Ejector Swipe with new brass?

[slickyboyboo]

Can a .0095" difference in shoulder datum length between a new and once fired case, cause a very very light ejector swipe from setback on ignition and contact with the boltface?

 

[MagnumManiac]

Depends on the case type.
A belted mag...no.
A rimless case...yes, depending on load.
An oiled chamber can also show this as backthrust is at maximum and may include a stuck bolt.
Need more info, rifle type, cartridge and load.

Cheers.

 

[slickyboyboo]

Depends on the case type.
A belted mag...no.
A rimless case...yes, depending on load.
An oiled chamber can also show this as backthrust is at maximum and may include a stuck bolt.
Need more info, rifle type, cartridge and load.

Cheers.

It's a 1964 Rem 700 rebarreled and chambered in 280 AI. No oiled chamber. Peterson Brass, 155 gr Absolute Hammer, 60.6 gr of RL16.

 

[MagnumManiac]

Often, a near max load in NEW cases is fine, shows no flattened primers, ejector swipes or craters...but a once fired case WILL show the above because the case is not expanding to fill the chamber as much and losing energy like a new case does.
Have you chrono'd the load in either brass?
I will guarantee there is a velocity difference.

Cheers.

 

[slickyboyboo]

Often, a near max load in NEW cases is fine, shows no flattened primers, ejector swipes or craters...but a once fired case WILL show the above because the case is not expanding to fill the chamber as much and losing energy like a new case does.
Have you chrono'd the load in either brass?
I will guarantee there is a velocity difference.

Cheers.

I've always been told that new brass can show a very light ejector swipe, due to extra headspace and not being tight against the boltface, causing it to be forced back on the boltface on ignition.

I've only shot and chronoed these in new brass so far. But it's not given me a tight or sticky bolt at all.

 

[MagnumManiac]

I've never experienced faint swipes on new brass, that's a new one for me.

Cheers.

 

[ThrdKllr]

Excess head space can cause ejector marks on brass caused by the case getting a run at the bolt after being driven forward by the firing pin. With the .0095 difference between new and fire formed brass, I believe I would expand the necks of the new brass to 30 caliber and then back down to 284 in increments until they chambered snugly for fire forming. I would definitely use a less expensive bullet to do my fire forming with.

 

[GLTaylor]

Fireform your cases with cup and core bullets touching the lands. This prevents case movement during fireforming. Fireforning like this wll prevent the ejector marks.
Once formed, clean your bore well,then shoot the Absolutes. Absolutes are very slick and offer little resistance.

 

[slickyboyboo]

Fireform your cases with cup and core bullets touching the lands. This prevents case movement during fireforming. Fireforning like this wll prevent the ejector marks.
Once formed, clean your bore well,then shoot the Absolutes. Absolutes are very slick and offer little resistance.

That's my game plan now, I've got a few boxes of Hornady seconds that I can shoot.

 

[Shane Lindsey]

I get swipe on virgin cases with out firing them on a few rifles. I insert empty virgin cases, close bolt, release bolt and extract the case. Swipe. It may be the opposite of excessive head space, but too short a chamber.

Try this without firing and see what it looks like.


One a Ruger 300 win mag. The other a Rem 700 300 RUM.

 

[ThrdKllr]

On the 300 Win Mag it is because it headspaces off of the belt and not the shoulder unless you are using the Peterson Long brass.

 

[slikmrc]

I would treat this as a pressure sign until I ruled out a few things. Is this a new lot/brand of brass, is bolt, barrel and lug recesses clean? I usually start with 3 or 4 cases on new lot of brass or load and work load up until I find signs of pressure and work back from there. With some of this new stronger brass, by the time you see typical pressure signs you can get beyond safe working pressures.

 

[slickyboyboo]

I dug out some old Hornady 162 SST seconds, going to fireform with them and some SW Tactical Rifle powder I have, and set them on the lands. Then will go back and start again with the AHs.