help figuring COL AND freebore for .300 Weatherby

L

lightjunkie

New member
well I have been fiddling with my loads for my .300 Weatherby and found where my bullet meets the rifling but how can I figure out the freebore that Weatherby cartridges require for velocity and keeping pressure spikes down sorry if this sounds like a dumb question or I'll worded but if anyone can help me figure how to measure the free bore boy where the rifling starts for COL I would really appreciate it.
 
Not sure why you posted this question in a Handgun forum instead of placing it in the Reloading section. PM a moderator and ask if he/she would move it for you as you will get more responses there.
 
Moved it for ya! :)

And, to answer your question, you already know. :D

my .300 Weatherby and found where my bullet meets the rifling
Click to expand...

"Freebore" is the distance the bullet travels before it contacts the rifling.

how can I figure out the freebore that Weatherby cartridges require
Click to expand...

The cartridge itself does not require a set distance. Anything where the bullet does not touch the lands when chambered will work fine. However, certain combinations of factors work better than others.

Benchrest shooters discovered a long time ago that seating the bullet so it is just off the lands usually gave the best accuracy. And by what I read, a great many people today think you "have" to do it that way.

You don't.

Unless you are looking for that nth degree that wins benchrest matches, or pops the prairie dog at 300+ yds.

Weatherby rifles (at least the older ones, I don't know about today) were made with about 1/2" of freebore. A lot more than anyone else at the time. This, along with the huge cases powder capacity, gave Weatherbys higher velocity than anything else (again, at the time).

The bullets essentially got a good long running start, before hitting the rifling.

This usually does not give absolute top end accuracy, BUT, does give accuracy well within the needs of a big game hunter, and slightly higher velocity.

I do not know if other gun makers who chamber the .300 Weatherby use the same amount of freebore that Weatherby did. I do not think they do.

What rifle do you have?
 
lightjunkie,

The amount of jump you need to hit minimum pressure varies with the bullet shape. It's a function of how much of a gap there is around the bullet for gas leaking out around the case mouth to bypass the bullet and thereby stall the rise in pressure.

Two graphs are below. One is pressure measured on a 6 PPC rifle with the the same powder charge, but with the bullet touching the lands for three shots, and with it seated 0.030" away from the lands for four shots. The pressure difference is about 20% with the pointed bullet.

The other graphs is for a .30-06 with a round nose bullet. The sides of a round nose bullet taper more gradually than the pointed bullet does, so needs to be a bigger distance from the lands to allow equal gas bypass as compared to a pointed shape. In this instance the bullet moves a full quarter inch back before peak pressure is minimized. Below that point, however, pressure increases with still deeper seating because of the amount of space the bullet is taking away from the case volume. With this nose form the pressure difference from touching the lands was only about 10%.

With kind permission from Jim Ristow to reproduce this RSI site image. Ovals and labels mine:

RSI6PPCthroatjam2_zps7abe8a9a.gif


seatingdepthvpressure_zps326eb859.gif
 
Forget about seating bullets longer in 300 Weatherby. Standard chambers have a very long freebore and Weatherby says the freebore in a 300 Wea. is .361". You can't get bullets to touch the rifling because they will not cycle through the action that long PLUS the freebore is there to reduce the initial pressure. Also the bullets would be too far forward in the case neck for proper bullet tension. Seat your bullets to recommended Weatherby overall lengths. The freebore with no rifling and at bullet diameter will not cause accuracy issues. Most Weatherby rifles shoot very well with the freebore. Looking for accuracy, try different bullets, powders, and load levels. Keep your rifle safe by reloading to recommended oal's. My 300 Weatherby shoots 150 and 180 grain Hornady Spire Points very well loaded at 3.562" which is what Weatherby recommends. I just experimented a little with powder charges. You may have found where the freebore starts but you're still a long way to the rifling.
 
Last edited:
If you look closely at the the SAAMI drawing for 300 Weatherby Magnum, you'll see there is a small 0.015" taper off the case mouth to the freebore, so the freebore itself is actually 0.3457", but still very long. I'd heard, but not confirmed, that not all production Weatherbys had such a long throat. The early ones did, but I read they'd shortened it some later. But I don't know for sure. If someone does and could post whether that was accurate or not it might affect the outcome of the discussion.

As to whether you need to adjust seating or not, it depends on the gun and bullet. Trying it is the only way to tell. Berger reports some rifles just would not shoot their secant ogive VLDs well without doing it. So, it depends.
 
From Weatherby's Frequently asked Questions:
What is the throat length (free bore) on your Weatherby rifles chambered for Weatherby magnum calibers?

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

http://www.weatherby.com/support/faqs.html
 
44amp

thanks 44 amp Iam shooting for everyone to know a factory chambered released in 1989 remingto 700 classic so I don't know what the chamber throat or freebore is of where to start and as other my experienced reloaders here know the freebore is there to keep pressure down , I am using
a Lee collet dies amd a lee deluxe case trimmer with the 300 Weatherby die set at 2.800 "o just don't know where to start or how to find free bore on a Remington, I can find where the rifling starts on the olgive bit Iam worried about screwing up the recommended freebore .Thanks for all the words of wisdom
 
How are you determining the distance to the rifling? You said that you have this distance. That distance is only good for that one bullet.

As noted find out what length round will feed from the magazine. Usually that is the max length you are going to reload to assuming that length will not be on the rifling/lands.
 
