7.5 FK Brno cartridge revisited


In your add for the 7.5 mmFK Brno cartridges (good price!), one comment puzzles me. You say “this caliber is not a necked down version of any other caliber.” How did you determine that?

I ask only because I have two prototypes of the 7.5 FK, formed and loaded in the Czech Republic using Starline 10 mm Magnum cases. I also have a properly headstamped, production 7.5 FK cartridge.

The prototypes I have arbitrarily designated “Prototype 1” and “Prototype 2” which are not designations assigned by the company that made them, rather simply for clarity here. Prototype 1 has a pretty normal-looking GM HP Bullet, with six splits at the mouth; Prototype 2 has a very pointed brass-color bullet with a small diameter meplat. The serial production round has a copper semi-pointed bullet, the only load I have seen to date and the same one in your ad.

Following are case measurements of the three:

Prototype 1 :

Head (rim): 1.64 mm (0.419")
Base, just above extractor-groove bevel: 10.69 mm (0.421")
Case just below the beginning of shoulder: 10.66mm (0.4195")

Prototype 2 (note, measurements are in the same order as for Prototype 1, as will be the measurements for the factory serial-production cartridge:

Head (rim): 10.66 mm (0.420")
Base: 10.69 mm (0.421")
Case below shoulder: 10.68 mm (0.4205")

It seems to me, since the factory cartridge is well within the specification spread for both of the prototypes, that the parent case for the 7.5 FK round is the 10 mm Magnum cartridge case. Brno made have made some internal modifications to the web for added strength, but the external measurements, in my mind, show the Brno cartridge to be a necked-down 10 mm Magnum.

I base my belief here on the fact that many cartridges, such as 9 mm Para, have varying internal measurements, despending on the maker, to accomodate higher pressures than envisioned with the original design of the cartridge, but we still do acknowledge the origin of the cases, and not give the cartridges a different name.

Just wondered on your comment in the ad. I am certainly not any kind of expert on case design, or metallurgy involved in redesigning a cartridge case (ie: necking down,composition of the brass material, etc.), but I feel the parentage of the 7.5 FK case is obvious.

Edited for removal of typos only.

John Moss

1 Like

Per the importer’s web-site

O.K. That’s understandable. Advertising Hype on their part.

John M.

Yes I would assume your correct on the Hype, as the Pistol has a very high retail of over $9,000.00 in the USA. I spoke with the importer and they plan on a poly model for $2,000.00 soon?
I might consider it at ? $500.00?
Please see below as copied from importer web-site, as I don’t wish to vary from the maker or importer’s web-site:
" 7.5 FK BNRO Ammo is a completely new proprietary cartridge caliber. The case is 27 mm long, the total length of the cartridge is 35 mm, and the head diameter of the case is 10,8 mm. This caliber is not a necked down version of any other caliber. The case is designed to withstand higher pressures than is usually used in pistol calibers.
Our FK BRNO Ammo will not fit in any magazine, nor will it function in any current production model pistol.
Muzzle velocity: 610 m/s (2000 fps) Velocity at 100 m (110 yds): 465 m/s (1525 fps) Muzzle energy: 1200 J (880 ft/lbs) Energy at 100 m (110yds): 700 J (520 ft/lbs) Bullets weights: 6.17g (95 gr) Hollow Point All Copper
The History:
The 7.5 FK BRNO Ammowas initially developed to fulfill a requirement for a new cartridge, by a private customer in 2010. That requirement was addressing the shortfall of hand held and shorter/smaller firearms that were used in their relevant theater of action, and bridged the gap between standard/popular pistol caliber and rifle calibers.

This requirement was subsequently canceled; however, the initial tests showed a very high accuracy potential which prompted the developers to continue with the Cartridge as a target and long range pistol competition round.

The main parameters were as follows:
Cartridge must be short and small enough to be used comfortably in magazine fed / in grip magazine, size of firearm.

Ballistics must be designed for a max barrel length of 150 mm, and projectile must be supersonic at 150 meters. Recoil force should not exceed power factor 230, [ .45 ACP +P ]

Accuracy/ precision at 100 meters must be less than 100×100 mm rectangle.

Projectile permanent wound cavity in Ballistic gel at 150 meters must be minimum 35 mm diameter and 300 mm in length." UN QOUTE

Any questions on my web-site pages www.ammo-one.com in the future, please feel free to e-mail me directly at info@ammo-one.com or hurdcall@yahoo.com or phone me at 207-648-4087. I am always wanting to correct any errors.
However I plan on a new e-mail address in near future due to issue with my provider…
Thank you
edited for my poor grammar and spelling only :-)

Dave - thank you for that information. I see several things I would consider inaccurate in their description, including the fact that the case is totally unique. They say the “requirement was subsequently canceled, … to continue with the cartridge as a target and long range pistol bullet” yet the only factory load so far seems to be, as a cavernous hollow point, aimed at hunting. I would not describe it as the type of projectiles found in match ammunition for any type of competition. To nit pick, just for the pure fun of it, they speak of “precision at 100 meters must be less than 100x100 mm rectangle.” When I went to school, 100 x 100 mm would be a square, not a rectangle. :-)

The information, if for the most part true (?) is interesting however, and adds much to the file on this cartridge. Thanks for going to the trouble to post it, and I really mean that.

I totally agree, by the way, with your initial comments on price of the pistol. I might be more generous, and say that there $9,500 dollar pistol is, due to finish, small quantity, etc., and honest 2,000.00 handgun. But 10,000.00 (actually more than that in states like mine with near 10% sales tax and high registration fees)? Insanity in my view.

Again, thanks for the info.