Home Forums Hunting & Shooting Ask The Gunwriters Cold barrel pressure/velocity?

Do shots from a cold barrel typically generate higher pressure/velocity? When chronographing loads it seems (although I haven't collected data) my first 1 or 2 shots are higher velocity (100-150 fps in a 7 mag) faster than after the barrel warms (and expands?).

If this occurs it seems it could be pronounced if you shoot if 50F degree weather and then hunt in 10 degree weather.

I did a quick search and didn't find any info.

Thanks,

David

I often chronograph loads during range trips when that is the only thing on the agenda. I can't say that I have ever seen any noticeable variation in velocity between the first couple of cold barrel shots and subsequent shots--certainly nothing like 100-150 fps. Sounds like YMMV. Curious.

About all that I can offer is that my barrels never get very cold as they come out of a safe in the house and get put into soft cases for transport to the range.

Not seen any science on that one.

I haven't seen any evidence of that kind of spread.

Jerry

Is that off of a clean barrel or fouled barrel?

Good point - it's generally a clean barrel.
Thanks for the replies.

At one time I had strain gages mounted on three different rifles (.300 ultramag, .308Win and .270WSM). They all registered higher pressures on a clean cold bore shot. IIRC the pressure was an average of 4.3kpsi higher than supsequent shots.

First shots can go either way. Typically the first shot from a clean barrel is lower than average.

SAAMI procedures require two or three "warmers" immediately prior to their 10-shot tests.

Watch out for powder position during firing. The "SAAMI Twist" with careful handling to assure that powder ends up at rear is essential. I've seen extreme changes with powder position, but haven't seen as many changes with first shot.

KenO

As you know, that can be very important when loading powders that don't occupy most of the case capacity (low load density). This thought hadn't crossed my mind, ...well, because I don't use/load reduced loads AND I use 'slow burning' rated powders FOR the cartridge.

Just another example of Dr. O's astuteness .

Thank You

Jerry

Upon further review, that Speaks volumes.

**dkim - If, since, Dr. O hasn't seen "as many changes with 'first shot' ", it makes me think something is up. Don't know what to suggest but if it were me, I'd be checking- double checking - nearly everything including your chronograph. No aspersions, just check.

Jerry

Thank you again for all of the feedback - your experience is very helpful. I've never considered powder position - There is room for it to move.

Chrono (Magnetospeed) seems OK - consistent readings on factory ammo, and loads for another rifle.

As I mentioned I did not systematically collect data so this could be one of those "impressions" that needs more validation (if it is real). Nevertheless I am going to check powder position and explore using a slower burning powder that uses more space.

David

IME, running loads over the cronie, a clean lubed barrel, a barrel with oil in it, has produced first shot vels lower than the norm. A dirty barrel has produced the same vels as the rest of the string. A clean barrel wiped dry of oil has vels on par with the rest of the string. My experience with my rifles.