PSA Bolts out of spec?

[stonehog]

I have a 20" PSA upper that has always been a bit sketchy, but was my first Grendel. Since I got this I've added a 12" Odin and 18" Faxon. I now have bolts from:
PSA
Odin
Monster (2)

After some strange results with a go/no-go gauge I started wondering about the spec of these bolts so I ordered a depth gauge to check the bolt faces. I found:
1. Odin = .136"
2. PSA = .133"
3. Monster 1 = .136"
4. Monster 2 = .1365"

I'm calling all of these OK except for the PSA bolt. Anyone else found this on their PSA bolts?

[VASCAR2]

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”. I’ve never seen a specified tolerance for AR-15 bolts but I would suspect .001”-.002”.

The specification I’ve found documented for AR-15 firing pin length is 3.2800” maximum length with a tolerance of -.009”. I’ve 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. Brownell’s 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

[65Carcano]

I have a 20" PSA upper that has always been a bit sketchy, but was my first Grendel. Since I got this I've added a 12" Odin and 18" Faxon. I now have bolts from:
PSA
Odin
Monster (2)

After some strange results with a go/no-go gauge I started wondering about the spec of these bolts so I ordered a depth gauge to check the bolt faces. I found:
1. Odin = .136"
2. PSA = .133"
3. Monster 1 = .136"
4. Monster 2 = .1365"

I'm calling all of these OK except for the PSA bolt. Anyone else found this on their PSA bolts?

Could you go into more detail about what makes your PSA upper sketchy? I have the same one, and wondering if mine is sketchy too. I noticed my PSA bolt has much looser tolerances and is far easier to assemble/disassemble than the Ruger 5.56 bolt, which I suppose is nice for cleaning but a bit alarming otherwise. I haven't measured bolt faces etc though.

[montana]

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”. I’ve never seen a specified tolerance for AR-15 bolts but I would suspect .001”-.002”.

The specification I’ve found documented for AR-15 firing pin length is 3.2800” maximum length with a tolerance of -.009”. I’ve 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. Brownell’s 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

From the tail to the face of the bolt is 2.675 + - .022
From the face of the bolt to the out side of the lug face is .100 -.003
The firing pin length is 3.277
This is from my TDP sheet

[CJW]

Interesting read V2

[montana]

Could you go into more detail about what makes your PSA upper sketchy? I have the same one, and wondering if mine is sketchy too. I noticed my PSA bolt has much looser tolerances and is far easier to assemble/disassemble than the Ruger 5.56 bolt, which I suppose is nice for cleaning but a bit alarming otherwise. I haven't measured bolt faces etc though.

If the head space is good with your PSA bolt, then you could check the bolts firing pin hole. Spec is .625 to .70..I prefer no more than .645 ..

If your firing pin protrusion passes as VASCAR2 recommended, then you would need pin gauges to check the 3 bores in the bolt carrier..The best fit between the bolt shoulder O.D. and support bore I.D. in the bolt carrier for accuracy will have no more than .001 difference. If you have .004 or more difference, then your bolt is going to be sloppy in the bolt carrier which could effect accuracy and bolt life..

The other two bores have to do with gas efficiency and if your rifle is functioning reliably, I wouldn't concern myself with them for now..

If your gas rings are worn, then the bolt will assemble and disassemble easier..Some bolts will have shallower cuts in the bolt gas ring channel, preventing the rings from compressing as much compared to other bolts. As long as the BCG passes the gas ring check you should be good...

Always check your firing pins tip for any cratering or chips. Be sure the firing pin slides easily in the bolt..

Check the cam pin to bolt cam pin hole for side to side play. If there is a lot of play then you would need pin gauges and a taper pin gauge to see if the cam pin hole is too big or if the bolt is stretching. A common sign for a stretched bolt is if the firing pin will not slide freely in the bolt.. A bolt that will pass a taper pin gauge is a sign the bolt is about to break..

[stonehog]

It has never been real reliable. I had feed failures, click-no-bangs. These are likely not related to the bolt-face (?) but my 12" Odin and 18" Faxon have been better feeders in general. I had been thinking about the headspace and bought gauges to check them all as I have been building uppers and want to make sure I'm not setting up excessive headspace. When I checked the PSA it was not quite right on the go-gauge.

[montana]

It has never been real reliable. I had feed failures, click-no-bangs. These are likely not related to the bolt-face (?) but my 12" Odin and 18" Faxon have been better feeders in general. I had been thinking about the headspace and bought gauges to check them all as I have been building uppers and want to make sure I'm not setting up excessive headspace. When I checked the PSA it was not quite right on the go-gauge.

Short chambers are much more common than over sized chambers and can be the cause of many types of malfunctions, popped primers, excessive pressure and inaccuracy.. Disassemble your bolts extractor and ejector, reinstall in the bolt carrier and then test your Go gauge. Apply only 8 Lbs or less at the rear of the bolt carrier and the bolt should close easily if the chamber is long enough..The same procedure is done with the no go gauge..