Crooked chambers/ uneven lands

[urbanrifleman]

I guess it all depends on what you consider shooting well? Yes lots of factory barrels have crooked chambers. They do because these big gun makers chambers these barrels off a live center. They don’t dial in a single thing I’ve seen myself this process at one of the more well known and trusted competition AR barrel makers shop. I was truly in shock. I’ve personally never seen a crooked chamber shoot better than 1/2” consistently. Ya maybe a wallet group here and there but never with any consistency. Stranger things can happen I guess.
Lee Gardner Precision

As far as I know, people didn't dial in barrel chambers as a common practice until the 1990s.

Before that, I'm pretty sure most of the world record groups were set with barrels that weren't dialed in. They were all chambered on centers.

I think some of those groups stood for decades. Certainly better than half an inch.

I know people that I know that have set world records with barrels that weren't dialed in.

 

[urbanrifleman]

listen to the target not the pictures of the barrel

I asked one of my friends who was a high master Palma shooter and had gone to Gordy Gritters gunsmith School. I asked him what they did to chambers before you could buy it borescope relatively inexpensively. He said, " we would go shoot them ".

 

[gunsandgunsmithing]

I've seen a few where the lands are cut to the same length but the grooves cut more on one side than the other.
Since most smith's use piloted reamers that are supported by the lands, someone would have to explain to me how the Smith or the reamer did that. Seems to me it'd have to be unequal groove depths.

 

[DaveTooley]

I've seen a few where the lands are cut to the same length but the grooves cut more on one side than the other.
Since most smith's use piloted reamers that are supported by the lands, someone would have to explain to me how the Smith or the reamer did that. Seems to me it'd have to be unequal groove depths.

FB diameters too small and groove diameters larger than nominal. It's a very very fine line. Close fitting bushings don't help. YMMV

I was "DIALING" in barrels in 1983 and many more were as the transition from lathes with a small diameter spindles to newer, imported lathes arrived on the scene.

 

[DShortt]

I've seen a few where the lands are cut to the same length but the grooves cut more on one side than the other.
Since most smith's use piloted reamers that are supported by the lands, someone would have to explain to me how the Smith or the reamer did that. Seems to me it'd have to be unequal groove depths.

Yes. That's where bores that aren't uniform can affect the outcome.

The truth is, there's no one thing that causes a barrel to be more accurate than another. I do believe it's best to start with a blank with a uniform bore and cut a concentric chamber and a concentric crown. By and large barrels that fit this description will shoot well and that's where consistency comes it.

If one or more of the above are off, it *might* shoot well, but my observations have been that such is the exception and not the rule. It also depends upon the rest of the components of the shooting system and the skill of the shooter. Again, there's no one answer or one 'magic trick'.

 

[urbanrifleman]

I've seen a few where the lands are cut to the same length but the grooves cut more on one side than the other.
Since most smith's use piloted reamers that are supported by the lands, someone would have to explain to me how the Smith or the reamer did that. Seems to me it'd have to be unequal groove depths.

Exactly.

 

[urbanrifleman]

FB diameters too small and groove diameters larger than nominal. It's a very very fine line. Close fitting bushings don't help. YMMV

I was "DIALING" in barrels in 1983 and many more were as the transition from lathes with a small diameter spindles to newer, imported lathes arrived on the scene.

So, my statement that it didn't become a common practice until the 1990s would sound about right.

 

[PRR1957]

I've seen a borescope video of a Rem700 .308 with the bore 40 thou eccentric to the throat. Surprisingly, it didn't shoot well..

Was Remington using a chamber reamer that did not have a bore pilot ?

I remember reading somewhere about high-volume production firearms where the chamber reamer does not have a pilot to guide the reamer while cutting the chamber.

 

[DShortt]

Was Remington using a chamber reamer that did not have a bore pilot ?

I remember reading somewhere about high-volume production firearms where the chamber reamer does not have a pilot to guide to reamer while cutting the chamber.

I have no inside information to confirm this but given the number of mass produced factory barrels I've seen with non-concentric chambers I believe many manufacturers are relying on CNC equipment which isn't a problem *if* the machine is set up correctly.

I personally suspect that's where many non-concentric chambers in factory rifles come from but again, I've no inside information so it's nothing more than a hunch.

