Lets Talk Freebore

[Hoot]

Ok Gurus out there. Some of whom may have caught my mention of this in the Bolt Action sub-forum.

I just got a new 450b barrel for one of my Savage Model 12's. I visually inspected the bore before doing anything with it. Looks Great. I got it headspaced, torqued, mounted in a nice stock and finally got around to doing some preliminary checks prior to reloading, starting with measuring the Freebore. It came out to .072 as opposed to the SAAMI spec of .200. I suspect the gunsmith who chambered it used a non-throating reamer. For the unwashed masses, you can get them either way. Ones that cut the main chamber and the freebore and ones that cut a minimum and leave the remainder to be cut with a separate throating reamer, for those who want a non-standard freebore. I contacted him and he took ownership of the mistake, offering to buy a throating reamer and cut it to whatever length I wanted. I told him to sit tight until Monday while I consider this issue.

Those of you who have followed my work, know I like lighter (shorter) bullets traveling faster as opposed to heavy (longer) bullets lumbering along. One of the limiting factors in my original 450b barrel and now the Bartz is the lighter bullets, when seated close or into the lands, tend to lack sufficient seating depth. So, I grabbed some of the lighter ones that I still have. The C.O.P. 160, 185 and 200gr as well as the 200gr FTX and XPB bullets. With the shorter freebore, I can now seat them long without running out of case. Hmmm...

This leaves me with a conundrum however. I was perfectly happy with my AR 450b but wanted to be a contributor again and all the hubbub around here is mainly concentrated on bolt actions lately. Many of which are stoked for velocity by loading them longer which affords more case capacity for powder, not to mention greater overall strength and a few other benefits.

I'm caught wanting to speed up those lighter bullets more than I ever could with my AR platform but I also want to throw some heavier bullets with thunder. I'm only out the cost to ship my barrel back to LA where the gunsmith lives to get the barrel properly throated and the turn around time. Its at least another month until comfortable shooting weather returns up here in MN so I'm not in a hurry. There is the alternate direction of wanting to seriously kick those lighter bullets in the butt. There is a compounding factor however. This new barrel is a 1:16 twist and yes, too high an RPM can make bullets come apart in flight. Yes, it is a real issue. Had this barrel been the 1:24 like my AR barrels or even a 1:32, it would be no contest. Don't get me started on why 1:16 is even made in this caliber as 1:24 is a fast enough twist for up as high as 325gr bullets, regardless of whether you choose to shoot them super or sub sonic. That's a debate for another time and place.

I started writing this with the goal of asking your feelings on which way to go but I think that just writing it down has convinced me of what needs doing.

Nevertheless, feel free to chime in with your feelings. I'm always prone to persuasion.

Hoot

[coyote wacker]

Myself I rather have a l o n g e r free bore than to short...but also I only shoot unleaded....one thing to remember how did Roy Weatherby chamber his rifles with a long free bore and there bullets move at some high velocities because of it....

A little story back in the early 70's I bought a new Vorehe Rifle in 300 Weatherby took it home mounted a Redfield 3-9 scope on it and took it to the range....in September I was going to Wyoming hunting and it was going to be used there....first round I fired it kicked and when to open the bolt and it was very hard to eject....looked at the primer and it was flat with a mushroomed primer....factory ammo and it was to real HOT....
There was a gunsmith at the range so I took it to him and he looked at it....there was no freebore like a Weatherby rifle has....that is why the load was to HOT....
Lucky I only bought one box of factory ammo...I pulled all the bullets and ended up using a starter load that shot very good but was 150 fps slower than a factory load....

[Hoot]

Myself I rather have a l o n g e r free bore than to short...but also I only shoot unleaded....one thing to remember how did Roy Weatherby chamber his rifles with a long free bore and there bullets move at some high velocities because of it....

A little story back in the early 70's I bought a new Vorehe Rifle in 300 Weatherby took it home mounted a Redfield 3-9 scope on it and took it to the range....in September I was going to Wyoming hunting and it was going to be used there....first round I fired it kicked and when to open the bolt and it was very hard to eject....looked at the primer and it was flat with a mushroomed primer....factory ammo and it was to real HOT....
There was a gunsmith at the range so I took it to him and he looked at it....there was no freebore like a Weatherby rifle has....that is why the load was to HOT....
Lucky I only bought one box of factory ammo...I pulled all the bullets and ended up using a starter load that shot very good but was 150 fps slower than a factory load....

