Gunsmithing Stupid Question Alert: Can I slide a reamer in a chamber?

[OzzyO20]

I know the tolerances are extremely tight, and this might not even be closer to possible. I think my chamber was cut with the wrong reamer (too little free bore is my guess) and I'm wanting to purchase the correct reamer anyhow. It'll be a good while before this barrel is shot out, but I was curious if I bought the reamer now if I could slip it in the chamber and verify the throat is too shallow?

I forewarned everyone this was a possible stupid question, so take it easy lol.

 

[Mike_in_FL]

I'm no machinist but when my friends who are do barrels, the barrel spins in the lathe and you push the reamer into it to cut the chamber. Generally you'd have a roughing and finishing reamer just for the chamber. You cut a little and install lug and action, put in bolt and headspace gauge. If the bolt doesn't close you cut the chamber deeper.

If your gun headspaces correctly now, it could be a short throat or tight neck. There are specific reamers that could open these up without affecting headspace but I think you're getting ahead of yourself.

Before you start reaming the chamber I'd buy a Hornady OAL gauge and test with the bullet you want to use. There's a good discussion on that tool in the Reloading forum right now.

 

[OzzyO20]

@Mike_in_FL that's the thing, I have measured the OAL after seating .020" off the lands and the designer said should be in the 2.760 range. I'm closer to 2.580" OAL.

 

[Mike_in_FL]

If this is brand new, it would have to be a hell of a burr in the throat to make that much difference in OAL. I would take it back to whoever cut the chamber and let them look at it. Again from my friend's perspective, how sharp the reamer is, how many chambers cut, makes a difference. That's why you don't try to cut the entirety of it with the finishing reamer.

The only other thing I can think of is that the chamber was not cut perfectly centered. I had a rifle where the chamber was cut wrong, .007 off center and it took about .080 off what the OAL should have been. This was a whoopsie where the barrel was cut on a vertical mill and that particularly Bridgeport did not have a "memory" to hold where that actual zero on the x and y axis were.

 

[Steel head]

I know the tolerances are extremely tight, and this might not even be closer to possible. I think my chamber was cut with the wrong reamer (too little free bore is my guess) and I'm wanting to purchase the correct reamer anyhow. It'll be a good while before this barrel is shot out, but I was curious if I bought the reamer now if I could slip it in the chamber and verify the throat is too shallow?

I forewarned everyone this was a possible stupid question, so take it easy lol.

If it’s a bullet seating position issue a far better alternative is a chamber throating tool.
Right tool for the job.

 

[DAVETOOLEY]

Have you talked to your gunsmith about this? While a bit tricky it's very simple to lengthen the throat with a throating reamer.
No two reamers are exactly the same size. There are +/- tolerances to everything.
At the very least you run the risk of ending up with a less than desirable finish.

 

[fdkay]

take an empty case, insert your bullet of choice, seat to your desired length. Slowly chamber the round.
The bullet will be pushed into the case.
Do this slowly, do not force it.
It works best with a case fired in that chamber, then neck sized only tight enough to lightly grip the bullet.

 

[OzzyO20]

take an empty case, insert your bullet of choice, seat to your desired length. Slowly chamber the round.
The bullet will be pushed into the case.
Do this slowly, do not force it.
It works best with a case fired in that chamber, then neck sized only tight enough to lightly grip the bullet.

I'll have to get a different bushing. I'm guessing a slit case isn't accurate enough for this?

 

[spife7980]

I'll have to get a different bushing. I'm guessing a slit case isn't accurate enough for this?

Much better alternative.


Because if just trying to chamber it you can both set the bullet back into the case as well as jam it some indistinguishable amount and that amount may not be trivial.

A crooked chamber can cause an issue with this method though, get a bore scope and/or some cerrosafe chamber casting compound to see if its visibly out of whack. and not evenly cutting the lands on one side of the chamber vs the other.

 

[Supersubes]

PTG makes something called a uni-throater for running the throat out on an assembled rifle. I think the other manufacturers make a similar tool. Never used them, as I’d rather do it in a the lathe. Like Dave mentioned, reamers vary, even if they’re made to the same print. You risk cutting in places you didn’t want to, and with no means to support the back of the reamer coaxial with the bore/existing chamber, you’re gonna mess things up.

Have you talked to the gunsmith who built it? If it was chambered with the wrong reamer, that seems like it’s the builders problem.

 

[Millsworks]

There hopefully is a good reason you don't want to take the rifle back to where it came from?
What cartridge is it chambered for?
Maybe think about a rechamber to something else.
An Ackley of some sort would likely clean it up.
Don't know your situation.
But it seems it needs serious thought.

 

[Rubicon Precision]

Chances are, as long as the new reamer freebore is longer, it’ll work just fine, even by hand. With a proper fit pilot bushing, the alignment will be just fine. The rear of the chamber isn’t going to change and you’ll easily feel the shoulder contact and shouldn’t change headspace.

There’s a slight chance of a small step in the freebore if the first reamer had a larger freebore diameter either by design or allowable tolerances.

 

[Millsworks]

Old school chamber casting is the route I would take after a bore scope.