There are really a couple other things to take into consideration besides the bolt face depth. The critical component is firing pin protrusion. The specification for AR-15 firing pin protrusion is minimum .028 to maximum .036. The overall length of the bolt can have a direct impact on the firing pin protrusion along with bolt face depth and firing pin length. Bill Alexander used a bolt length of 2.8100 because he used a .136 bolt face depth. The spec for 5.56/223 bolt face depth is .125 with a bolt length of 2.800. Ive never seen a specified tolerance for AR-15 bolts but I would suspect .001-.002.
The specification Ive found documented for AR-15 firing pin length is 3.2800 maximum length with a tolerance of -.009. Ive measured all my AR-15 bolts and firing pins and all my 5.56/223 and 6.5 Grendel are within spec.
I suspect that during assembly the BCG is checked (or should be) for firing pin protrusion. Brownells sell a firing pin protrusion gauge. If a firing pin has excessive protrusion there is a greater chance of a slam fire, pierced primers or out of battery ignition. If the firing pin protrusion is to short there is a higher chance of failure to fire.
If your bolt is a little long 2.815 and you have a .133 bolt face depth with 3.276 firing pin your probably gtg. The issue is tolerance stacking. A short bolt, deeper bolt face and maximum length firing pin 3.2800 or longer.
As an example if you add you all in spec parts, bolt length 2.810 + bolt face depth .136 + Firing pin 3.279 = 6.225. If your total is within .008 (tolerance in firing pin protrusion) your probably gtg.
Just a possible example. Bolt 2.800 + bolt face depth .133 + FP 3.2790 =6.212 there is .013 difference and is probably going to have excessive firing pin protrusion.
This is not the best way to verify your within spec but will give you an idea if your rifle is close to spec. Measuring the bolt length, bolt face depth and firing pin length should give you an idea if your within spec. I would be very cautious and not mix up my firing pins as they have the greatest difference in tolerance.
If at assembly there is a pile of bolts, bolt carriers and firing pins it would be easy to check the firing pin protrusion. If out of spec try a different bolt and firing pin till it measured within spec.
Here is a link to a similar thread.
https://www.65grendel.com/forum/showthre...rendel-BCG
The specification Ive found documented for AR-15 firing pin length is 3.2800 maximum length with a tolerance of -.009. Ive measured all my AR-15 bolts and firing pins and all my 5.56/223 and 6.5 Grendel are within spec.
I suspect that during assembly the BCG is checked (or should be) for firing pin protrusion. Brownells sell a firing pin protrusion gauge. If a firing pin has excessive protrusion there is a greater chance of a slam fire, pierced primers or out of battery ignition. If the firing pin protrusion is to short there is a higher chance of failure to fire.
If your bolt is a little long 2.815 and you have a .133 bolt face depth with 3.276 firing pin your probably gtg. The issue is tolerance stacking. A short bolt, deeper bolt face and maximum length firing pin 3.2800 or longer.
As an example if you add you all in spec parts, bolt length 2.810 + bolt face depth .136 + Firing pin 3.279 = 6.225. If your total is within .008 (tolerance in firing pin protrusion) your probably gtg.
Just a possible example. Bolt 2.800 + bolt face depth .133 + FP 3.2790 =6.212 there is .013 difference and is probably going to have excessive firing pin protrusion.
This is not the best way to verify your within spec but will give you an idea if your rifle is close to spec. Measuring the bolt length, bolt face depth and firing pin length should give you an idea if your within spec. I would be very cautious and not mix up my firing pins as they have the greatest difference in tolerance.
If at assembly there is a pile of bolts, bolt carriers and firing pins it would be easy to check the firing pin protrusion. If out of spec try a different bolt and firing pin till it measured within spec.
Here is a link to a similar thread.
https://www.65grendel.com/forum/showthre...rendel-BCG