Failure to fire

G

Gene DeLoney

New member
I recently built a hunting rifle on a BAT VR action in 7mm-08 caliber. When we tested it, we had 2 rounds out of 20 that would not fire. The ammo was Winchester Supreme 140 gr. We had fired a full 20 rounds of Remington before with no problems. On returning home I checked the headspace and the bolt will close on the Go but not on the NoGo. Firing pin protrusion is right on at .055. The distance from the bolt face to the cartridge head on these 2 rounds is .009 and the primer depth is .008. The primers on these 2 rounds show medium to light indents. My question is this.... Could that accumulated distance of .017 be enough to cause misfires. The other 18 fired just fine and after firing show full indents.
Thanks, Gene
 
The headspace is good but the cartridge head gap is terrible... in effect creating the same problem as 9 thou headspace. With the primer in 8 thou I would say the problem was probably that 17 thou...

Slightly off the topic... when fire forming brass it is advisable to create a "false" shoulder in some way so that you feel the bolt close on fully sized brass. That insures the brass forms to the chamber with the greatest strength. Jamming a bullet into the rifling will not give the same fire forming result as the firing pin drives the case onto the bullet and the case will stretch back when the pressure rises.
 
Gene,

Try checking the primer depth on similar rounds that you haven't attempted to fire. If they aren't suitably bottomed out, then you could dissipate striker power with that combined with the headspace.

On the other hand, my first IA is to strip the firing mechanism out of the bolt & look for crud or grease that might be interfering with firing pin fall.

John
 
Hi Gene,
This is only a guess. Custom action manufacturers are sensitive about bolt lift. This can mean that they may not fit their actions with the heaviest of springs. They may also build in less striker fall, which further reduces striker energy as compared to "factory" actions. I also think that the situation is exacerbated by the shallow shoulder angle of the 7mm-08.

Years ago, a friend had a 22-250 AE built (probably a little long on headspace) on a Panda. He was fire forming factory ammunition. One brand, I forget which, was a little shorter from shoulder to head and had several failures to fire.

If your rounds, that failed to fire, happened to be floating back near the bolt face, when the trigger was pulled, the cartridge would have been "taking a run at" the chamber shoulder, and would probably have been driven further forward in the chamber in the process than one that was initially positioned against the shoulder of the chamber. I believe that this would tend to dissipate striker energy, possibly resulting in your misfire. Look around and see if you have a heavier spring that you can fit to the action, and let us know if the problem goes away.
 
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I agree

I think an accumulation of tolerances, plus a weaker than required firing pin spring is probably the culprit.

I agree with Boyd. I see custom actions with firing pin springs that are simply too weak, But customers demand that easy bolt lift, so that is what you get.

You might check one other thing. A friend had a Custom Action a while back that would not fire the case. He had bought it second hand. Upon inspection, we noticed that the bolt handle was not in the correct position. When you closed the bolt, and pulled the trigger, the cocking piece was hitting the cocking cam way off center, and absorbing all of the energy. Getting the thing in time solved the problem.........jackie
 
Thanks

Thanks guys for the responses. I measured some Remington ammo on hand and the head clearance is .004 and the primer depth is .003. All of this stuff fires just fine. When we reload these fired cases I think all will be OK.
Gene
 
Lynn,

Would that change anything? I understood that the storage capacity was independent of degree of compression up to the elastic limit - but that research was long ago.

John
 
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