Hi PA JOE

I I smoked the bullet and ad soon as the rifling marked the bullet Iarked ran it 10 times and used the average but now I don't know how to figure out the free bore
 
You don't calculate freebore. Using the measurement you have (which I assume is (Overall Length) you seat the bullet a few .01's from that length. But once you do that try feeding that round through the magazine to see if it will feed correctly.
 
I don't know how to figure out the free bore
Click to expand...

I am the fan of the running start, I want my bullets to have 'that jump'. I determine the distance the bullet runs or jumps with a cleaning rod. I make test cases I call transfers, everyone else uses dummy cases.

I start by drilling the primer pocket/flash hole out on cases that fit my chamber. After drilling the flash hole/primer pocket I make sure the case has all the bullet hold I can get, then I seat a bullet I am going to use. After seating the bullet I chamber the transfer then I use the cleaning rod to push the bullet out of the case neck until it contact the rifling.

After the bullet contacts the rifling I remove the transfer then use it to adjust the seating die to 'ZERO' off the lands.

If I wanted to know the distance from the bolt face to the beginning of the rifling I would measure the distance from the case head to the rifling print on the bullet. After that is A - B = C.

I have tested rifles that had long throats, meaning I have pushed bullets out of the case neck before the bullet contacted the rifling, and no, the answer was not 'use a longer bullet'.

F. Guffey
 
F.Guffey

thank you I have seen a you tube video where the primer pocket was drilled out and tapped with threads then by using an all thread long bolt you could keep treading the rod untill the bullet contacts the thread,but I still don't know how to get the freebore for my chamber,I may be making this harder than it has to be but Iam afraid of not using the reebok that the Weatherby cartridges are designed around and I don't want to build and excessive pressure I don't k ow how else to put what I thinking onto print (Which is scrub because Iam so simple minded) So that's my dilema
 
I don't want to build and excessive pressure
Click to expand...

I have new, factory, over the counter Weatherby ammo. I am sure you have had factory Weatherby ammo. I suggest reloaders save a few rounds of new factory ammo for comparison. It comes in handy after a reloader takes all the advise available from the internet and applies it to their methods and techniques. Normally what happens their reloades will not allow the bolt to close. Then? If that happens to me I dig out a factory, new, over the counter round and compare it to the round that will not chamber.

I want to know the length of the chamber from the rifling to the bolt face. There are rifles that have gone through some creative hands. There was a time when "all you have to do is etc." to increase case capacity. On rare occasions I have pushed the bullet out of the case before the bullet contacted the rifling. On one rifle the bullet was not in the neck and did not contact the rifling, and a bullet that was heavier and longer did not exist that was long enough, meaning there was no purpose for the long throat.

F. Guffey
 
Hi PA JOE

I I smoked the bullet and ad soon as the rifling marked the bullet marked ran it 10 times and used the average but now I don't know how to figure out the free bore
 
I totally understand wanting to find the maximum length you could seat the bullet before hitting the lands in your rifle. However like most have said, this is usually a moot point unless your looking to shoot matches and are considering single loading your rifle.

In most cases the magazine will set the limit to what you can use for an OAL since the rounds will need to feed from it in order to work properly. This is for hunting however where you might use a follow up shot. I have two rifles myself in which I can install a BR follower which effectively converts them to a single shot. On those two I DO know the max OAL to the lands so that I can seat my bullets out to .010" from the lands. Those are both used for hunting of coyotes and feral hogs where I don't usually get but one shot, but it is usually plenty.

I myself usually use the longest length that will feed reliably from the magazine, and then start seating deeper in .005" increments after finding my desired velocity window with my load. This sometimes will open up groups a bit then they tighten back up again after a couple more moves. If I don't find anything good or better after around .030 - .050" I usually call it and move on to the next best load. This is simply my own regime and works for me, where my friend found that while seated .015" off the lands shot decent, after playing with it for a while he finally set the OAL to the book listed length and it ended up being .115" off but his groups went from 2.5" at 300yds to around an inch or less. So it is simply a matter of playing with things and your loads and rifle to see what is going to work out the best for what your looking to do in the end.

Hope this helps.
 
help figuring col and freebore

One way I heard to measure free bore is to use a long bullet, jacketed, reversed in a case neck not sized down or barely crimped a bit so that when the bullet contacts the lead of the lands it is pushed back into the case.
The bullet projecting from the case is the free bore.
Weatherby did use longer freebores. At some point, perhaps when the Japanese produced the rifles for them the free bore was decreased.
The old manuals, like my Lyman, listed more powder and higher velocities.
The newer manuals from some point decreased the loads to keep pressures at 65,000 lbs or below. I don't think I have manual that list the load pressures in CUP, for Weatherby.
Someone that sells chambering reamers would possibly have the different specs.
They tell me my barrel will burn up rather quickly. Perhaps having the chamber reamed with an old spec reamer to extend the free bore, might extend the barrel life by removing burned metal area.
New Weatherby barrels in .270 anyway 26 inches are 540.00 installed
There is a Weatherby service center in Tn north of Jackson.I can't remember the name of the town just now. Perhaps I will get the chance to ask him. A call to Weatherby should get a reply. They are nice people.
 
thanks again

for the input,the issue isn't getting maximum velocity but keeping chamber pressures down and the other big issue is my riffle is a Remington 700 if it was a Weatherby I would try starting off with Weatherby specs,I settled with 3.540"it cycles well . Anyhow am reading and taking in everything .Keep the information coming and I'll keep trying. thanks all
 
You must log in or register to reply here.
Back
Top