Interesting. Have you ever tried any bullets kissing or into the lands? That can enhance accuracy of a load but not always. Depends upon the bullet ogive. I have a box and a half of Barnes 200 gr XPB bullets. The pointy ones designated for the 460 S&W, not the gaping mouth ones that bear the same model name. In this chamber, they can go as long as 2.43 COL before hitting the lands. So figure 2.40 with a 30 mil jump. As you suggest, the are long and lean compared to most cup and core 450 bullets that I have. The 275's are even longer but I'm out of them, so I couldn't check. It would be educational to know how long you can load any of the bullets that I have, to compare freebores.

Some that I have:

200, 225, 250 and (300 aka SST/ML) FTX
135 and 250 Lehigh Xtreme Penetrators (all copper)
160, 185 and 200 C.O.P. (Copper Only Projectiles)
230 FMJ RN and FP
240 and 300 XTP Magnums
A bag of mystery 230gr JHP that a member sent me (I forget who) (Don't grow old!)
1) Hornady 245gr Interlock that someone sent me to give a look. May be more in a bag under the clutter on my desk.

Hoot

[Al in Mi]

Measure a few of your .451 bullets, find the smallest and seat the bullet backwards as long as possible. Just doing a quick check g to see if the freebore is undersize.

Read where guys use one of those $50 endoscope gizmos off Amazon to check for throat wear, might have to look into getting one of those someday.

[Hoot]

Measure a few of your .451 bullets, find the smallest and seat the bullet backwards as long as possible. Just doing a quick check g to see if the freebore is undersize.

Read where guys use one of those $50 endoscope gizmos off Amazon to check for throat wear, might have to look into getting one of those someday.

Al, that how I've always done it. I take a flat base bullet seat it backwards in a regular case until it is almost flush. I then chuck the case in my lathe and carefully face off the small radius it has. Then using an inertial bullet puller, I extract that bullet and put it in my Stoney Point (now Hornady) Overall Length Gauge and use that to shove the bullet up until it cant go any further. Somewhere on this forum, way back, there was a discussion about freebore and I espoused the same information along with an image of what it looks like. That's where I got the length I mentioned. This is a new barrel, so I also gave it a good look with my borescope, comparing it to my AR 450b. The difference is clear to see. After the headspacing ledge at the end of the chamber there's hardly any space before the rifling begins and the rifling rises quite quickly.

I am considering eroding it a little by shooting some bullets embedded with NECO bore reconditioning abrasive. AKA Fire Lapping. Neither he nor David Tubbs sell pre-treated bullets in this caliber, or I would just buy them and do it. That process is known to move the throat forward. The double benefit would be saving me from doing a separate barrel break in.
I'm leaning more in this direction.

-or-

Disassemble the new rig, send the barrel and a couple of example dummy rounds back to the gunsmith and have him do it. Once it returns,
I'll still have to do a regular barrel break in. He's waiting for my decision, so I have to make it soon.

Hoot

[Hoot]

I gotta learn to trust my gut more often. It got up to 42 degrees today, so I loaded up 5 rounds using a mild charge and 220 grit lapping compound embedded in the bullets. Wow, did that help! it went from .073 to .133 freebore. In hindsight, the throat cut looks a little rough and my guess was that the bullets were hanging up on the annular rings so often left behind when the throat is cut. Pretty hard to avoid from what I've read but usually smoothed out by shooting lots of bullets down the pipe. The grit just accelerates the process. A patch slid through like butter.The rest of the chamber cut looks good. the throat will smooth out more with a couple of additional treatments.

Its a keeper.

Hoot

[Al in Mi]

If he rented a reamer it might be on it's last regrind. This SAAMI print shows freebore at .453 +.002, doesn't take much at the low limit to interfere with bullet fitting.

[Hoot]

5 more 220 grit bullets later (10 total), the freebore is now up to .143. Not as great a jump as the first pass but still headed in the right direction. The throat is looking a little less rough but still not smooth as I would like. I may try one more pass with the next finer grit to see if I can best the .143, which is a good compromise between the SAAMI spec and what I began with. The key here is knowing when to say when. As the barber was fond of saying, "I can always take a little more off but putting it back on is tricky."

Hoot

[Hoot]

Got it up to .150 freebore and going to stop there until I can actually get some rounds downrange in a month or so. For sake of reference, the 250 FTX hits the lands at 2.36 COL or thereabouts. That's fine as I want to be at .020 off the lands and still have 1/2 caliber shank down in the case. It originally only got out to 2.29 or thereabouts. To be continued in the original thread in the Bolt Action sub-forum.

Hoot

[Texas Sheepdawg]

Awesome