Received my new 2010 production Oehler 35P about 2 weeks ago. I also have an Oehler 33 and PACT PC2 chronographs which I've run in tandem the past several years. I wanted to run all three chronographs concurrently by mounting all 7 skyscreens on a single rail. I was having difficulty converting my original skyscreen rail so I decided to purchase $35.00 worth of aluminum material from the local Steel supply retailer and welded together a new skyscreen rail as illustrated in the following photos:
5' 4" of 2"x2"x1/8" angle aluminum
6' 8" of 5/8" solid aluminum rod
4 aluminum braces cut out of 1/8" scrap angle aluminum and two end protectors from 1/8" thick aluminum plate obtained from my neighbor's bone-yard.
The 2"x2"x1/8" angle aluminum is drilled and tapped for mounting to a standard camera tripod. After welding, the rail was spray painted with dull red primer paint to prevent glints of sun reflection from a shiny rail to the undersides of the bullets while passing over the skyscreens. I then carefully measured for separation distance and mounted the 7 skyscreen rails.
The Oehler 35P primary channel skyscreen spacing is 6'. Proof channel @ 3' spacing. The Oehler 33 spacing is also 6'. All Oehler skyscreens are mounted on the 5/8" solid aluminum rod. The PACT PC2 skyscreen spacing is 4' 8". The PACT skyscreens mount on a flat surface, so they're mounted on two of the aluminum angle braces. The two end plates protect the skyscreens from the lumps and bumps associated with transportation and also serve to protect the skyscreens from muzzle blast.
Here are the data from the first string of 8 shots fired:
Oehler 35P1 1212 1222 1210 1217 1186 1177 1210 1204
Oehler 33... 1210 1221 1211 1220 1188 1179 1212 1206
PACT PC2... 1213 1222 1208 1216 1183 1175 1208 1202
Oehler 35P2 1216 1226 1212 1220 1188 1179 1211 1203
The 4th row of data are the 35P Proof data collected over the 3' skyscreen spacing. However I was tweaking the separation distance of the middle 'Proof' skyscreen during the first 5 shots to best match the 6'-spaced primary skyscreen data. The last three shots were taken with no additional changes to the Proof channel skyscreen position, and the maximum difference between the primary and proof channel data for these last three shots was 2fps.
The first 4 shots were from a semi-auto rifle chambered for 9mm pistol ammo. The last 4 shots were 22 long rifle from a bolt action rifle.
With this setup, I'll now obtain four velocity data for each shot fired. This will generate relatively high confidence in my MVs and down-range velocities. It should now be relatively easy to ID which unit throws a bad number when that happens. And that does happen every now and then with any chronograph.