12-09-2022, 04:39 AM
The 6Arc bolt, like the grendel bolt, is a wider inside diameter because the case is thicker 0.441, so yes the "face wall" is thinner. The designers wanted to keep the 223/556 dimensions all the same as much as possible. That JP bolt is one of the best, I have not used it but all the users on 65Grendel will say that. The monster bolt is also right up there.
No you cannot add back the wall material in that bolt face area, to do so would either prevent the case from inserting into that area or cause you to need a non-AR15 spec bcg/upper/barrel extension/etc re-design.
The saami max pressure for the 6.5 Grendel and the 6mm Arc has been lowered due to the larger surface area and thus the larger bolt thrust during the firing sequence. 223 is 56,000 roughly, 556 maybe 58-60 (the exact # escapes me), but the 6.5 grendel and 6Arc are 52,000 psi. Thrust/force = PxA, so a larger case diameter (0.441 vs 0.378) means the P must be reduced to prevent excessive thrust and broken bolts/lugs/kabooms in your face.
I just today found out about a newer bolt design, patented, by SRC arms...
https://www.srcarms.com/bolts/6.5-grendel-type-2-bolt
you can look at it via the link. Don't know anything more about it.
The bolt face depth for a true grendel/6Arc is 0.136, this in order to again, maintain the firing pin as a standard AR15 pin, the bolt body has been lengthened in the rear by that 0.136, so the bolt is "longer" but the pin works fine, this in order to allow a deeper seating of the case into the bolt, allows for a better extractor geometry. Again over on 65Grendel there are several threads that tell all about this, better than I can.
Really a lot of design and engineering work went into the grendel design and the 6Arc just brought those design parameters and benefits over to itself.
No you cannot add back the wall material in that bolt face area, to do so would either prevent the case from inserting into that area or cause you to need a non-AR15 spec bcg/upper/barrel extension/etc re-design.
The saami max pressure for the 6.5 Grendel and the 6mm Arc has been lowered due to the larger surface area and thus the larger bolt thrust during the firing sequence. 223 is 56,000 roughly, 556 maybe 58-60 (the exact # escapes me), but the 6.5 grendel and 6Arc are 52,000 psi. Thrust/force = PxA, so a larger case diameter (0.441 vs 0.378) means the P must be reduced to prevent excessive thrust and broken bolts/lugs/kabooms in your face.
I just today found out about a newer bolt design, patented, by SRC arms...
https://www.srcarms.com/bolts/6.5-grendel-type-2-bolt
you can look at it via the link. Don't know anything more about it.
The bolt face depth for a true grendel/6Arc is 0.136, this in order to again, maintain the firing pin as a standard AR15 pin, the bolt body has been lengthened in the rear by that 0.136, so the bolt is "longer" but the pin works fine, this in order to allow a deeper seating of the case into the bolt, allows for a better extractor geometry. Again over on 65Grendel there are several threads that tell all about this, better than I can.
Really a lot of design and engineering work went into the grendel design and the 6Arc just brought those design parameters and benefits over to itself.