Model: CB-625 MK4 Manufacturer: Combro. Contact E-mail: info@combro.co.uk Web Address: www.combro.co.uk Type: On-barrel optical chronograph. Cost: AUS $80.00, delivered from UK to Australia. Features: : Max velocity 2000fps : Min velocity 1-2 fps : Max power 50+ ft.lbs : Imperial/metric display : Service/ all spare parts available : Accuracy better than 1% : Computer interface by optional cable (free software) : LCD display : Compact design Assessment: After speaking with Robin from Combro, I purchased the chrony online and it arrived one week later. I was a liitle concerned by the cheap price, but actually found the cb-625 to be a very easy to use chrony, with accurate, repeatable performance. Initial setup was fairly simple, and the unit is narrow enough that it won't get hit by neighbouring barrels. Ausralian cannon are legally required not to exceed a set muzzle velocity, so foam penetration testing is not accurate enough for our needs. Would I go so far as to recommend this unit as a replacement for current foam penetration testing in other countries? Thats up to other clubs to decide.
I would like to use a set velocity over the foam test for several reasons: accuracy, less waste from foam targets, and would put the different shell sizes into perspective, ie... a BB traveling @ 165fps would not hit with the same force as a 1/4" berring traveling @ the same speed
I would also like to use velocity over the foam test. My club (the WWCC) USED to have a chart containing the chrony equivalent of the foam test for each caliber of shot, but it was dropped from the rules before I joined. Pity, too. I would prefer to know I'm 5 FPS under the limit than to know that my guns didn't blow through the foam.
Would one be using the same muzzle velocity for the different calibers? That would seem the most reasonable. And what of torpedoes? It would make sense to me to use the same there as well. Keep things as standard as possible across the board.
That's exactly what we do. One max velocity across the board, means smaller projectiles have less force than larger ones. Just like real life.
Sorry for reviving an old thread but I started experimenting with one of these chronoscopes today. I am very impressed. However, has anyone gotten accurate fps values as compared to the foam penetration testing? It will save me some time to not have to make my own charts
On my chronometer BBs penetrate the 2" foam above 195 ft/sec. Between 185 and 195 ft/sec they sometimes penetrate, and usually don't penetrate below about 185 ft/sec. Is this the kind of information you are looking for?
Yeowch. The Ausbg is limited to 165fps, max. We sometimes get hits that bleed a little, but at 195fps? A 1/4" bb at that velocity is gonna hurt like crazy...
Does the AusBG limit all round sizes to 165 fps or does the limit vary by size? How did they arrive at those speeds? Does the AusBG often test with a chrono or are they still usually using foam?
I believe that it's part of our legal requirements... I'm not too sure of the full technical reasoning, but it has something to do with our Federal firearms legislation. It's what is in our rules, so I stick with that. All rounds, regardless of size are limited to the same max muzzle velocity. It's actually 50 meters per second, but I put up the approx fps for the US guys, as it's what you're used to. There were some blocks of foam that had been used for testing in the workshop of the local club president, but they were old and covered in dust when I joined, many moons ago. We haven't used foam for at least ten years. Foam is subject to too many variables to be an acceptably accurate method. All our clubs, and many individuals have chronys now.
Darren, how well do .177" rounds penetrate the heavy 1/8" balsa at 165fps, at long range and at 4 feet or less? And have you ever had issues with old balsa getting too hard from built-up patches, paint, etc?
Ok, here's the odd bit about our hobby here: We can't use .177 bb's as they are considered firearms ammunition by our government. Go figure. The smallest shot we use is 3/16, and at all but very short ranges, its not very effective against Battleship armour. It is, however, effective against thinner-skinned cruisers and deadly against unarmoured transports. Basically it means you won't kill a Yamato with a Belfast, unless you get very, very lucky. Old balsa is rarely a problem, as most ships get reskinned once every year, some two or even three times! We battle hard here in the AusBG. There is the compensation for the smaller calibers of a greater rate of fire, with 3/16 getting a four second interval, 7/32 gets six seconds while 1/4 is a once per eight second deal.
