Another experimental cartridge - 5.7 Czech

[GunTech]

Looking for input again.

I've been playing with iterations of the 7.62x45 Czech case, and here is another one that looks to have promise, but I'm interested in input.

This case started out as the desire to add more velocity to the CZ-527 varmint rifle. It developed into a cartridge that could also fit and function in a suitably modified AR.

The requirements were for an operating pressure suitable for the AR and CZ-527, set at 4050 barr, equal to 5.56x45 NATO. Max over all length was set at 2.260 inches. The 7.62x45 has the same casehead size as the 7.62x39mm Russian, so that bolts are available for the AR, and the CZ-527 is made in the 7.62x39 so the only conversion required would be a barrel change.

The resulting cartridge I have named the 5.7 Cz, in honor of it's parentage. It is simply the 7.62x45 necked down to 0.224.

5.7 compared to 223

I ran the numbers through QuickLoad. I selected a 24 inch barrel and the Sierra 52gn MK for comparison. Here are the predicted velocities for 223, 5.7 and 22-250:

223 - 3289 fps
5.7 - 3566 fps
22-250 - 3774

Any thoughts or interest?

 

[GunTech]

Cartridge          : 5.7 x 45 Czech
Bullet             : .224, 52, Sierra HPBT MatchK 1410
Cartridge O.A.L. L6: 2.260 inch or 57.40 mm
Barrel Length      : 24.0 inch or 610.0 mm

Predicted Data for Indicated Charges of the Following Powders.

Matching Maximum Pressure: 51397 psi, or 354 MPa

or a maximum loading ratio or filling of 100 %

These calculations refer to your specified settings in QuickLOAD 'Cartridge Dimensions' window.
C A U T I O N : any load listed can result in a powder charge that falls below minimum suggested
loads or exceeds maximum suggested loads as presented in current handloading manuals. Understand
that all of the listed powders can be unsuitable for the given combination of cartridge, bullet
and gun. Actual load order can vary, depending upon lot-to-lot powder and component variations.
USE ONLY FOR COMPARISON !

109 loads produced a Loading Ratio below user-defined minimum of 90%. These powders have been skipped.

