trim or turn first?

Ive got about half (50) my 6br brass expanded to 30br using a PMA expander. Now do i trim to length first or turn first?

I will be using a Forster original to trim to length of 1.500 for my 1.510 chamber and will be using a PMA model a neck turner. I was thinking of turning them all to about .012 first then resetting the turner to turn them down to 0.010.

Thanks

 

I clean, resize, trim than turn

 

I learned back years.ago if i trim new brass to trim to length before fireforming invariably fired brass is shorter than trim length. I trim less and.less frequently. In fact some of my 40 degree shoulder brass is never trimmed for the life of the case. I never trim all the way to trim to length. I do want a group of cases to be trimmed to the same length.

I neck turn new brass cutting slightly into the shoulder. No trim. Shoulder will probably move forward during fireforming.

 

I did neck turn some fire formed 6BRA last week and the length of neck varied enough to make trimming to the shoulder less consistent. This is because I had set the depth of my turning mandrel for one piece of brass and it wasn’t the longest one.

Are you setting your neck turning mandrel on the deep side and manually stopping when you begin to clean shoulder metal? If so then it would be easy to fire that brass again and trim after it’s had time to settle in dimensionally.

David

 

That is what I always do manually run it to it cuts into the shoulder like I want it. I also use the pma neck turner. I am sure you already know this but using the right.angle on the cutter makes those shoulders.nice. after fireforming I do another neck turning cleanup. Of course i like playing with my brass.

 

For me, it's important the the distance from the case mouth to the shoulder junction is the same so that I get the turned neck cut consistently on the shoulder junction area. So, I always FL size my cases where I have the shoulder's bumped to the same place (like within .001) and then trim the cases to length using my Giraud trimmer, which uses the case shoulder for setting the trim length. Then when I turn necks, I get very consistent cuts down to where I want it on the shoulder's.

 

Just a heads up my 30 br chamber was supposed to be 1.510" but was actully 1.542" so I just trim all of them to the shortest one I found in the bunch.Didn't trim till after fire formed and yes they did get shorter.Dont have my notebook in front of me,so Cant remember what my trim length actully ended up being...

 

I should probably get the stuff to actually measure it.

I know the print i sent to Manson stated 1.510 for this custom reamer.

 

if you want consistent shoulder cuts, trim to a number.
not necessarily chamber trim length just a reference point for uniform turning.

 

sent u a pm

 

^^^^^THIS^^^^^ Do not trim before fireforming!! The brass will shorten, I speak from experience!

 

The thing is with this brass is that its already too long. It needs to be trimmed.

How do you fireform then trim if the brass is already longer than the chamber?

They are averaging around 1.522 when the chamber specs are only 1.510.

 

Not mine but i like this plan

An easy way to check this is to neck up a case to 30, turn the neck to .328, but don't trim the neck length..most Lapua cases will be around 1.535-ish long after being necked up from 6BR. Anyway, with the f-p assy removed from the bolt, try to chamber the case. Then, trim off a few thou. (.002-.005) at a time until the bolt closes. You've just found your max. chamber length and now know exactly what to trom your cases to. I like 'em about .020 short (1.500 case in an 1.520 chamber).

 

I would trim to 1.500/1.505 like you suggested. Then I'd chamber one and verify I have a little end clearance with my borescope. It has to fit safely to fire form, above all.

I haven't had my Model A for very long but I do have the cutter that matches my shoulder angle. So I set the mandrel in deeper and freehanding the depth of cut seems to work very well. I just go until the cutter kisses the shoulder 75% of full clean. Once the cutter touches the actual shoulder it slows down making it easy to get very consistent depth. I will always do this going forward.

David

 

Just another thought, my concern is to make sure that I am cutting into the shoulder the equal amount. I measure my brass and determine the shortest length then trim all to that dimension. Then after fireforming I repeat the process to insure all are at the same. I started this process based on finding in some cases where you are blowing the should forward it will actually shorten the neck. I think this process keeps as much neck as possible and maintains uniformity.

 

Agree
And by turning into the shoulder some you have less chance for donuts to form.
Wayne

 

Have you actually measured chamber.From my experience they can be alot longer then what the print says.My 30 br measures 1.542 and the print said supposed to be 1.515 or 1.520 Cant recall exact measurement but I was surprised by how much longer the chamber actually was. I do not trim or anything else for that matter,besides running through a neck die before fire forming.Then I will do my brass prep.The brass will actually get shorter after fire forming,so you really dont know the brass length is till after fire forming.Im sure others may do things different.Just passing along what works for me.Sent you a pm earlier on how I measuered chamber.Hope this helps and good luck.

 

Meant to mention if your chamber allows it I would find shortest piece of brass in lot and trim to that length.

 

Can you chamber a case? I would try that and if it will I would ff, if not then yes I would trim to were it would fit the chamber, fire form then trim to the desired length.
I didn't have that problem of not being able to chamber the expanded case

 

No I cant chamber a case as the necks need turned before they will fit.