Clean bore vs fouled bore

[bobinpa]

This may seam like a dumb question to some of you but I never knew the correct answer or "technical" answer to what changes the POI from a clean bore to a fouled bore and why?

Every year for deer season, hunters go the range and check their guns for deer season. They start with a clean bore and won't clean it until after hunting season because the POI changes with a dirty bore.... What makes the POI change? Does the barrel get faster or slower with a trace of copper in it? Or does it get faster with a trace of carbon in it?
Thanks

 

[bobinpa]

Wow.... I thought out of all the combined knowledge on this forum, someone would know...

 

[Richard Coody]

Well the only shot that usually counts with a hunting rifle is that first cold bore.shot. many rifles take 4 or 5 shots to settle down after cleaning.

If your rifle prints that first shot out of a clean cold bore in the same POI as all your other shots then clean away.

For me before hunting season i always take my hunting rifle with me on every range trip. All i want to do is fire 1 shot each trip to verify POI. I don't clean until the end of the season.

 

[ckrifles]

This is an impossible question to answer. I have been shooting and hunting for 63 years. During that time I have shot factory barrels that looked like that the rifling was cut with a chain saw to custom barrels that were lapped by hand and never accumulated copper. So did one go faster than another with a clean bore? I don't know, to many unknomes to verify. But nobody shoots just one round from a clean barrel and calls their rifle sighted in. The next round will be from a fouled barrel unless you clean it again.

 

[Paddyd]

I'm no expert, but I'd wager that the clean bore would be ever so slightly slower. Once fouled there is more resistance and therefore more pressure and pressure normally = velocity. Only way to verify would be go out and buy a cheap chronograph and test it.

 

[K22]

Here's my experience from a hunting perspective.

For deer hunting, I run a dry patch down a lubed clean bore to remove any excess lube before shooting. If I've used a heavy viscous oil or grease for long term storage then I run a patch of mineral spirits down the bore to remove all traces of oil/ grease then dry patch. I also patch out the chamber to make sure there is no accumulation of lube. I've shot several deer from both a fouled and clean barrel.

For precision varmint / predator hunting I use a light lube after cleaning, i.e. Barricade which provides corrosion protection while idle in the short term. These rifles are used all year around so I don't use a heavy oil or grease after cleaning for corrosion protection since they are in long term idle storage. I run a dry patch down the bore to remove any excess lube before shooting. Also dry patch the chamber. I've shot many of ground hogs and a fair number of predators from a clean bore.

 

[BartsBullets]

This may seam like a dumb question to some of you but I never knew the correct answer or "technical" answer to what changes the POI from a clean bore to a fouled bore and why?

Every year for deer season, hunters go the range and check their guns for deer season. They start with a clean bore and won't clean it until after hunting season because the POI changes with a dirty bore.... What makes the POI change? Does the barrel get faster or slower with a trace of copper in it? Or does it get faster with a trace of carbon in it?
Thanks

The first shot out of a clean bore is always significantly slower. Once the barrel is fouled the bullet will speed up. With a bench gun it usually takes two shots after cleaning to get the barrel up to speed.

Bart

 

[rwj]

The first shot out of a clean bore is always significantly slower. Once the barrel is fouled the bullet will speed up. With a bench gun it usually takes two shots after cleaning to get the barrel up to speed.

Bart

My clean/cold bore shot impact is consistently .5 MOA low. Though I’ve not verified via a chronograph, I’ve always believed that it’s due to slower velocity as noted in @BartBullets post above.

 

[mikecr]

Not only does fouling change things, but different fouling (like from another load) also affects expected results.
If you leave a petroleum base in after cleaning, it can take 6 or more shots to burn it out and dry foul a bore. It can be that many shots to stabilize results.

For at least 30yrs now I've worked around this with dry pre-fouling as my last step of cleaning. I put guns away ready for use.

 

[spclark]

It's all about vibrations - in your rifle, its components, and of those all-important bullets you're firing.

The vibrations affecting how a rifle performs when fired with a squeaky clean bore will be different than those in a rifle fired with a fouled bore.

And it's not just copper either.

Powder manufacturers go to significant lengths developing their propellant recipes to include a number of compounds that affect not only how they perform once ignited but also what gets left behind in the bore after the bullet's gone.

Some of those compounds are there to help the bore withstand the temperatures and pressures of bullets passing at speed.

Others are to control or prevent vaporized copper from re-plating itself back onto the bore's surfaces.

Those and more play a part on how vibrations are generated and how they affect how the rifle 'system' reacts once a cartridge is ignited. Those vibrations in turn affect how bullets behave inside the bore then as they pass the bore's crown exiting at the muzzle.

Those fouling compounds go a long way to even out vibrational inconsistencies so the predictability we desire is achieved by a fouled bore over what a "cold, clean bore shot" will more often than not leave you with.

