Free Bore

[Bucksnort1]

A friend in Colorado is new to reloading. He has been talking to an acquaintance who also reloads. The acquaintance says he tweaks bullet depth in his 300 RUM until the bullet, near the ogive I assume, barely touches the lands and grooves at the rear of the barrel.

When loading to the specifications in a reloading manual, to include COAL, will the bullet touch the lands and groves or will there be some free bore?

[30Cal]

There should be some jump if you load to the length given in the manual. Probably bunches of it if you have a factory barrel. Usually you run out of magazine length before you can touch the lands.

Loading at the lands is varsity level stuff--going to see high pressures that way. It's not something that's done for most applications.

[T. O'Heir]

The whole off-the-lands thing is a load tweaking technique that can be ignored entirely. It's a 100% trial and error thing that is different for every single rifle made. (Every single chamber is slightly different. Mostly in length, but the throat will be slightly different too.) It's not necessary and isn't done until you have worked up a load. Then you fiddle with the OAL until you find what is called the "sweet spot" for that particular chamber. There is no formula for figuring out just where it is either.
OAL is measured from the end of the bullet to the flat of the case head. No ogives involved. However, if your buddy opts to play with the off-the-lands thing, it's to the ogive. Said ogive being different for every bullet shape.
OAL specifications in a reloading manual is from SAAMI(Sporting Arms and Ammunition
Manufacturers' Institute). It's to ensure all ammo will chamber in all like chambered rifles. They have nothing whatever to do with where the rifling starts. It's best to use the Max OAL given in your manual when working up the load.

[RC20]

Short version do not do it until hitting the Varsity level as noted in first replay./

In all the shooting I have done (maybe 15,000 round over the last 5 years) I have one load that likes being close.

Find the Lands with a dummy bullet is fine, setting it back .015 fro there is a good starting point (no matter what the COAL says)

And COAL can in some guns put the bullet in the lands.

Load a dummy, find out. It will be hard to close the bolt, COAL may be shorter coming out that going n and it may stick.

There is no SAMMI spec of bullets, mfg decides what is safe.

Mostly its well clear, have had a few that were not.

[F. Guffey]

Free bore; I am the fan of bullet jump, I want my bullets to have that running start.

F. Guffey

[RC20]

I think you need a powder charge going off to get the bullet to jump, fans limited static pressure is pretty low.

[Reloadron]

"When loading to the specifications in a reloading manual, to include COAL, will the bullet touch the lands and groves or will there be some free bore"?

Going to totally depend on who made the barrel. Some manufacturers allow more free bore than others. Years ago Remington rifles were noted for having quite a bit of free bore. Common off the shelf rifles will allow enough free bore that anything loaded to specifications be it a reloading manual or factory ammunition the bullet start of ogive will be well off the lands.

Once a shooter gets real comfortable with loading and understands pressure curves they may begin experimenting with distance off the lands. While I am not a bench rest type I shoot at a bench rest range. I have watched guys load on the range and only start a bullet into a case and literally allow the chamber to seat the bullet as the bolt is closed literally "jamming the lands". Apparently it works for them.

To answer your question, yes, there will be some free bore assuming a chamber cut to specifications.

Ron

[Unclenick]

From the drawing in the SAAMI standard, If the part of the bullet that first contacts the lands (0.300 inch diameter point) is made level with the mouth of a case trimmed 0.010 inches shorter than maximum, you would have almost 0.170 inches of bullet jump to the lands. In practice, bullets are usually seated with that part further out of the case than that. How far is not something you can determine from COL, as some bullets have longer ogives than others. But in the main, no, it is not normal to seat bullets right up close to the lands in commercial ammunition and load data because it raises pressure to about 20% to start a bullet that far forward, meaning the load has to be developed for it.

Starting loads are usually safe for a bullet jammed into the lands, but you may not get much higher before pressure signs show up.

[F. Guffey]

no, it is not normal to seat bullets right up close to the lands in commercial ammunition and load data because it raises pressure to about 20% to start a bullet that far forward, meaning the load has to be developed for it. Starting loads are usually safe, but you may not get much higher.

And then there is me; I do not want my bullets to 'have that jump with the running start and then have to slow down to get started, I just hate the feeling I get when not knowing if the bullet is ever going to get started before the bullet gets past the rifling.

I want my bullets past the rifling before the bullet ever realizes they are there.

F. Guffey

[Nathan]

Free bore; I am the fan of bullet jump, I want my bullets to have that running start.

F. Guffey

Can you explain why?

When loading to the specifications in a reloading manual, to include COAL, will the bullet touch the lands and groves or will there be some free bore?

The manual oal should result in free bore or jump in all SAAMI chambered rifles. This is not a bad way to start. Bullet makers know what oal’s shoot well in average rifles.

