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Brno ZKK 600 update

14 Dec 2015
@ 03:33 am (GMT)

Mike Dewey

Been a lot of load development since my last update. I check the stores often when in town and have a fair selection of powder now: IMR 3031, 4895, 4064 plus H4350 and Win 748 for the 9.3x62. Short barrel (20”) so have to push things to get any speed. With 286 gr Nosler Partitions can reach or exceed 2400 fps with any of them without pressure signs except for the Win 748 which showed tight bolt randomly at all loadings from medium to high.
The original stock is European style with a short, slender Schnabel fore end and what I’ve heard called a “pig back” butt stock. Quite a bit of drop at heel, I presume so as to transfer some of the recoil to an upward barrel movement with less rearward push as well as working with low iron sights. Trouble is that at the upper velocities I had difficulty getting consistency, often getting 4 to 6 inches of vertical stringing. So I backed off and found consistency and good accuracy at 2260 fps with IMR 4320 although 4895 and 4064 were fine as well.
Decided to try a straighter recoiling stock and settled on Boyd’s since I like wood and steel. Heard of problems there but did finally get to order what I wanted. Thought about ordering checkering or stippling but decided to go plain and add grip later if needed. Nice that Boyd’s offered a fit for the Brno; chose the Platinum style, upgraded to standard walnut instead of laminate, 14” LOP, KICK EEZ recoil pad, black grip cap and unfinished (more expensive than finished!). After a lengthy visit at Canada Customs it arrived. Took a little sanding to get the barrel to fit right and opened up the action screw holes to fit the pillars (spacers) I’d made by slitting aluminum tubing, but no more than pleasant fiddling. Sanded the stock with progressively finer sandpaper, raised the grain several times taking off the roughness with steel wool or 3-M cloth, then finished with Minwax Antique Oil Finish. The wood had prominent dark ring stripes so I went quite dark on the stain to even it out with a little red stain added. Turned out ok and the recoil is now much more straight back with way less barrel lift.
Boyd’s puts hidden screws behind the recoil lug and magazine cutout much like cross bolts but I glass bedded the front of the receiver, recoil lug, pillars, tang and an inch of the barrel. I’ll need to do more load development since recoil should be more manageable now.
For bedding, I like a stiffer glass mix and I’ve found that the clay dams work better for me if I form them with a strip of masking tape (painters tape) on top of the slightly proud clay surface. The tape doesn’t stick to the metal but takes the shape when the action is pushed into place. Then using the edge of the tape as a guide I can cut a smooth, straight line with a sharp blade. Works pretty good. The other thing I’ve found is that Teflon plumbers thread tape works well to mask the action screws or guides (you try finding 6mm x .75 machine screws). It seals the threads and keeps the glass from sticking. Sometimes it’s possible to build up the thickness to help keep glass out of pillars.
Hoping to find some of the new IMR 4166 or 4451 to try for its temperature stability and copper fouling reduction. Quite a difference in temperature from spring/summer load development and end of hunting season! Barrel likes copper for accuracy but enough is enough.
Will report further on the Brno and on my Rem 700 7mm Rem Mag next spring. Got it back in August after getting re-barreled and tuned up. Would like to get a Sightron FFP 6 – 24 x 50 scope. Took a small mule deer with a long-range load at 35 yds (160 gr Accubond @ 3080 fps… devastating!).

I enjoy your work, Mike


14 Dec 2015
@ 08:54 pm (GMT)

Nathan Foster

Re: Brno ZKK 600 update
Thanks Mike, sounds like you have been very busy.


We are a small, family run business, based out of Taranaki, New Zealand, who specialize in cartridge research and testing, and rifle accurizing.