 

[BartsBullets]

It's all about vibrations - in your rifle, its components, and of those all-important bullets you're firing.

The vibrations affecting how a rifle performs when fired with a squeaky clean bore will be different than those in a rifle fired with a fouled bore.

And it's not just copper either.

Powder manufacturers go to significant lengths developing their propellant recipes to include a number of compounds that affect not only how they perform once ignited but also what gets left behind in the bore after the bullet's gone.

Some of those compounds are there to help the bore withstand the temperatures and pressures of bullets passing at speed.

Others are to control or prevent vaporized copper from re-plating itself back onto the bore's surfaces.

Those and more play a part on how vibrations are generated and how they affect how the rifle 'system' reacts once a cartridge is ignited. Those vibrations in turn affect how bullets behave inside the bore then as they pass the bore's crown exiting at the muzzle.

Those fouling compounds go a long way to even out vibrational inconsistencies so the predictability we desire is achieved by a fouled bore over what a "cold, clean bore shot" will more often than not leave you with.

I think it comes down to simple pressure. A clean barrel is slicker and doesn’t produce the same amount of pressure as when the barrel starts getting fouling in it. I’ve ran a chronograph over nearly every shot for three years in practice and during matches. A clean dry bore will consistently shoot 80 to 100 feet slower.

Bart

 

[bobinpa]

The first shot out of a clean bore is always significantly slower. Once the barrel is fouled the bullet will speed up. With a bench gun it usually takes two shots after cleaning to get the barrel up to speed.

Bart

Am I correct in assuming that it is from more drag created by a clean barrel?

 

[BartsBullets]

Am I correct in assuming that it is from more drag created by a clean barrel?

I believe it’s the opposite! The barrel when it’s clean creates less drag ie. It’s easier for the bullet to pass through.
Bart

 

[garandman]

Not only does fouling change things, but different fouling (like from another load) also affects expected results.
.

Thats my experience. Theres really very little universal about fouling. My every rifle / load is different.

 

[1911nut]

I think it comes down to simple pressure. A clean barrel is slicker and doesn’t produce the same amount of pressure as when the barrel starts getting fouling in it. I’ve ran a chronograph over nearly every shot for three years in practice and during matches. A clean dry bore will consistently shoot 80 to 100 feet slower.
Bart

My experience is, and I’m not anywhere near Bart’s level of rifle shootin but I have shot a lot of his 52g bullets, -a couple of my heavy bench guns put the clean barrel first shot in the group and sometimes it’s the best group of the day.

My other rifles, 22 Varmint rifles also, 12+lbs, that don’t put the clean barrel shot in the group they almost always go high.

Is that a barrel time / recoil thing? My wad gun shoots lighter loads higher.

Or different barrel vibration from slower bullet?

 

[clunker]

I've only been doing this for less than two years, but I've never noticed a difference between my first clean bore shot and those that follow. Maybe it's because my first three shots are getting sighted in, and I don't really count them.

 

[bobinpa]

I believe it’s the opposite! The barrel when it’s clean creates less drag ie. It’s easier for the bullet to pass through.
Bart

Thanks for the clarification.... I didn't see this reply when I posted my last response.

 

[BartsBullets]

My experience is, and I’m not anywhere near Bart’s level of rifle shootin but I have shot a lot of his 52g bullets, -a couple of my heavy bench guns put the clean barrel first shot in the group and sometimes it’s the best group of the day.

My other rifles, 22 Varmint rifles also, 12+lbs, that don’t put the clean barrel shot in the group they almost always go high.

Is that a barrel time / recoil thing? My wad gun shoots lighter loads higher.

Or different barrel vibration from slower bullet?

At 100 yards you can have a huge difference in velocity and not see a POI Shift. Try that with 105 gr bullet at 600 and you’ll see a large change in POI.

 

[1911nut]

At 100 yards you can have a huge difference in velocity and not see a POI Shift. Try that with 105 gr bullet at 600 and you’ll see a large change in POI.

Ok, I can see that.

 

[Paddyd]

Am I correct in assuming that it is from more drag created by a clean barrel?

No it is because the clean bore has less drag and less drag equals lower pressure which equals lower velocities. When the bore is fouled the powder charge generates higher peak internal pressure due to the bullet/bore resistance and the velocity increases. In short, the fouling restricts the bullet very slightly and increases combustion efficiency. This is more prevalent with slower burning powders that benefit from longer barrels, heavier bullets AND that little bit of extra resistance. A fast burning powder will reach peak pressure near the chamber vs progressively increasing as the bullet travels down the bore. Quicker burning propellants are less effected by a clean vs fouled barrel as they make their peak pressure closer to the chamber before all that bore fouling has much effect on restricting the bullet. There are more variables to this phenomenon than just clean vs fouled.