New and old cartridges doing (nearly) the same

[Chuck R.]

A way out....

 

[Jim Watson]

Special forces have had discretion to step outside of standard supplies lines when missions called for it for as long as there have been special forces. It's very much part of what they do.

I just hope they can do their special stuff and get out before they run out of special supplies.

the US military is currently in the process of replacing 300 Win Mag with 300 Norma Mag.

Worse than I thought.

 

[MarshallDodge]

Part of the reason for new calibers is the fact that bullet design has matured and we now have bullets with better ballistic coefficiency. We can look at 2.43 and 6 Creedmoor as one example or 6.5x55 or .260 compared to 6.5 Creedmoor.

I'm still debating about what caliber to go with for my PSA PA-10. I will most likely go with 6 Creedmoor simply because I can use the same bullets for it as I do for 6 ARC.

Please don't let me stop you from buying another AR, but why not just stay with 6ARC?

I have too many different 6mms, all in bolt actions, and I am thinking of pairing a few of them down to 6GT when I finish these barrels.

6GT is a new caliber which I am sure there is an old caliber that can do what it does, but there are several companies making brass for it, or I can form from 6x47 or 6.5x47 brass, and it is very efficient.

 

[mcb]

I just hope they can do their special stuff and get out before they run out of special supplies.



Worse than I thought.

Having shot a fair amount of both 300 WM and 300 NM in my time I like 300 NM a bit more but it does not fit well in a 700 Long Action and its clones. Case head is so large it barely fits a 700 bolt face. IMHO It needs an action running a larger diameter bolt for the 416 Rigby family of cartridge; they are a bit sketchy in a 700. The 300 NM like most of the current trends gives you a bit more room in front of the case for the long VLD bullets compared to 300 WM in the same magazine length. A bit more case volume too due to the larger diameter body, so for the same bullet weight you get another 100-150 fps. IIRC the load the military load is using a 215gr VLD bullet launched at ~3000 fps from the new Barrett ASR (MRAD).

 

[12Bravo20]

Please don't let me stop you from buying another AR, but why not just stay with 6ARC?

I have too many different 6mms, all in bolt actions, and I am thinking of pairing a few of them down to 6GT when I finish these barrels.

6GT is a new caliber which I am sure there is an old caliber that can do what it does, but there are several companies making brass for it, or I can form from 6x47 or 6.5x47 brass, and it is very efficient.

I'm not buying another AR. I've had my PSA PA10 for about 7 years now and 308 is too much on my shoulders now days. All I would need to do to switch calibers on that rifle is buy a new barrel. And if I go with 6 Creedmoor in the PA10 then I can use the same bullets for it and 6 ARC. Plus 6 ARC is way too short for a large frame AR.

 

[jdsingleshot]

Having shot a fair amount of both 300 WM and 300 NM in my time I like 300 NM a bit more but it does not fit well in a 700 Long Action and its clones. Case head is so large it barely fits a 700 bolt face. IMHO It needs an action running a larger diameter bolt for the 416 Rigby family of cartridge; they are a bit sketchy in a 700. The 300 NM like most of the current trends gives you a bit more room in front of the case for the long VLD bullets compared to 300 WM in the same magazine length. A bit more case volume too due to the larger diameter body, so for the same bullet weight you get another 100-150 fps. IIRC the load the military load is using a 215gr VLD bullet launched at ~3000 fps from the new Barrett ASR (MRAD).

 

[mcb]

I'm not buying another AR. I've had my PSA PA10 for about 7 years now and 308 is too much on my shoulders now days. All I would need to do to switch calibers on that rifle is buy a new barrel. And if I go with 6 Creedmoor in the PA10 then I can use the same bullets for it and 6 ARC. Plus 6 ARC is way too short for a large frame AR.

I have a 700 in 6mm Creedmoor and have really enjoyed the cartridge. From a two hundred yard zeros and a properly setup copy of Stelok (RIP) got me first round hits out to 1000 yards on targets ~2-3 MOA in size using factory Barnes ammo. The smallest group I ever shot was in the shooting session for that 200 yard zero where I shot a .38 MOA (.80-inch) 5-shot group at 200 yards. One of these days I going to take it hunting...

