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+--- Thread: 6.5 Grendel Bolt Measurements (/showthread.php?tid=18959)
6.5 Grendel Bolt Measurements - rack04 - 05-14-2019
I just received a new 6.5 Grendel BCG. I took some quick measurements because I know there are differences in the bolt length, bolt face depth, and firing pin length. Here are my measurements taken with a caliper using 3 measurement averages.
Length of bolt = 2.8020"
Length of firing pin = 3.2780"
Bolt face depth = 0.1375"
Is this bolt confirmed 6.5 Grendel?
6.5 Grendel Bolt Measurements - A5BLASTER - 05-14-2019
Who is it made by? Are who did you buy it from?
6.5 Grendel Bolt Measurements - VASCAR2 - 05-14-2019
Bolt depth should be .136 + or - 001 so it is a little deeper. The firing pin is full length but has the shorter 2.80” bolt length. With a 2.800 bolt length the firing pin needs to be .01 shorter than standard length firing pin 3.279-3.280 length.
I think this combination will give excessive firing pin protrusion. Minimum firing pin protrusion is .028” to maximum .036” or .008” tolerance.
You can buy a firing pin protrusion gauge from Brownell’s to verify the protrusion is out of spec. If the firing pin is to long you’ll get pierced primers or have a greater chance of a slam fire when chambering a round. I think the firing pin needs to be shortened to 3.269”-3.270” or shortened by .01”.
When Alexander Arms introduced the 6.5 Grendel they lengthened the tail of the bolt to account for the deep bolt face depth. Original 5.56 bolt has a .125” bolt face and a 2.80” length bolt. AA 6.5 Grendel bolts are 2.810” long with .136 bolt face depth. Adding .01” length permits standard AR-15 firing pins to be used with AA bolts. Some manufacturers did not add .01” to the bolt length.
6.5 Grendel Bolt Measurements - rack04 - 05-14-2019
A5BLASTER Wrote:Who is it made by? Are who did you buy it from?
https://www.wcarmory.com/toolcraft-inc/toolcraft-bcg-6-5-grendel-type-ii-bolt-carrier-group-sbn-9310-mpi-complete.htm
6.5 Grendel Bolt Measurements - rack04 - 05-14-2019
VASCAR2 Wrote:Bolt depth should be .136 + or - 001 so it is a little deeper. The firing pin is full length but has the shorter 2.80” bolt length. With a 2.800 bolt length the firing pin needs to be .01 shorter than standard length firing pin 3.279-3.280 length.
I think this combination will give excessive firing pin protrusion. Minimum firing pin protrusion is .028” to maximum .036” or .008” tolerance.
You can buy a firing pin protrusion gauge from Brownell’s to verify the protrusion is out of spec. If the firing pin is to long you’ll get pierced primers or have a greater chance of a slam fire when chambering a round. I think the firing pin needs to be shortened to 3.269”-3.270” or shortened by .01”.
When Alexander Arms introduced the 6.5 Grendel they lengthened the tail of the bolt to account for the deep bolt face depth. Original 5.56 bolt has a .125” bolt face and a 2.80” length bolt. AA 6.5 Grendel bolts are 2.810” long with .136 bolt face depth. Adding .01” length permits standard AR-15 firing pins to be used with AA bolts. Some manufacturers did not add .01” to the bolt length.
Bolt face depth could be operator error. Using my caliper I was getting widely different depths. Ill confirm the bolt length and firing pin length and confirm if the firing pin needs to be shortened. Thanks.
6.5 Grendel Bolt Measurements - VASCAR2 - 05-14-2019
When Toolcraft first started selling 6.5 Grendel BCG they used 2.800” length bolt. Recent production TC bolts have been 2.810” in length. I suspect you got new/old stock. You might contact Toolcraft and explain your concern. That is a good price for the BCG. If you shorten the firing pin there is no safety concern IMHO. You just have to remember this bolt needs a shorter firing pin and not to get it mixed up with another AR-15 firing pin.