Powder type          Filling/Loading Ratio  Charge    Charge   Vel. Prop.Burnt P max  P muzz  B_Time
                                      %     Grains    Gramm   fps     %       psi     psi    ms
---------------------------------  -----------------------------------------------------------------
IMR 4895                            94.8     34.0     2.20    3566    99.0    51398    9315   0.999  ! Near Maximum !
IMR 3031                            93.6     32.4     2.10    3562   100.0    51398    8930   1.019  ! Near Maximum !
Ramshot BigGame                     96.2     36.8     2.39    3550    97.5    51398    9587   1.019  ! Near Maximum !
Winchester 760                      98.0     38.4     2.49    3545    93.0    51398    9833   1.020  ! Near Maximum !
Vihtavuori N550                    100.0     37.9     2.45    3539    95.9    50998    9812   1.032  ! Near Maximum !
Alliant Reloder-15                  93.5     34.7     2.25    3530    97.0    51398    9473   1.027  ! Near Maximum !
Accurate 2495                       93.4     32.7     2.12    3518   100.0    51398    8794   1.061  ! Near Maximum !
Hodgdon H414                        93.8     37.0     2.40    3518    93.7    51398    9635   1.030  ! Near Maximum !
IMR 4320                            95.5     34.8     2.25    3518    97.4    51398    9162   1.010  ! Near Maximum !
Accurate 2520                       90.8     34.7     2.25    3515    99.6    51398    9028   1.040  ! Near Maximum !
Accurate 4064                      100.0     34.6     2.24    3513    99.9    51179    9066   1.062  ! Near Maximum !
Hodgdon H4895                       95.9     34.4     2.23    3506    99.3    51398    8872   1.015  ! Near Maximum !
Hodgdon H380                        94.9     35.9     2.33    3501    95.6    51398    9383   1.034  ! Near Maximum !
Vihtavuori N540                     93.0     34.9     2.26    3486    99.8    51398    8817   1.030  ! Near Maximum !
Hodgdon VARGET                      95.7     34.3     2.22    3484    96.8    51398    9038   1.017  ! Near Maximum !
IMR 4064                            96.5     33.8     2.19    3483    97.0    51398    8966   1.021  ! Near Maximum !
Vihtavuori N135                     99.3     33.4     2.16    3482   100.0    51398    8314   1.032  ! Near Maximum !
Vihtavuori N140                     98.6     35.1     2.28    3459    98.5    51398    8685   1.026  ! Near Maximum !
IMR 4007 SSC                        96.1     36.1     2.34    3444    91.9    51398    9046   1.034  ! Near Maximum !
Hodgdon H4350                      100.0     36.9     2.39    3431    92.5    46118    9491   1.061
Vihtavuori N133                     92.4     31.3     2.03    3424   100.0    51398    7780   1.021  ! Near Maximum !
Ramshot Hunter                     100.0     38.3     2.48    3410    92.0    45539    9488   1.076
Vihtavuori N150                    100.0     35.0     2.27    3380    98.3    46992    8620   1.073
Accurate 2700                       97.0     37.1     2.40    3379    91.7    51398    8487   1.039  ! Near Maximum !
IMR 4350                           100.0     35.5     2.30    3331    90.0    42587    9107   1.103
Accurate 4350                      100.0     35.4     2.30    3256    91.8    38873    9122   1.176
IMR 4831                           100.0     35.5     2.30    3232    92.0    38656    8849   1.170
Alliant Reloder-19                 100.0     37.1     2.40    3227    85.0    39914    8829   1.142
Hodgdon Hybrid 100V                100.0     34.6     2.24    3192    93.5    37362    8518   1.173
IMR 7828 SSC                       100.0     38.1     2.47    3134    79.2    37317    8661   1.178
Hodgdon Supreme 780                100.0     39.3     2.55    3128    83.3    38370    8360   1.168
Hodgdon H4831 SC                   100.0     37.5     2.43    3125    80.4    38442    8231   1.164
Vihtavuori N560                    100.0     37.9     2.45    3101    77.9    35128    8734   1.209
Alliant Reloder-22                 100.0     37.5     2.43    3091    81.2    34486    8692   1.218
Accurate MAGPRO                    100.0     39.4     2.55    3035    74.8    33855    8466   1.241
Winchester WXR                     100.0     36.7     2.38    2994    78.8    31749    8313   1.259
Hodgdon H4831                      100.0     36.0     2.33    2985    77.3    33812    7740   1.228
Vihtavuori N160                    100.0     35.5     2.30    2980    79.6    34212    7536   1.225
Vihtavuori N165                    100.0     36.7     2.38    2959    81.4    32572    7684   1.252
IMR 7828                           100.0     36.0     2.33    2929    74.2    31153    7858   1.264
Ramshot Magnum (Big Boy)           100.0     39.7     2.57    2900    73.5    31277    7945   1.282
Alliant Reloder-25                 100.0     36.9     2.39    2888    79.4    28927    8102   1.306
Accurate 3100                      100.0     35.0     2.27    2803    80.7    26589    7523   1.365
Norma MRP 2                        100.0     37.1     2.40    2740    69.9    25613    7461   1.395
Hodgdon H1000                      100.0     36.7     2.38    2701    67.8    26892    6750   1.349
Vihtavuori N570                    100.0     39.1     2.53    2650    59.1    25082    6956   1.411
Hodgdon Retumbo                    100.0     37.3     2.41    2591    65.1    23459    6580   1.431
Vihtavuori N170                    100.0     36.7     2.38    2564    62.1    23629    6240   1.458
Vihtavuori 24N41                   100.0     39.5     2.56    2532    53.7    24885    5828   1.427
Hodgdon H870                       100.0     38.3     2.48    2418    54.5    20434    5856   1.541
Hodgdon 50BMG                      100.0     37.6     2.44    2349    46.6    20487    5178   1.540
Hodgdon US 869                     100.0     38.3     2.48    2306    49.4    19249    5081   1.588
Accurate 8700                      100.0     37.9     2.46    2165    45.5    17274    4396   1.664
Vihtavuori 20N29                   100.0     39.9     2.58    2164    44.6    17205    4563   1.669

 

[JesseL]

The only thing I'd point out is that using the same pressure as the 5.56 NATO, while going to a larger case head, bolt thrust is going to be way up.

I'm pretty sure a standard 7.62x39 AR bolt won't take it, and it's beyond the normal working pressure of the stronger-but-dimensionally-identical 6.5 Grendel bolt too.

It will probably be fine in a CZ-527, but I think it will cause problems in an AR.

