03-26-2014, 05:13 PM
This recent drama over throat dimensions has been, in my opinion, Much Ado about Nothing.
The recent debates have been over various opinions about the dimensions of the throat of chambers the 6.5 Grendel. I really don't want to rehash the arguments about throat dimensions. I just want to try to put things into some perspective. So I am providing an EXAMPLE of what that might look like.
The recent drama has resulted in the commercial production of yet another Grendel variant - the Grendel II. My understanding is that the driver behind it was to have a longer throat than the SAAMI 6.5 Grendel in order to seat long-for-caliber bullets farther out of the case.
Now there has also been a debate as to whether this new variant is an answer to a question not being asked, because the SAAMI 6.5 Grendel can handle bullets up to the 156 gr Lapua Mega. This was done by Lapua, one of the contributors to the development of the SAAMI 6.5 Grendel. Moreover, the primary medium sized game that the Grendel is well suited to take can be easily handled with projectiles weighing 125 gr or less, and fit nicely into the 6.5 Grendel compound throat. The need for these large projectiles really is questionable. What advantage to they bring?
But the idea of getting more powder in the case for the long bullets is an intriguing one. So how much more powder is it really?
A recent post (#412) by Mark at Precision Firearms recounting a discussion with Dave Kiff at PTG says the Grendel II is the same as the .264 LBC-AR. (http://www.65grendel.com/forum/showthrea...rns/page42) except having a neck diameter of 0.300.
And several people have reported that you can seat bullet out 0.1" farther - e.g. 2.350" vs. 2.250"
If you assume the case is already completely full, what does moving the bullet 0.1" further out really get you in the way of more powder?
Well, if you evasion the bullet moving forward 0.1", then a void would be created behind the bullet with the dimensions of 0.1" long by 0.264" in diameter (for a flat base bullet to keep it simple, boat tails would actually be much less). The volume of that void would be calculated by:
volume = pi x radius^2 x height
volume = 3.14 x 0.132^2 x 0.1
volume = 0.00547 cubic inches
How much powder will fill the void of that volume?
The density of CFE 223 is 15.957 grains per 1 cc.
- 1 cubic inch is 16.387 cc's.
- so 0.00547 cu in is equal to 0.089 cc's
So the amount of CFE 223 that would fill 0.089 cc's is 1.4 grains (15.957 x 0.089).
So the longer chamber would enable one to add 1.4 grains more per case.
What does that get you? About 30 - 50 feet per second higher velocity depending on the bullet.
What does that mean to the hunter? About 30 yards longer hunting reach. Hunting reach is here defined as the distance at which the bullet drops below is minimum recommended velocity for proper expansion.
YES - there is measurable advantage for a subset of 0.264 projectiles available to the reloader if a longer chamber is used.
I will put forth that the average hunter will not be able to see any real world advantage here.
And I'll repeat - these longer bullets are not needed to take most game folks are going after (see 6.5 Grendel Reloading Handbook Volume 2 and http://shootersnotes.com)
Again, so much drama and energy spent on negligible benefit.
The recent debates have been over various opinions about the dimensions of the throat of chambers the 6.5 Grendel. I really don't want to rehash the arguments about throat dimensions. I just want to try to put things into some perspective. So I am providing an EXAMPLE of what that might look like.
The recent drama has resulted in the commercial production of yet another Grendel variant - the Grendel II. My understanding is that the driver behind it was to have a longer throat than the SAAMI 6.5 Grendel in order to seat long-for-caliber bullets farther out of the case.
Now there has also been a debate as to whether this new variant is an answer to a question not being asked, because the SAAMI 6.5 Grendel can handle bullets up to the 156 gr Lapua Mega. This was done by Lapua, one of the contributors to the development of the SAAMI 6.5 Grendel. Moreover, the primary medium sized game that the Grendel is well suited to take can be easily handled with projectiles weighing 125 gr or less, and fit nicely into the 6.5 Grendel compound throat. The need for these large projectiles really is questionable. What advantage to they bring?
But the idea of getting more powder in the case for the long bullets is an intriguing one. So how much more powder is it really?
A recent post (#412) by Mark at Precision Firearms recounting a discussion with Dave Kiff at PTG says the Grendel II is the same as the .264 LBC-AR. (http://www.65grendel.com/forum/showthrea...rns/page42) except having a neck diameter of 0.300.
And several people have reported that you can seat bullet out 0.1" farther - e.g. 2.350" vs. 2.250"
If you assume the case is already completely full, what does moving the bullet 0.1" further out really get you in the way of more powder?
Well, if you evasion the bullet moving forward 0.1", then a void would be created behind the bullet with the dimensions of 0.1" long by 0.264" in diameter (for a flat base bullet to keep it simple, boat tails would actually be much less). The volume of that void would be calculated by:
volume = pi x radius^2 x height
volume = 3.14 x 0.132^2 x 0.1
volume = 0.00547 cubic inches
How much powder will fill the void of that volume?
The density of CFE 223 is 15.957 grains per 1 cc.
- 1 cubic inch is 16.387 cc's.
- so 0.00547 cu in is equal to 0.089 cc's
So the amount of CFE 223 that would fill 0.089 cc's is 1.4 grains (15.957 x 0.089).
So the longer chamber would enable one to add 1.4 grains more per case.
What does that get you? About 30 - 50 feet per second higher velocity depending on the bullet.
What does that mean to the hunter? About 30 yards longer hunting reach. Hunting reach is here defined as the distance at which the bullet drops below is minimum recommended velocity for proper expansion.
YES - there is measurable advantage for a subset of 0.264 projectiles available to the reloader if a longer chamber is used.
I will put forth that the average hunter will not be able to see any real world advantage here.
And I'll repeat - these longer bullets are not needed to take most game folks are going after (see 6.5 Grendel Reloading Handbook Volume 2 and http://shootersnotes.com)
Again, so much drama and energy spent on negligible benefit.