shoulder bump 0.002 , case-chamber fit

[walchi]

hey guys, i was already looking through the forum but didnt find any specific answer to my question so mayby you can help me.
i switched from necksizing to bumping shoulders in my 308 win ssg 69 p2 with a 0.002 bump a while ago with my rcbs fl die. recently i found out that with this method the cases in the chamber have a fair amount of play/ wobble in the chamber due to the body shrinking a fair amount during the resizing. it's logical for me that this is normal that the die is reducing the casebody diameter but now i am questioning myself if my rcbs standart fl die doestn fit my chamber at all since the idea is to work the brass as little as possible for a reliable feed but still get a good chamber fit.
thanks a lot for your help.

 

[rijndael]

Measure your fired brass vs sized brass. Measure at the .200" line and at the body-shoulder junction. What are the differences?

 

[M-61]

You lost me.
Switching from neck sizing to bumping shoulders is like switching from shoes to neck ties
Two different operations resulting in two different results
You’d like to have less brass working? Do you think bumping does less?
Have you thought of neck tension?
I may be misunderstanding your question

 

[Coyotefurharvester]

Did you stop neck sizing because the brass was tight closing the bolt? Have you had to trim the brass since FL sizing?

 

[walchi]

i am very sorry if i didnt ask my question clear enough. english is not my native language. i am aware that bumping the shoulders is working the brass harder than necksizing only ^^, but the fact that i was necksizing was more meant as an intro to my question. i stopped necksizing because of the hard bolt closing and still having to fl size from time to time anyway to get rid of it. reading several articles it is suggested to bump size every time to get consistency. i measured fired brass and set the die so that the shoulder gets set back 2thou and keep this setting for every resizing process to get easy feeding but not working the brass as hard as by setting the die touching the shellholder.
my question is now more oriented to the case-chamber fit and i hope i get it right now. bumping the shoulder back 2thou is not a lot. but with this method my die is reducing the case web/ base as far as if i set it touching the shell holder. at least from the feel when moving it from side to side in the chamber. when necksizing the brass stays fire formed to chamber and has a snug fit. no play at all which is logical. but when i set it for only 2 thou setback and get the case web/base shrunk this much that the case has a really loose radial fit in my chamber i am asking my self if maybe my die isnt the right one for this process or i am misunderstanding the idea of the 2thou bump at all. thank you very much for your help

 

[rijndael]

I asked for actual dimensions of your brass because there's more to sizing than just bumping the shoulder. I have a Forester NM die that oversizes certain parts and shortens brass life. Not all dies are created equal.

 

[GetReal]

If yer bumping the shoulder back 0.002.... yer only bumping the whole body back 0.002.... right?

A 0.002 shoulder bump should not lead to a case fitting loose / wobbly in the chamber..... methinks...

I got the sizing die my bbl manufacturer recommended to avoid overworking the brass by excessively sizing it.

 

[Murray Brook]

It should be easy enough to see if your sizing die is sizing too much. As @rijndael pointed out measure you fired cases vs your sized ones.

 

[M-61]

No apology needed as English is not my first language so what I write doesn't always have the correct wording.
"Bumping" the shoulders (IMO as is everything else) is a corrective measure. To me this is not a step in say normal reloading but rather to correct a problem. One may find excessive bolt lift and that would be a time to consider bumping. Granted .002 is not as you say 'is not a lot" but if you make this part of every reload the add all the .002 up. Each time fired your case will reach the datum lime and if you take the initial headspace and the to that add .002 it is a lot. Now in hunting rifles one hears they want to insure that the round will chamber. I no longer hunt but when I did I chambered EVERY round after it was loaded to ensure in the field there would be no problem.
As stated above all dies are not created equal and neither are chambers. Your die may indeed be excessively sizing (down) the whole case therefore your 'loose' round.
Some like the 'bump'.....I see it as strictly correcting a fault.
I'm sure many of the knowledgeable folks on this site have different opinions.
The above is merely mine.
Good shooting!

 

[GetReal]

It should be easy enough to see if your sizing die is sizing too much. As @rijndael pointed out measure you fired cases vs your sized ones.

Methinks there's really two sizing dimensions.... (1) shoulder / body bump back and (2) case body diameter. Measure both to see how aggressively your die is sizing the brass.

 

[bks22345]

The brass should not wobble in the chamber. It has been suggested to compare the sized brass to the fired brass, which I agree with. However I would also compare both to SAAMI specs. You might have a bad die, or you might have a bad chamber.

 

[Coyotefurharvester]

How would/could you manage to know the cartridge wobbles in a bolt gun? Bolt holding base, neck held on the other end. Especially with die set for 2 thou bolt face clearance(shoulder of case tight to chamber).

 

[Migolito]

 

[dgeesaman]

Factory dies in my experience often size too much on body diameter when used to bump the shoulder correctly. .005 to .008 sizing on body diameter isn’t uncommon and I agree it’s hard on the brass. Even if you anneal, this is down low enough on the case that it won’t solve the problem.

I suppose you could get things right using a body die and shoulder bump die to control those resizing dimensions separately but I’ve gone to using dies that are sized to match my fired brass.

 

[bks22345]

How would/could you manage to know the cartridge wobbles in a bolt gun? Bolt holding base, neck held on the other end. Especially with die set for 2 thou bolt face clearance(shoulder of case tight to chamber).

If the cartridge headspaces on the shoulder and the body diameter is much smaller than the chamber, I could see where you could wobble the bullet without the bolt in. Maybe not.

 

[Hoot]

If you did not live in Austria, I would recommend sending your FL die and a couple of unsized cases to RCBS to have the die opened up a little. They are very nice people to deal with. As has been repeatedly mentioned, you should take some precise measurements at the 5mm line and body to shoulder junction points. I for one, set all my different caliber shoulders back .03-.05mm.

Hoot

 

[BoydAllen]

What does your target tell you about the effect of FL sizing? I would only make a change if your targets tell you to.

 

[walchi]

thanks for all that input i will meassure the cases this afternoon. i checked the play when i saw a video on youtube von erik cortina

where he mentions at 5.25 an on the chamber fit ....and got curious what would my case fit in. had the bolt out and inserted a case and wobble it with my finger on the base and it reminded me of that part of the video. there fore my question. but i will make the meassurement first and tell you as i got em. again thanks for all your help and input

 

[JFrank]

I like to draw out the cases and record the radial sizing and expansion before and after ignition, headspace I control via a threaded die
Too much sizing overworks the brass while not enough creates hard bolt lift or resistance to closer.
The benefit of correct sizing is free chambering before and after.

 

[dgeesaman]

I like to draw out the cases and record the radial sizing and expansion before and after ignition, headspace I control via a threaded die
Too much sizing overworks the brass while not enough creates hard bolt lift or resistance to closer.
The benefit of correct sizing is free chambering before and after.

This. The guy in Erik’s video clearly has not explored this and is probably struggling with a major sizing die / chamber mismatch.

ETA: not to mention that for whatever reason, the video guys shoulder bump was varying by .030”, which is hard to even do on purpose. Factory brass is about 10x less awful than that. My shoulders bump within .001”, making a .002” headspace gap a reliable method.