Barrel heat and load testing

[blkexp98]

I just ran through probably 25 rnds over probably 1.5 to 2 hrs but had some inconsistency. I had about 33 rnds loaded to test in a round robin and quit almost all the way through. It seemed like even though the velocity was the same by the time i got to the 3rd set the shots were all falling below the first two sets. My barrel was pretty clean beforehand and the velocity was still up so I dont think it was fowling. On the other hand my barrel is a 18" ar15 barrel with a fairly heavy profile so I wouldn't think the heat would have made it sag that fast. When I shot I single loaded each round into a 20rnd magazine so it would be as consistent as possible. I did find one load that shot great but of course it was one i didnt shoot the third round in so it really didnt count. It was about 1/2" not moa at 200 yds with no real vertical difference. 24.7 gr RE15 with 69gr SMK at 2.260 OAL with the tips uniformed.

I did learn that my RCBS 750 scale may not be the best reloading scale. I noticed some variation in the velocity even though I pretty carefully trickled and weighed each charge. I guess it may be time to upgrade to one with more resolution and accuracy. With that variation though the drop was too much to be attributed to that.

So what do yall think? How hot is too hot for the barrel and do you have any other ideas what may be causing my issues?

 

[K22]

I do all my load testing from a fouled barrel and allowing 5 minutes between shots, even for my heavy barrel varmint rifles.

Furthermore, to prevent fatigue and lost of focus on proper shooting technique I don't try to test too many loads in one session (for me, three loads at one session which is about fifteen rounds - same powder).

 

[jlow]

It’s an interesting question. I’ve been waiting between 1-2 minutes between shot but 5 min seems like a long time.

I’ve not done any study to check chamber/barrel temps but I can actually pick a hot case up with my finger tips right after it is fired (I do have a bit of high pain tolerance ;D), and it’s comfortable after about 30 seconds. With a heavy barrel to suck the heat out, it would seem that 1-2 min should be plenty but this is a bit of conjecture and would like to hear from someone who actually measured chamber temps.

 

[amlevin]

Most of my shooting is done in ambient temps that range from 55-65 degrees lately. I shoot a max of 50 rounds in 90 minutes and don't seem to see any degradation in accuracy in my 5-R Milspec. In fact some of my best groups have been with the warmest barrel, ALMOST too hot to touch.

I look back at my shooting sessions and almost always it is ME that causes the opening of the groups, not barrel heat. For those that feel that inaccuracy is falling apart due to barrel heat, could it also be that the shooter is getting tired, overlooking some part of the process, good position, good steady aim, proper trigger action, in other words, not rushing the shot(s)?

 

[thefitter]

Personally I would tune my loads to what ever type of environment/shooting/competition timing I would be using them in. I would not want to use loads I developed at 1 round/5min intervals in a competition that required faster shooting or vise a versa. But that's just me.

 

[blkexp98]

thefitter: Thats a good point too especially getting back to the chamber temps. If the powder is sensitive to that it could cause issues.

amlevin: Thats something ive thought about too. I could have also changed something about my position. It was humid, about 90 degrees and I had to keep cleaning the sweat/ fog from my shooting glasses so I wouldnt rule out shooter error.

Jlow: My brass was HOT from the start but throughout the whole ordeal i could easily hang onto the barrel. Ha my brass actually melted onto my high dollar shooting mat/moving blanket a couple times if I didnt flick it off fast enough. by the time I moved it to the opposite side and fired another shout i could repete the process and easily pick it up. I have to wonder though if I have a heavy barrel where it gets hot slower and cools slower how does the unsupported weight of the heavy barrel effect things when the core ill call it is hot. Like you said short of a chamber and maybe bore reading who knows how hot it really is.

K22: Another odd thing that happened was my normal 100 yd zero was perfect and just slightly low for my first sighting shot at 200 yds. Then I had 5 rounds loaded about halfway into my range of loads to foul the barrel and zero at 200. Well my first shot with that was on the next target about 6 inches to the right and about 4 inches low. I installed a new QD suppressor mount right before coming to the range and Im curious if that first shot released some kind of tension the barrel had from me installing the mount. It was torqued to ~18 ft lbs. After I rezeroed the rest of the ammo shot right where it should. Im curious to see what happens next time.

 

[K22]

Personally I would tune my loads to what ever type of environment/shooting/competition timing I would be using them in. I would not want to use loads I developed at 1 round/5min intervals in a competition that required faster shooting or vise a versa. But that's just me.

That's an interesting point, I never thought of load development in that light. I always focused on testing the accuracy capablity of the load trying to eliminate as many variables as possible. It just so happens (not by design) that my shooting discipline is varmint hunting so the one shot / 5 minute interval fits my shooting scenario since I rarely shoot at any shorter intervals.

I use the 5 minute interval not only to make sure I'm shooting from a cool barrel but also to force me to take my time, think about my technique. It also keeps me out of the wife's hair longer ;D.

 

[jlow]

Thefitter - The way I look at it, when I do load development, I am not really trying to imitate what I am going to do in real life, at least not yet. I am simply trying to determine how the round would do under an ideal situation i.e. if you let the barrel cool properly. There is just so many things that affect load development that unless I keep to keep it consistent and controlled, its hard to figure out what is doing what. Eventually, I would agree that you need to get the rounds to work under specific situations I would be using the rounds for. I am not at that stage yet.

Blkexp98 – yea, ambient conditions makes a huge difference. In Michigan when I am out shooting in the winter, I am sometimes almost grabbing the cases as they come off the chamber and wishing that it does not cool off so fast – LOL! When it is in the upper 90s, it’s the other way around. As for a heavy barrel, my understanding is that it can draw the heat away from the chamber faster.

 

[tenring]

In timed competition matches, shooters are required to put down 5 record shots, plus as many sighters they want, in 6 minutes. Some shooters can get off 25 shots in that time frame. It does not seem to affect accuracy unless the barrel gets too hot to touch. It might affect barrel life.