First Rounds from New Build

[kpswihart]

LRRPF52 - Yeah, after I measured it that's what I expected. Thanks for taking the time to confirm and for all of your posts. I really appreciate you and the other forum members sharing information and experiences.

[LRRPF52]

One of the firing pins I saw from an imitation Grendel bolt caused a crater in the face of the tip of the firing pin, which will lead to primer flow, cutting, and piercing when there is no reason for piercing.

There are tons of reasons why AA did as much research and testing as they did in the beginning, so we wouldn't have to have these problems.

[kpswihart]

Odin asked that I send the bolt back for examination and has offered to replace it if found out of spec. Customer service is a big deal with me and I'm glad to see a company that is responsive and trying to make things right.

[kpswihart]

Just heard back from Odin. Their response is below. Think I'll pick up another bolt and shoot the remaining SST's that were cratering for comparison. I'll probably try the AA bolt and firing pin if I can figure out shipping. UPS ground was the only option showing, but ground to a remote island in SE Alaska was $70, there's got to be a better way.

Kelly,

using a z-height gauge on a granite table I measured your bolt at 2.799, which is nearly perfect. Nominal is 2.8, that's a difference of .001. Your firing pin is .010 shorter than a .223 pin, so that should be good as well.

Everything checks out on my side. Factory Hornady ammo is known to be hot, I think that's all you're seeing.

Aaron

[Bruw]

I was not aware that the firing pin should be shorter than a standard .223/5.56 firing pin. Is that correct?

[BluntForceTrauma]

Factory Hornady ammo is known to be hot, I think that's all you're seeing.

It is my impression that factory Hornady seems overly conservative, quite the opposite of hot. With a 24" bbl their 123gr offerings get 2580 fps. I really think they can get AT LEAST 2620 without breaking a sweat, and 2650 with a clever factory blend. No?

The firing pin length is going to depend on your boltface depth and the overall bolt length.

With a 0.125 boltface depth and a standard overall bolt length of 2.80, you'll want a standard firing pin.

With a 0.136 boltface depth and an overall bolt length of 2.811, you'll also want a standard firing pin.

Not sure why they'd recommend a shorter firing pin?

[LRRPF52]

Just heard back from Odin. Their response is below. Think I'll pick up another bolt and shoot the remaining SST's that were cratering for comparison. I'll probably try the AA bolt and firing pin if I can figure out shipping. UPS ground was the only option showing, but ground to a remote island in SE Alaska was $70, there's got to be a better way.

Kelly,

using a z-height gauge on a granite table I measured your bolt at 2.799, which is nearly perfect. Nominal is 2.8, that's a difference of .001. Your firing pin is .010 shorter than a .223 pin, so that should be good as well.

Everything checks out on my side. Factory Hornady ammo is known to be hot, I think that's all you're seeing.

Aaron

If they are making a ~2.800" Grendel bolt with a .136" face depth, then you need a shorter firing pin.

The AA, PF, JP, and Group Buy bolts here are meant to work with standard AR15 firing pins for ease of compatibility for the market.

Bolt length is one of the first things companies overlook when embarking on specifying their own Grendel bolts from their machine shop vendors, or trying to make their own without doing some simple measurements on Grendel bolts from sources that have been in this game since the early 2000s.

Metallurgy is another aspect that isn't understood by many new entrants, but good engineering staff can figure it out.
Processes is another aspect of bolt strength and durability.

In my experience of shooting factory Hornady since it came out, ordered by the case, it is slower than AA 123gr and PF 123gr loads. It's not so slow that it doesn't perform well, and is within 50fps of them.

Since Hornady took it to SAAMI, and has good QC on their ammo in general, I wouldn't characterize it as hot.

Joe has also pressure-tested it periodically and found it to be under 50ksi working pressure, so if anyone is seeing pierced primers, something is wrong.

Keep in mind Grendel doesn't go anywhere near the higher pressure territory of common cartridges like .308 Win. or 5.56 NATO, 6.5 Creedmoor, .260 Remington.

If you are seeing pierced primers in Grendel, it's usually a mechanical problem with firing pin protrusion and FP aperture, and/or a short chamber that is jamming the lands.

I've seen that combination before.