Change in Speed

[chavezz556]

I didn't shoot for 2 months and my pet load is now 40 fps faster.

All speeds taken with Magneeto speed sporter

Rifle

Bergara LRP Premier
24" 1/8 twist
6.5 Creed
640 rounds (purchased w/100)

Load @ development 12/22/18, Don't have the DA or SP off hand but let's say it was around 30 degrees and sunny

42.3 Grn H4350
140 gr ELD-M
Peterson SRP Brass
CCI 450
20 th off the lands
2810 FPS, SD-7, ES-24 (over 24 rounds)

Load as of 3/26 and yesterday

Same as above, but on 3/26 my gun was not clean. (just putting out all variables) Also these loads were all loaded in February when there was 2 feet of snow on the ground.

2854 FPS SD-8, ES-26

My question is could the difference in 25* make that much difference in speed or did my barrel speed up? Or a combination of the both?

No change in signs of pressure.

I also loaded 150 rounds of 140 grn BTHP Hornady's @41.7 which has about the same SD's and usually are right around 2750-2760 now they are 2800!
I even went back and pulled one of these and one of the ELM's and the powder charge was correct

Should I be worried about this or just go with the flow. I shoot H4350 so I don't need to switch loads during the summer.

What should I do? BTW the load is 1/2" and no change in zero

 

[sobrbiker883]

H4350 is pretty temp insensitive, but not completely stable.
Rounds’ length of time in warm chamber, maybe dew point is different and minute mount of condensation in bore, holding your jaw differently, who knows?

I’d log the data and keep an eye on it. I prefer to load develop when it’s warm and have to adjust the other way, and if developing cold I don’t shoot for the top node for sure.

 

[Ranger188]

I've seen where someone has loaded rounds weeks even months earlier and the speeds
have increased caused (sometimes) by the neck tension changing ( more ) and causing
the rounds to speed up.
H4350 is pretty stable, even at .5 fps per 1 deg change ( which is alot, closer to .25-.3 ) would equal 12.5 fps

 

[chavezz556]

I have a few left. Maybe I'll bump them back .001-2 and see if that changes anything

 

[ShtrRdy]

I had a similar thing happen to me except I experienced an increase of 25 fps. In my case it is a 6mm Creedmooor, running a Berger Hybrid and H4350. At this point I'm wondering if the room humidity, when I loaded them, had something to do with the outcome.

 

[Deleted member 10043]

Method of least squares states don't worry about it.

A line of best fit can be roughly determined using an eyeball method by drawing a straight line on a scatter plot so that the number of points above the line and below the line is about equal (and the line passes through as many points as possible).

A more accurate way of finding the line of best fit is the least square method .

Use the following steps to find the equation of line of best fit for a set of ordered pairs (x1,y1),(x2,y2),...(xn,yn) .

 

[jd5521]

How many rounds down the tube? Barrels tend to get faster as they are shot more. Mine normally speed up after 300 or more firings.

 

[WinJim1863]

With a similar load (H4350)/bullet I will get 40-50 FPS change from 25 to 70 degrees (LabRadar). Surprised me as I thought 4350 was supposed to be pretty temp insensitive. This was the first time I shot through the winter and saw that difference.