Hot Barrel and it's effect on burn rates.

[HighDesertHunter]

Did a little test at the range yesterday. I was shooting my Bergara B-14 HMR 6.5 Creedmoor. I shot 15 rounds then did my slow fire soak test. There was some cooling between the 15 rounds and the time it took me to reload the mag and the rifle does have a bull barrel but as you can see in the attached image, it only took two rounds to get it hot enough to affect powder burn rate. The shot sequence is right, left then lower, lower, lower. The hot barrel and round soaking in that heat definitely slowed the burn rate of the powder. I was using  43g of H4350 with 120g Nosler ballistic tips. Not very scientific since I didn't have the LabRadar with me but I think the results do show that there is an effect.


Side note: Best group was with 41g H4350 and 129g Nosler ABLR's

[dubyam]

While I applaud the effort to determine these sorts of things, there may be other factors involved. I'm thinking it could be what you suggested, or it could be inherent stresses in the steel or very slight variations in the steel density causing the point of impact to shift, or it could be the overall warming of the barreled action causing a shift in the bedding of the rifle or a pressure point somewhere.

Still, interesting experiment and one which warrants further investigation. Thanks for posting.

[HighDesertHunter]

While I applaud the effort to determine these sorts of things, there may be other factors involved. I'm thinking it could be what you suggested, or it could be inherent stresses in the steel or very slight variations in the steel density causing the point of impact to shift, or it could be the overall warming of the barreled action causing a shift in the bedding of the rifle or a pressure point somewhere.

Still, interesting experiment and one which warrants further investigation. Thanks for posting.

The barrel steel is cryogenically stabilized and the stock is an over molded aluminum chassis. The barrel is a #5 bull barrel with a polished 11 degree target crown. If I shoot fairly fast it still shoots sub moa when it's hot, it's only when I allow the cartridge to soak in the heat that it does this. Throw away the first shot to the right, that was me.

[dubyam]

Interesting. Good case for heat soak changing things. I'd still wonder if you shot it until it was hot, then let it sit long enough to heat up everything else, and then shot it fairly rapid would it throw the rounds down? Maybe that's what you did, but I'm not sure I understand that. Cool experiment, for sure.

[eford]

Is the barrel free floating? Hat was the air temperature during your test? A buddy has a rifle like your Bergara but I don’t know much about its accuracy.

[HighDesertHunter]

Is the barrel free floating? Hat was the air temperature during your test? A buddy has a rifle like your Bergara but I don’t know much about its accuracy.

Air temp was 43 degree. The Bergara B-14 HMR starts out life as a Hunting/Match rifle in a bench rest stock. I have since blue printed the action, trued the bolt face and lugs and re-bedded the stock. The barrel floats .030 except at the chamber where it is fully bedded. The rifle shoots 1/2 moa if I don't get bored and start jacking rounds through it.


It's important to remember that I was soaking these rounds for a minute or more before I fired. During normal 5 round groups I rarely exceed 20 seconds.

[zonie]

I'm kind with Duby on this one other things involved.  when you say heat soaked what exactly did you do ?  leave a  cartridge or cartridges  in the chamber to heat up ?  were heat reading taken on the rifle chamber , etc.   Interesting subject these are subjects I enjoy.  thanks.

[HighDesertHunter]

I'm kind with Duby on this one other things involved.  when you say heat soaked what exactly did you do ?  leave a  cartridge or cartridges  in the chamber to heat up ?  were heat reading taken on the rifle chamber , etc.   Interesting subject these are subjects I enjoy.  thanks.

Yes, the round was in the chamber for over a minute before being fired. 15 rounds had been fired before these and the only break was to reload the magazine. Each subsequent round fired raised the temp further so each subsequent round was warmer than the previous one.


You can do this test yourself if you would like.

[zonie]

Since I live and hunt at times in the desert   imo heated ammo, rifles and outside temps  can make differences in how heated ammo left in the sun or in a heated rifle  increase pressures.  IMO how a person  re-loads, re-loading practices,  components used can change how powders react.    I'm not so sure I could replicate what you did.    Where I would most likely start if I were going to do this test would be to have 2 different brands of  6.5 creedmoor test rifles,  different types of stocks, using the same handloads,  side by side targets , under the same conditions  and rotate shooting one rifle then the next to lessen any outside influences .  The cheap way  go find a friend with a different kind of Creedmoor and go shoot them and see if there is a difference.   Another idea  borrow a  digital thermometer hand held tester and aim it at the receiver then end of each barrel,  2  temp readings per shot per rifle and write the test reading down on paper.  Keeping track /record of the target shots on paper for later reference.  Then I  could have a better understanding of what's going on.  If both rifle's  pulled the shots downward  the same amount as in your picture then I would have some questions,  same thing if using 2 of the exact same rifles with the same bedding pressures, etc.  possibly changing bedding pressures and see if it makes a difference.   There's so many things to cause these bullet drops you would almost need a process of elimination to be sure,    It's interesting to talk about, not something I going to go out any try.

[musicman]

When competing in NRA High-Power matches years ago, in the final 600 yard slow-fire stage, you would watch your wind/mirage/light conditions for the best shot.  You would have your cartridge resting on the follower, and not chamber it until you were ready to touch it off.  The theory was, that if you chambered it and waited for the best shot conditions, the cartridge would get hot, and you would lose powder burn rate/velocity consistency.  Some guys, if they chambered it, but did not squeeze off the shot within say ten seconds, they would pull the cartridge, and start over with a cool one.  At six hundred yards, you fight for every inch of accuracy.  MM

[HighDesertHunter]

When competing in NRA High-Power matches years ago, in the final 600 yard slow-fire stage, you would watch your wind/mirage/light conditions for the best shot.  You would have your cartridge resting on the follower, and not chamber it until you were ready to touch it off.  The theory was, that if you chambered it and waited for the best shot conditions, the cartridge would get hot, and you would lose powder burn rate/velocity consistency.  Some guys, if they chambered it, but did not squeeze off the shot within say ten seconds, they would pull the cartridge, and start over with a cool one.  At six hundred yards, you fight for every inch of accuracy.  MM

The reason I conducted the simple non scientific test was because of a video that I saw that showed it. I wanted to see what if any effect it had with my precision rifle. I can see that it seemed to by my poi change. I know that rifle can shoot 1/2 MOA at 100 yards. I'm convinced that it does but I would not be concerned about this when I'm hunting because I would never shoot 15 rounds at an animal and then slow fire as a last ditch effort. Well, maybe I would if my only choice of weapons was and AR .223 and I was hungry and came upon a Moose that I had a tag for. Hypothetical conditions are always fun to imagine. LOL..

[African Leadwood]

I am more interested in how the ballistics changed. I.e. what did the chrony say.

But tue phenomena is real https://en.m.wikipedia.org/wiki/Cooking_off

Thanks for sharing.

[danno50]

Your cooking-off article is very interesting, thanks for posting.

[224KING]

What was it that Sergeant Schultz always say? Very Interesting

[Big Muddy rancher]

What was it that Sergeant Schultz always say? Very Interesting

I think that was Klink

Schultz said" I know nothing, I see nothing"