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:rolleyes:
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:wink:

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]

Like this:

[jope]

d-mon thanks for the tips:

How is the case volyme in caliber 50/50/70? Does it use the same barrel diameter as 50BMG? Lothar Watlther has just a wee little too much carbon and cromium for welding. That extra makes the barrel stronger but practically impossible to weld without getting a brittle heat affected zone.

tp555:

How is the case volyme in the phantom compared to 510 whisper and suitability for shooting heavy (750gr and up) subsonic loads? Phantom has the .50BMG barrel diameter, right?

Whats the thicknes at the thickest point in those cases? .510 Whisper is quite straight which is good because then there will still be some material left around the chamber. Especially if I end up building this on my thin Encore barrel.


Anybody know mathematical formulas for the strength calculations?

- Jope

[tp555]

Can't help you on this. I made the brass from jeffreys (machined the head and cut down to size).The phantom stamped brass is original samples.All have been shipped out already. regards.

[d-mon]

Hello Jope,

The 50/70/750 would be the case with the smallest wall diametre I believe. The 510 whisper being based on the 338 lapua, might have a diametre a bit bigger.

Remember, the encore works best with rim cartridge.

If you look into the old Handloaders, you will find an article about that calibre and the contendre barrel that goes with it. (at least 4 or 5 years ago).

For strenght calculation, ask Dr. Kolbe about it, he is a Dr in Physics and know a lot about these things.

I assume that if a contender barrel could be chambered in that calibre, then the outside diametre of that barrel would give you a good Idea of what can be achieved.

ND

[jope]

D-mon:

Can the old handloaders articles be read anywhere on the internet?

And it uses the .50BMG projectiles right???

I wrote border barrels last weekend to ask about the twist for 510 whiper and awailability of suitable barrel blank but no reply so far...

I had ordered .300Whisper reamer from pasific tool and gauge but when I received ot yesterday, 300 hush was written on it. I wrote dave kiff confused to ask about this, but no reply form there either. I hope they just call the whisper hush and its the right reamer and there hasnt happened any misundestangind.

- jope

[d-mon]

Hello Jope,

Regarding Border,
Maybe, You would have been better asking for a quote for a barrel of x dimensin, y profile...etc ,in .50 cal and then asking for their advice in term of twist for stabilising an a-max bullet.

I have somewhere a program to calculate the twist, if you have an a-max close to your hand with a caliper , I should be able to help you. (i will ask you for certain dimensions of the bullet later on).

Regarding the handloader, it is June 1995, page 18. Yes it shoots .50 cal projectiles and the a-max.

I got a reamer from Pacific tool and gage in 30/221 which is what I wanted. I have built one rifle, that I did not have the chance to try yet. (I am in New Zealand and the rifle in Europe). I used a Border Barrel.
They call it Hush because they cant use the "Whisper" name that belongs to SSK I believe.

ND

[jope]

Got a reply from PTG and its the same reamer.

Still no reply form border barrels.

I attached some measure pictures of the 750gr amax. It would be a great help if you d-mon could help me and count the neccesary twist. Shooting subsonic up to 300meters from a 16-20" barrel.

How is the legistlation in the UK. Do you need a license or any paper to buy a barrel blank??

Border barrels exporting license sounds like a big paper mess. In Finland you dont need any license or permit for a rifled barrel as long as it is un chambered. I'm thinking visiting the UK anyway and then I could just pick up the barrel and save all the paper mess. If it goes the same way as here...? Anybody know?

- Jope

[d-mon]

Hello Jope,

No, getting a barrel shipped to Finland must not be a problem. i am sure that if you provide a paper from your police or custom services stating that you do not require a licence for import, Border will do his bit on its side and you should get your barrel quickly.
Delays are at least a month, sometime up to 3 depending of their production.So the paperwork is done meanwhile.

Yes, a barrel unchambered is not subject to any license in the UK as well. But I would not risk a trip just to see that you barrel is not finished yet. And they are in a very very remote and private place...
Thank you for your pictures.
I will work on the programme and give give you an answer in 2 days.

Good night.
ND

PS: I am in NZ now.

[jope]

Hello!

Have you had success calculating the twist?

Is there something bad if a choose a twist too tight? Im thinking the 1 in 7.5 from border barrels.

- Jope

[d-mon]

hello jope,
yes I have been struggling calculating the twist. something wrong with the program with such a big bullet maybe? I will investigate that.

I don't think you can go wrong with 1 in 8.
The risk with overstabilising the bullet, is that at long range you might have it planning and arriving sideways or even bottom first in your target,specialy with subsonic, where the departure angle is further up to compensate for the banana trajectory.

Again, I think that if you write a letter to border regarding your project, they will defenitly answer to you and help you with what you are looking for.

regards.
ND
PS: I will probably be visiting them in june, i can for more info if you want.

[jope]

It would be great if you could find out what they know off about the twist needed for stabilizing the heavy subsonic 50bmg projectiles.

Anybody know what the minimum barrel thickness should be for .510Whisper? I wouldn't like the barrel to blow up on my face. Encore barrels outer diameter is one inch. I could bore through an old encore barrel and put the new .510barrel in it. Then the new 510Whisper barrel couldnt be thicker than aproximately 20mm/0.79 inch.

For reference, does anybody know the outer diameter in the 50 Beowulf barrels used for AR? I belive .510 whisper wouldnt have to be any thicker...?

- Jope

[d-mon]

If you intend to use a encore barrel, you could actualy ship the barrel to border, then he could rebore it to 0.50 cal and do the cut rifling in fresh metal.
You then do the chambering, but you have only one chance!:grin:


ND

[dflicker]

The current issue (June) of SAR has an article on 50 cal cartridges. The one that caught my attention is the 11.35 Madsen. It looks like it would be perfect for subsonic, possibly even in an AR10 type rifle, but I doubt that the brass is available. Has anyone looked into this cartridge? What would it take to have brass made?

David