Head-scratcher of the week, freebore coming up very short.

[eddief]

Access to an optical comparator for reamer measuring?

One of the reasons I prefer reamers .0008" to .001" over bullet diameter, for the freebore diameter.

 

[ridgeway]

He's probably running a different bullet. FB is often misunderstood. Throat in a second op for the intended bullet.

 

[LVLAaron]

185's and 200.20x's are all he uses. Pretty standard FTR fare. I just did a dummy stub from a barrel and it's fine. I'll report back when I have his stuff in the shop. It's an interesting one.

 

[Alex Wheeler]

Have him spin the round hes using to check touch on a concentricity gauge

 

[DaveTooley]

Rule #1 larger freebores don't make the phone ring.

 

[LVLAaron]

Rule #1 larger freebores don't make the phone ring.

I was waiting for you to say something about that.

The ones I've designed/ordered I've had done a full thou, or 1.2 thou over. This one isn't my doing.

 

[DaveTooley]

I was waiting for you to say something about that.

The ones I'veAlso we use abrasives, sometimes aggressively, to remove carbon. I've had done a full thou, or 1.2 thou over. This one isn't my doing.

I'm in Barcelona and have had a very nice evening.

 

[LVLAaron]

Long story short... freebore diameter...

The patient will be getting a new reamer.

 

[wedgy]

Long story short... freebore diameter...

The patient will be getting a new reamer.

Was the old reamer bad or he just wants something else ?

 

[Acyr]

Long story short... freebore diameter...

The patient will be getting a new reamer.

Did you run a throating reamer in it to bring up to size? I've had to do this.

 

[LVLAaron]

Couple of things... bullets that measure .3083-.3085 and a reamer that cuts .30850... I chalk it up to a tiny of normal runot, causing friction.

@Acyr yes.

 

[AlNyhus]

Couple of things... bullets that measure .3083-.3085 and a reamer that cuts .30850... I chalk it up to a tiny of normal runot, causing friction.

That's a pretty standard setup in the 30BR's with free bore lengths from 'zero' to .025-ish. I imagine the length of your free bore section is magnifying what's really a runout issue.

With the 'Touch Point' aka Wheeler method, you'll see a scuff mark all around the bullet if the shank is larger than the free bore diameter. You can also see this if the runout is enough that the free bore self centers the bullet. Can you see such a mark?

 

[Jud96]

Couple of things... bullets that measure .3083-.3085 and a reamer that cuts .30850... I chalk it up to a tiny of normal runot, causing friction.

@Acyr yes.

Good find. We had a couple customers having issues with 6.5 PRC barrels. They were shooting factory ammo and complaining about the rounds being hard to chamber. After inspection, we found that the bullets in the lots of ammo they were using measured 0.2645, same diameter as the freebore on the SAAMI reamer. We were able to have the reamer resharpened and changed the freebore diameter to 0.265 and at the same time we changed the 0.200 line to 0.535 to help with clickers.

 

[Alex Wheeler]

The 6.5 aw2 has a .2648 freebore diamer as well. I noticed it was tight. They went .3088 on the 300 prc though. Somethings got missed on that prc design

 

[LVLAaron]

Definitely going with .309 or .3092

 

[Old Navy]

I'm hoping it's that. This is hard to describe, but I know with my hornady comparator, you can push the bullet in and feel a light "stop" but you can push it over that hump and get it into the lands.

I have a barrel like that.

 

[FireMedic]

Curious, was it a 5 groove?

 

[LVLAaron]

Curious, was it a 5 groove?

Yes

 

[FireMedic]

Yes

I’ve had a custom rifle come in the shop from a well know builder that wouldn’t chamber factory ammo. This rifle was chambered in 6.5cm which already has a smaller freebore diameter. The reamer pushoff in the 5 groove caused the freebore to be cut undersize. It was visible with the bore scope.

I’m sure you have your process dialed in, but I had to change a few things when dealing with 5 grooves to get them to come out perfect every time.

 

[LVLAaron]

I’ve had a custom rifle come in the shop from a well know builder that wouldn’t chamber factory ammo. This rifle was chambered in 6.5cm which already has a smaller freebore diameter. The reamer pushoff in the 5 groove caused the freebore to be cut undersize. It was visible with the bore scope.

I’m sure you have your process dialed in, but I had to change a few things when dealing with 5 grooves to get them to come out perfect every time.

That crossed my mind, more than once. I pre-bore, use a spiral rougher, and bore the lands so the finish reamer has minimal contact with the lands... It's always worked for me before, but I'm sure this one could have gotten away from me.

The good news is, it's shooting bugholes now, so it all worked out.