Gunsmithing Can someone please explain so my head wont explode barrel chambering

[newbieshuter]

Hey guys, so i was at my buddies shop the other day while he was chambering a barrel for a new 6.5 prc. I looked at the muzzle end that was in the spider on the lathe and it was walking probably .600" around. I said something to him and he looked at me like i was stupid lol. The chamber side dialed at .0001 on his range rod but the muzzle end was everywhere. He tells me that it is perfectly normal and thats how he chambers and does muzzle breaks too. Is this normal? I cannot wrap my head around how you wouldnt want the whole bore and chamber concentric all the way through to run a true center.

 

[noisewaterphd]

The OD of a barrel is not concentric to the bore. A rifle bore is not perfectly straight. He's going to indicate at 2 different points on the chamber and dial it to zero. The chamber will be perfectly concentric with the first little bit of the bore. At least enough for the bullet to present itself to the bore properly.

Just reverse that idea for muzzle threading,

 

[The King]

Yeah - he's doing it right.

When you drill a gun barrel before rifling it its never straight - the gun drill is 3 foot long and being fed into the bore.

Maybe later there may be a way, like a casting out of some new super alloy that does rifling at the same time. Or wire EDM or a laser cut bore.

The main issue is - you don't have to have it straight. It just doesn't matter.

 

[Mordamer]

Walking .600"??? I think you have this measurement estimation off. I'd say that having the muzzle end with .030" of run out would be a lot. You can easily see .010" of run out and 0.025" looks like a lot. Your friend is doing it right from the sounds of it.

 

[newbieshuter]

cool, yah his rifles have always been absolute tack drivers but for some reason i couldnt wrap my brain around why one end was wobbling so drastically out of the spider end, .600" wasnt an exasperation either lol it was a conservative number. But i know they are tack drivers but just didnt know how with witnessing that much movement.

 

[300sniper]

“The right way” is still debatable. I suppose if you are getting the results you are after, it is the right way. I still think bores are much straighter than the internet makes you believe. My hunch is there are a bunch of barrels being bent into submission between spider chucks chasing a perfect number on a range rod. Once the stress from those spider chucks is relieved, I’m guessing the barrel relaxes into a state completely different than it was while the chamber was being machined.

 

[FUNCTIONAL]

“The right way” is still debatable. I suppose if you are getting the results you are after, it is the right way. I still think bores are much straighter than the internet makes you believe. My hunch is there are a bunch of barrels being bent into submission between spider chucks chasing a perfect number on a range rod. Once the stress from those spider chucks is relieved, I’m guessing the barrel relaxes into a state completely different than it was while the chamber was being machined.

I agree but a barrel will 99% of the time have some difference between breech and muzzle. Always left the outbound finger snug while i dialed the chamber and then did tail tighter to get my second point. Even go as far as loosening one screw and tightening the opposite to avoid over pressure. Still some wobble regardless. Some barrels even from the same manufacturer vary in the amount quite a bit. I agree its not extreme but the way the bores are drilled currently you cant avoid some drill bit wandering.

 

[Supersubes]

Hey guys, so i was at my buddies shop the other day while he was chambering a barrel for a new 6.5 prc. I looked at the muzzle end that was in the spider on the lathe and it was walking probably .600" around. I said something to him and he looked at me like i was stupid lol. The chamber side dialed at .0001 on his range rod but the muzzle end was everywhere. He tells me that it is perfectly normal and thats how he chambers and does muzzle breaks too. Is this normal? I cannot wrap my head around how you wouldnt want the whole bore and chamber concentric all the way through to run a true center.

Did you just eyeball this? Consider for a bit that what you were seeing was total runout. The actual amount from center (if there was .6” total) would have been half that. I got into this discussion with a guy I did a barrel for. He couldn’t wrap his head around it either. Lol. What he as looking at was maybe .050 total runout at the muzzle end. As has been mentioned already, bores/barrels vary a bit.

 

[Mordamer]

“The right way” is still debatable. I suppose if you are getting the results you are after, it is the right way. I still think bores are much straighter than the internet makes you believe. My hunch is there are a bunch of barrels being bent into submission between spider chucks chasing a perfect number on a range rod. Once the stress from those spider chucks is relieved, I’m guessing the barrel relaxes into a state completely different than it was while the chamber was being machined.

This is true. However, there are ways to dial the first 3 inches of bore straight on the chamber end without bending the barrel at all. There are probably a lot of gunsmiths not employing these methods and bending their barrels as they adjust the outboard spider.

