Effect of heat on barrels/accuracy and barrel life

G

Ghys_T3LSS

CGN Regular
Rating - 100%
4   0   0
Location
Sherbrooke, QC
Hi,

anyone would have a good reading about the effect of heat when shooting?

for example, what really happens to the barrel if you shoot 10-15 high caliber rounds vs letting the barrel cool down...

how and how much does it affect barrel life? let's say accuracy remains ok for me, to shoot gong @ 500 or 600 yds. what is the downside to keep shooting when barrel is hot...?

i would imagine it is not good.... but how much not good? :)

we think it's hot, but when you consider steel annealing or hardening temperatures... we're probably way way below... so what is the real effect?

if by shooting 10-20 shots back to back I cut barrel life in half, i may be ok with that (more fun to shoot than to wait...)
If accuracy degrades very quickly then I may reconsider...

Thanks all!
 
When I used to shoot in the US their matches were 2 sighters and 20 for score in 28 minutes if I remember correctly. My stainless barrels would be hot enough to leave your fingerprints on it if you were careless enough to grab it by the barrel. I also found that by the end of the string shots would start to go low, but only by about 1/2 MOA at 600 yards. Barrel life was reduced by roughly 500 rounds compared to our style of shooting in pairs or 3’s alternate shots.
 
it's the mirage on the barrel (heat) that distorts the sight picture in the scope that causes inaccuracy people tend to associate with a hot barrel - some people even have a mirage blocker to prevent this from affecting their scope. Once you have throat erosion your bullet tends to have to jump more to get into the rifling - extend your COAL accordingly and your accuracy should return - if your barrel shows fire-cracking and is starting to look like alligator skin "do not over-clean your barrel" with a fouled up barrel you are essentially filling in those cracks and you will notice that it shoots better.

Once you have shot out / toasted your barrel there are several barrel makers that will be more than happy to sell you another one
 
IvoB said:
it's the mirage on the barrel (heat) that distorts the sight picture in the scope that causes inaccuracy people tend to associate with a hot barrel - some people even have a mirage blocker to prevent this from affecting their scope. Once you have throat erosion your bullet tends to have to jump more to get into the rifling - extend your COAL accordingly and your accuracy should return - if your barrel shows fire-cracking and is starting to look like alligator skin "do not over-clean your barrel" with a fouled up barrel you are essentially filling in those cracks and you will notice that it shoots better.

Once you have shot out / toasted your barrel there are several barrel makers that will be more than happy to sell you another one
Click to expand...

Best way/only way to check for throat erosion or fire cracking is with a borescope?

At how many rounds would you recommend to check the inside of the barrel from brand new?
 
The first thing I do when I have a situation where someone says they have a high round count barrel that won't group well is clean it!
I scope my barrels every session now when I clean them. Even from brand new . The only way besides cutting a barrel on half to examine throat erosion and copper fouling in a barrel is with a bore scope. I have a cheap one but it works very well.

I have two 308 barrels i took off that are over 8,000 rounds and the one in particular was shot many times until the barrel was extremely hot . When we scoped it , the throat erosion and copper fouing were both extreme.
I kept cleaning it with Wipeout in three 24 hours sessions before I got all the copper out of it .
Accuracy went from 4MOA to just about 1 MOA at 500 meters fir a five shot group .
Cat
 
maynard said:
I also found that by the end of the string shots would start to go low, but only by about 1/2 MOA at 600 yards.
Click to expand...

The effect Maynard mentions here of rounds going low as the barrel heats up is generally thought to be attributed to thermal expansion of the barrel which increases the bore diameter enough to reduce velocity slightly. The effect is quite common, but depending upon stress in the barrel, it could relax into a different position but not likely with a good match grade barrel like Maynard would be using.

If there are other interpretations, I would like to hear about it.
 
Maple57 said:
The effect Maynard mentions here of rounds going low as the barrel heats up is generally thought to be attributed to thermal expansion of the barrel which increases the bore diameter enough to reduce velocity slightly. The effect is quite common, but depending upon stress in the barrel, it could relax into a different position but not likely with a good match grade barrel like Maynard would be using.

If there are other interpretations, I would like to hear about it.
Click to expand...
Wild guess from a guy who knows way more about physics than rifles, but if I could arrange a test, I'd try the following:

Quick chrono test: Shoot a hot string like maynard's and see if the velocities start to drop as you approach shot #20. If this is consistent, this may reinforce the idea of the bore expanding a bit and generating lower pressure.

Just thinking out loud: An alternate theory is barrel temp could slightly alter the rigidity of the barrel, so it could flex more under pressure. This may alter the sweet spot bullet velocity for a hot barrel.

If I could replicate a situation like maynard's, where a string would start to shoot 1/2 moa low after 20 shots, I might be tempted to try some rounds with a slightly different powder charge. For example, at shot 21, maybe just a hair lower charge, and maybe it'll move the POI back where it should be? Or maybe it needs to be a slightly higher charge?

Maybe the tuning is so sensitive no charge would be good for all 20 shots? Or maybe if the stars align, a tiny tweak could make the group be better as the barrel warms?

I'm just throwing his out there as a point of discussion, since I know squat about this stuff. Math and physics I get. Rifle stuff I'm green as hell. lol!
 
I think the effects are largely overstated. Typically mirage happens first. I find that people tend to be superstitious about letting their rifle cool after only a couple shots.

It’s mostly used as an excuse for guys to BS or smoke cigarettes at the range.
 
odsixer said:
Some good stuff from Paul Harrell on the topic:
https://youtu.be/xLOmWC_NfdA
Click to expand...

Keep in mind that Maynard wont get out of bed to shoot at 100 yards with a rifle, a shotgun maybe. The closest he shoots is 300 meters and he does not run an AR. Most of his shooting is between 300 and 900 meters.

You need to shoot accurately enough to even notice the effect and that Harrell video is too close for such a velocity spread to make a POI difference.
 
When shooting near the end of a 2&20 round string the elevation starts to go down, it just doesn’t drop out. Shots will start to go low or below the waterline and I might not adjust until I am out of the x ring but still in the bull. Maybe come up 1/4 then a few shots later come up another 1/4. So my finished sight setting is usually 1/2 MOA up from where I started the string. I very well could just leave the knobs alone (advice I have been trying to talk myself into for years) but always try to get that extra X or V.
I would think that F-Class guy shooting single string might also see something happening elevation wise especially if shooting on electronic target. Shooting TR I take the rifle out of the shoulder each shot. On manual targets I can fire the shot, open the bolt, remove the spent case, load a new round, shoulder the rifle, close the bolt and be on aim ready to shot when the target comes up. I have seen F-Class guys shoot When the target stops at the top.
 
You must log in or register to reply here.
Back
Top Bottom