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Seasoned Vet
 
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tx65,
Since the new Remington SPC uses a 43mm case length and a 45mm case length was tested and worked in an M-16 mag, was there any thought about using the old Czech 7.62x45mm case necked down to 6.5mm and cut down to 43mm OAL during the Grendel development? Wouldn't this allow for more powder and a higher velocity than the Russian M43 7.62x39mm type case? Something like that might become a 6.5mm Grendel Magnum if it works.
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Cherry
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quote:
Originally posted by Delta_6
tx65,
Since the new Remington SPC uses a 43mm case length and a 45mm case length was tested and worked in an M-16 mag, was there any thought about using the old Czech 7.62x45mm case necked down to 6.5mm and cut down to 43mm OAL during the Grendel development? Wouldn't this allow for more powder and a higher velocity than the Russian M43 7.62x39mm type case? Something like that might become a 6.5mm Grendel Magnum if it works.
Delta 6,
On the Grendel, the PPC was used for development after evaluating many different case options including the 30 Remington. When you compare the PPC and 30 Remington cases,, the most striking difference is head size with the PPC having .020 inch larger diameter. At equal case length, a PPC based case has greater powder capacity.
In deciding case length, the key element in making this determination are the bullet dimensions and their releationship between case length and cartridge OAL. The magazine OAL restriction of 2.255 inches set one of the boundries, so the key became finding a combination that offered the best solution and flexibility.
I can go through the decision process of why 6.5 mm and why not 6mm, .257, .270 or 7mm if you like, but in the interest of being brief, I can offer the conclusion that 6.5 mm offered the best ballistic properties and selection of bullets in the weight range for a cartridge restricted by the M16 platform.
So I have a selection of 6.5mm bullets and a case offering the maximum powder capacity for the platform. In determining case length, I looked at everything from 37mm to 45 mm as a case length. In the decision process, as case length increased, the selection of bullets that would fit within a 2.255 inch OAL decreased. Since part of my goal was to maximize long range ballistic properties, I had to look at the velocity obtainable vs the ballistic properties of the given weight bullets. For example, when comparing a 100 grain bullet with a .350 BC, a 108 grain bullet with a .473 BC and 123 grain bullet with a .547 bullet. Using any cartridge case, the gain in velocity of the lighter bullet does not offset the ballistic advantages of the heavier ballistically superior bullets. Therefore, based on the powder capacity available, a 39mm case gave the maximum number of bullet options within the 2.255 inch magazine length restriction. For the majority of people, having the ability to run everything from a 85 grain bullet up to a 144 grain bullet is an advantage. For maximum long range performance, the "sweet spot of bullet offerings is going to be bullets in the 114-130 grain weight range with ballistic coefficients in the .540-.566 range.
Now, if a large organization with substantial purchasing power asked, " you know, our needs would only be to 500 meters and we dont want a bullet with a BC over .360, but we want to run velocity as high as we can go to have maximum on target velocity with that bullet so tell us what you could do"
My response would be I could easily stretch the case and run the velocity of a 100 grain 6.5 bullet at 3,000 fps from a 16 inch barrel. At that point, it would have a bullet of a similar ballistic coefficient to the 6.8 115 grain bullet, but the 6.5 bullet would be running 350 fps faster. In response to such a request, I could have a test rifle running within 90 days.
In answer to your question about using the Czech case and shortening it, the easier alternative was to use the 220 Swift case. Also, as a note, the PPC and 7.62x39 only share a common rim diameter and case length, the body taper, shoulder angle, primer size and flash hole size are all different.
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Seasoned Vet
Group: Past PNET Supporter
Last Login: 9/7/2005 7:22 PM
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quote:
Now, if a large organization with substantial purchasing power asked, " you know, our needs would only be to 500 meters and we dont want a bullet with a BC over .360, but we want to run velocity as high as we can go to have maximum on target velocity with that bullet so tell us what you could do"
My response would be I could easily stretch the case and run the velocity of a 100 grain 6.5 bullet at 3,000 fps from a 16 inch barrel. At that point, it would have a bullet of a similar ballistic coefficient to the 6.8 115 grain bullet, but the 6.5 bullet would be running 350 fps faster. In response to such a request, I could have a test rifle running within 90 days.
Well, that was what I was thinking about. Something like a 100 grain 6.35 or 6.5mm with a 43mm case length using a large diameter case like the 6.25x43mm Brit cartridge with a velocity of 3000 fps.
quote:
In answer to your question about using the Czech case and shortening it, the easier alternative was to use the 220 Swift case. Also, as a note, the PPC and 7.62x39 only share a common rim diameter and case length, the body taper, shoulder angle, primer size and flash hole size are all different.
Yes, I have heard of using 220 swift and 6.5x54 Mannlicher-Schonauer brass to make 7.62x45mm Czech brass:
http://www.mauser98.com/brass.html
So it stands to reason they could be used to make a 6.35 or 6.5 by 43mm case.
Thanks for the info tx65.
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Cherry
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Delta,
If the 6.35x43mm case is the same rim size as the PPC, you would be able to build a 43 variant that is bullet restricted to say 100 grains within a 2.255" OAL in a similar fashion to what I outlined.
For anyone thinking of new cartridge ideas, I offer these words of wisdom and warning. Be sure to look at the other factors in design process such as the engineering limitations of the rifle and how factors such as bolt thrust will limit the performance. There are serious safety risks if you don't.
Of course, keep in mind that bigger is not always more and more is not always better.
Feel free to email me if I can offer feedback.
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Seasoned Vet
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Thanks again for the input tx65, I'm just doing a little brainstorming here on what might be possible. I'm sure you have probably tried many of these ideas and combinations already.
All things considered, the 6.5mm Grendel looks like an outstanding long range competition cartridge. I will be having a very tough time trying to decide whether to get a 6.5mm Grendel or a 6.8mm SPC upper for my AR-15 next year.
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Seasoned Vet
Group: Past PNET Supporter
Last Login: 9/7/2005 7:22 PM
Posts: 6,666,
Visits: 289
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