by putting the shell back in and trying again wondering if it is weak spring, chamber space problem or what. Any ideas?

barrel was replaced. Excessive headspace can easily cause this problem.

Excessive dry firing can cause the firing pin to blunt out. Very common on Rugers. If the case has an excessively large hit Re square and flatten the face of the pin where it strikes the case. DONT SHORTEN. Just make it a bit narrower. J.Michael

If it is headspace, what is the cure without getting complicated and expensive? I don't remember ever having a problem with the old barrel so I fear it is headspace (I drew a blank on the term and said chamber space).

It could be something simple, like a spring or firing pin tip as JMichael mentioned. But it is highly suspicious that it appeared after a barrel replacement.

Can you post a pic of a fired case?

Was accuracy poor when shooting it? Sometimes indicative of excessive headspace as ignition is erratic.

There a rectangular firing pin strike but it is a very shallow indentation.

Tom, I just looked at some of those cases and the pin strikes are fairly well shaped, just very light. Even the ones that fired the first time have very shallow indentations. On the ones that had to be hit twice, the first mark is almost not there.

The case heads do not appear to be expanded as I would expect if there was too much headspace.

--
Of the Troops & For the Troops

Do have a 223 brass slinger though...

• Ensure there's no crud that would not allow the firing pin to travel fully forward.
  
  
• put a bit of "pre-load" on the existing spring by placing a shim (washer of some sort) to enhance the power of the spring.
  
  
• Install a new spring.

Shim in the bolt. Sounded like a pretty simple fix. Apparently pretty common when changing barrels in them.