true freebore

Discussion in 'Reloading' started by ballistx, Mar 6, 2014.

  1. ballistx

    ballistx Well-Known Member

    Messages:
    48
    Joined:
    Mar 8, 2011
    I've searched quite a bit on various forums and get a variety of definitions. None of which I can accurately relate. So, here is my question.
    Based on SAAMI 30-06 the measurement from base to the end of the case is 2.502". Measurement to the taper to inside neck diameter is 2.5228" (.0208" difference). the measurement to the beginning of the lands is 2.7442". This results in a distance of .2422" from the front of the actual case to the beginning of the bore.
    Assuming that the lands begin at the exact point of the beginning of the bore (2.7442") is the "freebore" then .2422"?

    I guess what I'm asking is if the "freebore" is the distance from the front of the case to the beginning of the lands?

    As a case in point, my Remington 700 30-06 has a base to lands distance of 2.846". Using the SAAMI distance (case length) of 2.494" base to end of case, my freebore would be 0.352". Ammunition loaded to placate my Marlin XL7 (with 165 grain Nosler Partitions at 3.26" COAL & 0.036" jump) would have a "bullet jump" of .240".
     
  2. idaho elk hunter

    idaho elk hunter Well-Known Member

    Messages:
    542
    Joined:
    May 7, 2013
    You pretty much have the concept. Remember on the oversized mags they have to have freebore to avoid pressure spikes and cross bridging with certain powders. The best cartridges built (Weatherbys) have upwards of .37 to .40 freebore. The ultra mags especially the 7mm rum has generous amounts of freebore. Most of the time freebore rifles usually like harder bullets like the Barnes. You can get them to shoot if the bolt is trued. The chamber is tight, especially in the neck and the barrel is aligned perfectly. OR YOUR REALLY LUCKY.
     

  3. wyomingblizzard

    wyomingblizzard Well-Known Member

    Messages:
    173
    Joined:
    Nov 8, 2011

    Maybe I am Not reading or under standing you right, but it seems you are mixing head space and freebore mesurements togather. My understanding of freebore is the distance of the ogive to the lands and has nothing to do with case length. Case length, base to shoulder has more to do with head space.
     
  4. ballistx

    ballistx Well-Known Member

    Messages:
    48
    Joined:
    Mar 8, 2011
    That is the confusion. If it is the ogive, then there is no absolute freebore measurement for any rifle. It is relative to the cartridge/bullet combination. So, the term "the rifle has ".xxxx" freebore is meaningless.

    However, headspace should be limited to the case and should be independent of the bullet relationship to the bore/lands. Headspace should be limited to the body segment of the chamber, not the barrel segment.
     
  5. Mikecr

    Mikecr Well-Known Member

    Messages:
    4,264
    Joined:
    Aug 10, 2003
    No, this is JUMP(roughly).
    Freebore is set by the chamber reamer, but there are several common ways to consider it:
    -Chamber neck end to land begin
    -Chamber end to land begin(lead)
    -Same references but to ogive contact(as set by ogive radius/type & leade angle)

    The value that matters to me is seated distance to land contact -per bullet.
    Predicting this up front for filling out a reamer print, etc, is not very easy. Best done with a program, and reamer makers can do it for you.
     
  6. Edd

    Edd Well-Known Member

    Messages:
    2,394
    Joined:
    Jan 26, 2011
    One thing that may be confusing you is, you are looking at a 30-06. It doesn't have any freebore. The throat starts at the neck/bore transition angle. Look at the modified 30-06 reamer print at this link. It has a .086" freebore. You still have to consider the total distance from the base of the case to the lands when seating bullets.


    Rem 40XL: .30-06 Long Action
     
  7. ballistx

    ballistx Well-Known Member

    Messages:
    48
    Joined:
    Mar 8, 2011
    For that reamer, I would calculate the "freebore" to be 2.603" - 2.517" or 0.086".
     
  8. Canadian Bushman

    Canadian Bushman Well-Known Member

    Messages:
    1,650
    Joined:
    Jan 24, 2012
    Yes that is correct.

