Loose bore = Less Velocity?

[WeiserBucks]

Just run it at 165,000 psi itll be alright

Is that Richard I hear?

 

[dennisinaz]

I get 3000 with the 340 Wby. Similar with 338 Norma.

 

[VinceMule]

Slugging the bore may give results unless like VinceMule says it may be loose in the middle which would be hard to see from slugging.
I'm following this also.

Old Rooster, with a very tight punch type of jag, with a barrel that opens up in the middle, you would start the patch off very tight in the throat, then the patch will 'feel much looser" and then tighten again at the muzzle. It takes a slow, deliberate push on the cleaning rod with a focus on the "feel". I am dealing with a barrel like that right now. Chances are that that the heat treat is "off" on that barrel.

With the OP's barrel, he should just:

Find pressure on what is the max load for that powder/bullet
Back off 3.0g from the max load
Work up an accuracy load
Velocity is what it is, accuracy trumps all because stuff is not hard to kill when you can put that bullet where it is supposed to go!

 

[Old Rooster]

Makes me wonder how many barrels get kicked out the door with a condition like that.

 

[VinceMule]

Trombone barrels and barrels with open bores in the middle have been rare in my experience.

Rough cut rifle barrels are not uncommon.

 

[Shane Lindsey]

Find pressure on what is the max load for that powder/bullet
Back off 3.0g from the max load
Work up an accuracy load
Velocity is what it is, accuracy trumps all because stuff is not hard to kill when you can put that bullet where it is supposed to go!

Yupp. That is where I am at.

 

[Radman]

I have seen bores that measured tight on the breach end and tight at the muzzle, opening up in the middle, and bores that measure tight on the breach end and open up toward the muzzle(called trombone barrels) exhibit issues like Shane describes.

There are many factors that can contribute, but barrels are individuals. Rough barrel bores are another type of animal to deal with.

The fouling build-up in the bore can do some strange things. I saw a 6.5 x 55 exhibit over max pressure on below minimum charge due to copper fouling.

IMO: Lots of wisdom in your words. Well-said! Like people, every barrel is likely different.... somewhere. During production tooling changes, (due to temperature & wear), hydraulic oil temperature changes, (which often controls cutting feeds & speeds), plus coolant flow & temperature on drills, reamers & buttons. Ever wonder how much coolant actually makes it down the barrel as the bore fills with the ever-penetrating drill or reamer filling the void. If a drill or reamer gets hotter at certain points as it moves through the stock it naturally gets hotter = cuts more material! I would think even ambient temperatures where stock is stored obviously matters. Also IMO: straightening barrels BEFORE machining is ultra important. (Sure you can straighten them afterwards but then you may likely have a barrel with a bore that isn't straight or concentric)
You frequently bring up GREAT points VinceMule.

 

[FullCurl8]

Your loose bore theory makes sense. One way to test it is to make a cast of your bore with Cerrosafe. If you go this way, be sure to give it 30 minutes after removal to return to bore size before taking measurements.

As for reaching pressure before desired velocity, I find that is an indication that a faster burning powder is needed.

How does a guy Cerrosafe his bore?

 

[VinceMule]

Some years ago, a friend took a lathe, removed the headstock, attached a computer with a long stylus. He could measure the twist rate in .200 length increments and plot on a graph. It was amazing how twist rate changes in a barrel. He also invented and patented a new Barrel button that does not tip.

Anschutz and Pac Nor purchased those twist-rate measuring lathes that I know of.

 

[just_jon]

How does a guy Cerrosafe his bore?

Plug the chamber with cleaning patches.

 

[VinceMule]

How does a guy Cerrosafe his bore?

I think that it is a waste of time. Focus on load development, one bullet and one powder at a time, not a mish-mash of loads you read on the internet.

 

[MagnumManiac]

It is my experience that low velocities than expected are caused by roughness inside the bore, not the bore diameter. I have my comp barrels deliberately turned tighter in the bore diameter. Have had several loose barrels that were FASTER than a tighter barrel.
This is one of the slowest 338 barrels I have ever seen…
It fouls so fast it's ridiculous.

Cheers.

 

[Phil Rizzo]

Copper mine?
Sounds like it's still "producing"

 

[HRM Johnny]

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