 

[300sniper]

If they are doing that without bending the barrel, they sure aren’t seeing anywhere near .06” (assuming that’s what the OP really meant) of runout. Probably under .01” TIR at the muzzle.

 

[Wannashootit]

For cripes sake, couldn't have been over a HALF INCH on any decent barrel!
The crap Mosin military barrels I pull (or not) nearly every day aren't close to that- and I can turn .020 thou off on side of a really bad one before the cutter touches the opposite one. I refuse to believe any barrel worth installing would show .600 tir opposite the dialed in end. I mostly work between centers but those I've done through the spindle don't show anything near that.

 

[newbieshuter]

ill take a quick video next time im out with him while hes chambering one up, Heck ive seen when he was doing a muzzle brake the rear tang of the action behind the spider moving literally 1/2-3/4 inch wobble. Im pretty good with measurements to the guy that asked if i was sure i wasnt looking at .060. 7 years as a dimensional engineer in the aerospace field does that to ya. Anyways yah ill take a quick vid if hes ok with it and show ya what im talking about.

 

[300sniper]

Ok, if you you are serious about .6” of runout at the other end, that barrel is being bent in the lathe. I can promise you that. The barrel makers gundrill would have popped out the side of their stock if that is really what was going on.

 

[300sniper]

I’m no math magician but if he had the breech and 3” forward dialed in, assuming it is linear, that’s like .026”/inch of deviation. I’m finding that really hard to believe.

 

[Killswitch Engage]

ive chambered a shit ton of barrels and seen some crooked shit but i have never seen anything more than .050 tir. i think your .600 is probably a touch off unless he happens to have the most crooked barrel ever made.

 

[Geno C.]

In a 30cal barrel you could look down the bore and not hardly see any light if it was out .600 on the end. A person that has never seen a barrel before would know that is a crooked barrel

 

[Mordamer]

If it really is 0.600" then there is something terribly wrong. It can't be running true in the lathe. If it were true on one end and .600" bent over the length, it would be visibly bent as seen by the naked eye.

 

[bucklowery]

Is he talking about comparing the o.d of the barrel or the bore. On some of the rough blanks the difference looks very drastic sometimes

Thanks

Buck

 

[Gene Poole]

The next time I true up a barrel, I'll try to make a video clip of the runout for reference. In the mean time, assuming no one complains about copyright (I'm claiming "fair use") here's a short clip from Gordy Gritter's video showing typical runout. I'd say this is about 15-20 thou of runout which is typical. I've seen probably 60 thou before, but 600 thou, if that is indeed the case, is grounds for tar and feathering the barrel maker for allowing that off their production line.

 

[hunter223]

If it’s that much he’s bending the F outta the barrel

 

[newbieshuter]

wow thanks gene pool, i will video it next time im out at his place, ive just never been able to wrap my head around why its so far out yet still absolute tack drivers. I trust his work as he was the main gunsmith for a very large high end hunting rifle company. recently left to do his own thing now at his own shop.

 

[BillyGoatMachine]

I run a true bore alignment system to eliminate and flex on the barrel at all. I also measure the 12oclock position before ANY stress is added to the barrel and any cutting is done. I've never been a fan of finding 12'oclock on a barrel when it's twisted between two spiders.

 

[LRI]

Hey guys, so i was at my buddies shop the other day while he was chambering a barrel for a new 6.5 prc. I looked at the muzzle end that was in the spider on the lathe and it was walking probably .600" around. I said something to him and he looked at me like i was stupid lol. The chamber side dialed at .0001 on his range rod but the muzzle end was everywhere. He tells me that it is perfectly normal and thats how he chambers and does muzzle breaks too. Is this normal? I cannot wrap my head around how you wouldnt want the whole bore and chamber concentric all the way through to run a true center.

If the assumption is made that the holes is straight and the outer portion is running on the common center then sure, your 100% correct. This however rarely, rarely happens. The idea here is to get the portion of the bore your machining to run common to spindle center. Both in concentrically and in axial parallelism. That's all your buddy is doing. The rest of the barrel is just along for the ride. It's very typical.

I personally don't do the range rod thing as I've found them to be riddled with flaws, but folks have (for years) and built guns that perform.

If your into the whole clocking thing the easiest way to do it is with an open spindle and a sharpie marker. Chuck up the breech side in a scroll chuck or a collet and fire up the spindle at a low rpm. Slowly walk a sharpie marker at the muzzle end. Just to where it makes a partial mark. Now reverse the spindle and repeat. Split the difference between the two marks and you have your index point.

Easy, drama free. None of this is Ouija board dependent.