OK, I got my new CZ416 Rigby. Trouble is I do not want a 416 Rigby. Nothing wrong with it I just want something bigger. I thought about the 450 D, 475 A&M, 475/416, that MOBOGO thing but I think I've settled for a 500A2. Now I know its a .510 dia bullet and based on 460 W brass and I know it has a belt but my wallet says its the cheapest and fastest way to get a fifty. My question is if I wanted to shoot BMG bullets in it, how will I handle this, I know I'll have to ream the chamber out a little but I still want decent accy out of 500 to 600 grain bullets. I'll be useing a Pac Nor or a Krieger bbl. I do not expect match grade accy by trying to find a happy med between BMG bullets and say 600 grain Barnes. I just want a thumper that will do what I ask of it within reason. Has anyone built one of these and solved all my probs before I undertake this project. I know the action is big enough to handle the cart' but if anyone has built one on a CZ 550 please let me know how you did it.
Thanks in advance: Steve

Just a couple of questions. Have you shot many big bores before as in 50 calibers shooting 600 grain bullets at 2400 fps. Try your gun out for a while as a 416 Rigby you may find that you really like it. See if you can try someone elses 500 A-Square and make sure it's what you want. If so then more power to you.
Take care and best of luck with your project,
470 Mbogo

slimmpd,
When I first started into this over three years ago, I had Kevin Jenkins rebarrel a .416 Rigby Ruger No.1 to 500 A2.

I then asked him to extend the throat to allow the maximum OAL with a Hornady A-Max 750 grainer. This cartridge OAL is 4.760". Any longer than this and you start getting into the boattail of the bullet and the case will not grip it properly.

The standard 500 A2 chamber reamer by Clymer has 0.400" freebore plus a leade of 1 degree tapering into the rifling. Leade plus freebore equals throat. The amount of added freebore to seat the A-Max way out was 0.188", plus a 1 degree 30 minute leade, from a Dave Manson throating reamer with a live pilot.

I then fireformed cases in this chamber and loaded some dummies with blacktip milsurp AP 700 grainers, crimping in the middle of their cannelure. I sent the dummies to Dave Manson and asked for a throat that was custom fitted to this bullet with minimum freebore.

Thus, I arrived at the .510 JAB reamer, by Dave Manson. It has only 0.300" freebore and a 1.5 degree leade. After doing the trigonometry, this gives a total throat length of 0.529", with only 0.300" freebore.

This chamber will handle any common milsurp bullet, and any hunting bullet, with a tighter throat than the standard 500 A2. However, this .510 JAB chamber will only allow a max OAL of 4.722" with the 750 grain Hornady A-Max, as best I can tell, without touching the lands. This is only slightly shorter than the absolute max for that bullet of 4.760" cartridge OAL.

My first attempts at rethroating the 500 A2 may hve resulted in excessive throat length due to runout from concentricity in my dummy ammo.

Really, the standard 500 A2 has plenty of throat for use with milsurp bullets if you load your ammo well with good concentricity/minimum runout.

The value of my .510 JAB reamer may be in its excellence all around, aside from the special throat, due to having been made by Dave Manson. A lot of gunsmiths will recognize that quality.

My .510 JAB reamer does have excellent target potential; 705 grain "Harlow" target bullets by AAA Ammo will go into 0.170" for three shots at 100 yards.

Kevin Jenkins, of Brentwood, Tennessee, was the gunsmith in this experimentation. He insists on live pilots and oil grooves for the reamers he cuts chambers with.

The second rifle was a BRNO ZKK 602, which has the same reciever, magazine, and bolt as the CZ 550, same geometry, made on the same machines by the same company: CZ.

Your CZ .416 Rigby is the quickest route to this most practical stopping rifle and 1000 yard target rifle that delivers about 75% of the velocity of the 50 BMG with the same bullets in a much lighter and handier package, with a much shorter barrel.

I used a McMillan fiberglass stock. The barrel was a stainless, 1 in 10" twist, 23" long, 0.870" at the muzzle, and with a straight taper target barrel contour, by McGowen (his No. 8 target contour). The screw on muzzle brake is welcome at the bench, but not in the veld. Without brake and with express sights the rifle weighs 10.75 lbs.

Though the 15" twist is standard for the 50 BMG, I truly believe a faster twist is needed for the slower velocities of the 500 A2 equivalent, with the long and heavy target bullets.

The fast twist will improve up close penetration with the "stubby" 570 to 600 grain hunting bullets, IMHO.

It is a most amazing package. The be-all and end-all of big bores, as long as nostalgia is not important.

Just a little bit of trivia, to bring this thread back up:

The .50 Cal. BMG/US Ord. chamber has freebore of 0.2500". It handles all those milsurp bullets just fine.

The .50 BMG-Match chamber has only 0.1300" of freebore. It has the case capacity to seat the super long target bullets deeply.

With the 500 A2 you want a longer throat to seat the target bullets out to maximize case capacity.

If you want to just shoot milsurp bullets for fun, the standard 500 A2 chamber with 0.400" freebore is just fine.

Concentricity of chamber and bore, and minimum bullet runout of ammo is the key to minimum throat, smooth function, and best accuracy in the 500 A2.

The 500 A2 is a fun little plinker. Nothing mysterious about it.

A nice resource is the Clymer reamer design web pages. Have a search through their list of reamer spec drawings. There are things like the 50-505 Gibbs in this listing:

http://www.clymertool.com/cgi-bin/reamer.cgi