dvc4you Posted June 1, 2014 Share Posted June 1, 2014 Soooo the only powder I could get to run my new open blaster is IMR SR 4756. I am using MG 124 g out of Shuemann Tribrid II with winchester SR primers and armscor 38 supercomp brass. The following are the results I got from my brand new Prochrono Digital: 8.2g 1272 fps 158PF 8.4g 1322 fps 164PF 8.6g 1480 fps 183PF Does it make sense such a spike? All were chonoed on the same session several times using 5 bullets at a time....Powder is all from the same lot. Clear skies and 78 F. Link to comment Share on other sites More sharing options...
Steve RA Posted June 1, 2014 Share Posted June 1, 2014 I used to use 4756 in 9 Major and .38 Super and never had any spreads that large ( with that small a change in powder weight). You might try using a different chrono just to check yours since you mentioned it being new. Link to comment Share on other sites More sharing options...
peterthefish Posted June 1, 2014 Share Posted June 1, 2014 I've heard that 4756 has a reputation for spiking near max fill / load, which may why Hogdgons has neutered their published load data for this powder. Link to comment Share on other sites More sharing options...
lee blackman Posted June 1, 2014 Share Posted June 1, 2014 Maybe the powder charge compressed at 8.6gr, that would cause it. Link to comment Share on other sites More sharing options...
Justsomeguy Posted June 1, 2014 Share Posted June 1, 2014 Or maybe the chrono's sensors come into direct sunlight as the day wore on. Since a chronograph generally reads the bullet's shadow to give the speed, different sunlight conditions can produce some weird readings. That is why on sunny days you should always place something over the skyscreens to shade the sensors. Link to comment Share on other sites More sharing options...
Hi-Power Jack Posted June 1, 2014 Share Posted June 1, 2014 How did the primers look? Link to comment Share on other sites More sharing options...
dvc4you Posted June 1, 2014 Author Share Posted June 1, 2014 The primers looked fine. All of those are compressed charges Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
Hi-Power Jack Posted June 1, 2014 Share Posted June 1, 2014 The primers looked fine. If primers look fine, I'd chrono 20 of the 8.4 and 8.5, and see how that looks. IMHO, five shots thru a chrono is a good start, but not sufficiently large to be accurate - 20 of each should tell you a lot more - and I'd shade the chrono. Link to comment Share on other sites More sharing options...
dvc4you Posted June 5, 2014 Author Share Posted June 5, 2014 I will go back to the range this afternoon to re-chrono my loads of SR-4756 of 8.6gr and 8.5gr. It is a sunny day, almost no clouds, what do you suggest? Induce some shade on the sensors, paint the bullets black with a marker? Link to comment Share on other sites More sharing options...
Hi-Power Jack Posted June 5, 2014 Share Posted June 5, 2014 Induce some shade on the sensors, paint the bullets black with a marker? I haven't tried painting the bullets, but its not a bad idea. But, yes, shade the sensors. Can't wait to see the results:)) Link to comment Share on other sites More sharing options...
Steve RA Posted June 5, 2014 Share Posted June 5, 2014 Put a target - USPSA - on top of the sunshades with the white side down. Link to comment Share on other sites More sharing options...
dvc4you Posted June 6, 2014 Author Share Posted June 6, 2014 (edited) So I was lucky enough that the sky was overcast. Results are more consistent. Using MG 124 g out of Shuemann Tribrid II with winchester SR primers and armscor 38 supercomp brass. OAL 1.235. IMR SR-4756. 20 rounds through Prochrono Digital: 8.5g AVG 1306 HI 1333 STD 12 161.9 PF 8.6g AVG 1323 HI 1340 STD 14 164.1 PF Primers show no sign of pressure. Next step 8.8gr and 9.0gr Edited June 6, 2014 by dvc4you Link to comment Share on other sites More sharing options...
Hi-Power Jack Posted June 6, 2014 Share Posted June 6, 2014 Sounds like you're on the right track. The PF 186 for 8.6 gr didn't sound right - PF 164 makes much more sense. Link to comment Share on other sites More sharing options...