    Free bore is the amount of "bore" a rifle has before the rifling starts.
    Ive seen this measured from the bolt face, from the end of the neck of the case, and from the start of the bore to the start of the rifling. Like you just did for the said print.

    However the actual amount of free bore a rifle has is quite useless, like mikes comment stated.

    From a reloading standpoint the importance of freebore is its relation to your bullet.
    What COAL does my bullet contact the rifling? Once this is known you can properly load for a rifle with the knowledge of how far your bullet is jumped/jammed?
     
  9. ballistx

    ballistx Well-Known Member

    Messages:
    48
    Joined:
    Mar 8, 2011
    For me it is part of my engineering OCD. I have numerous centerfires that I reload for. I have multiple bullets for most. What I have done is create an Excel spreadsheet that lists the dimensions of each. In that way I can predict, and verify the outcome.

    I just found a new Marlin XL7 stainless in 25-06 at Sportsman's Warehouse for $359. I already have a Remington 700 ADL in 25-06. So, how do they compare?

    I will determine the COAL by inserting one of the bullets in the barrel up to the lands. I will hold it in place with a cleaning rod from the rear. Then I will measure the distance from the muzzle to the point with another rod. Then, I will measure the distance to the bolt face. By inserting those two numbers into the spreadsheet, I now have all the information regarding the jump, possible maximum length, comparative jump between the 2 (or more) rifles. I also have immediate measure of the amount of bullet held in the case.

    Each of my bullets is cataloged for the length, base to ogive, and tip to ogive. This is correlated with the OAL.

    I have 4 243's that shoot 5 different bullets. Hard to keep it straight.

    So, in all this, I need to identify what is the "rifle freebore" that will be used. What I am, and will be, using is the length from the front of the chamber neck (actually slightly ahead of that) (don't know what the tiny distance is called where the chamber drops from the outside of the neck to the inside of the neck) to the beginning of the lands.

    For my "cartridge freebore" I will use the distance from the front of my case to the lands. To me that is the actual freebore.

    For my true "bullet jump" I will go from the front of my actual case OAL to the lands, less the length of the bullet to the ogive that is outside the case. In other words, from the ogive to the lands.

    May not be real productive, but it has helped me understand the chamber, cartridge, barrel relationships and will help me understand the freebore relationship to accuracy with my individual rifles.
     
  10. Mikecr

    Mikecr Well-Known Member

    Messages:
    4,264
    Joined:
    Aug 10, 2003
    Ogive is not really a datum(it's a nose shape parameter). There is no 'standard' datum that is a land contact point on the nose. OAL is measured with calipers, and you should do this as described for each different bullet. With a cartridge built to your max COAL, you can then log any local ogive datum to base(referred to recently as CBTO). In other words, you don't need any bullet parameters at all, given that you're directly measuring based on your max COAL, and the results only apply to your chambers/bullets. Hope this makes sense..


    Why? What are you doing with the term?
     
  11. ballistx

    ballistx Well-Known Member

    Messages:
    48
    Joined:
    Mar 8, 2011
    That is the way that I catalog the bullets. I use .002 below the base diameter as the reference for the ogive.

    The "cartridge freebore" is my working freebore. That is what the cartridge actually sees. There is no support between the end of the case and the beginning of the bore. That includes the distance from the front of my case to the chamber end of the case. In the 30-06, that is my case length of 2.494" (or thereabouts) and the SAAMI of 2.5228" (not the actual for that chamber though).

    On my 243 loads with the Nosler SHOTS 55 grain bullets, I have the bullet set with the ogive at the face of the neck. There is NO bullet shank exposed at all. That means that the bullet "jump" is truly from the front of my case to the lands. It is supported only by the case neck (roughly), the chamber neck area (more loosely), then the chamber or rifle freebore for 0.204" and then the actual or excess freebore beyond the SAAMI specifications. Gets to be quite a distance. Then when you figure the bullet is jammed ahead by the firing pin, then stops, then pushed forward some more when the primer ignites, then pushed harder as the powder ignites, it gets to be a rough ride for that little feller.

    None of this can really be quantified until you have specific data points and specific names for those data points. Most are well clarified. Freebore happened to be one that has a number of meanings to different people. I am basing my definition on what it appears the reamer manufacturers are defining it as.

