Barrel Design and copper fouling

[Donkey]

Hello everyone.

I have a question about how to reduce copper fouling when running 3000fps + The rig I am referencing off is the 308 limited to 156gr projectiles.

Ideas so far:
Friction proofing projectiles.
Polishing the bore finish.
Using radially tapered lands to easy the projectile on the face so that it doesn't cut into it.

What else is there?

Also: For the same velocity the higher the twist the more copper fouling right near the throat right?



Many thanks in advance
Jason

 

[BoydAllen]

Do you have any hand lapped barrels? The reason that I ask is that the best solution to the problem that you have described is a top grade barrel, properly chambered, and broken in. I have barrels that I did five shots of one shot and clean, and just started normal cleaning cycles from that point. If the barrel is top grade, and the work done right, there shouldn't be a problem. What sort of barrels have you been shooting?

 

[Donkey]

Hi Boyd.

I'm going off other peoples experience here with a new barrel in mind. So I'm looking for rules of thumb, things to be aware of and what are the less considered factors that influence a barrels propensity to copper foul. Can you tell me what specifics you are referring to when you say a 'top grade barrel' and which work in particular needs to be done right with regards to copper fouling.


Many thanks
Jason

 

[RonAKA]

Jason, here is an article you may find interesting.

Barrel Fouling

 

[Heavies]

I use HBN coating on the bullets to minimize fouling. After 60 round match there is minimal copper coming out of my Mcgowen barrel in 6br. I am not at 3k fps, but the HBN seems to help alot.

 

[BoydAllen]

Depending on what you are doing, Bartlein, Krieger, Shilen, Hart, Obermeyer, Rock Creek, Broughton, only their top grade if they have more than one. For a heavy bullet .308, perhaps some version of a 5R or 5C rifling profile. Pick your smith with care, someone who shoots Benchrest knows what the highest level of work entails, preferably who uses a muzzle flush reamer cutting fluid system. Never go with the local guy that has no competition qualifications. Start with an completely straight action. Just because you cannot see this, do not skimp. Pay a LOT of attention to reamer design, and how it coordinates with your brass and FL sizer dimensions. Stay away from strong cleaners. If the work is good, you shouldn't need anything stronger than Butch's, patches, and bronze brushes. Buy the best rod(s) and cleaning rod guide that they make. Take your time when stroking the rod. Its not a clogged sewer. Yes, that is way more than you asked.

 

[Donkey]

That is great Boyd.

Thank you. Got any thing else?

Cheers
Jas

 

[Forum Boss]

There is some evidence that 3-groove barrels, with their relatively flat, wide lands, are gentler on jackets. We've seen that at both ends of the caliber spectrum -- from .204 Rugers to 50 BMGs. 3 grooves are now preferred by most 50 BMG shooters because, with the solids, 3-grooves foul less and produce more velocity.

But... whether it can make a difference with your .308 is an open question. If you are working with a factory barrel, pretty much any custom lapped barrel should be better. Potentially way better.

I had a factory .260 barrel that looked like it was threaded inside. It took literally hours to clean with brushes, mops, JB, you name it. It was replaced with a barrel that cleans with 4-5 wet patches and a good soak with Wipe-out.

 

[BoydAllen]

Make some things that function as wind flags. Sticks and surveyor's ribbon are fine. Get set up to load at the range, nothing fancy, just functional. You will save a lot of barrel steel, components and fuel. Pay attention to your bench setup. You can send me some pictures if you like, and I may be able to make suggestions. Use a camera with a delayed timer and tripod so that we can see what you are doing. Let the rifle surprise you when it goes off (Don't pulse the trigger, when shooting from supports, squeeze.). Try to watch the bullet hole appear in the target (follow through). Little things add up to become significant totals...good and bad.

 

[Donkey]

Now we are talking Forum boss!

I'm shooting off the elbows with around a 7kg weight limit and a 156gr max on projectiles. Ideally I would like to be pushing 3120fps + out of a 34" barrel. Krieger or Trueflight probably. I would like it to shoot 45 rounds before it needs cleaning and not copper foul excessively though I will almost definitely be developing some kind of friction proofing. So lets talk rifling profiles and twist.

-Who is doing great work with the wide flat 3 land profiles? Why are the easier on jackets? How about projectile stability?
-Does more twist = more copper fouling?
-If it is going to be a friction proofed only barrel should I have is cut slightly tighter?

By the way thanks for your thoughts Boyd. That topic is of vital importance and often over looked. The way I see it is this is the best gun tech forum in the world which is why I'll keep a tech focus here at least.



Cheers guys
Jason

 

[TonyR]

Donkey.
I believe that it is important to have your testing and load development procedures mirror your competiton formats. Like you, I shoot a lot of 20 round strings with unlimited sighters so I try to shoot test strings of similar length, even though there might be 3 or 4 different 5 shot groups of different loads within the string, and I don't clean the gun all day. Frequently, my last 5 shot test string will be fired with up to 90 rounds already fired since it was last cleaned and I want that string to shoot as well as the first string of the day if they are the same load. I think you will have adopt a test procedure something like this if you want to sort out this fouling issue or, at least how it is likely to effect you under match conditions.

