Ceska Zbrojovka Vzor 70
Welcome to the subgunner.com CZ 70 Project Page
CZ 70 disassembly document in .pdf form click HERE (77 KB)
CZ 50/70 owners manual in .pdf form click HERE (5.1 MB) (If you have a better manual please email it to me!)
January 2008 CZ 70 Project - History & Background
Long story short: Back in 2003 I saw a 7.65 mm (.32 AP) suppressor at Rock Creek Gun in Bessemer, Alabama on a Czech Scorpion submachine gun and was impressed with how quiet it was. Since there aren't any transferable Scorpions, or at least none I've ever seen, I started thinking about a 7.65mm pistol to serve as a suppressor platform. Obviously, the first gun to come to mind when thinking about 7.65mm is the long-time side arm of James Bond, the Walther PPK. However, back in 2003 the PPK was fairly hard to find and expensive. There were plenty of American made PPK/S's available but Smith & Wesson had not yet entered into a deal with Walther to produce the PPK in America so most PPK's were original German guns brought in before the 1968 import ban. I couldn't bring myself to buy the PPK/S because I've always thought it was the "bastard" version of 007's famous Walther. After looking for I while, I settled on another fairly rare gun the Sig P230. Most Sig P230's are chambered in .380ACP but Sig produced the gun in .32 for the European/Asian market. A few of the 7.65mm guns made it to America and I managed to get my hands on one. The original plan was to thread the factory barrel of the Sig and make an adapter to extend the barrel out past the end of the slide much like the Walther P-22 adapters that have become so popular. Due to some unforeseen circumstances the project got stalled at the machine shop and pretty much sat untouched until late 2007 when I "got my cart ahead of my horse" and bought a .32 suppressor without a gun to put it on. HERE IS WHERE THE TROUBLE STARTED..................
Most American suppressors are threaded 1/2" x 28 tpi, however, most 7.65mm barrels are not a half inch in diameter so the less common thread size of 7/16" is what you have to work with. Since deviation from standard thread sizes gets really expensive really fast because of the cost of custom taps and dies, there was no way to make an adapter threaded 7/16" and it not be "paper thin". It became clear the the only way to get a solid mount that would withstand the weight of the suppressor itself along with the sustained recoil of repeated semi-auto fire was to go with an extended barrel. Sounds simple enough, right? WRONG! Try finding a 7.65mm extended barrel for a Sig P230 or even a reasonably priced 7.65mm barrel blank for that matter. They don't exist! I looked for what seemed like weeks and finally came to the conclusion that I was going to have to change platforms or abandon the the project all together. Then one night while surfing the internet, I stumbled on Numrich Gun Parts Corporation's website. They didn't have anything for a Sig P230 but they did list several extended barrels for the Walther PP-PPK-PPK/S family. Since most 7.65mm pistols have a non lugged, frame mounted barrel, I began to wonder if the Numrich barrel might be machined to fit another pistol other than the PP series. Since I had already made a significant investment in the Sig, I didn't want to rush out and buy a Walther PPK, which by 2007 were more plentiful but still fairly pricey. Changing barrels is usually difficult when the barrel is made for the gun you are working on, but when you are trying to put a barrel made for one gun into another gun it really gets troublesome. I didn't want to take the factory barrel out of the Sig not knowing if the swap was even feasible so I started looking for an inexpensive pistol to experiment with. After almost buying the Hungarian FEG model 32 from Centerfire Systems, I stumbled across the Ceska Zbrojovka Vzor 70 more commonly known as the CZ 70. It seemed to have all the qualities I was looking for: the Numrich barrel at 4.3 inches would extend just over half an inch past the CZ's 3.6 inch slide, there were spare parts readily available in the United States, it was relatively inexpensive ($141 delivered with two mags from Century Arms), and it came from the same folks that made the Czech Scorpion that started this whole project in the first place.
I'll note right here that I never could have done this project by myself. I'm very lucky to have a friend/mentor who is a master machinist and gunsmith. He has taught me skills and techniques that would have taken me many years and many broken guns to acquire on my own. Without his knowledge and skill this project would not have been possible.
January 2008 CZ 70 Extended Barrel Swap
1.) The CZ barrel is pressed into the receiver frame and held in place with a roll pin. To remove the barrel you must drive the pin out with a punch, being careful not to bend it. It will be reused with the new barrel. Driving the pin out is not difficult once the gun is field stripped with the pistol laying on the workbench.
2.) The barrel can be driven out with a hammer. This is easier if you place the gun (muzzle up) in a rubber jawed vice. To minimize any damage to the original barrel, take a penny and drill a small hole through the center. Place a nail through the penny and place the penny over the muzzle end of the barrel with the nail sticking down into the barrel. The penny is soft and will prevent marring the end of the barrel while you are driving it out with the hammer. The nail acts as a guide and prevents the penny from jumping off the end of the muzzle while you are striking it. The penny will start bending after only a few strikes and it may take as many as three of them to get the barrel out of the frame. The whole set-up worked very well and the barrel came out with no major effort or marring. To prevent striking the end of the frame with the hammer we used a brass punch about the same size as the barrel diameter. One of us supported the frame in the vice and held the bottom of the punch on the penny while the other held the top of the punch and struck it with the hammer.
