Cartridge capacity

S

stdukehart

Guest
Is there a scientific reason there are no popular cases with a capacity of around 60 grains of water? The .223 is 31.4 gr, .22-250 is 44.6 gr.308 is 53.5 gr, .30-06 is 68.0 gr, and .300 WM is 90.4 gr according to one chart I am looking at. Why no case with 60 grains it should be flatter and faster than the .308 without the kick of the .30-06. I was wondering, I am looking at building an F class rifle for 500-100 yards, and want more than a .308 but don't want a mag.
 
Well, if you don't want an '06 but want a "factory" chambering, you might look at the 7.5x55 Swiss case. Just a touch smaller than the '06.

When you could get RWS brass in the States, that was a real plus. Now, it's Norma brass only.

An a touch smaller, right about your 60-grain mark, would be the old 7x57 case necked up & "improved."

This is Benchrest Central, and those of us who shoot .30s in benchrest tend to go a bit bigger. For those of us skipping out on the 30WSM, something right about the size of a .308 Norma Mag (77 grains water) is working well.
 
284 win is about 66 to the neck but more like 61 with a .300 seating....

mike in co
 
New member here but been checking in once in a while. I have just built a 7x57 and was looking for a case that I could use to make a snug neck case from and have used a 5.6x57 necked up as it starts out with a .028 neck wall thickness. This has allowed me to neck turn and by only sizing the first portion of the neck in Wilson dies get a .001 release clearance for my target brass. I use Graff cases that allowed a .017 neck thickness for .0035 release clearance for hunting and have the ability to use factory (shudder) ammo in desperate. The tapered chamber neck brings its own idiosyncrasies and I sized with and polished 30 cal expander button and necked just the mouth of the case as this gave me a touch along the neck length with enough clearance for pressure but centered the neck in the chamber for straighter fireformed brass. Not as simple as parralell necked cases but very rewarding when it delivers what I thought it could. The capacity of the case allows good bullets at suficient velocity to get out there and do the job when loaded properly. I throated my barrel for the 160 to 175 gn bullets and so far it has performed as I had hoped.

Von Gruff.
 
Except for no rebated rim, the 7.5x55 Swiss case is a ringer for the .30/284. But because the rim isn't rebated, you have to open up the boltface to use it, so I'd skip that one on a Remington. Yes, you can rebate the rim on a 7.5 Swiss to fit, but the extractor groove doesn't go up as far as with the .284, so on a Remington, I believe the front of the case above the rim *might* hit the front of the bolt. Not sure.

Shehane use to use this case as a substitute for the .284 in his 6/284. He did have Tooley get a different reamer to fit the Swiss brass at the base; it is not an *exact* match. I used the case too in 6mm, holding the reamer in .020, which made it exactly the same capacity a .244 Remington Ackley Improved (which was based on a 7x57 via the Roberts). Too much work to make the short version! But it is a very nice case, with a .494 body diameter.

Tooley has *significant* supply of RWS 7.5x55 brass. Good 284 cases seem to be in the 6.5 chamberings, to they would have to be necked up.

What we really need is somebody to import RWS brass; there are any number of cases that are "just right" for a number of purposes without much necking up or down -- .5 mm or so. And it is very nice brass.

Except for the brass problem, the old .30/6 is still a nice case, esp. improved. But even Lapua brass is pretty bad, out of 200 pieces, I got 50 that had case wall variations of less than .005.

If you don't shoot *benchrest* pressures, Norma brass holds up well and is dimentionaly quite good. But I've never met a benchrest shooter who isn't in love with 65,000+ psi. Sadly, me too.

FWIW
 
If you decide to explore the .284 case at least take the time to check out Winchester brass. You may be pleasantly surprised.

Buy it NEW and in bags of the same case lot.

I've ordered a bag from Sinclair, Graf or Powder Valley after ascertaining that they've got plenty more of the same lot and then ordered 3-6 more bags of the same lot a week later. So far I haven't turned down a lot (out of four) and have only missed out on getting more once. Or, if you've got a big store in your area have them set aside some brass while you take a bag home to spec out.

It's more work than Lapua but will take much more pressure than Norma.

al
 
stdukehart said:
...I am looking at building an F class rifle for 500-100 yards, and want more than a .308 but don't want a mag.
Click to expand...

stdukehart,

If you're looking for an F-Class rifle, and are prepared to endure a moderate amount of recoil, then I would suggest that 7mm is a better way to go than 30 cal as a bore size - the reason being that you will get better long range (wind effect) performance for a given amount of recoil. Let's consider Berger projectiles for example, and using a 168gn 7mm VLD which has a BC of .617. Now in the Berger 30 cal range, you need to go right up to the 210gn VLD to get a similar BC rating (.619). So to get the same wind performance you will need to push these bullets at about the same speed, and you don't need to be a rocket scientist to know that the 210gn is going to cause a lot more recoil that the 168gn at the same velocity. You can take that even further down the calibres to 6.5mm where Berger has a 140gn BT Long Range projectile with a BC of .618. That is probably one of the main reasons the US F-Class Team has standardised on 6.5-284 - with the currently available projectiles, 6.5mm has less recoil for the same wind performance. And any experienced F-Classer will know that wind performance is a huge factor in that class.

Good luck with your project.

Alan
 
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