Variation in headspace

[PMR14]

New to the board, need some help.

I have taken several measurements in headspace and seem to have a variation of 3/1000 from fired to sized. However, after neck turning and case trim, I am off another 3-4 thousands. Does anyone know if the process of neck turning or case trim can affect headspace that much. Just curious...

Results from the range last month were pretty good. 5 shots 200yds, .405" (7mm Mag Sendaro), so I am not complaining just curious if the I need to change my process and be a little more gentle with the brass during the prep.

Thanks,
RG

 

[turbo54]

Neither neck turning nor trimming should affect the casehead-to-datum length of your brass.

 

[PMR14]

Thanks Turbo54,

My concern was that I gerenerated heat while neck turning and may have pushed just enough to lose a few more thousands. I believe I am taking the right steps to minimize heat, I am still figuring this out and appreciate the feedback.

Which 7mm brass has worked best for you?

RG

 

[PMR14]

After checking carefully, I believe I found that the process of expanding the brass through the expand mandrel can cause my shoulder to be bumped 2-3 thousands in headspace measurement.

My expand mandrel has a stop at the base, which I may have hit if I am was not careful. The manufacturer has a device that I believe may give me more clearance, decreasing the possibility of accidentally hitting the top.

Turbo54, have you or others run into this before?

 

[ZiaHunter]

I neck turn new brass before the initial firing. Running the case neck into the stop on the mandrel can possibly result in moving the shoulder back slightly. Lubricate the inside of the necks before expanding with the mandrel as well as when turning. I keep a can of air handy and blow the shavings off the neck turner between cases. BTW my favorite brass is Lapua but their offerings are limited and use Norma when not available in a particular caliber.

 

[Squid284]

The expander die should have (depending on the brand) a locking ring you can adjust to raise the die higher in the press so the case mouth doesn't bottom out on the end of the mandrel. I would recommend adjusting your sizing die to bump the shoulder just over .001" instead of .003" (brass should still chamber easily though, with only a slight amount of drag when closing the bolt handle).

 

[PMR14]

Thanks for the responses.

I use Imperial wax with my expand mandrel and while neck turning. It seems to work well.

I own the K and M shooting neck turning tools. Great equipment, owner is not only helpful but knowledgable. He recommended I get the window riser to help during the expansion process to help improve the process. I have tried to higher the mandrel, but believe I am at the highest point.

I appreciate everyone's feedback. I think I need to make sure not to bottom out on the mandrel.

 

[AKMarty]

I got to use my expander today for the first time. Bumped the shoulder a little... looked kinda like a mushroom after that. Caught on to raising the die up higher.