 

[jdsingleshot]

Seems to me that most of the new is better faction are confident that things will continue much as they have been. But it seems to me that since the first cartridge guns appeared, there are many times more cartridge designs that are now unobtainable than that are easy to find. Some that are still made are nevertheless rare. And lots of cartridges, such as the 6.5x55 and 7x57 were limited not by their design or material, but by the guns they were used in. I suspect either of them in a Rem 700 could safely operate at 55,000 psi instead of the original 40,000. In that case nobody would have been looking to replace them.

 

[silicosys4]

Most of these newer cartridges are filling niches, as far as I can tell. Nothing is revolutionizing the market or sending older, more established cartridges out to pasture just yet. Maybe in a generation or two.
They are all for the most part, evolutions in current cartridge design, taking advantages of the small but significant technological advances that have taken place over the last few decades and cater to a market that is shifting away from the needs of hunters, and more towards the needs of long range paper punching.

 

[herrwalther]

I had a similar thought looking at ballistic comparisons between (old 1906) 35 Remington. And the new niche 360 Buckhammer from last year. Only difference is the new hotness is a straight wall for the silly hunting states.

 

[CraigC]

Even when you don't fit into whatever niche, sometimes you want a new cartridge that does what an old one does because you get tired of scrounging around for brass and other components. I got a 6.5JDJ barrel for my Contender and it's hell finding .225Winchester brass. Same for my Ruger .250Savage and .405Winchester. Sometimes you just wanna shoot.

 

[wombat13]

If you are going to compare 300 WM to 6.5 CM in a military setting then at least use the ammunition the military is using in your comparison.

For 300 WM the military is using the Mk 248 Mod 1 ammunition. This is a 220gr Sierra Match King (G1 BC: .629 >2100fps, .624 1700-2100fps, .608 <1700 fps) pushed at a specified 2850 fps from the M2010 per the military spec.
For 6.5 CM the military is using the Law Enforcement Hornady 6.5 CM TAP Precision. Using the available specs on Hornady's Law Enforcement & Military website that is a 147gr ELD-M bullet (G1: 697) pushed to 2655 fps.
300 WM has a modest velocity advantage but 6.5 CM had a modest drag advantage. This adds up to fairly similar trajectory with 300 WM being marginallly flatter.

At 500 yards its 42.8 vs 49.9
At 1000 yards its 360 vs 401

Given the skill of the men that are shooting these that is not a big deal. Consistence of the ammunition will play a bigger role than the flatness of the trajectory at these extreme ranges.

Also consider the platforms:
300 WM is being used in an M2010 (or PRS) it weighs in at 17.5 pounds (PRS a bit over 18) without suppressor, is a bolt action, scope 6.5-20x50 (5-25x56) and a 10rd mag.
The 6.5 Creedmoor is being used in the M110 (among others) that weighs in at just shy of 14 lbs, semi-auto, scope 3.5-18x44 and a 20rd magazine.
Both cartridges and rifles are going to excel at different rolls but I suspect (from having the opportunity to play with both rifles in a non-active military settings) the M110 (in 308 or 6.5 CM) is a significantly more versatile weapon.

*And I am not sure this comparison is as valid as it was given that the US military is currently in the process of replacing 300 Win Mag with 300 Norma Mag. The Remington M2010 and PRS both used 300 WM (PRS also could use 7.62x51 and 338 Lapua Mag). The replacement for these two sniper rifles is the new Barrett ASR (MRAD) and it using 7.62x51, 300 Norma Mag and 338 Norma Mag. So for the dedicated long range anti-personnel sniper rifle 300 NM is taking over that role from 300 WM. For the more designated marksman role 6.5 CM is being tested by special forces along side the proven 7.62x51 and no doubt the new hotness 6.8x51.

-rambling

Based on my data, the 6.5CM drops 21% more at 500 yards and based on your data it drops 17% more at 500 yards. So, like I wrote earlier, 6.5CM does not shoot as flat as .300WM. Your post has a lot of other important considerations, but 6.5CM just isn't as flat as .300WM. Those other considerations would all be important in choosing a cartridge/platform for a particular job as would considering how flat of a trajectory is necessary. But that's moving the goalposts, because the claim that I was addressing was that 6.5CM shoots as flat as .300WM, which it doesn't.