Well, as many of you know I have designed a monster 50 cal round on the standard 50BMG case. Basically a version of an improved 50 BMG which I have named the 510 Allen Mag.
The rifle was built on an Armalite AR-50 which I pulled the barrel on and gave the receiver a full accurizing which I will admit did not take much cutting. That receiver was pretty damn square right from the box. I was very impressed.
After I was finished though she is as true as my Rem 700 actions are after accurizing.
The barrel I used is a Lilja 35", 1.750" straight cylinder SS 1-15" twist which I had Dan order a 7/16" wide flute cutter for this very large barrel. The flutes are simply cosmetic on this size of a barrel but they do look pretty cool!! [img]/ubbthreads/images/graemlins/grin.gif[/img] Got to have that Cool factor in there!!
Because of the design of the AR-50s stock, there is no bedding needed. IT is a huge alimunum V-Block that the receiver sit in and which also has a V-Block that matches the stock. Solid is an understatement.
That receiver could easily handle 45" of barrel of 2" in diameter and not blink an eye doing so!!!
Other additions to the rifle was a Prince Bipod from Armalite which will be getting worked over here soon for better performance. The trigger was replaced with a Rifles Basix 1.5-3 lb trigger set at 1 3/4 lbs. Which on this 38 lb rifle feels about like a 1/2 lb trigger pull.
The Armalite standard 15 moa rail was replaced with a 50 moa rail base and I mounted my 4-16x 50mm USS Xotic in a set of Badger Ord Max-50 six screw cap rings.
The most important thing on this rifle was the brake. My performance goals are to break 2900 fps with the 750 gr class bullet and possibly push 3000 fps. Better yet, drive 835 to 1000 gr bullets to 2700 fps and 2500 fps respectively. Going for max hitting power here combined with high ballistic potential but mostly raw power!!
As such, recoil was a consideration. I decided to machine a brake and after talking with Shawn C. about this I decided on a 5 port partition style brake. They are easy to machine, work very well and look nice in my opinion. I machined the brake out of a section of Lilja barrel stock which I purchased from Dan. I really like making brakes out of the same material the barrel is made from.
The brake is 1.750" in diameter and roughly 5 1/2" in length. The ports were designed pretty large to release ALOT of gas volume nearly instantly. Will this be loud, YOU BET, but its the only way to control recoil and keep it comfortable in this 35 lb class rifle.
The ports are each roughly 5/8" wide by 1 7/16" tall. The bore hole was reamed 20 thou over bullet diameter which is as tight as I like on a parition style brake.
I spend all day Saturday working on the chamber and barrel work and then Sunday worked on customers rifles until about 5:00 in the afternoon then I switched over to milling on my muzzle brake. You should see the pile of chips that built up on my mill from this project!!! What a mess but proved well worth it.
This morning earily I did the finish work on the brake and matte finished it to match the barrel and she was finally finished
This pic shows the 510 Allen Magnum compared to my 224 AM. The 224 is basically the same size as a Rem 700 heavy varminter but with a 27" barrel. This pic give you an idea of the size of this rifle.
It may be the only rifle I ever build that makes Black Sunshine look small, well, not small, just not quite as big as before!!
Having the rifle finished I HAD to pull the trigger once before I started working in the shop for the day on customers projects. I dug up an old test load I had for my old LAR Grizzly rifle. The load used 225 gr H-50BMG under the 750 gr A-Max bullet. This load produced 2730 fps in my LAR and was far to warm for my liking. Recoil in that rifle was enough to need a couple tylonal after a shooting session to prevent a significant headache from setting in.
My comfortable load in my LAR was 210 gr H-50BMG under the A-Max which was good for an average velocity right at 2600 fps. I predicted this much hotter load would produce about the same in my 510 AM chamber.
I set the rifle up to shoot into my backstock beside my shop, chambered the big round, grit my teeth and and let the trigger slip. I was amazed to be greated with 25-06 level recoil, IF THAT!!! The recoil was nothing to even talk about, the muzzle blast, well, thats a differnet story.
My mother in law has a flower garden next to my shop. It was about 15 feet from the muzzle of my 510 AM when I touched it off. Lets just say the flowers were much fuller and prettier earlier this morning!!! There were flower pettels blown over 20 sq yards!!! I may get a chewing for that but at least I know the brake works amazingly well. Far better then I was even expecting!!!
When I lifted the bolt, there was no resistance at all and the case pretty much fell out of the chamber. The shoulder angles were still pretty heavily rounded. I would guess the case formed to about 85% of what it should have. Plenty for fireforming but still pretty rounded shoulders.
In this pic you can see the standard 50 BMG on the left, my 510 Allen Mag in the middle with a 835 gr ULD RBBT SP sitting in the case where it will be for the throat on the 510 AM and for size comparision, a formed 30-06 AI case on the right.
I measured case capacity and the partially formed 510 Allen Mag case holds about 30 gr more US869 filled to the case mouth then a 50 BMG case does. With a full fireform I predict the 510 AM will hold about 35 gr more powder then the standard 50 BMG.
I will admit this is about 10 grains less then what I was predicting but nothing to worry about. Its like taking 10 hp off a 600 hp V-8 and complaining about it!!!!
Now onto barrel break in which on a 50 cal is critical in the extreme. You really have to take your time and go slow but if done properly, they clean very easily after the break in. You do not want a 50 cal that copper fouls or you will be removing about 3 cents worth of copper out of your barrel after about every 25 rounds.
More to come. So far I am amazed with the performance of this brake. SO much so that I am considering making one for my 338 Allen Mag. It is simply amazing. I would live to remove it and see what the difference in recoil is but I admit I am not man enough to do that!!!
Now I just need to get the barrel broke in and then get some 1000 gr pills from Richard Graves and really start making some gravel!!!
Will keep you posted.