If the lands and the bore are off by .015", shouldn't the barrel maker exchange the barrel?
Is it possible for the bore and the chamber to be non-concentric ?
- Thread starter hemiford
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I had a 300 wsm proof barrel chambered by a reputable gunsmith only to find out after a frustrating 5-6 months and 250-300 rds later it wasnt cut true. Wouldnt shoot sub 1.5" (5 shot group) with any load after trying 3 different powders, 4 different bullets and 3 shooters.
Hummer70
Member
Assuming you are going to cut your own chamber (as I do) when I get a new barrel blank in I chuck it up with 4 jaw chucks on both ends of lathe head. I have pilots turned for the caliber I am chambering and I place them in both ends of barrel and use a dial indicator to get both ends turning on center. (Takes about 90 minutes to dial it in correctly but I have always got positive results.
Order a barrel contour that is bigger than you need so you can remove stock and still have enough to thread.
I then turn the outside of the barrel on the chamber end so when I thread the barrel it is well centered.
Also what you need to look for is the bore being crooked inside barrel. Do that first and if you detect a crooked bore take no further action.
Also if you have a round action chuck it in 3 jaw and turn the front end off as it is likely to have high spots that will contact barrel when screwed in and bore centerline will be off.
Order a barrel contour that is bigger than you need so you can remove stock and still have enough to thread.
I then turn the outside of the barrel on the chamber end so when I thread the barrel it is well centered.
Also what you need to look for is the bore being crooked inside barrel. Do that first and if you detect a crooked bore take no further action.
Also if you have a round action chuck it in 3 jaw and turn the front end off as it is likely to have high spots that will contact barrel when screwed in and bore centerline will be off.
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Short answer is yes, it is possible. There are several ways for it to get that way, just as there are several ways to indicate a barrel for chambering. Everyone thinks their method is best. Add to the fact most barrels have a bore that is not perfectly concentric to the OD, most bores are curved, and you have to decide for yourself the method of chambering that will yield the best results.
TRexF16
Well-Known Member
I've found three off-center chambers just in the relatively short time I have had my Teslong borescope. In the chamber throat, a couple lands run all the way to the case mouth on one side of the chamber.
Magnum, are you sure that that the decimal place is not off on this .015, .0015 would be a country mile!
WOW! Now THAT is an excellent extreme example!
That hurts, not just financially.
I had a factory 700 chambered in 7mm RM. The chamber was so far out of alignment with the bore that fired brass would wobble when it was rolled across a flat surface. It would shoot 1/2" moa with new brass but shot horrible with once fired brass
Black Hole Weaponry, now called Columbia River Arms, did a 6 x 6.8 that was off. Took a CerroSafe mold of the chamber/throat sent them a pic. It was a 3R barrel, that the rifling started at the case for 1 land. .050" away from the case for 1 land, the third land was .100" away. Swapped it for a .264 LBC which I now longer own.
Yeah I also have a 6.5 prc barrel for the same action and shoots amazing but it was so frustrating the time and money wasted on that paper weight of a barrel. I wanted to take the 300 wsm on my elk hunt but instead the 6.5 prc is going with me. I did buy a new .30 cal barrel but havent had it chambered yet.
Being a machinist I can say without a doubt things can happen. Most barrels are made in steps . Outer diameter profile, gun drill ,cut rifling, cut and crown etc . So you can see there is many steps and many machines and setups to making barrels. The chamber is usually cut after the barrels are set with rifling it doesn't take much just a .001 tilt in the barrel when moved to the next step will 
as the lenght increases. Just to be honest I'm not a gunsmith or maker . I am a aerospace machinist so if it flys,drives ,or blows crap up I've probably made something for it. I just recently had a gun at the smith's for a muzzlebreak and was informed the original crown was off to the bore so my smith re- cut the crown and set it up with a self timing break all for free as it was going to a giveaway I do to promote youth hunting here in Arizona.
as the lenght increases. Just to be honest I'm not a gunsmith or maker . I am a aerospace machinist so if it flys,drives ,or blows crap up I've probably made something for it. I just recently had a gun at the smith's for a muzzlebreak and was informed the original crown was off to the bore so my smith re- cut the crown and set it up with a self timing break all for free as it was going to a giveaway I do to promote youth hunting here in Arizona.Barrels are most likely the root cause. A lot (most?) of bar stock is NOT straight when new. IMO great barrel manufacturers check or straighten EVERY barrel BEFORE any machining process. (NOT just one per batch) If it's not straight before machining ain't nuth'n going to be straight or concentric after machining. Both V35BTC & Hummer70 allude to this & they're right-on. We must remember that the vast majority of barrels are mass-produced on machines designed to crank 'em out. (We like to picture a dude operating his lathe in his shop taking his time to eventually make one perfect barrel at a higher price. That MAY happen in some cases but not likely for most mass production) I worked for a major corporation for years in Quality Control & I can tell you that EVERYTHING affects a true bore, a straight/square steel stock, concentricity & bore diameters. Things like ambient temperature of the facility verses barrel stock temperature. Hydraulic fluid temperatures. (We never turned our pumps off!) Speeds & feeds. Tooling sharpness/wear. Even coolant temperature. (Most folks never stop to think: How can I get enough coolant on the cutter when it's halfway down the barrel?) Factors like this affect a uniform minimal rifling ID down the length of a barrel. As a drill or cutter heats up, ir expands, & makes a bigger hole. Sure, it can be fixed by the next operation but everything passes on down the line you see?) JMO
Everything matters....
Well said Sir. I was writing my long harangue before I saw your reply.Being a machinist I can say without a doubt things can happen. Most barrels are made in steps . Outer diameter profile, gun drill ,cut rifling, cut and crown etc . So you can see there is many steps and many machines and setups to making barrels. The chamber is usually cut after the barrels are set with rifling it doesn't take much just a .001 tilt in the barrel when moved to the next step will
