Freebore

[Deleted old_dood]

I've read where users state what their freebore is. Is there a method for measuring it? The reason I ask is in anticipation of a barrel change. Right now I've got a Savage 12 6mmbr 8 twist. I'd like to be able to shoot bullets in the 62 to 70 g range but they're so short there's no way I can get close to the lands and still have (what I think) is enough of the base in the neck. I'd like to be able to specify what I'd like for freebore but don't know how to specify it without knowing what I now have.

another related question. Would a 12 twist barrel usually have a smaller freebore than an 8 twist? Has anyone used a 3rd party pre-fit in their Savage that allowed them to use bullets in the 60-70 g weight range?

thanks, Al

 

[cjames]

Contact Dave Kiff at Pacific Tool & Gauge about the freebore.

 

[JohnHenry]

In my experience for a 6BR shooting bullets in the 60-70 grain range, one wants a zero freebore.

 

[fdshuster]

Al: That's just one of the many advantages of having a chamber cut to YOUR specifications, and when dealing with a factory, mass produced rifle, you have little or no choice in the matter. Savage will not even discuss freebore as it relates to their chamberings------ you take whatever they give you.

I have been using zero freebore reamers (PTG) for years for both my 6ppc's & 6BR's, with short bullets, and as John Henry said, that's the way to go.

Even if you go with a pre-chambered barrel for your Savage, they (the shop that does the work) will want to use one of the reamers they have in stock, although they will try to come close to what you want. If they would not have the freebore of your choice, they will give you the choice of paying the extra charge it would cost them to buy that reamer, or you could buy your own & they would use it to cut your chamber, and return the reamer to you. I personally would go for the second choice.

 

[Deleted old_dood]

if the chamber is cut with a zero freebore reamer, what, exactly, does that mean? The bullet is always seated in the lands or is there some seating depth where it does not. One of the reasons I bought the Savage was because of the number of barrel makers that offer pre-fit barrels. Do you know of any of those manufacturers that will use a reamer that PT&G (or me) provide or will they all?

 

[fdshuster]

old_dood: The position of the bullet in relation to the start of the rifling (the leade) will depend on the bullet being used, and that depends on the ogive.

For that reason, when specing a reamer, it's a simple matter to contact Dave Kiff, (or other reamer makers) and give him your first bullet of choice to be used, as an example, the 68 gr. Berger #24411. Tell him you want it to touch the lands, with the base of the bullet just in front of the case neck/shoulder junction. He loads that information into his optical comparator & will provide the exact freebore dimension that will fit your needs.

With the 6BR case and that particular bullet, a zero freebore will work fine. You will still have the option of using other short bullets in that same weight range, and even though there will be some variation of seating depth, (because of the shape of the ogive), the majority will work fine. As erosion develops you will be able to seat the bullet(s) further out to stay in contact with the lands, and still have plenty of bullet to case neck contact.

I personally cannot accept paying for a custom barrel and the cost of fitting and chambering, (that will be at or close to $500 total), and then take whatever chamber dimensions I get, based on whatever reamer(s) the shop happens to have available. And, after the chamber is cut, you always have the option of selling the reamer, if you are sure it will never be needed again. Once used reamers can be sold for 70 to 80% of their original cost. There is also the benefit of having your chamber cut with a new, never before used reamer, versus one that may have cut a large number.

Longer brass life will also be realized if chamber neck diameter is specified, as an example, a tight, no-turn neck. With the new blue box Lapua 6BR that would be approx. .270".

Individual company policies as to if they would use a reamer that you provided would have to be taken up with them. Some probably will & maybe some won't.

 

[expiper]

HI AL...here is the ammount of shank (bullet bearing surface engaged in case neck) with a 6mm BR Kiff reamer with .040" FB.... SHANK SHIMS LOAL hits-donut ((max shank .300/.335 neck length))
H-H 68's .140 2 2.245 BR seater stem--1.700"
Hammons 62 .100 1 2.210
BIB 65 .140 2 2.250
Watson 68 .200 0
Euber 68 .125 6 2.270 2.075
Bart 68 .120 6 2.270 2.080
Berger 69 .190 5 2.312
Fowler 66 .185 2 2.220 2.075
Berger 80 .280 2 2.205 ---Good with 14 tw.
Fowler 80 .240 2 2.220 2.150 ---Fair with 14 tw.
Berger 88 .275 9 2.345
95 VLD .160 6 2.345 2.205
Berger 90 .210 5 2.285
105 VLD .255 6 2.335 2.290

These are measurements taken from several of my bbls. that have been chambered with a .040" FB reamer,,,these are from my experience of shooting a BR since the 70's,,,not hear say or conjecture or supposition,,,,this is more than adequate seating for this series of bullets,,,I have found over the years that the minimum shank of most bullets (espcially 6mm) is ~.050" ,,,any less and you can pull the bullet with your fingers,,,no matter how much tension your neck has,,,,.050" is my personal minimum when shooting from a bench,,however I prefer .080" or more for any rough handeling such as hunting or field use,,,most true benchrest chambers in ppc or BR have ~.030" FB +/- .010"...
Any gunsmith that wont use "your" own personal reamer is one to walk away from,,,,I have found that most of the men that do my work prefer to use the customers reamer and headspace guage,,,,
Hope this helps with your decision,,,Roger
PS...as stated earlier,,,call Kiff,,,he is the best in the business ,,,,he will give you advice not opinion,,,if you will take a measurement on a common bullet (LOAL--to the tip) and send it to me I will tell you the aprox FB that your chamber has,,,

 

[lpreddick]

i wish i'd had fdshucter's and others advice before i ordered my reamer for a 6 BR with .040 freebore as i shoot 60-70 gr bullets. no freebore is the way to go with the slow twist/light bullets. i now appreciate the difference in case length and chamber length (mine is .010) that is added to the freebore when determining how far out to seat a bullet to just touch the lands. if i have another chambering, i'll consider having kiff regrind to a no freebore...i think i saw they do that. another advantage to no freebore is as the lands recede, you'll have a lot of distance to move the bullet out to maintain the same relationship to the lands.

 

[fdshuster]

Ipreddick: .040", as suggested by Roger will work fine also, and there might be an advantage of having a little more space for powder. Not much of a problem with the 6BR since it has a nice, long case neck. Bullets can be set further out to chase the lands, and you will still have plenty of bullet/neck contact.

p.s.: Yes they will regind to a shorter freebore length. $25 when I had one of my reamers done, a couple of years ago. fds

 

[Tim Singleton]

I have a McGowen 12 twist savage prefIt. And a CBI 8 twist savage prefIt
It seems the manufactures who produce the prefits use a reamer designed to allow seating of the heaviest bullet for the twist of that barrel.
My 12 twist shoots 80gr Berger great and I can get a good jam into the lands. I can get to the lands with a 65 gr but just touching.

Like others have said if you have the time ordering a reamer to exactly what you want is the way to go.

For my use I am perfectly happy with my prefits

 

[Deleted old_dood]

thanks for all the great responses. I feel I have a much better understanding of what I need to do when it's time to do the barrel swap.

Al