Sudden Chambering Problem

[Bigwheels]

I just encountered a problem chambering in my 300WM. As some of you may know, I have been reloading for this rifle through about 6000 rnds, & 2 brls now (this brl is @ 2485 rnds now), & the batch of 4th fired, annealed @ 3rd time suddenly started to chamber hard. I have checked for any buildup in my chamber (nothing), rechecked my sizing die (same as before), resized a few more 4th fired brass, & they all chambered hard. I sized 1 of a batch of 2nd fired brass, & it chambered fine. I have mic'd the bases, & the belts, same size, trimmed to the same length (the 2nd fired one was .005" longer), & am going to get a insert for my comparator to double check the shoulder measurements. This is the 1st time I have ever had a problem chambering brass after sizing, & I have several hundred that are on their 6th firing, annealed every 3rd time.
Anything I'm missing?

 

[shooter98]

Are you neck sizing or full length sizing? Are you measuring from the shoulder to the base? Try measuring a piece of brass that chambers good at the shoulder and then compare to the one that doesn't chamber well. Sorry if this is basic and you've already checked these. I had a similar problem recently with my 25-06 and found it was because I was only neck sizing, and after about the 6th reload on the brass I needed to do fl sizing to get the shoulder lengths back in spec.

 

[FLIGHT762]

The shoulder bump insert will likely show what the shoulder number bump is. However, in the meantime, You can always screw your F/L die in 1/12th or 1/24th of a turn and run a couple of the hard to chamber pieces of brass and see if that will do it. Just could be that batch of brass has gotten hard and is springing back too much.

 

[Bigwheels]

Thanks guys. I am FLS with a S type die. I did measure the shoulders, & they were consistent to .001" between them, but I also screwed the die in another 1/8 turn, & the problem is gone. I think the pivot pins on my Rock Chucker are wearing. That's all I can come up with.

 

[jagged77]

Check the body diameter or the brass above the belt - can you see any scrape marks around the circumference? One trick is to use a permanent marker and cover various suspect areas and then chamber a round, makes identifying tight spots easy. I mention the area above the belt as its a difficult one to spot but can cause problems (to fix you end up screwing the die down further but this causes excess headspace and all the problems associated) therfore you should check any bulging there with case wall thinning above the belt.

 

[Bigwheels]

No bulge above the belt. I used to use an IT die to correct this, but since switching to the S-die I don't need to any more.

 

[steveptr]

I had the same problem with my 308 did what you did turning the die in another 1/8 of a turn and bingo solved I came to the conclusion that my shoulder wasn't far enough back.