6.5 PRC Freebore and Cartridge Base to Ogive help

[DBoone]

After months of back and forth with a gunsmith, I received my custom 6.5 PRC yesterday. So tonight I performed a lands test on my top two picks of hunting bullets. And this is where I think I have a problem...

During the build process I sent the same 2 bullets to the gunsmith to identify my CBTO and COAL touching lands and confirm it would fit in the detach mag I had chosen. So they got back to me with the info using their .180"ish freebore reamer. I crunched the numbers and decided I'd like to have more room to chase lands during the life of the barrel. So I spec'd a .130"ish freebore reamer, which would then need to be ordered.

... Back to tonight's results, my one measurement was identical to the info they sent me, and the other was off by .010".

Did they not use the reamer I had spec'd?

I'll start by putting my results up here in hopes others can do the same. I will try and test a few other bullets I have also... 135 Classic Hunter, 143 ELDX, 160 Matrix VLD.

Freebore - ??????

142 grain Nosler ABLR - 2.380" CBTO

140 grain Berger VLD Hunting - 2.317" CBTO


Thanks

 

[dok7mm]

How did you take your measurements?
Did you use the same exact bullets that you sent your smith? Could be a variance in bullet form. Also, in a new chamber there can be a burr causing a slight difference.

 

[DBoone]

How did you take your measurements?
Did you use the same exact bullets that you sent your smith? Could be a variance in bullet form. Also, in a new chamber there can be a burr causing a slight difference.

Measured with Hornady tools, averaged five measurements.
Same exact bullets.
It was a brand new barreled action they had in the shop. So equal chance for a burr in both I suppose.
I was expecting to see ~.050" difference in my new measurements compared to the ones they provided. That's why I was hoping others could chime in with some results with known freebore.

 

[fabricator21]

I have a .188 freebore with the 142 ablr my cbto is 2.381

 

[BrentM]

Not sure if this helps but my proof is 3.020 COAL to the lands with a 147. I am running them for testing at 2.998. I have a TL3 and MDT coming and will run AICS mags.

ELD's run the boat tail junction right at the neck/shoulder junction. It's not bad but I would have liked to see less free bore. Proof never did answer me when I asked what reamer they used.

 

[Ladd-]

My Christensen Arms Ridgeline 6.5 PRC has a 2.334 CBTO with the Berger 140 gr VLD.

 

[Zhomeguy]

Good question...I'm trying to chase down the preferred reamer specs for most guys...seems at first the question was whether running from a mag or not, then can run without a buffer... so I'm vacillating but leaning towards the .188 freebore

 

[Rhett Crider]

Mine has 0.155 freebore and here is what my measurements are.

 

[codyadams]

I have found the hornady type measuring tool (and pretty much every other tool I have tried) to have variences in it's numbers, no matter how careful you are. I have used a few different tools, and actually found a method without using tools to be much more accurate and repeatable.

Watch this, try it and then see what numbers you come up with. You may find the discrepancy is in the tool itself.

 

[DBoone]

Updating my bullet list, its not as nice as Rhett's but it will have to do. All bullets gently jamming lands.

Freebore - ??????

142 Nosler ABLR - 2.380" CBTO
- 2.995" COAL

140 Berger VLD Hunting - 2.317" CBTO
- 2.957" COAL

160 Matrix VLD - 2.377" CBTO
- 2.976" COAL

143 Hornady ELDX - 2.337" CBTO
- 2.974" COAL

135 Berger Classic - 2.340" CBTO
- 2.935" COAL

 

[DBoone]

I have a .188 freebore with the 142 ablr my cbto is 2.381

Thanks, looking like I have a .180"ish freebore to me.

Proof never did answer me when I asked what reamer they used.

When I inquired with Proof they told me they only do SAAMI spec chambers.

Watch this, try it and then see what numbers you come up with. You may find the discrepancy is in the tool itself.

I agree there is room for error in tools and people using them. I'd be ok with +/- 0.010" between numbers with that in mind. My concern and why I'm not seeing the 0.050" difference between reamers. If I work Rhett's numbers (135 Berger @ 2.315" with a .155" freebore) compared to mine (135 Berger @ 2.340") it still puts me around that .180" freebore range.

 

[live2huntmt]

Is there a way to look at a SAAMI drawing and see what the freebore is? I ordered a Proof prefit for a bighorn TL3...if they are chambering it to SAAMI dimensions, what will my freebore be?

 

[jpndave]

Is there a way to look at a SAAMI drawing and see what the freebore is? I ordered a Proof prefit for a bighorn TL3...if they are chambering it to SAAMI dimensions, what will my freebore be?

2.2447-2.0568 = 0.1879 or rounded to 0.188 as specified above.

 

[jpndave]

These two: