Oval chambers

[R.G. Robinett]

Interesting thread . . .

Yes, that is exactly Al's point. Mine too. And most all rifle builders I know. The way to convince us we are wrong is not to go off into a world most of us don't live in, we'll ignore you no matter what you say. The way to convince us is to build several (the repeatability factor) competition rifles that are clearly superior at their job -- shooting higher scores or smaller groups. At that time, you won't have to bother saying anything except "It'll cost X and the wait time is Y"

Charles, back to your original question: a pal of mine once had a Remington 788, chambered in 22.250, with an 'oval' chamber. The chamber was so out of round, that unless [fired] cases were 'properly oriented', they could not be re-chambered - not until they were FL re-sized. On his NECO run-out device, the cases showed 0.007" of TIR: fired/indexed, and neck-sized cases would fit back into the chamber . . . and shot remarkably well. After messing with this rifle for a while, my buddy asked if I'd re-chamber it for him: during set-up, the chamber displayed about the same run-out as the fired cases; following the re-chamber, the TIR was reduced to just under 0.002" - still pretty UGLY! However, at that point, indexing [neck-sized] cases was no longer necessary, and grouping improved. How Remington produced such an oval hole remains a mystery. BTW, when I have done my own chambering, on new barrels, the chambers, from mouth-to-shoulder-neck, have never displayed over 0.0002" of TIR . . . and better yet, all have proven capable of winning BR tournaments. I am NOT a gunsmith, only do fit & chambers for myself. RG

 

[4Mesh]

As I touched on above... Somebody ought to mention that, much of this talk of ultra high precision is dependent upon the material being worked. You will NEVER hold the sort of tolerances on 416R that someone could in say, 52100 that's hard. No more than you could grind aluminum. Now, I can't wait for someone to come here and say they grind aluminum parts every day!

The material itself has to be pretty nice stuff, and hard, before you can give it a surface finish that allows measurement to tolerances like suggested above. Within the context of competitive rifle building, My thoughts are, the dimensions in the chamber should hold true to the tolerances of the casework. If I guy shooting a ppc holds 10th's on his necks, then certainly he needs a chamber that is round within close to that. If a guy FL resizes and gives a case .002 of clearance in the chamber, then the chamber better be round within .001 for certain. (hopefully, a lot closer). But, if one guy has .0003 or eccentricity and another has .000001, will we see that on a target when both leave .002 clearance on the case? I doubt it.

If a guy uses any care at all when doing a chamber job, things should be lined up and round within acceptable BR limits, regardless what equipment he's using. If your lathe is a p.o.s., then rough the job out and finish up with the barrel in a vise and use a tap handle on the reamer. It's supposed to be a hand reamer anyhow. Stick a stop on it, and go in small increments. The finish will be beautiful and the chamber will be as round as anyones. And if you want to know what makes the rifle really shoot, talk to the guy in the last post.

 

[TRA]

C'mon 4mesh, your not really living in the dark ages are you?

As I touched on above... Somebody ought to mention that, much of this talk of ultra high precision is dependent upon the material being worked. You will NEVER hold the sort of tolerances on 416R that someone could in say, 52100 that's hard. No more than you could grind aluminum. Now, I can't wait for someone to come here and say they grind aluminum parts every day!

FYI, Not that it matters, BUT, Here's just one of many companies that do, "grind aluminum every day.
http://www.arrowgrinding.com/?gclid=CIOa-Pa7hKoCFYeD5QodMEA10A

BTW, no one said you "must" keep using 416R, no more than anyone would grind 6061.

 

[nhkuehl]

Some hammer forging mandrels include the chamber... I don't know which manufacturers do that, but I would say that could open all kinds of possible irregularities. If you have an oversize chamber, wouldn't the first obvious sign be primer strikes that aren't centered (barring an off set firing pin or a non-concentric bolt bore.), either randomly or opposite the extractor. At some point the case rim will contact the side of the bolt face, instead of the case body in the chamber. I found the rim diameter of .308 Lapua brass was 0.010" more than the rim diameter of FC brass and the Lapua brass centered better. Extractor grooves are different diameters also and some of the claw extractors put a fair amount of pressure on a shallow groove. Most factory rifles that I've bore scoped have some degree of 'off set' in the throat. On one of the other posts someone said he'd wished he'd taken his bore scope to the store when he bought his rifle... maybe not a bad idea. Too bad you can't test fire them. - nhk