Stay tuned for the .416/350-grain TTSX and the .416/300-grain X-Bullet (original, noncannelured XFB, discontinued) re-sized to .408.
C.O.L. 3.770" and 3.800" respectively.
They both work through the box of either a CZ 550 Magnum or MRC PH M1999, and are tough enough to stand up to the velocity.
Ditto the 350 and 400 grain TSX bullets.
Re-sizing .416 bullets to .408 is a great use for old bullets gathering dust,
as well as repurposing any new .416 bullets.

Dummies for C.O.L. determination.
The discontinued .416/300-gr XFB is interesting in providing a throat guage.
If it is seated out to 3.930" it touches the lands in the leade at .408" diameter.
50-thou off the lands is at 3.880" C.O.L.
3.800" C.O.L. is shown just to show how short you can go.
The 350 and 400 grain Barnes TTSX and TSX bullets when crimped all end up at 3.770" C.O.L.
The 350-grain TTSX has more jump to lands, could be seated a little longer if not crimped, than the 350 and 400 grain TSX.
The latter two bullets share the same nose shape, nose contour and nose projection are same for those two.

HOW CZ-USA BUILDS A .505 GIBBS

First turn a CZ 550 Magnum .375 H&H box into a 3.950"-long .505 Gibbs box:
Cut off the front wall except for a small band near the bottom.
Weld in a box extension, inside the box to expand the box length.
Feed ramp now overhangs the front inside box wall a wee bit.
Place a 0.1"-thick rubber pad inside the front of the box, later ones were steel instead.
Box length is back down to about 3.85" with the bumper inserted inside front of box.

If instead, one trims about 0.050" off the rear edge of the feed ramp,
and then reinforces the front of the box outside, with a steel plate,
then magazine length is a functional 3.950" inside of the box:




Top front of box:



Bottom front of box:



Side of box:



Front of box:



Exquisite polishing of inside sidewall of box:



Top view of box:



Where the box goes:




Box inserted:












Adding a Wisner pocket plate would relieve crowding a bit too ...
... Timney trigger, Lapour safety, CZ/B&C Kevlar stock, etc., etc. ...

On second thought, adding 0.100" thickness of steel to the inside front of the box, and beveling it up to flush and smooth with the feed ramp,
would seem to be the better plan here.
Just replace the rubber bumper I removed with a piece of steel.
I have plenty of bullets that will work through a 3.85"-long box. Re-sized .416 bullets.
Still have to single load the long-nosed .408 bullets anyway.

On third thought ... having 3.95" of box length is not a bad thing, only about .112" shorter than the MRC PH box.

Removing that tiny little lip of feed ramp is going to make no difference in action strength.
Removing about 0.1" of stock wood to fit an outside box front reinforcement may weaken walnut stock?
Weakening of aluminum bedding block in magazine well of CZ/B&C Kevlar stock by about 0.1" thinning?
I think the Kevlar has strength reserves that are untouchable.
Better consult a real gunsmith called "Slick" about this.

Hey RIP, in the interests of thread resurrection since I cant PM you.
A 408 shell necked up to 416 firing the 450gn hornady hpbt in a 30" barrel
with an OAL of 4.240" and Retumbo.
133gn 2760 ft/sec one shot
134 2830ft/sec average for 5 shots at this charge.
135 2835 one shot
136 2865 one shot
137 2921 one shot
Can you model QL to find pressures please.

Hi DJS,

My 2012 version of QuickLOAD was pretty good with Retumbo, my lot of Retumbo.

I can do that pressure estimation, but to make it worthwhile, you must tell me some more numbers.

I don't have that bullet to measure. How long is the "Hornady 416 Cal 450 GR BTHP Match" bullet?


http://www.hornady.com/store/4...l-.416-450-GR-Match/

I estimate it to be between 1.840" and and 1.879" long, depending on which image of it I am measuring.

Minimum diameter and length of the boat tail base are needed also, but I can guesstimate those (close enough) if I know the bullet length.

Also, what is your brass length and the gross water capacity of the fired case?
What make of brass?
I used Jamison brass, and my water capacity was 169.0 grains for the .408 Chey Tac, for once-fired brass filled to top, to a flat meniscus.
That is "gross water capacity" in grains.
Wikipedia says the .408 Chey Tac case capacity is 159 gr H20. Not mine.

Just pulling these three numbers out of my hat would not be as good as getting them out of yours,
for your .416/.408 CheyTac:

Bullet length in inches?
Brass case length in inches?
Brass case gross water capacity in grains?

450 grains at 2900+ fps will shake you up. I'm happy at with 450 grains at 2600-2650 fps. 500 arNyati

If I ever get the rifle Dave Viers at Snipetac was going to build me a 416 on 585 case, it would have been interesting to see performance differences. RIP what did you finally settle on as far as powder and velocity. Did you ever shoot it long range?

quote:

Originally posted by LR3:
... RIP what did you finally settle on as far as powder and velocity. Did you ever shoot it long range?

