Thumper

[Topshot]

Not sure what to make of this little project of mine. A silly little idea seems to have taken on a life of its own and I ended up with this thing on the left with a .338 RUM on the right for comparison.

It is a .510/505 Gibbs (.510 Beecher) with extended throat to maximise case capacity.
Holds 179gn H2O to level with the case mouth.
The Bullet that I will be using will be the 750gn Hornady A-max.

I have the barrel, brake, reamer, brass etc ready and will have it all put together over the holiday period.
The brass is high pressure Bertram brass designed to run at Cheytac cartridge pressures.
For a launch platform, I will remove the barrel off my .375 Cheytac. It has a 408 Stiller single shot action so should be good for 65kpsi
No idea what load to use but hope to live to tell about it.

 

[MudRunner2005]

That looks nasty... Looks like an overgrown version of my .308 Win with Berger 210 VLD load. LOL

 

[Topshot]

Yeah, its a bit of a beast.
Its will be quite interesting to see how it shoots.
I'm expecting excellent accuracy but not great velocity. If I can get to 2400fps I will be very happy.
That will get me to 1000 yards with about 5000 ft/lbs and less than 4 moa of wind drift in a 10mph wind.
That A-Max should make a nice hole in deer too...

 

[Bravo 4]

Interesting build, I like it!
I did something along the same idea, just not as big. Mine is a cut down .300 RUM case, built on a Savage action with 16" barrel and a suppressor. I wanted to the capability to go subsonic also. I was wanting to shoot the 750 Amax as well but am not getting the accuracy I want, at least not good enough to take advantage of the Amax's high BC. These Lehigh bullets have some rather nasty terminal effects.

I got to 1700 with the 750's and stopped. The recoil on my little rifle can be pretty brutal, especially with the suppressor off.

 

[Topshot]

How do you headspace that sucker?
Those pills look like they would open up ok.

 

[Bravo 4]

How do you headspace that sucker?
Those pills look like they would open up ok.

Headspaced on the case mouth, I just have to stay on top of the case length.
I have been messing with the internal box mag to make it a repeater, so far so good.
Those are subsonic fracturing bullets. The petals break off at a pretty low impact velocity and then you have a long .510 caliber slug that will probably penetrate length wise through a deer.

 

[Deleted member 46119]

First, I must say I'm very impressed . I'm not going to make one.

Second thing to say is ouch.

Down to brass tac drivers.

If you have a 32" barrel, IMO your goal of 2400fps seems very doable. I have not cut my Jamison brass in half to measure but we are lead to believe it will take 65k psi.

I ran the numbers in QL with a seating depth just shy of seating bullet body below the shoulder.

COAL: 4.730
Usable capacity: ~137grms
Powder: Reloader-17
Charge: 125grms
Extimated PSI: 61k
Estimaed MV: 2400fps
Energy at the muzzle: ~9500
Recoil: Enough to launch you into the next county
Drop at 1750 yards: ~1350", ~75MAO
Energy and fps at 1750 yards: ~2400'lb at ~1200fps
Subsonic distance: ~2000yards
Energy at 2000yards: ~2000'lb

So there you go. More than one person (you and me) thinks you can get there from here.

Oh my god cool and show pics please.

 

[Bravo 4]

What are you projecting the weight to be? If the weight is kept down that would be a heck of a hunting rig...for anything.
I'm sure the 750 Amax will be an effective killer even at lower velocity. I have had the aluminum tips come off and the end of the bullet deform pretty well in wet media at below 1000 fps. They will penetrate pretty good too, completely through about 18" of newspaper/phone books.

 

[Bravo 4]

Here is a photo of some I dug out, two on the end are M33's along with a loaded one. Not a good picture but you can see what they can do at even lower velocity.
Edited: sorry about the turned pic...uploaded from a cellphone.

 

[elkaholic]

Topshot......I like wildcats and this one is definitely unique! I wouldn't be afraid to go after a Griz in the alders with that baby!
If it is shoulder mounted though, the Griz might be a better option
Way to go.......Rich

 

[Topshot]

First, I must say I'm very impressed . I'm not going to make one.

Second thing to say is ouch.

Down to brass tac drivers.

If you have a 32" barrel, IMO your goal of 2400fps seems very doable. I have not cut my Jamison brass in half to measure but we are lead to believe it will take 65k psi.

I ran the numbers in QL with a seating depth just shy of seating bullet body below the shoulder.

COAL: 4.730
Usable capacity: ~137grms
Powder: Reloader-17
Charge: 125grms
Extimated PSI: 61k
Estimaed MV: 2400fps
Energy at the muzzle: ~9500
Recoil: Enough to launch you into the next county
Drop at 1750 yards: ~1350", ~75MAO
Energy and fps at 1750 yards: ~2400'lb at ~1200fps
Subsonic distance: ~2000yards
Energy at 2000yards: ~2000'lb

So there you go. More than one person (you and me) thinks you can get there from here.

Oh my god cool and show pics please.

jfseaman,

Thanks for the Quickload help.
My loaded length is 5.100" and I will be throating the chamber for that length.
Filled to level with the shoulder is 140gn of H4350 powder. I could get a few more grains in there so about 145gn I would say.

I have a 30" cromolly barrel waiting to be fitted to the rifle. Here is the rifle with its current 32" barrel chambered in .375 Cheytac. It weighs 24lb at the moment and will come in at about 23lb with the slightly shorter .510" barrel fitted.
I will post up a few pictures when its done and give a report on how it performs. I expect recoil to be manageable at this weight.

 

[Topshot]

Merry Christmas everyone.
Hope 2015 is a blast!

 

[Topshot]

Here is some of my initial test results.

COAL 5.052" Fed 215 Mag Primer. Bertram Brass. 750gn A-Max.
H4350 powder 112gn 2106fps
114gn 2124fps
116gn 2120fps
118gn 2157fps
120gn 2142fps
122gn 2162fps
Case is about 85% full at the highest load.
Still a long way off my target speed of 2400fps but pressure seems light so far with no extraction problems or obvious pressure signs.

 

[AZShooter]

Like your project. Always thought there is a place for slow heavy bullets. High BC longer barrel life and in some instances moderate recoil.

A few years ago Cheytac had the .375 350 gr Sierra MK made for them. I wanted to try that bullet in my 375 Taylor unfortunately the twist wasn't fast enough. When I built a 338 RCM sporter I borrowed some 300 gr Sierra MK from a friend and tried them. Got over 2200 fps from a 22" barrel and the light bulb went on.

I built a long throated 338 RCM in a LA to shoot the 300 gr Sierra MK and then later switched to the 300 gr Bergers when they showed. Am getting 2525 with a 30" barrel and it is lots of fun to shoot. Long strings before barrel gets warm. Excellent accuracy and moderate recoil. Fouling is also minimal. Downrange drift and energy is impressive too.




Keep us informed on your progress.