Barrel Temp Test

[Nature Boy]

I did a little test to record how hot my barrel gets and what affect it has. I also tried one of those compressed air cans to see how well it worked. You guys be the judge if this data speaks to you.

Conditions for the day were 90-92 degrees, wind 10mph SSW.

I was shooting my .308 FN SPR with fluted barrel.


I used hand loads made with 110g VMAX, 47g Benchmark, Winchester brass, and fed 210 primers. I figured since that's a lot of powder and these little bullets fly at 3,200 fps, there would be a lot of chemical and frictional heat generated.

I shot 5 rounds to warm up, then 15 rounds in succession with no more than 30sec between shots, recording the temp just ahead of the throat and at mid barrel using an infrared thermometer, measuring at the trough of the flutes.

Here's the graph of the temp data. As you can see, the throat area stayed under 95. Mid barrel reached a max of 104


Here's the down range results at 100 yards. Group 1 was the warm up. Interestingly, the warmer it got, the tighter the groups. That may just be coincidence.


I then used the can of compressed air. Going from the chamber I gave the barrel a 30sec blast and the mid barrel temp dropped from 104 to 97. The throat stayed at 93.

Conclusion: I probably need to continue shooting at the same rate to see a real drop off in accuracy. If barrel temps start to affect accuracy, one of those cans of compressed air is probably a good thing to have in your range bag.


ps: I had intended to get chrono data to go with this but the insert pulled out of the bottom after the housing cracked



Tell me what you guys think

 

[243winxb]

Would seem low. But you do have a longer time between shots and a 10 mph wind. The M16 firing a shot every 6 seconds for 140 rounds produce about 575 F degrees. Were you able to keep your hand on the barrel at its hottest? I know i cant with a 223 or 243. http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA019649

 

[taliv]

interesting test. thanks for sharing

 

[Nature Boy]

I think the 10mph wind definitely helped. The top of the flutes were consistently 10 deg cooler than the troughs, for what that's worth

 

[243winxb]

Good test. To bad the chrono wasn't working. Would be interesting to see if velocity changed and had an effect on groups.

 

[Reloadron]

Did you note the time between shots and I missed it? I did something similar but with .223 Remington in a Heavy Barrel old Remington 700 custom VSSF. Ambient was 72 F. Time between shots was 45 sec to 1.0 min. Temperature measured just forward of the chamber. The first 10 shots got me from 72 F. up to about 95 F. and it remained at 95 F. for the remainder of 50 rounds.

As to wind? I had none to speak of but guess it would depend if headwind, crosswind or how the wind crossed the barrel and subsequently removed heat from the barrel.

Ron

 

[Nature Boy]

No more than 30 sec between shots Ron. Wind was quartering from 8 o'clock-ish.

Looks like my results were similar to yours in the chamber area

 

[Bart B.]

I've seen a similar test showing a .308 Win barrel heating up over 20 shots fired 20 seconds apart. Barrel went from 80 to 130 degrees as I remember.

All 20 shots went into 1/2 MOA at 300 yards.

If your barrel walks shots as it heats up, have the receiver face squared up with the tenon thread axis. Then shimmed so it clocks into battery for proper headspace. Probably won't walk shots any more if it's properly stress relieved.

 

[Nature Boy]

Bart, my groups didn't change appreciably. Actually the best group was the last. I'll chalk to up to me warming up more than the barrel, which is typically needed. It often takes me 20 or so to get consistant