LR3,
My initial outing with the 26"-barreled, sporting-weight .408 Chey Tac gave me the load right off the bat:

.408/370-grain GSC HV
4.150" C.Oa.L.
Jamison brass 3.030" trimmed
GM215M primer
H1000 charge of 139.7 grains
5-shot chrono average at 5 yards = 2853 fps

Three of the 5 shots went into one hole at 100 yards, and I blame myself for the other two being just a wee bit off, pulled to the right by my developing flinch:
3 shots: 0.277"
4 shots: 0.648"
5 shots: 1.575"

ES was 20 fps, Sd was 8 fps for 5 shots:
2864, 2844, 2860, 2851, 2846 fps

Amazingly, my QuickLOAD simulation for that load gave exactly the same velocity as my chrono average: 2853 fps.
And the pressure was estimated to be 54,928 PSI for a mildly compressed load.

I quit right there.
That will do for any LR shooting if I ever get to a 1000-yard range. I am ready.

Meanwhile, I have been preoccupied with lower-recoiling sporters, including the 10.4 Spiridon Moor:

Lo and behold the 10.4 Spiridon Moor

This is a .408/.338 Lapua Magnum, and the rifle weighs exactly the same as the MRC PH .408 Chey Tac.
So that ought to cure my flinch.
From the other thread, linked above:

The dry rifle weight (minus scope and rings and unloaded of ammo) is 10 pounds and 10 ounces, 10.625 lbs.

This 10.4 Spiridon Moor will be comfortable to shoot compared to the ".408 Chey-Tac Sporter" that also has a dry weight of 10.625 lbs. (What a coincidence!)


.408 Chey Tac: Cross-bolted Walnut stock (fully bedded with allthread grip rod and pillars) plus MRC M1999 PH action and Lilja fluted, 26" barrel, No. 7 Sporter Contour (!!!), with 1.350" shank diameter:



10.4 Spiridon Moor: McMillan Magnum-fill stock (fully bedded with steel pillars and allthread crossbolts) plus BRNO ZKK 602 action and McGowen nonfluted, 25" No. 6 "Light" (!!!) Target Contour barrel with 1.200" shank diameter:



Same rings used on both rifles.
Any difference in rifle weight depends on the scope used.
The MRC requires a longer scope tube to bridge the longer ring spacing.
The Zeiss weighs 2 ounces more than the Leupold.

12.000 pounds for the scoped .408 Chey-Tac.
11.875 pounds for the scoped 10.4 Spiridon Moor.
I really ought to get a muzzle brake for that .408 Chey Tac,
and a weight lifting program for me.

I might want to try those Hornady .416/450-grain Match bullets by sizing them down to .408.
Just for kicks in the .408 Chey Tac.

DJS,
If you want the pressure estimate from my 2012 version of QuickLOAD:

Bullet length in inches?
Brass case length in inches?
Brass case gross water capacity in grains?

Nice build RIP!congrats ! I've been thinking about a .408 CT. I have a McMillan .50 BMG action on a Tac50 stock with a spare bolt with the .505 Gibbs bolt face. Think I'll get a barrel and brake and chamber it in .408CT. I'm interested to see what the .408 CT can do at real long range.

Thanks RIP. Here are the magic numbers.
Bertram brass
Case capacity 169gn av H2O
Empty cases av 361gn
Case length 3.030"
Bullet length 1.900"
Boat tail length 0.325"
Boat tail min dia 0.340"
Bullet bearing surface 0.600"
Chamber has 0.125" freebore.
Loaded round OAL 4.220"
Cheers

0.040" jump to lands.
Lilja barrel 30" long.
8 groove 1:12" twist.

quote:

Originally posted by Robgunbuilder:
Nice build RIP!congrats ! I've been thinking about a .408 CT. I have a McMillan .50 BMG action on a Tac50 stock with a spare bolt with the .505 Gibbs bolt face. Think I'll get a barrel and brake and chamber it in .408CT. I'm interested to see what the .408 CT can do at real long range.

If you push the Chey Tec I would expect that it would do 3150fps with the 370grain GSC.

Thanks RIP. Hope you get to try it at 1000yds plus.

For DJS:

Is it a typical bottlenecked cartridge with Weighting Factor (i.e., WTF factor!) of 0.50
or
is it an "over-bore" cartridge with WTF of 0.33?

I am not sure, so I did it with both WTF's:





Now I recall that my .408 Chey Tac Retumbo loads have given
greater velocity than QuickLOAD predicted.
Quite a bit more.
Example:
.408/370-gr GSC HV with 142.0 grains of Retumbo
QL predicted: 2797 fps at 47,852 PSI
Chronographed: 2899 fps average for 5 shots.
However,
H1000 was spot on for predicted and chrono'ed velocity.
I used a 0.50 WTF for both powders there.

So consider you might be getting higher velocities/pressures with your lot of Retumbo, like I did.

Here are the two WTF values for propellant tables, limited to 63,817 PSI (4400 bar) and 105% volumetric (mildly compressed) loads:

0.50 WTF:



0.33 WTF:



You get higher velocities and lower pressures with the 0.33 WTF.

In my .408 Chey Tac I would have to go with the 0.50 WTF and H1000 as being closer to reality with the 370-grain GSC HV.

