iIhad a new barrel installed on a 700 rem in 260ai. when trying to fire form the bolt ejector does not engage a new 260 unfired case. is this safe to seat bullet long to force case against the bolt to fire form. just want to be safe.
Gunsmithing head space question
- Thread starter dgray
- Start date
Re: head space question
How Ackley cartridges work.
When you chamber an Ackley cartridge the parent case GO gauge becomes the NoGo gauge.
This is for ANY true AI. Why is this?
When PO ackley designed his line of cartridges he set them up so that the neck/shoulder junction of the parent case has a .004" interference with the chamber. This "pinch" ensures the case head is firmly seated against the bolt face. This is to prevent stretching of the webs of the case. Case growth/alteration is limited to the OD of the shoulder and the angle. If the chamber is deep your trying to do too much.
So, a bolt should close with resistance when fire forming an Ackley cartridge. If it doesn't then you have an issue. Either headspace or undersize brass. Maybe both.
Extending the seating depth on a bullet can be used to fix this but understand its a bandaid solution. You don't have an ackley at this point. You have a problem.
Here's why: measure the web OD of the reamer at the web location and its likely around .472". Say the chamber is .05" deep. Measure the reamer further back and its increased in outside diameter even more. Maybe .4726"
Your brass is going to be anywhere from .464-.4705. Your dies will likley be .467_.469.
See what's happening? Your effectively taking a coat hangar wire and bending it back and forth. It eventually breaks. Work hardening . . .
Often what happens is a GS unfamiliar with the cartridges just opens a sts chamber to an AI and calls it good. You MUST set the barrel back to do it right. In a M700 its a good full thread to ensure enough fresh meat to get the "pinch" at the neck/shoulder junction.
My advise:
Get the right gauging and check it. Then you know.
C.
How Ackley cartridges work.
When you chamber an Ackley cartridge the parent case GO gauge becomes the NoGo gauge.
This is for ANY true AI. Why is this?
When PO ackley designed his line of cartridges he set them up so that the neck/shoulder junction of the parent case has a .004" interference with the chamber. This "pinch" ensures the case head is firmly seated against the bolt face. This is to prevent stretching of the webs of the case. Case growth/alteration is limited to the OD of the shoulder and the angle. If the chamber is deep your trying to do too much.
So, a bolt should close with resistance when fire forming an Ackley cartridge. If it doesn't then you have an issue. Either headspace or undersize brass. Maybe both.
Extending the seating depth on a bullet can be used to fix this but understand its a bandaid solution. You don't have an ackley at this point. You have a problem.
Here's why: measure the web OD of the reamer at the web location and its likely around .472". Say the chamber is .05" deep. Measure the reamer further back and its increased in outside diameter even more. Maybe .4726"
Your brass is going to be anywhere from .464-.4705. Your dies will likley be .467_.469.
See what's happening? Your effectively taking a coat hangar wire and bending it back and forth. It eventually breaks. Work hardening . . .
Often what happens is a GS unfamiliar with the cartridges just opens a sts chamber to an AI and calls it good. You MUST set the barrel back to do it right. In a M700 its a good full thread to ensure enough fresh meat to get the "pinch" at the neck/shoulder junction.
My advise:
Get the right gauging and check it. Then you know.
C.
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