Chronograph Question

[6.5_sWv]

Those of you that use a chrono in your load development or just general shooting, do you tend to notice that your first shot speed is much lower than each of the following shots?

My first shot from a cold clean bore is always much slower than the next shot even if I wait several minutes between shot 1 and shot 2. Any ideas as to why this happens ?

To get a more accurate reading, would I be better off to not record the first shot then start recording speeds after that first shot?

 

[ShadeTree]

Just going off your own words, the key is "clean bore," not cold bore. A clean bore shot will always be slower, and in some rifles pretty significantly off in point of impact from the rest of the shots, other rifles not so much.

Everybody has their own methods and I'm not trying to tell you to do anything different than what you like to do, but I clean rifle bores when they could use a cleaning, but before they're all fouled up. Most rifles that maintenance level is somewhere between 40-60 rds, some can go substantially more, some less. My 22-250 I clean at about 25 rds.

 

[6.5_sWv]

Shade Tree, I typically clean my rifles after a day at the range. A typical shooting day is usually anywhere from 15 to 30 shots. I never thought about the first shot from the clean barrel being slower. Thanks for your input

 

[ShadeTree]

Yep, will always be slower. Perhaps not in a really good custom barrel, don't know never owned 1. But in general it's just a mechanical function of physics that the first shot will be slower. Your bore when clean has plenty of imperfections in it. The first shot puts a fine layer of copper that fills in those imperfections. Like drywall mud on screw holes.

 

[Nimrod84]

I think ShadeTree's answer is on the mark. Clean is slower from the extra friction / lack of carbon and copper plus any residual liquids left behind.

I generally see a slight increase in the reported velocity the longer I shoot. I tend to do a quick clean (dry patch, or slightly damp with Hop #9) every 30-50 rounds to minimize the affect of cleaning but keep the carbon at bay; and only do a deep cleaning after 100-150 rounds (Patch-Out, Wipe-Out, Ballistol, M-Pro Copper, etc.) with long soaks and repeated anointings of the bore. I do tend to use anti-copper powders like IMR 4451 and RL-16.

I record my first shot as I want to know what to expect when hunting. I'll generally use the data if I didn't clean before the outing, if I did a deep cleaning I usually need to run 3-10 rounds (depending on caliber) to a get to a steady velocity. Again, I'll keep the data but generally won't use it for determining drop, ES / SD, etc.

 

[jimbires]

if you're watching chrony velocity ES numbers , I would not include cold bore velocities .

that first cold bore shot is what we get when we are hunting though , so the cold bore shot should be considered on a hunting rifle . I think to much emphasis is placed on temperature stable powders , and single digit ES chrony numbers for the majority of hunters . I'll guess most hunters are probably hunting inside 300 yards. at this distance it's going to take a lot of ES or powder temp change to put you out of the kill area .

it's been a few years since I've done this , but now would be a good time to mention it , maybe some of you guys would be interested in doing it . this will show how well you, and your setup, can preform at your max hunting distance .

at the start of the shooting season I took a target and placed it at my longest shooting distance , for me it was 500 meters . I only put my first round of the day, from my favorite rifle with a good load , on that target .it's a no-excuse target . some shots were cold clean bore , others were cold fouled bore , it was always my first shot of the day . you could also make target #2 , and put shot 2 or 2 & 3 on it to see how your follow up shots would be . I wanted data so I took this target to the range every time , even if I was working at 100 with a different rifle . you can date your holes , I didn't , to watch progress . it could be an eye opener by midseason . on the rifle I did this with I learned a little about cleaning it . I never do a heavy duty deep cleaning with the foam bore cleaners and other similar products unless I have a problem . I use a bronze brush sparingly , butches bore cleaner patches ,dry patches , and an slight oily patch , it's done. on this particular rifle if I finished up with a Kroil patch , instead of an oil patch , then pushed a dry patch through before I went to the range , my cold clean shot was much closer to point of aim , on that first round target .