Bore diameter effects on precision

[FireMedic]

I recently got a 30cal Hart barrel and it’s on the larger size of bore diameter. I was getting ready to chamber it, going through my routine inspection and sizing of a pilot, when I found it to be on the big size.

This barrel will take a .3006 pilot but not .3008

This is as large as I’ve seen for a 30cal.
Does anyone see any correlation between oversized bore diameters and loss of precision?

I know Hart claims to have a +.0005 tolerance.

Thanks

 

[jelenko]

With the lands at .300, how is a .306 pilot getting into the barrel?

 

[FireMedic]

With the lands at .300, how is a .306 pilot getting into the barrel?

.3006 pilot bushing

Spec for this barrel is .3000 bore diameter/.3080 groove diameter +.0005 tolerance

 

[LVLAaron]

Anecdotal.... I bought a barrel from wheeler that's spec'd to the larger side of the tolerance. It's a faster barrel, and my best shooter for a long shot.

 

[LVLAaron]

On the other end of the spectrum, I have several Bartlein 308 tight bore barrels that are fantastic...


I'm gonna go with "doesn't matter"

 

[FireMedic]

Anecdotal.... I bought a barrel from wheeler that's spec'd to the larger side of the tolerance. It's a faster barrel, and my best shooter for a long shot.

Kinda my thoughts as well but wanted to get a general consensus from everyone else.

I have built a few of these smokeless muzzleloaders for customers, and it’s amazing how well they shoot with bullets sized to bore diameter.

 

[Eagle Six]

You have a barrel that is for sure 1 ten thousands out of spec, possibly 2 ten thousands. If it were me I would chamber it and shoot it. On the other hand, if I was you I would use caution listening to me, I'm just a shooter and far from being a metal smith of any kind!! Well....I'm descent with a hammer, hack saw or file!!!

 

[FireMedic]

You have a barrel that is for sure 1 ten thousands out of spec, possibly 2 ten thousands. If it were me I would chamber it and shoot it. On the other hand, if I was you I would use caution listening to me, I'm just a shooter and far from being a metal smith of any kind!! Well....I'm descent with a hammer, hack saw or file!!!

I plan to do just that, but I figured it would be a good conversation to have.

The price of tuition in this game can be high…

 

[jackieschmidt]

I do not concern myself with bore diameter that much…….groove diameter, yes.

That is why I like cut rifled barrels such as Krieger and Bartlien. While their bore diameter might vary a tenth or two, Their groove diameters are dead on.

 

[jelenko]

.3006

What's a digit among friends?
Sorry about that.

 

[gunsandgunsmithing]

Shoot it. Been there, both directions. I'd put more emphasis to groove diameter but even there, if it's consistent, I'm not sure you'll ever know the difference at all within a couple of tenths or even more. Some makers, both cut and button, used to write those dimensions on the bbl. I've seen them vary more than you're talking about and they shot great! Worry about it if it doesn't do well on target but I'm confident that it will. Hart makes a good bbl. If it will make you feel better, rather than posting here, call them before cutting it and see what they say about it.

 

[FireMedic]

it doesn’t matter until it does! I’m just wondering at what point is a bores “volume” too big.

I know it’s probably bullet dependent as well.

 

[BoydAllen]

A friend has an excellent LV 6PPC. Working with bullets that have a shank diameter of .2428 and a barrel that had a groove diameter of ..2432, he was not getting the consistent results that he was looking for. (we are talking about almost half a thousandth difference between groove diameter and bullet shank diameter) He switched to a barrel, from the same cut manufacturer that is .2430 and it shoots better, really good, instead of good. He routinely measures barrel groove diameters.

 

[gunsandgunsmithing]

it doesn’t matter until it does! I’m just wondering at what point is a bores “volume” too big.

I know it’s probably bullet dependent as well.

...and pressure.

 

[gunsandgunsmithing]

Bore diameter is a starting point. How bout jacket thickness, annealing, bearing surface, bullet od, pressure? How much does the bbl expand under pressure..same for the bullet?? Lots of variables

 

[LVLAaron]

Bore diameter is a starting point. How bout jacket thickness, annealing, bearing surface, bullet od, pressure? How much does the bbl expand under pressure..same for the bullet?? Lots of variables

This makes me think about something I think about often.

It's a MIRACLE any of this works as well as it does. We like to stress over tenths and millionths because we can measure them... but what actually matters? We'll never know. We could have krieger make two "identical" barrels but change the dimensions... do a comprehensive test of both, post the results, and we'd still collectively find a legitimate reason to say the test was invalid.

There's a lot of black magic between the trigger and muzzle. Much we can't scientifically define. It's both interesting and frustrating

 

[Kurz]

Then there are the tight bores often used in Palma:

1 turn in 13 in
Bore/Groove: 0.298”/0.307”

Or

.3065/.298 or .307/298 barrels

 

[Alex Wheeler]

Anecdotal.... I bought a barrel from wheeler that's spec'd to the larger side of the tolerance. It's a faster barrel, and my best shooter for a long shot.

That would have been groove specs not bore. Bore has less effect. Bigger groove is faster for sure.