Twist rate and caliber for subsonic 50MBG payloads??

[jope]

Hello,

I'm thinking about building a .510 Whisper ( or similar if you can argument that something else is better)

I have read that the 750gr Hornady AMAX performs the best. I would intend to shoot up to 300meters at subsonic velocities projectiles 750gr and up. I would not like to have the barrel longer than 18".

I read from http://www.quarterbore.com/300whisper/sskwhisper.html that the .510 Whisper is capable of MOA accuracy at 600 meters. But there is no info about the barrel lenght, make, twist rate and projectile.

Some people say 1 in 10 is enought but I have allso heard form a reliable source that 1 in 6 plus minus is needed.

Lothar Walther can make up to 1 in 10 but i know a smaller gun smith that can make up to 1 in 7 from a special order.

Could you explain me whats the neccecary twist rate, and where can I get this barrel blank from? Lothar Walther barrels are the easiest for me to get.

Sincerely from Finland

- Jope

[d-mon]

Hello Jope,
You should be fine with the Lothar walter to stabilise the 650 grains military bullets, but I think you will struggle with the 750 gr amax.

As you are in Finland, I suggest that you send an email to Dr Kolbe of Border Barrels in Scotland. He can make any twist barrel you want , even in 50 cal.
His web site is www.border-barrels.com

Tell him what sre your requirement exactly (stabilising a 750gr amax at subsonic velocities) and He should point you toward the right direction for the twist rate.

Regards.
ND

[dflicker]

Hi Jope,

I would like to do something similar, but would probably try to optimize for some of the 800 grain or heavier turned solids. They generally outperform the Amax in 50BMG competition. Does anyone know of a case on which to base a 50 caliber cartridge that will allow a true shoulder to be formed without creating a turned shoulder like the 338 Lapua based 510W? You could always use a 50BMG case but my action weighs 12 pounds. Not something I would want to carry around in the woods.

David

[Spook]

Jope, i used a 1 in 9.25 for my 50EBG project, no complaints. My only problem with 510 cases is cost, and if I make them myself...time and cost
sixteen inches of barrel is plenty if subsonic is where you're heading. The whisper case has some extra capacity so if you want to go faster you could use a smidge more barrel.

David... JD has a 50 whisper now ,based on a 460 weatherby case. If you have to have a shoulder....This is the cartridge for you. Teppo Jutsu has the 500 phantom but brass is almost non-existent. Weatherby brass comes in at about two bucks a pop if you make them yourself, but you need a .588 (i think) bolt face, which means Sako or Weatherby......But I'd bet I can turn out a Savage bolt head that will work

Something important with either chambering: If you get your reamer set up for 750AMAX and plan to use milsurp.... The length difference is going to matter substantially if you want to seat milsurp at the cannelure... you'll be jumping almost .250 to reach the lands, otherwise plan on anything milsurp hanging out there a ways.

in case you havent read it http://www.quarterbore.net/forums/showthread.php?t=1303

[d-mon]

Hello,
Have a look at the folowing website:
http://www.stopsontfm.com/Historique%20ang3.htm

The ammo of that rifle is the french copy of the 500whisper.
It is based on a 460 weatherby mag case i believe.

ND

[dflicker]

Thanks, Spook. I found this on the 500 Phantom. http://www.feistyrooster.com/500phantom/index2.html

I appears to be exactly what I am looking for. Suppressed, short stroke piston AR10 type rifle (LWRC). I have several other subsonic projects ongoing at this time but perhaps brass will be more readily available when I am ready to take the plunge (probably a year or so). OAL might make a bolt action more realistic, though.

David

[Spook]

David, you can get info on any new brass arrivals here: http://458socomforums.com/phpBB2/
scroll down to "Other Cartridges by Teppo Jutsu"

[jope]

I just wrote Border barrels... lets see what they have to say about the twists?

Btw, does anybody know how to calculate the force directed on the barrel mount. Im currently working on .300 Whisper and .308Win barrels for my Encore. Im using a stainless Lothar walther barrel blank. According to what I have studied about this 1.4021 type of stainless steel it can not be safely (without brittle a HAZ) welded with out later heat treatment. Heat reatment can not be performed with out loosing the rifles from the barrel and having deformation.

1.4021 stainless:
C % Si % Mn % Cr % P % S %
0,19 0,50 0,63 12,13 0,022 0,025

I have decided to go on with a M20-1 threated muff joint. I don't know how make sure ( calculate) that barrel doesn't get too thin around the camber, and that the remaining muff has enough cross sectional area to hold the barrel attached to the lug.

Take a look at the cad pictures. I thought about leaving full thickness barrel for 2cm abound the chamber. So that the preassure wouldn't blow the chamber on my face. But I would like to know how to approximate the strength and thickness needed for different calibers and loads.

- Jope

[d-mon]

Hello Jope,
I think I guess what you are trying to do:

You want to make a barrel for your encore rifle.

Well the easiest would be to contact ssk industries and ask tem to make you one.

If you make one yourself, do you intend to build the lug your self or to use an old barrel that you want to rebore and use as a sleeve (i am talking about the first few inches past te LUG)?
I have done it like in the second way, with a 22 barrel on a contender barrel.

.50 cal is a different matter because of pressure...

One cartridge you should take a look at is the 50/70.
Brass is available, loading dies as well.

Ssk industries used to chamber a contender with it, they called the caliber 50/70/750 (as 750 gr A-max). But they stoped because of risk of blowing up the thin barrel of the contender. but in a encore it should work, no problem.

nd.
PS: the 416 steel used by border should weld quite well, but ask them confirmation

[tp555]

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