Free bore in general, leading to reamer inquiry

[cmc308]

I have been experimenting with free bore between a few rifles. Mixed results are the best description, then I come up against free bore spec for reamers in a custom build which I have no idea how I could even make that conclusion given that I have no real conclusive data through ongoing experimentation. I am having real trouble seeing material gains thus far in experimenting with FB. Not sure if this matters, but I am experimenting with one custom rifle match chamber .308, zero run-out, and two other factory "off the shelf" rifles .308 and 6.5CM. I have yet to see the FB gain in any of them, or maybe I am looking for something too obvious, or I probably don't know what I am looking for.
Notwithstanding magazine considerations, assuming that piece is figured in, can someone educate me on the FB piece and kind of help me understand my path? For further info, I am somewhat settled on my load recipes, though not entirely settled therewith due to various reasons. Regarding loads - I am not loading for top speed or for super-hot rounds, I am taking a very conservative approach on my load recipes trying to pull out "just what I need" and just what the rifle wants to give as opposed to forcing the rifle to accept what I want. Maybe this is wrong. You all can attack me on this as you see fit.
My preferred shooting is F-Class and I am looking to move into BR comps with calibers other than those aforementioned. So, shot grouping is what I am shooting for as opposed to PRS style. All of this inquiry precedes my intent to have a proper BR rifle built making these previously mentioned rifles my experimentation devices for all intents and purposes. I do occasionally shoot F Class T/R, but it goes without saying that any of the exotic and high custom rifles can smoke me any day of the week if the T/R class is lumped in with the Open Class. I am presently obtaining with handloads, consistent .240" groups at 100 yards with my factory 6.5 rifle, and similar sized and smaller groups with my custom. FB however is where I am not really seeing the light. All of my present COAL's are simply based on the factory COAL's. My magazines do not really allow a great deal of FB manipulation. What little various FB manipulations I have pushed to the magazine limit does not really seem to offer a gain that I can measure on the target. Can anyone offer any input, or nudge me in a direction that will allow me some better understanding?

 

[David Christian]

I have been experimenting with free bore between a few rifles. Mixed results are the best description, then I come up against free bore spec for reamers in a custom build which I have no idea how I could even make that conclusion given that I have no real conclusive data through ongoing experimentation. I am having real trouble seeing material gains thus far in experimenting with FB. Not sure if this matters, but I am experimenting with one custom rifle match chamber .308, zero run-out, and two other factory "off the shelf" rifles .308 and 6.5CM. I have yet to see the FB gain in any of them, or maybe I am looking for something too obvious, or I probably don't know what I am looking for.
Notwithstanding magazine considerations, assuming that piece is figured in, can someone educate me on the FB piece and kind of help me understand my path? For further info, I am somewhat settled on my load recipes, though not entirely settled therewith due to various reasons. Regarding loads - I am not loading for top speed or for super-hot rounds, I am taking a very conservative approach on my load recipes trying to pull out "just what I need" and just what the rifle wants to give as opposed to forcing the rifle to accept what I want. Maybe this is wrong. You all can attack me on this as you see fit.
My preferred shooting is F-Class and I am looking to move into BR comps with calibers other than those aforementioned. So, shot grouping is what I am shooting for as opposed to PRS style. All of this inquiry precedes my intent to have a proper BR rifle built making these previously mentioned rifles my experimentation devices for all intents and purposes. I do occasionally shoot F Class T/R, but it goes without saying that any of the exotic and high custom rifles can smoke me any day of the week if the T/R class is lumped in with the Open Class. I am presently obtaining with handloads, consistent .240" groups at 100 yards with my factory 6.5 rifle, and similar sized and smaller groups with my custom. FB however is where I am not really seeing the light. All of my present COAL's are simply based on the factory COAL's. My magazines do not really allow a great deal of FB manipulation. What little various FB manipulations I have pushed to the magazine limit does not really seem to offer a gain that I can measure on the target. Can anyone offer any input, or nudge me in a direction that will allow me some better understanding?