3.) The Numrich PP barrel has a smaller extractor slot than the factory CZ 70 barrel. The extractor slot in the new barrel must be opened up to the size of the original barrel. This could possibly be done with a Dremil® but it is much cleaner to use a mill.
4.) Since the outside diameter of the factory CZ barrel is ____ where it is pressed into the frame and the corresponding area on the Numrich PP barrel is _____, the new barrel must be turned down in a lathe. As seen in the photo above, the Numrich PP barrel also has a step up on the breach end that the CZ barrel does not have. This stepped up area is also turned down to the same profile as the area that is pressed into the frame.
5.) After turning the outside diameter of the Numrich barrel down to fit into the CZ70 frame, the barrel was threaded while still on centers to 7/16" x 32 tpi. Since threading the barrel 7/16" left almost no shoulder for the suppressor to square up on, we made a jam nut to hold the suppressor square to the threads. The suppressor has an outside diameter of 1" so we made the jam nut just shy of an inch. We also made a matching thread protector the same size as the jam nut. [I'll admit it looks too big when screwed on the end of the pistol and we will probably make smaller ones after we complete the project.]
6.) Once the Numrich barrel's outside diameter matches the factory CZ barrel, a barrel pin notch must be cut in the Numrich barrel. There are several ways to do this but we used a Dremil® with a cutoff wheel.
7.) The feed ramp angle of the Numrich barrel is much sharper than the angle of the CZ barrel. The new barrel must be ground/polished to match the profile of the CZ feed ramp or the pistol will not feed properly. You will also notice that the CZ barrel's feed angle is only cut to match the pistol's feed ramp while the replacement Numrich barrel has an angle cut all the way around the barrel. I suspect that the Numrich barrel is cut that way to reduce manufacturing costs, it does not seem to have any affect on the function of the CZ70 once installed. A Cratex® bullet shaped polishing tip was very useful in grinding and polishing the barrel. Its probably the perfect tool for correcting the feed angle while maintaining the bore's circumference.
8.) The new barrel is installed in reverse of the way the factory barrel is removed. Once again, the use of a penny (with a nail as a guide) will prevent barrel damage during the installation process. Since the feed angle of the new barrel is largely done by "hand and eye" we had to remove the new barrel once after the initial installation to make adjustments to the feed angle. The angle has to be fairly close to the factory angle when the barrel is installed but much of the final polishing can be done with the barrel in the frame. Take extra precautions to line the extractor cut in the barrel up with the corresponding cut in the frame before beginning to drive the barrel in. Obviously, its almost impossible to rotate the barrel once you have driven it very far into the frame.
March 2008 CZ 70 Extra Power Wolff® Magazine Springs
I went ahead and powder blasted the magazine finger rests to give them a nice matte finish and rebuilt them with the extra power magazine springs from Wolff. The spring has a leg that actually locks the floorplate to the mag body. They're a real booger to get off. The spring leg has to be pushed back into the mag body with a tiny flathead screwdriver or something similar before the floor plate will slide off.
March 2008 Strip and Refinish
We bead basted and parkerized the CZ this week. I'm very pleased with the new matte look. I powder blasted the grips to get rid of the factory high gloss finished and I think they really turned out nice. The grips really go well with the parkerized finish. This was our first experience with Palmetto's Manganese Phosphate and it produced a dark grey nearly black finish.
2008-2012 Heavy Recoil Spring
After initially not being pleased with the level of suppression I was getting due to gas/noise coming back through the ejection port as the case ejected, I changed to a heavier recoil spring. WOW! This made a huge difference in suppression. I used the heaviest Walther PP spring that Wolfe made. The heavier spring retarded the rearward motion of the slide by a fraction of a second but it was long enough to force most of the gas through the suppressor thereby reducing the sound made by the pistol. It still cycles 100% so naturally I'm looking for an even heavier spring with the idea that I'll try progressively heavier springs until I start to have cycle failures and then drop back to the last one that gives 100% cycling. Stay tuned for more on this as I continue to experiment.
I've been amazed how a blog that started out as a way for me to keep up with what we've done on this project has somehow been found by several curios surfers. I get at least one or two emails a month with questions. I'm going to try to re-write some of the blog when I get a chance to add some detail here and there. I was recently asked for some photos showing how we modified the PP barrel's throat to match the CZ's feed ramp angle. Since just a few photos can take forever to email, I decided to post them to YouTube. As far as a video goes, this one sucks and the guy narrating has the worst Southern accent I've ever heard, but there are a few decent photos of the project. The video is available in 720p HD once it starts by clicking on the resolution button at the bottom. I've embedded it below but you might want to turn off your speakers............