Justsomeguy Posted June 7, 2014 Share Posted June 7, 2014 Yes... cloudy days are much better for chrono accuracy, but can be done on sunny days when you properly shade the sensors. If you use a camera tripod to mount the chrono, you can also use the tripod's tilt feature to lay the chrono over 90degrees away from the sun and shoot through it like that. I always get good readings that way when the sun is directly overhead and I don't want to mess with taping something to the skyscreens which generally has to be larger than even a USPSA target is to properly shade both sensors completely. Link to comment Share on other sites More sharing options...
Hi-Power Jack Posted June 7, 2014 Share Posted June 7, 2014 ...lay the chrono over 90 degrees away from the sun... Great idea!!! Never would have thought of it ... That's the kind of thinking I love here at BE. Thanks for the tip. :bow: Link to comment Share on other sites More sharing options...
dvc4you Posted June 9, 2014 Author Share Posted June 9, 2014 Yes... cloudy days are much better for chrono accuracy, but can be done on sunny days when you properly shade the sensors. If you use a camera tripod to mount the chrono, you can also use the tripod's tilt feature to lay the chrono over 90degrees away from the sun and shoot through it like that. I always get good readings that way when the sun is directly overhead and I don't want to mess with taping something to the skyscreens which generally has to be larger than even a USPSA target is to properly shade both sensors completely. Thanks for the tip! I used the technique and it worked perfectly: 8.8gr avg 1350 hi 1375 lo 1322 PF 167 9.0gr avg 1365 hi 1384 lo 1346 PF 169 Link to comment Share on other sites More sharing options...
Neomet Posted June 9, 2014 Share Posted June 9, 2014 This is why I made my uber-high tech enclosed chrono. I took the box I got my RF100 in and cut a couple holes in what became the top that were slightly smaller than my sun screens directly in line with the chrono sensors. I racer taped the sun screens over the holes. Cut one hole in the front to insert the chrono and read the display and another hole above it front and back for the bullets to pass through. Gives me very reliable readings. It is a little clunky to carry and I need to set it on a table but with the AZ sun it is definitely worthwhile. Link to comment Share on other sites More sharing options...
GARD72977 Posted June 9, 2014 Share Posted June 9, 2014 We were using my crony to get velocity for a friends reloads. I had a spike of about 130 fps for a change of .2gr of powder. I thought he had made a mistake since he has not been reloading very long. I let another friend use my crony and he found that if you favored the right side you would get 100 fps difference than the left. He was shooting a paper target (with a air gun) and happened to change to another target without moving the gun. I would have never found this because I usually try to line up the middle of the crony with the target. Link to comment Share on other sites More sharing options...
RH45 Posted June 16, 2014 Share Posted June 16, 2014 Yes... cloudy days are much better for chrono accuracy, but can be done on sunny days when you properly shade the sensors. If you use a camera tripod to mount the chrono, you can also use the tripod's tilt feature to lay the chrono over 90degrees away from the sun and shoot through it like that. I always get good readings that way when the sun is directly overhead and I don't want to mess with taping something to the skyscreens which generally has to be larger than even a USPSA target is to properly shade both sensors completely. Thanks for the tip! I used the technique and it worked perfectly: 8.8gr avg 1350 hi 1375 lo 1322 PF 167 9.0gr avg 1365 hi 1384 lo 1346 PF 169 I hope you bought a 12# can. Every time I change lot numbers, I have to re-work my load. Link to comment Share on other sites More sharing options...
RH45 Posted June 16, 2014 Share Posted June 16, 2014 I used to use 4756 in 9 Major and .38 Super and never had any spreads that large ( with that small a change in powder weight). You might try using a different chrono just to check yours since you mentioned it being new. Steve Eventhough I can make major with 4756 in .38 Supercomp, I can't come close with either of my 9mms, and the case was FULL. Link to comment Share on other sites More sharing options...
Steve RA Posted June 17, 2014 Share Posted June 17, 2014 I was using 130 grain WW .38 super bullets and a case full of powder with the cartridges loaded as far out as the mags would allow. Went 1442 at a couple of matches, I always just let the brass stay where it fell. Was a totally stock 17L, one of the first in the country and never had a problem with it. Link to comment Share on other sites More sharing options...
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