Does a longer barrel heat up slower?

[Boltyboi]

Not sure what forum to post this to, so here goes.

How does barrel length effect barrel heat? Assuming all else (profile etc) being equal.
Short and long tubes would have about the same surface area to volume ratio, so should cool at a similar rate. But a longer barrel is exposed to burning over its bore for more time. Then again, pressure and temprature increases as you approach the chamber. Differential expansion would also have more space to work on the longer tubes... To first order, I'd guess that a longer barrel is going to be more effected. A shorter barrel is also stiffer. All that said, a longer barrel would have significantly more thermal mass, about a third more comparing 16 to 24 depending on profile.

My question is, is this appreciable? Can you get more shots off with say a 16 vs a 24 of the same quality and profile before you get stringing/worse groups?

 

[gnochi]

Barrel mass is the main driver behind how long it takes to heat up, and barrel surface area is the main driver behind how long it takes to cool down.

For barrels of the same profile (to a first order; clearly it’s different for a tremendous taper angle), a longer barrel will have slightly more heat imparted into it, but the heat generation per unit length goes down because of the reduced bore temperature and pressure. As such, the temperature will rise slower, since the barrel’s mass scales fairly linearly with length. The longer barrel also has more surface area, and with the reduced heat generation per unit length it will also cool slightly faster.

For barrels of the same mass, a shorter barrel will heat up less than a longer barrel - shorter dwell time means less heat transfer from powder to barrel, shorter length means less work done by friction on the barrel. The longer barrel will have more surface area, scaling roughly with the square root of barrel diameter.

Now, how much does this matter for stiffness? Cool longer barrels are whippier than hot shorter barrels of the same profile. Whether the whippier dispersion outweighs the velocity advantage is an entirely different question that is extremely dependent on the exact system.