Seating test & velocity swing

[HERMAN8R]

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

 

[archp625]

My guess is your barrel heated up causing an increase in pressure. Pressure = Velocity.

 

[HERMAN8R]

I was thinking the same thing but I waited a while between each shot & each set.

 

[HERMAN8R]

I think I will repeat the test.

 

[archp625]

How long between the first string and the second string?

What was the outside temperature?

How many rounds down the barrel?

 

[HERMAN8R]

About 5 min between string 1 & 2. Temp was 47-48 degrees & cloudy.
Prior to the test the round count was 50.

 

[archp625]

About 5 min between string 1 & 2. Temp was 47-48 degrees & cloudy.
Prior to the test the round count was 50.

I'm betting you have two things going on based on my personal experience.

50 rounds is not much at all. Most guys don't start developing a load until 100-150 rounds down the tube. Your barrel could be speeding up. Totally normal. Mine did a 129.

I would shoot 1 group wait 10 minutes. Then shot another group wait 10 minutes and so on.

See if that helps.

 

[HERMAN8R]

That is good advise. I will put some rounds down range and then start the testing again.
Thanks for your help.

 

[archp625]

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

 

[L.Sherm]

As stated above I dont get serious untill about the 100 round mark.
I use the chrono to tell me when the speed up happens after that it's what the target tells me.

 

[HERMAN8R]

Thanks L.Sherm & archp625 for the advise. I will load up some light loads and shoot thru the chrono & look for velocity increase. Or do you suggest using the load that I have been using. Was just thinking of saving powder.

Cheers

 

[L.Sherm]

Just go back to a know velocity load when you started and shoot the exact same charge and see the difference then you will know. Preferable not a max load.

 

[archp625]

Just go back to a know velocity load when you started and shoot the exact same charge and see the difference then you will know. Preferable not a max load.

Yep, agree

 

[baldhunter]

I had totally opposite results with IMR-4350 near 100 degree temperatures.Powders do different things in different situations.Reloader-17 is kind of a different powder in how it reacts compared to most powders I've used.Try the same test with a different powder and see if your results are the same.