.008 Bump Required to Smoothly Chamber Round??

[General RE LEE]

Interesting recent development loading my 6mm ARC Howa bolt action. If I bump shoulder .002", bolt is difficult to close. Virgin brass shoulder is .008" back from a fired case and chambers easily. I kept lowering my FL die in increments till case chambers smoothly, which is right about .006-.008" shoulder bump. Cases are not growing more than .003" when bumping shoulder back this much, which is interesting.

I've never had a chamber that needed more than .002" shoulder bump to smoothly chamber a case.

• Rifle has 1500 rounds on it
• Carbon ring removed in throat
• Bullet seated to jump .060
• Using .350 Hornady comparator and a fired case
• Loads are within Hornady load data and no over pressure
• Hornady 3x fired brass

I'm stumped. Any suggestions?

 

[EFouraker]

Are you taking the base to shoulder measurement with the case deprimed? The fired primer can sit proud and make you think headspace is more then it actually is..

 

[cohunt]

Are you having to bump the shoulder that far so that the base can be sized down enough? (Fld)

Try using black sharpie on the case to see what's actually causing the hang up

 

[Stammster2]

You're not measuring something right. 0.000 bump should still close with a bit of resistance. No way it should take 0.006.

Have you tried chambering a resized case before you primed, charged, and seated a bullet?

 

[General RE LEE]

Are you taking the base to shoulder measurement with the case deprimed? The fired primer can sit proud and make you think headspace is more then it actually is..

I measure a fired case with spent primer installed. I zero out my calipers and then measure a case after its been through FL die and primer has been removed.

 

[General RE LEE]

You're not measuring something right. 0.000 bump should still close with a bit of resistance. No way it should take 0.006.

Have you tried chambering a resized case before you primed, charged, and seated a bullet?

That's what I am thinking but, I've always done it this way.

 

[cohunt]

Try depriming then measure to see if primer is backing out

 

[98s1lightning]

Concentricity problem or Brass OAL reaching maximum allowance?

Maybe a tight chamber being fussy

 

[General RE LEE]

Concentricity problem or Brass OAL reaching maximum allowance?

Maybe a tight chamber being fussy

I trim brass before it gets beyond .005" of manual publish max case length. I eliminated that issue cause I considered it.

What's odd is any other cartridge I reload for, if I bump shoulder .008", the OAL case length will get substantially longer. When I'm sizing these little cases and according to my measurement bumping 0.008, the case is growing very little. This leads me to something else going on with measurements.

 

[Jeff Heeg osoh]

I'm guessing it's the spent primer, I just take my priming tool and push it back in the pocket then measure the spent case prior to sizing. You will be amazed at how much you move the primer back in place.

 

[98s1lightning]

Yes agreed that resize is got to be going somewhere

0.008" is a lot IMO

0.001" or 0.002" should get you back into smooth chamber and 0.003" for hunting purposes (no likely problems chambering.....)
Your experience may vary, but has worked for me

Heck, brass can back into same rifle w a neck size only......

Maybe you have a burred or rough chamber

 

[98s1lightning]

Try depriming then measure to see if primer is backing out

Don't forget to try this first
Great suggestion

Knock the primer out WITHOUT bumping shoulder and see how brass chambers

 

[General RE LEE]

Don't forget to try this first
Great suggestion

Knock the primer out WITHOUT bumping shoulder and see how brass chambers

If I bump shoulder .002 and knock the primer out, it's hard to close bolt. Hmmm

 

[98s1lightning]

Sounds to me your die is much larger than your chamber and your brass is getting fatter when you resize

Something along the lines of "small base" dies, I got zero experience w them.
But what I'm saying is there is variance between your once fired and the die on the tapered portion of the case.
My terms are not verified but I'm guessing your die is a "large base" where the taper portion of DIE is a couple thousands larger diameter than your chamber/once fired measures.

Discrepancy between dies versus your chamber