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What is the correct firing pin measurement at the face of the bolt? I have the correct Grendel bolt and firing pin length from other forum threads but the primer strikes still look deep.
Mopar Doctor
Mopar Doctor
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Who is the bolt made by? -
It came with my Brownells/Satern 24 " barrel. Bolt measures 2.808.Comment
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Firing pin OAL is 3.273Comment
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Don't quote me on this but it think the bolt should measure 2.810, I could be wrong.
Google AA grendel bolt on this forum you should find a post by LRRPF52 stating the correct bolt measurement laid out by AA so the mil spec fireing pin could be used.
Hope this helps sir.Comment
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I will measure mine right quick to give you a data point its a jp bolt and PF fireing pin, stand by.Comment
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Ok got messurments for you.
Two jp bolts
2.810 and 2.811
Two fireing pins one PF one JP
PF 3.280
JP 3.279
Hope this helps sir.Comment
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Just noticed you said it's a 24 inch brownells/Saturn grendel II.
What ammo?
I had one when I first got into the grendel got it here as a complete rifle but guy I got it from had it cut back to 21 inch.
It would show deep fireing pin marks on fired brass and I had several blown primers useing hornady sst ammo.
Had to use a adjustable gas block and tune it down because it was so over gassed due to extra large gas port hole in the barrel, once I tuned it the issue went away.
Not saying that's what's happening here but just more food for thought for you sir.Comment
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Toolcraft 5.56 NiB bolt 2.800"
Toolcraft 5.56 firing pin 3.2810"
AAC 5.56 NiB bolt 2.800"
AAC 5.56 NiB bolt 3.28010
Deadbolt TiN 5.56 bolt 2.8005"
Deadbolt firing 5.56 pin 3.2800"
Radical Arms 5.56 bolt 2.8005"
Radical Arms 5.56 firing pin 3.2810"
Toolcraft 6.5 Grendel NiB bolt 2.8035"
Toolcraft 6.5 Grendel NiB pin 3.2825"
Toolcraft 6.5 Grendel Nitride bolt 2.800"
Alexander Arms 6.5 Grendel bolt 2.813"― George OrwellComment
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I hate to bring this up again as it has come up before but when Alexander Arms intoduced the 6.5 Grendel bolt AA used a .136 bolt face depth. AA added .01 length to a standard AR-15 bolt which is 2.800 length so a AA 6.5 Grendel bolt should measure 2.810 from the outer most face to the rear of the bolt. AA used the 2.810 bolt length so a standard AR-15 firing pin can be used with an AA 6.5 Grendel .136 bolt.
There have been reports of pierced primers from excessive firing pin protrusion with 6.5 Grendel .136 bolts that are 2.800 length like Toolcraft. A milspec firing pin is 3.280 + or - .001 and will work as designed with a 2.810 AA 6.5 Grendel bolt. Using a milspec length firing pin in a 2.800 length Toolcraft .136 6.5 Grendel bolt may produce pierced primers. You can get an extra .01 firing pin protrusion from the shorter 2.80 bolt. Throw in the variation in manufacturing tolerance and you might experience pierced primers. Some manufacturers were supplying non milspec (shorter) firing pins with the 2.800 6.5 Grendel bolts.
Just something to be aware of if your .136 bolt face depth 6.5 Grendel bolt measures 2.800 overall length, probably should have shorter firing pin. A person can shorten a milspec firing pin by .01 to account for a shorter bolt length.
Brownell’s sell a firing protrusion gauge. Minimum firing pin protrusion on an AR-15 is .028 maximum length .036.
Last edited by VASCAR2; 08-15-2018, 01:43 AM.Comment
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Thanks for posting all that again sir.Originally posted by VASCAR2 View Post
So looking at the specs stated that puts my gear dead in the sweet spot of proper length, good enough for me.Comment
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Thanks VASCAR2 for the pin protrusion measurement and the tip on the measuring gauge. It will be ordered. The primer impacts looked deeper than what I've seen in the past on other rifles. This is a brand new build up Grendel that spawned from my 18" Grendel. I call it the "Beast" because it is so much heavier and longer. I now have 25 shots thru it now with getting it sighted in and the gas block adjusted. First 3 shots went into a group that a quarter will cover. This was at 50 yards using Hornady AG ammo. I pierced a primer on one of my reloads so that got my attention.
Mopar DoctorComment
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If your using standard rifle primers like CCI 400, Winchester or Remington standard primers you can get pierced primers in an AR-15 because the primer cups are thinner. It is recommended to use CCI 41 or Federal AR primers which have thicker cups and designed for the AR-15 floating firing pin. The CCI 450 and other magnum small rifle primers have thicker cups as well as a couple of bench rest primers.
There have been threads where a bolt length or firing pin were out of spec and have contributed to pierced primers or inconsistent ignition. I wish the other bolt manufacturers had used the 2.810 length bolt for 6.5 Grendel but they didn’t. When you move away from the 5.56/223 in the AR-15 into other calibers/cartridges there are inconsistencies in components.Comment
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I always use CCI 41 in my Grendel loads. I've seen what a Federal 210M primer can do to a M1 Garand so I know you need a tough primer. The reloaded case with the pierced primer may have been a high primer. My bolt seems to be .002 short of the 2.810 measurement and I am going to get another firing pin.
Mopar DoctorLast edited by Mopardoctor; 09-01-2018, 07:01 AM.Comment
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Many forum members are aware of the issue with the 2.800 bolts and firing pins but you never know if a new member is aware of this situation. Same thing with using standard small rifle primers in the AR-15 with floating firing pin. Kind of why I hated to bring up the bolt length since you’ve been on the forum several years. Wasn’t trying to hijack your thread.
I hope you get your rifle sorted out.Comment
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