Smeared throat

[Rflshootr]

What is the main cause of a brand new reamer causing a smeared throat using it on a factory chrome moly barrel? The reamer has only cut the length of the neck to set a barrel back, never a whole chamber. Is it the reamer, which looks fine, or maybe the barrel is on the soft side or something else?

 

[DaveTooley]

Are you talking about smearing the lands or tearing metal in the freebore?

 

[yotehater]

Loose pilot or undersized? Bore larger than the pilot?

 

[Rflshootr]

Are you talking about smearing the lands or tearing metal in the freebore?

Smearing the lands.

 

[clowdis]

Pilot too big? Does it fit the bore at the muzzle?

 

[paperpuncher]

Solid pilot reamer? Is the smear longitudinal or circumferential?

 

[Rflshootr]

Solid pilot reamer? Is the smear longitudinal or circumferential?

Removable pilot reamer. Circumferential smear of the lead/lands only. Pilot sized .0002 under bore size.

 

[DaveTooley]

You may be seeing a change in surface finish from the chips making metal to metal contact while the barrel rotates. If that's the case it's just superficial. If on the other hand you're rolling metal from the land into the groove you have a reamer problem. Is you freebore section one diameter?

 

[Rflshootr]

According to the drawing the freebore is suppose to be the same diameter. And yes it's rolling metal from the land to the groove. I also PM'ed you a copy of the print. I just looked at the lead section of the reamer with a 10x loupe and I can just barely see a small break down of the edge. Not what I would think would be enough to push the metal like it is. I can't see any healing marks either.

 

[gunsandgunsmithing]

Are you viewing this with a newly acquired bore scope? To some degree, it's normal, even in a perfect world. Add enough magnification, and these things show up. Break in should easily take care of any normal amount of this. Of course, sharp tooling minimizes it, but it's normal to some degree. It's the nature of machining with a reamer..or basically any kind of cutting tool to leave some amount of burring. Grinding instead of reaming the chamber or throat will greatly improve this aspect, but if it's what I'm picturing it to be, it's nothing to worry about...just a side affect of a bore scope. Lol!

 

[DaveTooley]

You have reamer problems. I see this in production barrels. It can range from a wire edge, a feathery expanded metal look to a piece of the land just rolled over into the groove.

Looking at the face of the flute if you can see the edge starting to get shiny you run the risk of pushing metal. Just reread your first post. I think you have a reamer problem.

How many rounds on the factory barrel?

 

[Rflshootr]

Dave about 200 give or take a few. So to solve the problem with the reamer, I should do what?
And the break in did make it disappear but when I do put a custom barrel on, which probably won't be too far in the future, I don't like the idea of those pieces of metal getting drug down the bore with the bullet.

 

[DaveTooley]

If you have a piece of barrel around, which I doubt since it's a 270, cut a dummy chamber, shoulder forward and then section it for a better look. If you still have problems send the reamer back to the manufacturer with the piece of sectioned barrel.

 

[gunsandgunsmithing]

If you have a piece of barrel around, which I doubt since it's a 270, cut a dummy chamber, shoulder forward and then section it for a better look. If you still have problems send the reamer back to the manufacturer with the piece of sectioned barrel.

Yes...I guess I didn't finish typing or failed to hit save in my post above. That's what I was saying and why I posted the pic of a cross sectioned barrel stub, as you describe. The pic is of one that looks as it should, but with enough magnification, there will be some very minor smearing. I did this to show what it should look like and to plant the seed to do the same to see if his looks like this or something more serious. Obviously, the one in the pic has very little freebore... .010" to be more precise.

 

[Rflshootr]

Any way to lap that burr off? A brass lap cut on the same throat angle maybe, turned by hand in the opposite direction?

 

[DaveTooley]

While you're lapping the burr you're also lapping the barrel. Why go down that path?

 

[Rflshootr]

yeah....you're right. time to call Kiff I guess. I'm just wondering if I missed some carbon and it dulled the lead a little. Probably would be cheaper to buy a throater and just touch it up at the end.

 

[Rflshootr]

Thanks Dave.