Slightly deeper down the rabbit hole is buying measuring tools from Hornady and pinpointing what is best in your chamber.

I tend to view the manual oal as a condition of the pressure measurement....as in a max charge seated shorter than manual may be over max pressure. Again, max pressure is for std sporting rifles. If you have a 2” barreled rail gu, that may not be max. Accuracy is a good guide to what max is, but there are other signs you should know.

[Bucksnort1]

My friend will not be pursuing this. His reloading acquaintance is into doing this. Thanks for all the input.

[hooligan1]

The whole off-the-lands thing is a load tweaking technique that can be ignored entirely.
With that said why even bother with any load tweaking.
Because we want our stuff to perform better than others strive for. Jumping or jamming bullets can be done before tweaking a load weight, I know it can because I've done it repeatedly, and it's saved me powder more than once for sure.
I like my bullets getting a running start like Guffey does, and finding what distance the bullet likes to jump can be done easily.
I don't know why anyone would even believe it doesn't work, or no one even needs to bother with it, life would be boring if you didn't try different methods of load tweaking.

[std7mag]

Thus far the only bullets that i've found that like to be up close and personal with the rifling are Berger VLD.
Everything else (for me at least) seems to like a start of 0.020-0.040".
I haven't played with mono bullets yet, but looks like i may be headed in that direction.

[44 AMP]

For decades, Weatherby advertised the 1/2" freebore in their rifles. Said it resulted in higher velocities. Weatherbys of that era were never noted for being "match" or "varmint" accurate, but then Weatherby wasn't selling varmint rifles, and their big game rifles were plenty accurate for big game hunting.

The exception was the .224 Weatherby, which was a varmint cartridge, I don't know if they used the same amount of freebore in that one, I do know you didn't see Weatherbys set up like Winchester or Remington "Varmint" rifles.

[LineStretcher]

Originally Posted by Bucksnort1

A friend in Colorado is new to reloading. He has been talking to an acquaintance who also reloads. The acquaintance says he tweaks bullet depth in his 300 RUM until the bullet, near the ogive I assume, barely touches the lands and grooves at the rear of the barrel.

When loading to the specifications in a reloading manual, to include COAL, will the bullet touch the lands and groves or will there be some free bore?

There will be adequate free bore if the rifle is chambered to SAMMI specs. Most reloading manuals list the COAL and may list a different COAL depending on the bullet. They are using SAMMI chambered barrels and have already determined the recommended COAL that works best with their bullets. You can use those COAL's reliably if your barrel is chambered to SAMMI specs.

The problem is that not all barrels closely adhere to the exact spec. Some may vary throat lengths (free bore) due to manufacturing inconsistencies. They tend to know these inconsistencies exist and will error on the side of safety vs. accuracy. The result is that you tend to end up with varying free bore lengths. Weatherby does it on purpose but they also swage in the free bore which is a whole different concept from standard caliber rifles. I did a cut away of a .257 WM barrel just to see what they were doing which is how I know that they swage in the free bore.

So if you're buying less expensive barrels and rifles, it won't hurt to know what the free bore is and then adjust COAL accordingly. You do need to be mindful of your magazine length max and concentricity might be a factor if you're finding you need to seat the bullet further out so just keep that in mind.

[F. Guffey]

Free bore according to Weatherby: Does anyone have a Weatherby catalog?

And then there was a great shooter that signed up for testing scopes, no wait, he was testing eye glasses with a rifle no one had because I believe he had it built. He had it chambered to a Weatherby chamber that Weatherby did not build because the rifle had a short throat.

And then there was a question about where his ammo came from. Anyhow, the rifle cam apart, the scope was rendered scrap and his sun type glasses failed him. It is my understanding the company that built the sun glasses took a beating and then there was the man that built the rifle.

F. Guffey

[Jim Watson]

I did a cut away of a .257 WM barrel just to see what they were doing which is how I know that they swage in the free bore.

Please explain what you mean by "swage in the free bore."
Do you mean the barrels are hammer forged, including chamber and freebore?

In olden times, freebore meant that the cylindrical chamber throat was greater than one caliber in length.

Once upon a time, when Weatherby guaranteed 1 1/2 MOA with factory loads, that was a real accomplishment.
Now people expect target or even benchrest accuracy from their plinkers and deer rifles.

He had it chambered to a Weatherby chamber that Weatherby did not build because the rifle had a short throat.

I have seen a couple of gunzine articles on the subject.
One guy wrote up a .300 Weatherby target rifle without freebore. to be shot with tailored loads. He knew that if he wanted to sell the rifle he would have to rechamber it for Weatherby ammo.
Another had a .458 Winchester with short throat instead of the Winchester long tapered leade, for better accuracy with light bullets. He was also smart enough to not shoot factory 510s in it and to not let go of it as was.

