ANOTHER ? CHAMBERING JOB

[superx10]

Well, so I thought and proceeded to blame the gunsmith for not getting the headspace correct. After driving about 280 km and having
many misfirings I was looking to blame someone, it must be a personality defect. So what was wrong. On measuring my firing pin extrusion on my Panda action it was measuring .045 or about 10tho under recommended, the cases I was were using were fired just once but on full-length sizing were about 8 tho under a fired round from shoulder to bottom of the case and the fact that I was using CCI small magnum primers a primer that has a reputation for tough skin. All this together made for the rifle not to fire.
I have since on taking my gunsmiths advice and jammed the projectiles with a decent amount of neck tension and used new brass wala they now go bang. Apology in-coming.


The link below is probably one of the best youtube clips on explaining headspace with the view of a cutaway chamber.

https://www.youtube.com/watch?v=vAgjvBxzng4

[RAVEN]

full length sizing and creating the correct shoulder bump is important for consistent accuracy and brass life
there are many gadgets (not expensive) to accurately measure and maintain the correct head space.
RB

[bruce moulds]

full length sizing and creating the correct shoulder bump is important for consistent accuracy and brass life
there are many gadgets (not expensive) to accurately measure and maintain the correct head space.
RB

and the best gadget of all is your rifle with the firing pin removed from the bolt, and you already have it.
bruce.

[Gyro]

Yes Bruce totally correct. For those that don't know : when the chamber is cut and the barrel fitted to the receiver and the bolt closed there is a tiny bit of float/clearance left between the bolt nose and the rear of the chamber/barrel. What this allows you to do is to feel that small clearance by just moving the bolt forwards and backwards. The clearance is only say 10 thou ( nominal ) so it's not much but is easily felt because the bolt when closed ON AN EMPTY CHAMBER will move forwards and backwards that small amount. REMEMBER TO HAVE THE FIRING PIN REMOVED otherwise you won't properly feel what's happening.

So when you now chamber a full length sized case the bolt should close on it without effort or at least with very minimal effort. If say the bolt closes on the chambered case and there is still felt that small clearance there that is felt with the chamber empty then clearly the shoulder has been bumped back too far i.e. the case has been pushed too far into the Full Length Sizing die. NOT good as you have created an excessive headspace condition.

What you need to do when setting up your FLS die to control the amount of shoulder bump is first chamber a fired case. Pick one that on closing the bolt it gives a firm feeling on closing the bolt. Now take that SAME CASE, lube it and run it into the FLS die at the setting you believe is right. Then put it back into the guns chamber and close the bolt on it. The bolt should JUST close on it with maybe just a very slight compression of the case.

I gotta go but just some fundamentals that the newer shooters I know have not grasped. And sometimes the case will not allow easy bolt closing despite being sized to the right length because it may be 'hanging up' in the chamber due to being over diameter ...... so there's some other wierd stuff that can sometimes catch u out too.

[superx10]

Hi Gyro
Thanks for the explanation.

[pjifl]

You can also place a small temporary shim on the boltface using grease to hold it in place and check headspace on a cartridge. Like in the field, as an emergency procedure, you can cut a small shim from a beer can. If you can then close the bolt on a round your headspace is more than is desired for target shooting and reloading. Other materials can be found. A layer of fairly rigid paper is another. Paper is usually about 3-4 thou thick. Remove firing pin to get a good feel. This is all a bit fiddly but still doable.

Peter Smith.

[cheech]

You can also place a small temporary shim on the boltface using grease to hold it in place and check headspace on a cartridge. Like in the field, as an emergency procedure, you can cut a small shim from a beer can. If you can then close the bolt on a round your headspace is more than is desired for target shooting and reloading. Other materials can be found. A layer of fairly rigid paper is another. Paper is usually about 3-4 thou thick. Remove firing pin to get a good feel. This is all a bit fiddly but still doable.

Peter Smith.

Thin clear sticky tape on the case head does a good job too