    Again, just my engineering OCD.
     
  12. Canadian Bushman

    Canadian Bushman Well-Known Member

    Messages:
    1,650
    Joined:
    Jan 24, 2012
    I dont mean any offense by this but i think youre making this more complicated than it needs to be.

    If you measure from base to ogive with the same comparator your cartridge freebore is the same as bullet jump and is independant of case length, actual freebore, chamber length and the plenthora of other variables that can cause confusion in your data.

    I find the lands with the bullet i intend to shoot and record the jump/jam i chose to use with that bullet. This provides a reference for tuning a load and is all thats really needed.
     
  13. ballistx

    ballistx Well-Known Member

    Messages:
    48
    Joined:
    Mar 8, 2011
    If working with one cartridge/load/bullet for one rifle, I would concur. But I have (2) 30-06. (2) 25-06, (4) 243, had (3) 222 and will have (4) 223 plus incidental like 22-250, 219 Zipper, etc. Trying to balance each one individually would mean individual loads, and conditions, for each rifle with each of its loads.

    I have (5) 224 bullets for (4) rifles in (4) calibers and will have 3 more of the 223 variety. Trying to develop a load that is a "GOOD" compromise and track it is a different matter.

    Most of these are either hunting, or casual plinking loads. None are for dedicated competition. But I do not adhere to the concept that a hunting rifle doesn't have to be "accurate", that "minute of deer (6"@100 yds)" is adequate. I am probably a 1/4" to 1/2" bench rest shooter. I am probably a 3" hunting shooter. If I have a 2"@100 yard rifle, that is now 5"@ 100 yards under hunting conditions. That limits me to 100 yards on deer. If I have a 1/2" @ 100 yd rifle, I now have a 3.5" @ 100 yard system and I can get almost to 200 yards. Therefore, to me, hunting accuracy is more critical than the majority of target shooting is.

    If I miss the X ring on a target I will likely forget it in a week or so. If I miss the 6" of a deer by 2" to the center of mass (gut shot) I won't forget that for a very long time. Or if it is running away with just the front leg dangling, well, you get the point.

    So, I want my hunting rifles to shoot under 1/2" @ 100 yards. That is THEIR capability, not mine. Mine has to be added on top of the rifle's. I limit myself to basically ONE hunting bullet. That is the Nosler Partition (180 & 165 308; 150 & 130 270; 120 25-06, 100 243 & 60 224). Those bullets have served me for over 40 years. Yes, others have come along that are nearly as good. Some will argue better. But for me, they are totally adequate for every hunting need (varmint not included). But they make an excellent coyote load with minimal pelt damage.

    The number of combinations are pretty rediculous and beyond common sense approach. I understand that. But with the spreadsheet approach, I get to apply my engineering OCD, and I get to do a lot of off season shooting, which helps in the overall to be a better shot. I have about 6,000 free 224 bullets that I load in my 223 and 222 for general field shooting practice.

    There gets to be another aspect of this. I developed an external ballistics program in the 80's that was sold internationally. It was recognized by the Army in VA as the most accurate they had at that time. The next step will be to take the chronograph velocity of the final loads and correlate those to the BDC scope. The scope manufacturers have finally gotten their act together and have a realistic BDC. Vortex has a good one at 1.5", 4.5", 7.5" and 11" at 100 yards. This can readily be correlated to actual POA at specified yardage. It won't be 400 but more like 423 or something. But with the range finding binoculars and the BDC, along with a scale taped to the rifle butt and reasonable accuracy can be extended to the 600 yard range. I don't believe wind judgement will allow for 1st shot ethical hits beyond that range. Elevation yes, windage no.

    Also, the scopes have turrets that can be set for various ranges. All that is needed is a scale saying 47 clicks for 423 yards. Can get both on the same reasonable hunting scope.

    Beats going out and shooting tin cans all the time.
     
  14. Canadian Bushman

    Canadian Bushman Well-Known Member

    Messages:
    1,650
    Joined:
    Jan 24, 2012
    Well i hoped we have helped you understand freebore so you can accomplish your goals.

    Happy hunting
    Tim L