 

[JesseL]

I'm also curious, are you spec'ing the chamber to allow necked down 7.62x45 brass to chamber without neck turning?

 

[GearHead_1]

The perfect solution..... for a problem that arguably doesn't exist? The niche appears to be narrow.

 

[JesseL]

The perfect solution..... for a problem that arguably doesn't exist?

The OP stated the problem - getting more velocity from a CZ 527 carbine. If he wants it enough to do the work of having reamers made, rebarreling a rifle, working up load data, forming brass, etc.; that's all the necessary proof that the need exists.

The world could probably live on five cartridges, but what kind of fun would that be?

 

[GearHead_1]

The OP stated the problem - getting more velocity from a CZ 527 carbine.

I did say arguably. The fact one desires to accomplish something doesn't mean there's a problem. I for one would like to run a little faster but the Olympic team isn't going to miss me.

If he wants it enough to do the work of having reamers made, rebarreling a rifle, working up load data, forming brass, etc.; that's all the necessary proof that the need exists.

The world could probably live on five cartridges, but what kind of fun would that be?

I didn't say I wouldn't own one. I like one off's. If one were offered to me at a reasonable price and I had the ability to reload the ammo, I would say thank you very much. I like the OP like to have things just because I can. I would not be so magnanimous, I would name it after me and to heck with CZ.

 

[GunTech]

Thanks JesseL.

IIRC, bolt thrust is a function of peak chamber pressure and internal case head diameter. In that case, the 5.7 would have exactly the same bot thrust as 6.5 Grendel since 5.56x45 NATO and Grendel have the same peak pressure - 4050 barr.

Unless that number has been changed.

 

[JesseL]

IIRC, bolt thrust is a function of peak chamber pressure and internal case head diameter.

Absolutely correct.

In that case, the 5.7 would have exactly the same bot thrust as 6.5 Grendel since 5.56x45 NATO and Grendel have the same peak pressure - 4050 barr.

From what I've read, the Grendel operates at 50,000psi or 3447 bar (some places list it as low as 45,000 psi).

 

[GunTech]

The number has in fact been lowered for Grendel. Looks like allowable peak pressure for Grendel is now 3600 bar, rather than 4050.

I have updated QL and QD with the latest numbers.

Using 3150 bar for max normal pressure, I still only get a 150 fps advantage if I load down to AR pressure levels rather than the 250 fps when loaded to the old 4050 bar levels.

I suspect the Grendel figure was lowered to make the cartridge more AR friendly as well.

 

[GunTech]

JesseL, right now I am working with unturned necks. With necked down brass, I am getting a loaded neck diameter of 0.255 vs 0.247 for some 223 rounds I have loaded into WW brass.

 

[GunTech]

JesseL, what about using a longer leade. Any thoughts?

 

[JesseL]

I'm not sure all the ramifications of a longer leade, but I am curious how this cartridge will perform with the heavyweight .224 bullets (70gr +), compared with .223/5.56. It seems that's where your increased case capacity should shine without needing to push the pressure too much.

 

[GunTech]

I actually thought about moving the shoulder back a couple to allow long bullets and still keep an OAL of 2.260. I've got some Berger 90gn VLDs that mike out at 2.400 when loaded into 223 cases. It does mean a more complicated case.

 

[SimpleIsGood229]

Moving the shoulder back, in my opinion, would be a smart move.

 

[GunTech]

I ran the number for the 70gn Berger VLD. 24 inch barrel.

5.7 = 3120 fps at 45,687 psi
223 = 2865 fps at 48,127 psi

 

[GunTech]

SimpleIsGood229

I moved the shoulder back 3mm, and changes the shoulder angle to 30 degrees (same as Grendel) to gain a little more capacity. The results looks good.

5.7x42mm should allow long bullets like the 70 and 80gn Bergers to fit into an AR magazine if desired.

With the 52gn SMK, 24 inch barrel

5.7x42 = 3430 fps
223 = 3289 fps

With 77gn SMK

5.7x42 = 2962 fps
223 = 2740 fps

However, the 77gn and the 80gn SMK loaded in the 5.7x42 will still fit into an AR mag (2.260 COAL)

 

[SimpleIsGood229]

If that would fit into an AR magazine with 80 Bergers, I think you could seriously be on to something!

 

[Kosh75287]

I've often wondered what this cartridge would do if necked down to 6mm or .257". It would almost HAVE to perform better than the 6x.223 or 6x .222 Mag, no?