Berger 6.5 MM 140 gr Hybrid Target - Required Freebore?

[RonAKA]

I am waiting for a new barrel chambered with a Match SAAMI reamer in 6.5 MM Remington Magnum. Since it is going into a long action 700 Remington, I thought I was free and clear on any issues with seating long bullets like the Berger Hybrid. Now, I have come to the realization that the 6.5 RM SAAMI was designed for a short action, and SAAMI has potentially set the Freebore for the standard 2.800" COAL in a short action. Ouch! I may not be able to seat those long bullets as far out as I think.

And so we don't go down a semantics rabbit hole, can we assume Freebore is the distance from the end of the chamber neck to the start of the taper into the lands. So it includes the short angled taper from the neck end to what I would call the throat which is typically just over bullet nominal caliber.

I've done a search here, and I find this require Freebore dimension is all over the map. Most discussion seems to end up with. "Just make a dummy cartridge with the bullet you want to shoot, and make it the gunsmith's problem!". I unfortunately don't have that choice. It is a REMAGE barrel and should come ready to use.

I have checked the 6.5 RM SAAMI, and with the definition above, I make Freebore to be 2.389" minus 2.194" = 0.195". I then check the 6.5x284 Norma CIP drawing to see what it has, as this cartridge was designed for a long action. I make the Freebore on this one to be dimension "s", or 8.02 mm, which is 0.3157". Ouch again!

So, now I am panicked, thinking I'm going to have to get this Freebore lengthened with a throating reamer, until I find a few posts here saying that Savage F Class 6.5x284 Norma owners were disappointed in their gun because the Freebore was way too long... It is likely built to CIP standards. And there are other posts which suggest that around 0.200" is fine??

I have tried in the past to calculate required Freebore theoretically using Berger's bullet dimensions, but that seems to result in a Freebore that is way to long compared to what custom guns are actually using.

So what is the consensus on Freebore for this 140 grain Hybrid? Is the 0.195" in the ballpark? Or should I be panicked?

 

[Auto-X Fil]

0.195" is a little bit long for the 140 hybrid. I certainly would not go any longer than that. You will have the base well above the donut with 0.195".

 

[WSnyder]

Not nit picking but your definition of freebore or what is commonly noted on some prints as "lead" does not add in the dimension of the transition from the neck to the lead. Most people refer to FB as the parallel (or near parallel) section as lead or FB. Obviously CIP is different but at least in general use here in the US it's not common or hasn't been in the past. So for the sake of you getting a good answer you might think about that. That said I would say your SAAMI FB is .1643" and yes it should be in the ballpark and I would agree for the hybrid .195" would be a bit long but should still work. The neck on the 6.5 Rem Mag is a little shorter than some more common 6.5 so I'd think you wouldn't want to go too short on FB. A 6.5 Creedmoor with a SAAMI .190" FB puts the hybrid bearing surface somewhere close to but a little less than halfway up the neck but keep in mind the Creedmoor neck is ~ .025-.030" longer than the 6.5RM. The SAAMI FB on the 6.5RM might be close to perfect but you or your gunsmith will have to figure that out.















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[RonAKA]

Not nit picking but your definition of freebore or what is commonly noted on some prints as "lead" does not add in the dimension of the transition from the neck to the lead. Most people refer to FB as the parallel (or near parallel) section as lead or FB. Obviously CIP is different but at least in general use here in the US it's not common or hasn't been in the past. So for the sake of you getting a good answer you might think about that. That said I would say your SAAMI FB is .1643" and yes it should be in the ballpark and I would agree for the hybrid .195" would be a bit long but should still work. The neck on the 6.5 Rem Mag is a little shorter than some more common 6.5 so I'd think you wouldn't want to go too short on FB. A 6.5 Creedmoor with a SAAMI .190" FB puts the hybrid bearing surface somewhere close too but a little less than halfway up the neck but keep in mind the Creedmoor neck is ~ .025-.030" longer than the 6.5RM. The SAAMI FB on the 6.5RM might be close to perfect but you or your gunsmith will have to figure that out.

Yes, I agree that the Freebore would be .1643" on the SAAMI if the taper from the end of neck is left out. If that is the common way of expressing it, and that is in the ball park then that is making me feel a little better. Thank you for that!

It still leaves me wondering though why the freebore is so short compared to the theoretical number you can calculate using the Berger dimension from base to ogive. I did that calculation and got 0.419" for required freebore! Seems to me that there has to be more to this than meets the eye. Possiblilities seem to include; Berger's numbers are not accurate or what is felt to be "to the lands" is really significantly into the lands. I guess I should do the math, but often bullets are a little undersized. I recall measuring some Bergers at 0.0002" under, and even the minimum SAAMI for the chamber is 0.0005" over nominal bullet size, and there is a +0.002" tolerance on top of that. Perhaps 2-3 thou extra diameter takes you a long way down that 3 degree taper into the lands, but I doubt that it is 0.2" down....

 

[WSnyder]

I should also state that the SAAMI Creedmoor uses a 1°-30' throat so my comments on where the 140 HYB is in the case neck should take that into consideration. The 6.5RM 3° with the same FB will be different. I can't say how much. I can't comment on how you are so far off when using Berger dimensions. I generally like to have the actual components in my hands when I'm figuring the dimensions for a reamer. Tooley has a simple method of getting close and if you search around you might find his comments out there but you'll need components in hand. There is a method from a reamer maker that's more accurate but it's a fair bit more complicated than Tooley's and he's taken a beating around here lately so I'll leave it alone. You also need components in hand for his method as well.

 

[RonAKA]

I should also state that the SAAMI Creedmoor uses a 1°-30' throat so my comments on where the 140 HYB is in the case neck should take that into consideration. The 6.5RM 3° with the same FB will be different. I can't say how much. I can't comment on how you are so far off when using Berger dimensions. I generally like to have the actual components in my hands when I'm figuring the dimensions for a reamer. Tooley has a simple method of getting close and if you search around you might find his comments out there but you'll need components in hand. There is a method from a reamer maker that's more accurate but it's a fair bit more complicated than Tooley's and he's taken a beating around here lately so I'll leave it alone. You also need components in hand for his method as well.

Thanks again. I will do some more searching. Have brass, lots of other 6.5 bullets, but not the 140 hybrid yet...