Now, how does the .416/.408 with 450-grain Hornady do? Is it closer to .50 WTF or .33 WTF?

All I can say is that if you are getting close to 2900 fps with your lot of Retumbo,
That might be fast enough.
Find an accurate load in the 2850 to 2900 fps range and watch for pressure signs.

If slower gives better accuracy, well, that is better.
2800 to 2850 fps and one-hole three-shot groups at 100 yards would be worthy of trying for 10-shot groups at 1000 yards.
Of course, if 2900 fps is most accurate and you, your rifle, and your brass do not complain:

At 2900 fps, your pressures might be in the 55,000 to 65,000 PSI range.
Best I can guesstimate.

Powder lots vary.
Your mileage may vary, etc., blah, blah, etc.
Wish I had pressure testing equipment: WTF!

OK, no more WTF confusion, pardon moi.
WTF is 0.50 for this "typical bottlenecked" cartridge, the .416/.408 Chey Tac wildcat.

Also, I decided to use the same bore area as Quickload defaults to for the .416 Barrett (0.133889 sq.in.),
not the .416 Rigby default (0.134246 sq. in.) that I used above.
Barrel is a wee bit tighter, I cannot actually calculate for every barrel make.
But the .416 Barrett does use a 1:12" twist. like DJS.







So this says that 142.6 grains of Retumbo is a 105 % volumetric load (mildly compressed)
and allowing for lot burn rate variations,
+/- 100 fps and +/- 12,000 psi would not be unheard of.
So:
The 142.6 grains of Retumbo Load:

2660 fps at 46,677 PSI: 10% slower burn rate
2806 fps at 59,088 PSI: Average burn rate
2900 fps at 73,827 PSI: 10% faster burn rate

Interpolate at will.

The 134.0 grain charge of Retumbo, DJS got 2840 fps by chrono, looks like this according to QuickLOAD:

2489 fps at 38,177 PSI: 10% slower burn rate
2652 fps at 47,924 PSI: Average burn rate
2756 fps at 59,732 PSI: 10% faster burn rate

I have seen this in my .408 Chey Tac: Retumbo gave 102 fps faster across the chronograph than QL predicted.
But that surely means the pressure for that load was higher than predicted too.

And furthermore ...

The Hornady manual has some .416 Barrett load data for this 450-grain bullet.

It is doing well to get 3000 fps with a 32" barrel.
They claim 2950 fps with 163.5 grains of Retumbo max manual load for Retumbo.
They claim 3050 fps with 184.2 grains of US 869, ball powder, max velocity manual load of all powders shown.

QuickLOAD defaults to 58,015 PSI (4000 bar) for the .416 Barrett.
That is 9.1 % lower pressure than the 4400 bar I allowed for the wildcat walking the ragged edge.

QuickLOAD says the case capacity default for the .416 Barrett is 228.0 grains of water, overflow/gross.

If the .416/.408 Chey Tac is 169.0 grains of water, then the ratio is:

228/169 = 1.349

I.e., the .416 Barrett has a 35 % greater case capacity than the .416/.408 Chey Tac.

By "Bore Law & Case Rule of Thumb" the .416 Barrett ought to get velocity of (1/4) x (35 %) or 8.75 % greater than the .416/.408 Chey Tac.
This assumes a comfortable pressure of 58,015 PSI for both.

Being generous, say the .416 Barrett gets 3000 fps with that 450-grainer at 58Kpsi with whatever powder lot works with no problems.

V = 3000/1.0875 = 2759 fps

Then the .416/.408 Chey Tac ought to get about 2759 fps with same 450-grain bullet at about 58K PSI,
with whatever powder lot works with no problems.

That is another way to look at it.

BTW, DJS, thanks for the bullet idea.
If I size down those .416/450-gr Hornady bullets to .408 for use in my Chey Tac ...
I expect the bullet to lengthen from 1.900" to 1.920".

In the .408, with a 450-grain bullet, Retumbo gives 40 fps faster MV than H1000 at max pressure of 63,817 PSI (4400 bar), according to QL.

But since my H1000 lot was exactly right with QL last time, and Retumbo gave 102 fps faster than predicted, if that carries on:

I expect 2689 fps MV with 135.8 grains of H1000 in a 26" barrel, probably at 63,817 PSI (4400 bar).

I expect 2729 + 102 fps = 2831 fps with 142.0 grains of Retumbo in a 26" barrel, but pressures might be closer to 78K PSI,
so I think I will start low, hoping for an accurate load at 2600 to 2650 fps,
in my smaller-bored, shorter-barreled, probably-lighter-weight rifle than you are shooting.
Mine is a "sporter" after all, for sport, and for kicks, as tolerated.

Thanks for that RIP.
Tried H1000 today. With virgin brass worked up from 125gn to 130gn for 2770fps.
Picked up 20 fps per grain till 129gn got to 2760 fps. Only another 10 fps
for the extra grain in the 130gn load.
Will try the fire formed brass from 128gn of H1000 to 133gm later.
Very similar points of impact to Retumbo loads.
Be interesting to see how it compare to Retumbo.
The Retumbo data seems to suggest that our lot is 10% faster.