switch barrel trouble

[paperpuncher]

Check the interface between the recoil lug and the barrel shoulder Some recoil lugs have a sharp edge on one side and a chamfer on the other. If the barrel has a radius at the shoulder tenon junction it could potentially interfere with the hole in the recoil lug if only one side has a chamfer. Unlikely but possible.

 

[10XSHOOTER]

Torque to at least 75 ft lbs

 

[686ppp]

Factory ammo shot fine. checked headspace and my brass is 1.040-1.081. The longer being the new once fired. I culled 1.074 and lower and will try again. Everything is marked 300BO but some of it is range pickup. When i resize i get 1.078.

 

[DShortt]

That's .041" difference. No wonder you were having ignition issues given that a firing pin protrusion isn't much more than that.
Secondly, while your chamber appears to be in spec with once fired brass measuring 1.081", it's likely on the longer side of the spec. Definitely not a minimum chamber.
That range brass ...... has it been resized? If so, someone has a die set-up problem. It should not be anywhere near 1.040".
If not, someone has an out of spec chamber for a 300AAC.
The drawing I'm looking at shows a minimum chamber of 1.0789 and a max of.1.0889. That 1.040 brass ain't gonna work.

 

[kawsam62s]

Two things come to mine first one if you suspected you had a headspace problem with the barrel you needed to put go no go headspace gauges in and that would’ve eliminated that? if your brass shoulder is short when you put it in the chamber, it’s not on a fire, especially if you’re using a hard primer like a CCI 450 I had the same problem with some short brass and ended up using Winchester, small rifle primers in order to fire form to get the brass to stretch to my chamber. after that first firing, they were all sized to my chamber and life was good again.

 

[DShortt]

Two things come to mine first one if you suspected you had a headspace problem with the barrel you needed to put go no go headspace gauges in and that would’ve eliminated that? if your brass shoulder is short when you put it in the chamber, it’s not on a fire, especially if you’re using a hard primer like a CCI 450 I had the same problem with some short brass and ended up using Winchester, small rifle primers in order to fire form to get the brass to stretch to my chamber. after that first firing, they were all sized to my chamber and life was good again.

I wouldn't attempt to use brass that's .040" or more undersized. Particularly if it's range brass and no telling what it's been through. But that's me.