 

[Donkey]

Hey Tony.

My current rig shoots really well even after 90 rounds but I am only pushing 2900fps. I'm thinking about the next barrel and trying to figure out some rules of thumb and the subtleties of the design parameters to help me reliably push those 155gr really fast.

Kind Regards
Jason

 

[Killshot]

My current rig shoots really well even after 90 rounds but I am only pushing 2900fps.
I'm thinking about the next barrel and trying to figure out some rules of thumb and the subtleties of the design parameters to help me reliably push those 155gr really fast.

Everyone has their own reasons.... but it brings to mind a fellow-member's signature line "Velocity is the girl to date but Accuracy is the one to marry for a lifetime!!!!!!."

 

[Donkey]

Oh you had to go there didn't you Killshot!

Put it this way. I want my bride to still be faithful to the long distance relationship. So I'm going to get her some canted, shallow grooved, well twisted, moly coated knickers and hope they don't get too easily fouled!


J

 

[Ing. Michael W. Mayerl]

Hello everyone.

I have a question about how to reduce copper fouling when running 3000fps + The rig I am referencing off is the 308 limited to 156gr projectiles.

Ideas so far:
Friction proofing projectiles.
Polishing the bore finish.
Using radially tapered lands to easy the projectile on the face so that it doesn't cut into it.

What else is there?

Also: For the same velocity the higher the twist the more copper fouling right near the throat right?



Many thanks in advance
Jason

I have a lot of experience with this:
- lapped barrel (best are hammer forged barrels because they have a very smooth surface)
- grooved bullets
- right break in with JB-Bore Paste

Thats the secret to reduce fouling to a minimum without any coating on the bullets.
Very popular is HBN coating - that can help too but I`m not a fan of bullet coating - but it could be good for sports to enlage the cleaning intervalls.

Today I shoot a Tikka T3 with my grooved AERO 115grain and 950 m/s. 6 rounds - no visible fouling.
Some weeks before I shoot a non grooved Hornady SST 165grain with 800 m/s - 5 rounds and very much visible fouling 10 - 15cm behind the muzzle.

Here a pic from my patented AERO bullets:

 

[frankgreen]

There is some evidence that 3-groove barrels, with their relatively flat, wide lands, are gentler on jackets. We've seen that at both ends of the caliber spectrum -- from .204 Rugers to 50 BMGs. 3 grooves are now preferred by most 50 BMG shooters because, with the solids, 3-grooves foul less and produce more velocity.

But... whether it can make a difference with your .308 is an open question. If you are working with a factory barrel, pretty much any custom lapped barrel should be better. Potentially way better.

I had a factory .260 barrel that looked like it was threaded inside. It took literally hours to clean with brushes, mops, JB, you name it. It was replaced with a barrel that cleans with 4-5 wet patches and a good soak with Wipe-out.

I've never seen where the number of grooves had any real bearing on accuracy, barrel life or fouling. Changing the bore surface area (tighter/looser) will effect pressure more and this can effect velocity but I haven't seen it with the number of grooves. I do feel that the odd number groove barrel will distort/upset the bullet jacket less and I feel this helps with bullet failure which is a problem for the long range shooter but not a short range shooter.

Also keep in mind as velocity increases (magic number is right around 3200fps) fouling can increase. Also keep in mind that bullets can vary from lot to lot. Different lots of jackets made on different lots of the copper material can effect the way the barrel fouls as well. Some lots can foul more and some less. It's not just the barrel.

Later, Frank
Bartlein Barrels

 

[RonAKA]

Ideas so far:
Friction proofing projectiles.
Polishing the bore finish.
Using radially tapered lands to easy the projectile on the face so that it doesn't cut into it.
For the same velocity the higher the twist the more copper fouling right near the throat right?

Not sure you read the article by Dan Lilja of Lilja Barrels, but he makes some interesting comments:

- He does not believe in friction proofing, and feels it may be counter productive.

- Over polishing the bore is likely to make fouling worse. He believe that powder residue needs to build up on the steel to reduce copper fouling and polishing removes that protective layer making fouling worse.

- Fouling is most likely due to surface finish, and not land shape.

- On twist near the throat keep in mind that the bullet is going very slowly at that point, and twist is not a big problem. Twist is more of an issue as velocity picks up in the second half of the barrel. Again surface finish is more likely to be the factor.
He also makes some interesting comments about higher twist barrels being more likely to foul. This may be an outcome, and not a cause. Barrels with a fast twist are likely for long range, and as a result will be longer, and heavy longer bullets are more likely to be used. The increased friction and longer barrel time is what increases the fouling -- not the twist.