Gunsmithing Question on Freebore for 6.5 CM barrel

[Baron23]

Hi guys - I'm having a new Bartlein barrel in .264 spun for 6.5 CM. Question is the SAAMI or the .150" freebore reamer that my chosen gunsmith offers.

I reload Berger 140 HT over 42.1 gr of H4350 in Lapua cases out of MDT mags with the binder plate which accommodate a max COAL of 2.87. I may reload 140 ELD-M in the future but I currently have a lot of the Berger.

I also shoot 140 ELD-M and Berger 140 HT factory ammo (yeah, when I can get it and afford it! haha) and other assorted similar stuff (e.g. I still have some Prime with 142 Sierra).

I have had two 6.5 CM barrels with SAAMI freebore which I believe is .199" if I'm reading the drawings correctly. In the past. I have found that the closest I could get to the lands was right about .080" while leaving .005-.010" of room off the mag binder plate for bullet OAL variation. I use a Hornady OAL gauge and yeah, it takes a bit of technique/learning, but with a little experience I found very good consistency over multiple measurements and outliers were very obvious.

With SAAMI chambers, I have done seating tests backing up from .080" jump to .120". But I can't really get closer than .080" to see if there is a better seating depth. And, .080 jump shot the best vs further out so I'm interested in getting closer and see if there is even better results with a closer jump.

I note that Preferred Barrels posted on their site some interesting results of various factory ammo with various FB with them finding that .150" was optimum.

https://preferredbarrelblanks.com/best-6-5-creedmoor-chamber-prefit-barrel-comparison/#110

I'm not really seeing any downside to the .150 FB. That should get me .049" closer to the lands for a min jump of about .030 on a new barrel while staying in mag length minus a bit. And I believe I certainly have room in the case to back up .050 or so to get back to the .080" jump (or further) that I've found in the past worked fairly well without compressing the load (if that's even an issue). Factory ammo is much shorter and I don't plan to reload any long bullets like Berger's LR 153.5's.

Am I missing something here. I'm no expert at this. What say you guys?

Thanks and remember....Check 6.

 

[Yondering]

Seems to me for your load, either the shorter freebore or mags without the binder plate would be the way to go.

I'm using the 145gr Match Burners in non-binder MDT mags though so it's hard to make a direct comparison. If I remember, I think my OAL is around 2.935" but it's been a while since I measured it, usually just looking at base to ogive.

 

[Char'ed Cuterie]

OP,

You'll note at the very bottom of that link, they mention that the 0.150 option is now an Alpha reamer with 0.160. I'd take that in a heartbeat given your variables. If your smith doesn't have the Alpha 0.160, you're probably entirely fine with 0.150 unless you're expecting to make sweeping changes in your setup.

As an aside, I ran into all sorts of internal feeding issues with long 6.5 Creedmoor even after going with a nice AccurateMag and notching my feedramp so they'd clear. I'm now in a similar position as you, loading to be safely inside a binder and/or thicker polymer magazine and taking advantage of the easier path to chamber in my action. The slight gain in performance wasn't worth the time lost to clearing feeding issues on the clock.

 

[Baron23]

Seems to me for your load, either the shorter freebore or mags without the binder plate would be the way to go.

I'm using the 145gr Match Burners in non-binder MDT mags though so it's hard to make a direct comparison. If I remember, I think my OAL is around 2.935" but it's been a while since I measured it, usually just looking at base to ogive.

OP,

You'll note at the very bottom of that link, they mention that the 0.150 option is now an Alpha reamer with 0.160. I'd take that in a heartbeat given your variables. If your smith doesn't have the Alpha 0.160, you're probably entirely fine with 0.150 unless you're expecting to make sweeping changes in your setup.

As an aside, I ran into all sorts of internal feeding issues with long 6.5 Creedmoor even after going with a nice AccurateMag and notching my feedramp so they'd clear. I'm now in a similar position as you, loading to be safely inside a binder and/or thicker polymer magazine and taking advantage of the easier path to chamber in my action. The slight gain in performance wasn't worth the time lost to clearing feeding issues on the clock.

Thanks for taking the time to reply. No Alpha .160 reamer as far as I know. Just .150 and that seems the way I should go.

 

[Baron23]

@spife7980 - any input my reloading sensei friend

 

[spife7980]

My saami chamber requires a binderless plate mag to seat my rdfs closer to the lands so I see no problem taking to .150
Can’t speak to factory hornady ammo fitting or not though.

 

[Baron23]

My saami chamber requires a binder plate mag to seat my rdfs closer to the lands so I see no problem taking to .150

Thank you. But not sure I understand. A binder plate, that shortens max mag length, is needed to get you closer to the lands??

 

[spife7980]

Thank you. But not sure I understand. A binder plate, that shortens max mag length, is needed to get you closer to the lands??

Corrected my typing, binderless

 

[tom12.7]

When Alpha first recommended to me to use the 0.160" FB in AR-10s, It was to be able to use the widest variety of factory loaded ammo offerings without pressure signs compared to 0.150".

 

[Baron23]

When Alpha first recommended to me to use the 0.160" FB in AR-10s, It was to be able to use the widest variety of factory loaded ammo offerings without pressure signs compared to 0.150".

Thank you for the reply, Tom. This is a bolt gun and even with .150 I should be .30 off jam at max mag length with a binder plate MDT mags I use. I like the binder plate for feeding purposes.

And that .30 figure was on a brand new, not yet shot, barrel. Of course throat erosion will cause that to go up over time.

And gee, pretty much all the factory ammo I shoot is a good bit shorter and I have room in the case to back up a fair bit without compressing the powder.

I’ll ask the smith about Alpha .160 but I don’t remember seeing that in his list of reamers.

I don’t think this .150 FB will in any way be a catastrophe, but if it is I assume I can get the FB reamed out just a bit more. But I just think that scenario is unlikely.

Thanks again.

 

[Yondering]

The feed question with or without binder plates seems to depend on the action. I'm using the no-binder MDT mags with a couple of humble Ruger American actions and have no feed issues at all with both 6.5 Creedmoor and the much shorter 6mm GT. (I went without binder plates on the 6 GT just to keep the mags common between them). I'd expect the same results from the Ruger Precision action too of course, since it's very closely related to the American. Other actions may be more picky, but mine haven't given me any reason to want a binder plate in the mags.

In fact the only feed issues I've had were with a Magpul AICS mag which I believe is of similar or even shorter internal length to the binder plate mags, but being a polymer Magpul it's really not that comparable.