First bullet the slowest-why?... chrono'd results


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Luggernut
July 17, 2007, 10:45 PM
I tested 30 rounds of .45ACP, S&W DK 1911, 5.2gr W231, 230 Berrys bullet, WLP primer, 1.260" COL. I loaded 8 rounds in the mag, shot the bullets, reloaded (no rushing either) and repreated. I've noticed the firsts round was noticably slower than the rest... about 40 ft/s slower than the average. The speeds below is the actual data- asterick is first round of mag. What up with that? The variation seems pretty poor on this batch...

699*
765
763
802
714
760
734
740
689*
685
727
736
772
718
734
756
667*
751
758
751
793
719
749
764
703*
743
738
735
743
719

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LexDiamonds
July 18, 2007, 02:31 AM
cooler barrel...

ReloaderFred
July 18, 2007, 02:44 AM
I would bump the load up until you're reaching around 800 fps. The higher pressure will allow for a cleaner burn of the powder, and probably closer velocities.

I have found though, that this kind of variation is pretty common, especially when chronographing outdoors. The chronograph measures the shadow of the bullet passing over the "eye", and unless everything is exactly the same for each bullet, there are factors involved that will affect the measurement.

Hope this helps.

Fred

Sharps Shooter
July 18, 2007, 03:24 AM
I don't know, but my money's with Fred - chronograph quirks.:)

GRIZ22
July 18, 2007, 03:42 AM
I don't know, but my money's with Fred - chronograph quirks

I'm with fred also. Many reloaders throw out the highest and lowest velocities when calculating ES and SD to account for this.

pinkymingeo
July 18, 2007, 06:32 AM
I've noticed the same phenomenon. Don't know what causes it. Those spreads aren't bad for 231 in 45acp. Variations in brass and bullet weights cause some of it. 231 doesn't meter particularly well, for me at least, and that contributes. Velocity spreads generally won't noticeably affect your grouping at handgun ranges, anyway.

griz
July 18, 2007, 09:41 AM
My guess is it is powder position. The effect is usually more noticable in revolver cases with their larger airspace, but it happens in pistol rounds too. It's caused by the powder in the first round being more forward in the case. To check if that's what's happening, just hold the gun muzzle up after chambering the first round. My experience is, at least in revolvers, the effect is much more common than most people think, even with powders like Titegroup that claim to be insensetive to position.

71Commander
July 18, 2007, 09:55 AM
Barrels cold. Shoot some before you begin your test.

Navy_Guns
July 18, 2007, 10:12 AM
The inertia transfer from your first shot causes the rotation of the earth to speed up. Since it is speeding up when the first reading occurs, the velocity reads lower. The remaining shots are counteracted by someone else shooting the same load in China, so the velocity stabilizes somewhat. The earth slows back down while you are both reloading so the process starts over.

Your chronograph is so accurate that it measures differences in the rotational velocity of the earth - your loads are perfect.

:neener:

Jim Watson
July 18, 2007, 10:17 AM
I'm with Griz. It is powder position, you probably droop the muzzle when you pick up the gun for the first shot over the chronograph. Recoil then redistributes the powder closer to the primer.

Run some by elevating the muzzle before each shot... then by depressing the muzzle before each shot and see how they come out.

Spartacus451
July 18, 2007, 10:24 AM
I'm with Griz. It is powder position, you probably droop the muzzle when you pick up the gun for the first shot over the chronograph. Recoil then redistributes the powder closer to the primer.
I have seen this happen with steel loads in .38 special. The difference is quite impressive.

Walkalong
July 18, 2007, 11:17 AM
I blew a primer with Blue Dot once doing that. I wanted to see if position inside the case would matter with that load. I held the muzzle up and brought it down to fire a couple of times and all went well. I then held the muzzle down and brought it up to fire and all hell let loose, well a little bit of it anyway. Blew the primer pretty badly. It went from no pressure signs one way to blowing a primer the other way. It was not a smart load by the way. Young and dumb. :)

jmorris
July 18, 2007, 12:02 PM
Hangout by the chrono and any major pistol match that has power factor rules and you'll know that Griz is correct. As Jim pointed out everyone that's "on the edge" elevates the muzzle to the sky and gently lower before firing.

The Bushmaster
July 18, 2007, 01:25 PM
I, also, have to agree with Griz on this. I have never suffered from this problem mostly because I was taught to start from a muzzle elevated position anyway. But tests that I have conducted with W-231 have proven Griz to be correct...

Luggernut
July 18, 2007, 05:24 PM
I like the reasoning that Griz gave as well... looks like I'll have to validate it with more tests. FWIW- as many of you may know there is lots of space in the .45 ACP case with W231. I don't recall dropping the muzzle before shooting but I'll make sure to lift the muzzle to see what happens.

Thanks for the ideas.. this jives with the fact that my 9 and .40S&W loads are so much more consistent with the same press- albeit Power Pistol- the cases get pretty full with 9mm.

I like Navy Guns' answer... but I had someone fire a similar load in exactly the opposite direction at exactly the same time, so it's unlikely the cause.

DBR
July 19, 2007, 02:40 AM
When I tested several common powders for position sensitivity in 38spl and 45acp, I found Green Dot to be the least position sensitive in both calibers at normal pressures. My tests included Titegroup. In general ball type powders were worse than flake.

PsychoKnight
July 19, 2007, 04:07 PM
The opposite usually true when 1/4mile testing car performance. The first run with a cold engine usually outperforms all subsequent runs, by a very small margin. If you don't believe me, try it on your own car. Sorry, off topic trivia.

txgho1911
July 19, 2007, 04:49 PM
Before further testing you may search this and other reloading forums for"detonation". More powder burn started earlier causing a pressure spike.

Jim Watson
July 19, 2007, 06:31 PM
If there is a risk of "detonation" with a standard load of dedicated pistol powder in a pistol cartridge, we all better take up a safer hobby.

R.W.Dale
July 21, 2007, 01:25 AM
.

I've noticed that with rifles that first shot from a clean oily bore can be over 150 fps slower than the rest of the shot string. I always run a fouling shot before shooting for groups for this reason.

This is why you hear some people state that they don't hunt with a clean rifle (myself included)

wcwhitey
July 21, 2007, 10:44 PM
Good points, I would either go with powder position or the the lubrication factor. It has been said that the lube on a bullet is for the next shot, not the bullet that carries it. Just a thought. Bill

RobZ71LM7
July 22, 2007, 12:37 PM
I've had the exact same chrono results with win231 in .45 (actually I use that same load). It doesn't matter if the barrel is cold or hot. I always thought it was the Chrono and the first shot but what others are saying about the powder position makes perfect sense.

phaed
July 22, 2007, 12:47 PM
because you are shooting "cold bore"

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