[Reloadron]

{Edit: The below definitions are from SAAMI's online glossary.}

FREE BORE
A portion of the chamber, usually cylindrical, forward of the casemouth of a diameter larger than the projectile in which rifling is not present. See Bullet Jump. See Throat.

BULLET JUMP
The distance that a bullet must travel from its position at rest in the cartridge case to its initial engagement of the rifling.
Also Known As: Free Travel

THROAT
The tapered portion of the bore of a barrel, immediately ahead of the chamber which is sized to provide clearance for the bullet of the loaded cartridge. Also referred to as Leade or Ball Seat and is associated with Free Bore. See Free Bore.
Also Known As: Leade, Ball Seat
Related Terms: FREE BORE

This old thread from October 2015 has some interesting freebore data on the Weatherby Cartridges. Post number 8 has some good data from a Weatherby Q&A.

Cartridge Throat length (free bore)
.224 Weatherby Magnum .162
.240 Weatherby Magnum .169
.257 Weatherby Magnum .378
.270 Weatherby Magnum .378
7MM Weatherby Magnum .378
.300 Weatherby Magnum .361
.340 Weatherby Magnum .373
.375 Weatherby Magnum .373
.378 Weatherby Magnum .756
.416 Weatherby Magnum .239
.460 Weatherby Magnum .756
.30-378 Weatherby Magnum .361
.338-378 Weatherby Magnum .361

Note a few with a freebore of greater than 0.750". Keep in mind when having a barrel custom chambered the shooter can have whatever they wish. For example you can have a standard SAAMI chamber or have a chamber cut with no freebore and using a throater have zero freebore slowly incremented up. The reamer guys like PT&G (Pacific Tool and Gauge) or Clymer will make any custom reamer the shooter wants for a custom reamer fee. I don't know of any factory rifles which come without any freebore and most have a generous freebore. Thing about freebore is you can always increase it but once metal is removed you can't put it back short of setting a barrel back and cutting the chamber.

Ron

[F. Guffey]

Free bore according to Weatherby: Does anyone have a Weatherby catalog?

I will take 'no answer' means no one has a Weatherby Catalog. I do not want to dig one out.

There were a few thinkers/shooters in the old days; sorta like a few shooters today that ere creative. From the beginning a few shooters thought the 300 Win Mag had a short neck, seems it was close to .267" long. One of the most accurate rifles I owned was a 300 Win Mag (still in the family); when setting it up the last five rounds when through one hole.

And then there were the thinkers that were creative. they wanted to get the bullet out of the case body so they formed 300 Weatherby cases to 300 Win Mag cases with long necks. They increases the bullet hold with the long neck and they increases the case's capacity. The Motive? They wanted a 300 Win Mag bullet to be able to keep up with the 300 Weatherby bullet.

It was not as simple as; "All you have to do...". they throated the old chamber to move the bullet out of the case and into the neck of the case. One old friend is still in the neighbor and still has the rifle. If what they did failed to increase the speed of the bullet these guys could have built their reamers, borrowed a reamer/finished the chamber to 300 Weatherby. they did not loose sight of the fact the 300 Winchester COL (Case overall length) as in the case + bullet had more to do with the length COL of the 30/06.

I had rather have the 338 Winchester or the 308 Norma Mag; wait I have both and went to gun store to borrow another reamer. Borrow. I need to finish the bench rest type rifles I committed to build. One reamer/chamber is just not that common, the other two are going to be 308 W.

F. Guffey

[LineStretcher]

Originally Posted by F. Guffey

Free bore according to Weatherby: Does anyone have a Weatherby catalog?

And then there was a great shooter that signed up for testing scopes, no wait, he was testing eye glasses with a rifle no one had because I believe he had it built. He had it chambered to a Weatherby chamber that Weatherby did not build because the rifle had a short throat.

And then there was a question about where his ammo came from. Anyhow, the rifle cam apart, the scope was rendered scrap and his sun type glasses failed him. It is my understanding the company that built the sun glasses took a beating and then there was the man that built the rifle.

F. Guffey

Go to Weatherby.com and look in the FAQ's. The distance to the lands is listed there for all the Weatherby calibers. What you may not know is that Weatherby specific caliber bullets are swaged as it enters the bore and before the lands. I have a cutaway of a .257 WM chamber that proves it.

[Unclenick]

Ron (and anyone else doing it),

Please give attribution to sources like the SAAMI Glossary when you quote them. Thanks.

[Reloadron]

Unclenick, my bad and will do. Thanks for fixing it.

Ron