Okay, that was a lot in your post. Let me see if I can simplify a few things. In my mnd:

• If I were shooting a rifle with a magazine I would probably not mess with the free bore as the mag length would be my ultimate arbiter.
• Assuming a bolt rifle with no magazine, I would want to measure how deep I wanted the bullet to be seated in the neck along with how much jump or jam I desired with my seating to determine how much free bore was needed in the chambering.
  • Longer bullets will need more free bore.
  • More desired jump will need more free bore.

Long story short, ask a few gunsmiths or find a few shooters using the same bullets and see what they are running. I don’t spend much time reinventing the wheel unless I know the wheel inside and out and then have an idea to make it better.

Practically, I would compare the CBTO of a loaded round to the free bore specs of the reamer to calculate how much jump or jam is possible. That math will tell me all I need.

 

[NZ_Fclass]

Just from my experience. 308 doesn't need any more free bore than it needs. If you are running 150g/155g - the answer is pretty much whatever the rifle came with. For match use, the M852 reamer works. However, if you want to shoot the heavies - say 185 Berger and heavier,, you will need to make room for the powder, so move the bullet forward. - I have just had my rifle rechambered with the 2013 US FTR TEAM reamer. This prevents powder compression and the bullet can seat allowing tuning of the load length. As the previous poster suggested - this only works for lengths not constrained by magazine length. IMHO - there is no accuracy advantage to be gained by playing with free bore.

I don't have much time with the 6.5 Creedmoor, For a while I thought it to be a bit of hype...now I own a couple (duh). But being a "new" cartridge, designed for long for weight bullets, the SAAMI chamber seems adequate for purpose and I'm chambering 140g bullets without issue.

I think that you should look at load length and neck tension, rather than free bore as a way of tuning your loads, as these have a far greater effect.

 

[cmc308]

Ok. That is exactly what I needed to hear from both of you fellers. I have been running up against shooters telling me their FB exploits so naturally my interest/curiosity pushed me down the path. I failed to understand or realize any gains in my current setups, but the bullet seating and powder compression matter did cause me some pause. Thanks for the input

 

[cmc308]

I shot a few F Class matches with my mag gun. I was not allowed to load my mag. I had to shoot single shot only. The reference to the mag piece and the related seating depth was for when I shot PRS matches. Clearly messing with seating depth becomes a concern for mag users.

 

[cmc308]

So to avoid offending anyone else like I offended the little fish there... I admit after reviewing my post that it was a bit vague on useful data and over spent on the description. So here it is - PRS matches the magazine matters, F Class, yes you do not use mags - credit to the perch.
The FB reference as it regards the mag becomes conjoined when the ammo will not fit the mag which affects PRS shooting. Using the same gun as I do, to participate in both match disciplines (PRS and F Class), it requires some separation of material, its intended uses and its subsequent deployment. With that said, I attempted to explore the benefits of FB while striking a happy medium between the two match disciplines.
I was introduced to FB while shooting an F Class match, with my magazine rifle, which I had to load single bullet at a time due to those regulations - credit to the perch again.
FB became a point of interest. I chased it [but wish to learn more.]

 

[Forum Boss]

If you are getting a .308 win rifle re-chambered for F-class you’ll probably want to go with significantly longer Freebore. This allows you to seat longer for a bit more powder, and you can use the big, long bullets favored in F-TR. You should consult with a couple of shooters and a good Smith to decide appropriate free bore length. Most of the F-TR guys I know are jumping their Bullets 10-20 thousandths or more. The advantage to jumping is that, if you have to clear (unload) a chambered round during the match, the bullet won’t get stuck, or move in the case neck.

 

[JEFFPPC]

Or you could but a throater when you buy a reammer. Make it whatever you want..

 

[cmc308]

@ JeffPPC - point taken. Thank you.
@ Forum Boss - Understood. I appreciate the constructive direction/feedback. As it regards the shooter at the match with whom I was discussing the matter of FB, I did notice that he had a similar rig to mine, but also he shot in the Open Class with a very nice high custom rifle as well. I believe he had to have been referring to something more substantial than the rifle I was using at that moment in time, and probably more like his custom rifle. Another thing about his rigs were that they were both single shot while mine was a repeater, with a magazine. So, thanks for all the input. I will put this to bed and get off the thread now. Thanks all.