Seating test & velocity swing

[1yotedog]

Something I've seen since I got setup to assemble my test loads at the range that may be related to the OP's question: I can ladder-up on charge wt. to find first signs of pressure. I've then gone down in charge wt. (retrace the test doing up to confirm POI, vel, etc) only to find that velocity, and sometimes pressure signs, are higher on the way down than I saw as the wts. were increasing. I've gone down as much as 1.2 grs of powder still seeing ejector marks that weren't seen as charge wts. were increasing. My guess was that I'm taking so long to be sure each shot is as absolutely perfect as I can make it, that the round is soaking up heat from the chamber. No matter how cool the day is, a warm chamber=warm cartridge. Lately, I've repeated some earlier problematic tests while making extra effort to not waste time with a round in the chamber and found more consistent results. Hope this helps!

 

[HERMAN8R]

Something I've seen since I got setup to assemble my test loads at the range that may be related to the OP's question: I can ladder-up on charge wt. to find first signs of pressure. I've then gone down in charge wt. (retrace the test doing up to confirm POI, vel, etc) only to find that velocity, and sometimes pressure signs, are higher on the way down than I saw as the wts. were increasing. I've gone down as much as 1.2 grs of powder still seeing ejector marks that weren't seen as charge wts. were increasing. My guess was that I'm taking so long to be sure each shot is as absolutely perfect as I can make it, that the round is soaking up heat from the chamber. No matter how cool the day is, a warm chamber=warm cartridge. Lately, I've repeated some earlier problematic tests while making extra effort to not waste time with a round in the chamber and found more consistent results. Hope this helps!

I thought about that. Barrel was barely warm between shots. Match barrel. Not saying the chamber didn't get warmer....that is a great idea to monitor. Next string I will take more time between shots & strings. My buddy suggested a digital infared thermometer.
The jump was not a lot. And it still shot bug holes most of the time.
Thanks again!
I did not keep the cartridge in the chamber

 

[vancewalker007]

Loaded some 123 SMK for my 6.5 CM to find an accurate load. I found that 42.5 gr of R-17 was very accurate and had low ES & SD in my prior test on target. I entered data of the different CLOA rounds into Quickload prior to loading the various rounds. Quickload showed that with the same charge weight, the more I seated the bullet, the velocity & pressure would increase. I did not find that to be true to the extent that Quickload stated.

DATA FROM QUICKLOAD

Bullet Jump	CLOA	Powder Charge	Fill. Charge	Vel.	Energy
		Grains	%	fps	ft.lbs
		RL 17
0 (ON LANDS)	2.833	42.5	94	2949	2375
0.010	2.823	42.5	94	2953	2381
0.030	2.793	42.5	95	2965	2401
0.050	2.773	42.5	95	2973	2414
0.090	2.683	42.5	98	3010	2474
0.130	2.553	42.5	102	3066	2568

I started the jump at .010, .040, .050 and .130 off lands. I shot 6 rounds each starting with 3 shots each in separate targets for each load. Then I repeated the excise again shooting the same targets for a total of 24 rounds. I did not fire fouling shots prior to starting this teat.

The strange thing is, the velocity jumped on my second string. The temp outside was 47 deg when & started and 48 when I finished. Cloudy skies.

Results: String 1 I String 2

	Load 1	Load 2	Load 3	Load 4	Load 5	Load 6	Load 7	Load 8
Shot #	.010 jump	.050 jump	.090 jump	.130 jump	.010 jump	.050 jump	.090 jump	.130 jump
Shot 1	2,904	2,921	2,919	2,940	2,975	2,961	2,966	2,965
Shot 2	2,930	2,921	2,931	2,933	2,959	2,957	2,969	2,953
Shot 3	2,923	2,936	2,935	2,935	2,959	2,958	2,968	2,964
Shot 4
Shot 5
Mean	2,919	2,926	2,928	2,936	2,964	2,959	2,968	2,961

Standard Dev.	13.5	8.7	8.3	3.6	9.2	2.1	1.5	6.7
Extreme Spread	26	15	16	7	16	4	3	12

The .050 jump was the tightest group at .40 inches.

I just don't understand the velocity increase on the second string.

Any Ideas??
Thanks for any advise.
Cheers

What Chrono are you using?

 

[HERMAN8R]

Vance, I have the Chrony Master. Beta model. I have black shade screens on each side.

 

[vancewalker007]

Vance, I have the Chrony Master. Beta model. I have black shade screens on each side.

I used one for many years. What I noticed as the day advanced and the sun changed position, even on cloudy days, readings can vary some. If you can borrow a magneto speed you might get some more consistent results. I used shields on mine to remove some of this variability but it still happened some. This may or may not be happening with your data here. Did you shoot the strings in your table from left to right? If you did, some time had passed between the first and last 2 strings and the lighting did change. Anyway you can check this by mixing up your test strings and shoot them in random order, or get a magneto speed.

 

[HERMAN8R]

I used one for many years. What I noticed as the day advanced and the sun changed position, even on cloudy days, readings can vary some. If you can borrow a magneto speed you might get some more consistent results. I used shields on mine to remove some of this variability but it still happened some. This may or may not be happening with your data here. Did you shoot the strings in your table from left to right? If you did, some time had passed between the first and last 2 strings and the lighting did change. Anyway you can check this by mixing up your test strings and shoot them in random order, or get a magneto speed.

I did shoot left to right within an 8" spread.
That make sense. I have really been thinking of getting a magnetospeed. My buddy is getting the Lab Radar. We are going to compare each of them. I am thinking the magnospeed will be easier to set up.

Thanks for your info!

 

[HERMAN8R]

Every barrel is different but I would at least put another 50 down the tube.

I was just wondering. Is the typical of a hand lapped barrel also? I have a Bartlein barrel.
Thanks

 

[archp625]

I was just wondering. Is the typical of a hand lapped barrel also? I have a Bartlein barrel.
Thanks

Maybe maybe not. I have a hand lapped barrel and mine took 126 to spped up. 127-199 all have been stable.