Barrel heat

[J.Murphy]

I have been testing a new load recently using a LabRadar chronograph. A wonderful device that records the velocity at the muzzle and a intervals downrange, average velocity, extreme spread, standard deviation for every shot in every string.
What I wanted to bring up for discussion is that during testing as the string progressed and the barrel heat increased, the velocity increased, and as I am trying for minimum SD. this bothered me. Now this seems obvious that a chemical reaction such as black powder ignition would be temperature sensitive, but I have never seen a discussion of barrel heat and velocity and it's effect on trajectory. My recent research makes me realise the extreme importance of SD in vertical dispersion.
I may have missed such a discussion, so I apologise in advance.
J.Murphy

[desert deuce]

Well J. Murphy, you are inquiring about a very important factor to deal with for Black Powder Rifle Competition.

Myself and fellow Long Range Black Powder Target Rifle Shooters have wrestled with this variable for many decades.

The problem for us that would help you with specifics is that you do not provide enough information for the well informed to formulate valuable advice.

Moreover, it is difficult to give detailed advice here because a few here will disagree out of hand never having followed the recommended procedures. This can become confusing for the new shooter. It has gotten to the point where I find these nay sayers amusing as they continue to lament about accuracy destroying barrel fouling while shooters on both sides of them are not having that problem. However, without comprehensive information provided by you the task is more difficult.

With that said, I do not have access to labradar and have not used one. I use an Oehler 33P sky screens placed 15' from the muzzle. I shoot cast lead alloy grease groove bullets exclusively and completely ignore Standard Deviation yet pay close attention to and record ES extreme spread.

I shoot in the open, not in the shade, and I am looking for a load combination that will record in the single digits for ten consecutive shots through the sky screens. Yes the external barrel gets hot but not has hot as the internal bore where black powder fouling and leading occur. Preventing black powder fouling completely in the bore has proven impossible, however, controlling black powder fouling to the extent that it does not adversely affect down range accuracy should be the goal and can be a real challenge here in Southern Arizona. (You did not indicate where you live and shoot.)

Tell us about the rifle and load and where you shoot and I think you will find some useful information coming your way.

[Don McDowell]

With proper foiling control the barrel heat by itself won’t affect a lot ,so long as the shots are spaced around 2 minutes apart
I have at times been. Rowded for time in a relay and come off the line with the barrel and nose cap so hot you could barely hang on to it.

IMHO the biggest affect from the barrel heating up is if there is a high spot in the bedding of the forearm putting pressure on the barrel causing some strange things to happen with both vertical and horizontal stringing

[J.Murphy]

desert deuce,
I have recently relocated to Idaho after living and shooting Silhouette in No. San Diego county. As a welder/fabricator I have always been concerned with the mechanics of the process of shooting. The LabRadar allows access to a great deal of data that was not easily available before. I shoot the 40-65 after playing with the 45-70, going with longer, heavier for caliber bullets somewhat similar to those opting for 38-55 heavy bullets. While working up a load for Silhouette distance grease groove bullets I noticed the velocity increasing as the barrel heat increased. Without the LabRadar I never would have noticed this fact, and just like you, I am concerned with ES. I was simply wondering why I had never seen a discussion about something that would have a large effect on vertical dispersion.
J.Murphy

[desert deuce]

Ahhh, the 40-65. Yes. Been there done that. Right up front I will tell you that I have no explanation for what you describe..........yet. The solution, if there is one, lies with you and all I can do is relate my at the range experiences.

What I will say is that we toyed with longer, heavier for caliber bullets for midrange (to 600 yards) and silhouette (to 500 meters) with about half a dozen known accurate 40-65's having 16 twist barrels and went with what shot the best groups under varying conditions. To put that experience into precise terms, the rifle and target told us what to do to obtain maximum accuracy at those distances. Nothing else. For me, going longer and heavier was counterproductive in those rifles based on down range results. I look for tried and true, not so much shiny and new.

Here tried and true is an unsized fire formed case, large pistol primer, somewhere between 53 & 56 grains of 1.5 Swiss and the Saeco #740 bullet.
Seat the bullet and adjust the wad column so the bullet lightly engraves the rifling when the cartridge is fully chambered. Shooting ladder loads at 200 meters will assist in finding the weight of charge and varying the compression may bring things a bit closer on target.

If that doesn't work start checking the rifle beginning with the firing pin.

[J.Murphy]

desert deuce,
I have had much success in heavy for caliber bullets in long range target and Varmint Silhuoette competition. The goal was simple, get from muzzle to target with the least deflection from wind or in deviation in elevation.
Here in BPCR the goal is the same, but soft bullets, weak powder, fouling, and the giant hump of drag generated by the sound barrier combine to make it harder. I love a challenge!
I agree that tried and true methods should be respected, but they operated under limits and technical restriction that may no longer apply.
The observation of increasd velocity with a hotter barrel was noticed in real time, as I shot, I could never have known that without a previously unavailable advanced chronograph.
The struggle continues.
J.Murphy

[semtav]

While working up a load for Silhouette distance grease groove bullets I noticed the velocity increasing as the barrel heat increased. Without the LabRadar I never would have noticed this fact, and just like you, I am concerned with ES. I was simply wondering why I had never seen a discussion about something that would have a large effect on vertical dispersion.
J.Murphy

Couldn't be as simple as barrel expansion. Less friction.

I know the best my old worn out engines run is right before they disintegrate.

[Lumpy Grits]

What was the air temperature and humidity when tested?
What altitude?

[Don McDowell]

Case neck tention inconsistency can give you fits
Trying to get away with some of the things that work in high power will give you a Goff game of chasing your tail

[J.Murphy]

The burning of black powder is chemical reaction, most chemical reactions are more vigorus at higher temperatures. This happened more than one time. I didn't record barrel temps, it is a polished stainless barrel, so an infrared thermometer won't work, maybe a termocouple epoxied to the barrel.

[steveu834]

Using my ancient Oheler chronograph I tested some 40-65 loads for a 12 shot string that had a es of 10 fps and a sd of 3. It was shot when the air temp was 83. I noticed that the highest velocity were early in the string.

FWIW
Steve

[ole pizen slinger]

In my experience, barrel heat is not going to cause you problems. The harder bore fouling caused by elevated barrel temperature is. Higher ambient temperature will also exacerbate barrel temps causing barrels to cool off more slowly. Learning to control fouling will reward you well.

OPS