 

[urbanrifleman]

I have no inside information to confirm this but given the number of mass produced factory barrels I've seen with non-concentric chambers I believe many manufacturers are relying on CNC equipment which isn't a problem *if* the machine is set up correctly.

I personally suspect that's where many non-concentric chambers in factory rifles come from but again, I've no inside information so it's nothing more than a hunch.

I really do want to know how someone is chambering with a CNC machine because I don't know how it's done. I certainly wouldn't know how the machine would establish concentricity.

 

[DShortt]

If a manufacturer is convinced it will cut production costs I'm sure that's what they do. Perhaps it's more a function of tooling but again, then it depends on the set-up, just like a piloted reamer does.

I do know non-piloted reamers are made so someone is using them otherwise there'd be no market for them. I have seen non-concentric chambers on pre-fit barrels from a couple of names that certainly surprised me.

 

[Webster]

I've seen a few where the lands are cut to the same length but the grooves cut more on one side than the other.
Since most smith's use piloted reamers that are supported by the lands, someone would have to explain to me how the Smith or the reamer did that. Seems to me it'd have to be unequal groove depths.

I know nothing about lathes. I read somewhere that you can buy chucks made to 3 levels of runout. Can you explain to us. What's the cost difference?

 

[PRR1957]

If indeed high-volume mass-produced rifle barrels are chambered with a non-pilot reamer, and the chamber is non-concentric with the rifled bore, could also be the result of the bore not being concentric with the outside diameter of the barrel.

So with high-volume mass-produced rifle barrels, after the boring, reaming, and rifling, I'm not sure if the chamber is cut first or the outside diameter and profile of the barrel is cut. Various different manufacturers would have their own sequence of production to accommodate what machinery they own. If the bore is not dialed in, or hung between centers with support along its length somewhere, a piloted reamer in a non-floating tool holder in the tail stock would end up breaking the pilot off the reamer. I believe this is where those non-piloted reamers are designated for high-volume mass-production.

I've been a machinist for a number of years. Both manual and CNC. Working at jobber shops, and a couple prototype shops. Plus also, I've spun a few rifled blanks in the past. Blanks were Willson, E.R. Shaw, and Lilja turned for a couple dozen or so AR10 uppers. So I'm not trying to imply I am some master machinist, but the ones I turned, were MOA or less. Not surprisingly, the Lilja barrels were the most definitive of the three brands, with a few fly busters. Runout with the Lilja barrels blanks between the bore and OD was .004" or .005".

And if anybody's interested.
EMCO 42" (I miss using that lathe.)
Clymer Ruffer (308 Win)
JGS Finish, Bushing Pilot (308 Win)
Cutting oil flush.

 

[LVLAaron]

I really do want to know how someone is chambering with a CNC machine because I don't know how it's done. I certainly wouldn't know how the machine would establish concentricity.

Dial it in, press go.

 

[gunsandgunsmithing]

I know nothing about lathes. I read somewhere that you can buy chucks made to 3 levels of runout. Can you explain to us. What's the cost difference?

I'm not following you. Yes, there are certainly some chucks better than others, if that's what you're asking. That's a strange and vague question, it seems. For all intents and purposes in this context, it's about setup being the best it can be and I don't think a more accurate chuck is generally the solution.

 

[urbanrifleman]

Dial it in, press go.

Dial it in? Like through the headstock?

You've seen this operation?

How does the reamer chips get cleared? Is there a pilot on the reamer?

 

[SKWERLZ]

I asked one of my friends who was a high master Palma shooter and had gone to Gordy Gritters gunsmith School. I asked him what they did to chambers before you could buy it borescope relatively inexpensively. He said, " we would go shoot them ".

Bore scopes won’t tell the truth like a bullet will.

 

[DShortt]

It would be interesting to know what the lifespan is on those barrels with non-concentric chambers that start put shooting great.

 

[SKWERLZ]

Dial it in? Like through the headstock?

You've seen this operation?

How does the reamer chips get cleared? Is there a pilot on the reamer?

I have a friend that works in a production barrel shop that does thousands of barrels for oem’s
I’ll ask him about his production set up

I do know they use CNC’s, Fixed reamer holders and through barrel pressurized lube system

 

[SKWERLZ]

It would be interesting to know what the lifespan is on those barrels with non-concentric chambers.

The wonky Shilen prefit I got lasted about the same as the more concentric ones but that wasn’t for top competition accuracy.
It would be interesting in a more demanding situation.