Reamer cutting off center in the throat

[Heavy barrel]

Just learning to chamber & I'm practicing on an old barrel. I indicated the muzzle & the neck area (I can only indicate to the neck area, indicator is not long enough to reach the throat, 308 win). Threading & reaming went smooth. The back of the chamber measures to the reamer specs but when I look at the throat with the bore scope I can see that the throat is off center a little. It's a 6 groove barrel & 3 of the lands are cut fully & the grooves are cut but on the other side the lands are not fully cut (can see lands down to the neck) & the grooves are only partially cut. I can't reach with my indicator to measure but must be off around a thousand or so. I'm using a snug fitting bushing. I drilled & bored before reaming. I made a reamer holder that uses a ball bearing at the back of the reamer & a flat pusher in the tail stock.

I hold the reamer holder in my hand. Could I be influencing the reamer with how I'm holding it? I would think the rear of the chamber would be oversized.

Is the bore ahead of the throat (where the bushing rides) making a turn pushing the reamer off center? Would taking the bushing off before getting to full depth help?

Or is there something else I'm missing?

 

[NickB1075]

Trust me I am not an expert and you got some excelent advice from a master already, but I will try to add this anyway. Leave the muzzle end alone and indicate in on the chamber end. I am sure you have heard that the no barrel is drilled perfectly straight and they are slightly curved. So in theory once the chamber end is dialed in the muzzle end will not be be in the same location. I hope this makes sense. Then you can also index the high muzzle location to 12 if you want.

Also Alex touched on it and said maybe something is moving. I personally check my set up every move I make. Probably more then I need but I can tell you this I am confident that when I do a barrel it didn't move out. And if it did I fix the issue before moving on. I don't do this for a living so how long it takes is not important to me when chambering or crowning and such. I just want the best I can do.

Also go get a good indicator that will work for how you want to chamber. I cried when I bought mine but it has made things way easier, and I use it as much as any other tool I have.

Good Luck I hope I helped.
Nick

 

[DaveTooley]

fat groove diameter and tight freebore possibly
add a bit of alignment problem and that might explain your results.

factory barrel or custom?

 

[DaveTooley]

Alex did you get my PM?

 

[Heavy barrel]

Dave, the reamer spec is tight in the throat (.3082) it's a Shilen barrel.

This is just practice with what I have on hand. I'll get a Grizzly rod & try Gordy's method.

I'm a palma shooter so having the muzzle in line with the action makes the most sense to me. I have a few barrels that I can't use levels to mount the front sight.

 

[DaveTooley]

That's too tight. You spec's +.0002 but what did you really get. The barrel could be 5 or 6 tenths or more over nominal bullet diameter. Perfect setup for what your seeing.
What bullets are you shooting and what do they measure? A lot of things can go wrong when working to those tolerances.
Not sure where you are in the process but drop a bullet in and see if you touch the lands or are you getting a ring or both. My guess is you can't comfortably get to the lands.

 

[Heavy barrel]

Dave, I'll try that when I get home tonight. The barrel is still in the lathe. I'm going to leave it there until I get a way to measure in front of the throat.

 

[Heavy barrel]

Alex, I guess it could have moved. I did check after each step though. I'm using a spider chuck with ball bearings in the bolts & pads to hold the barrel & when adjusting the muzzle end I moved the muzzle until it pivots at the chamber then let it relax. So the barrel is not flexed when indicated. The outboard spider bolts are just finger tight.

 

[Heavy barrel]

Dave,
An old timer engineer designed the reamer. His thoughts where if you spec the reamer tight after the reamer is made then ream the chamber you would likely end up with normal clearance. It can't be smaller, only larger. It sounded good to me at the time. My thoughts were if it was too tight I could run a throating reamer in to correct it.

 

[Cloudrepair]

 

[Shawnba67]

I just did a barrel today, i indicated the throat and the muzzle. Just for giggles i checked the very end before i started and had almost 0.0008 runout! That was only 2.75" from the throat.

 

[HCP]

I've seen this more than once from the hundreds of barrels I've seen. remember, depending on your reamer dimensions in the throat/lead area of your barrel you are normally about .0002-.0004 over groove diameter and a leade of 1.5 degrees so VERY, VERY minor variances look bad. On barrels I have seen this every time without exception, the bore has minute deviations (they are all crooked) from where you indicated and will give this appearance. My advice, take it out and shoot it, you may be pleasantly surprised. does it make a difference, depends how you can tune/read the flags.

 

[Heavy barrel]

I got a Grizzly rod & indicated the area ahead of the throat where the bushing rides when I reamed the chamber. Not totally sure I'm using the rod correctly but after indicating, the back of the chamber is 6 tenths out.

The bullet fits in the throat no problem. I loaded a dummy round with light neck tension & it didn't push the bullet back or leave any marks. I'll see if that changes if I can cut a straight chamber.

I'll cut it off & try again. I'm really enjoying the learning process but I'm going to have to tread lightly buying more tooling for a while, the wife is starting to look at me sideways.

 

[sdean]

Seems to me if you prebored the hole then you got it off center then. The reamer followed what you bored.

 

[Will Henry]

If you indicate at the throat and muzzle and the breech runs out at all, you have to bore a start for the chamber which is concentric with the throat. If you are working with a barrel which is already chambered, you cannot indicate on the neck of the chamber unless that chamber is perfectly concentric. There are various alternatives when it comes to dealing with crooked barrels and all are a pain in the ass. Ultimately, we just do what we can and send back any barrels which are curved enough that we don't want to deal with them. WH