View Full Version : 308 throat length

Bob Kingsbury
11-28-2008, 01:21 PM
The Factory throat in my 308 VS is a mile long. What would be
an ideal length for bullets not exceeding The 168 sierra

11-28-2008, 05:26 PM

I fired my first 1K F-Class match with a 700VS. This was after spending too much time trying 168SMK`s off a bench to get good groups at 100yds. When I switched to the 175SMK`s, I got better results from prone prior to that first match.

With the much regarded load of 45gr of Varget, loaded to an OAL of 2.810, I managed to post a score of 198 on the old F-Class target. (1MOA X-ring) I used Winchester brass and Fed210 primers. My 700VS sure didn`t mind the "jump" to the rifling. My results seem to match many others with a factory M700.

While you don`t have to try the heavier 175`s to confirm it, the 168`s at 2.800/2.810 OAL may prove satisfactory for you. You won`t know until you try it.

11-28-2008, 07:37 PM

If you can't reach the rifling, seat to 2.800-2.810-2.820 (whatever fits for mag-length in your rifle). Most .308 Win rifles will digest said ammo and put the rounds in little knots...

11-29-2008, 10:15 AM
Even though the seating depth and COAL have a relationship, they are two completely different measurments.

All factory 308 Winchester cartridges are loaded to SAAMI spec so they will fit into a 2.808 mag well.

The the throat of a barrel is the part between the leade and the rifling.

The back of the throat contains (approximately .310-.311 OD in a SAAMI barrel) the bearing surface of the bullet exposed out of the case neck. The front of the throat is the juncture where the bullet begins touching the rifling.
Throats are generally cut with a 1.5-1.75 degree taper.

Having a bullet touching or jammed into the rifling will vary the overall length varried by the bullet length and o'jive. Most factory 308 rifles will not accept loaded VLD bullets that will touch the rifling into a short action magazine and are shot single shot.

My model 7 with the deep throat (2.2605") with a loaded Swift Scirrocco touching the rifling is .1375"to long to fit into the mag well.

The factory barrel does not have enought metal in it for me to set it back enough to rechamber the barrel with a shorter chamber throat. This barrel has less than 250 rounds in it and I plan to send it back to Remington. It will be interesting to see what Remington says. If they say there is nothing wrong with this throat depth. I will tell them to send it back and I will sell it to who ever wants to buy it. I have a Broughton barrel ordered to replace it.
It will be interesting to see what they do if they agree that the throat is too long.


11-29-2008, 10:46 AM

I know different people use different terminology, but wouldn't this be the freebore that would be too long, that portion of the chamber before the leade to the rifling begins? Just as with Weatherbys, you might not be able to touch the rifling? It would seem the throat might be normal, but the freebore is excessively long.


Bob Kingsbury
11-29-2008, 10:53 AM
The 308 VS that I'm refering to is also not a candidate for barrel
set-back. The chamber is not in good alignment with the barrel.Neck
is also kinda big at .346. I do my own barrel work, and have for
years. Pacific Precision has a palma-95 reamer that is close to my
needs, but felt that with 168 gr SMK the .050 throat may be short.
I was just wondering if some one could give input in that arena. A
new barrel is in order, I am fond of Broughton barrels. Tim North
really cares about what he does

11-29-2008, 02:42 PM
What is the OAL with a Sierra 168MK and also a 175MK touching the lands? I didn't have either to test with, but I did have Berger 155VLD and Nosler 170 BT.

With the Berger touching the lands,the OAL was 3.000" there was aprox. .120" of the bullet shank contacting the case neck.

With the Nosler touching the lands, the OAL was 2.975" and there was approx. .210" of bullet shank contacted by the case neck.

How would the Sierra 175MK compare to these?
I suppose before I talk to my smith about setting the barrel back, I should ry some of the Sierras and I'm going to order them today. Even if they shoot OK in this gun, I still have an issue with it, if for no other reason, it just isn't right..

Asa Yam
11-29-2008, 05:00 PM
Even if they shoot OK in this gun, I still have an issue with it, if for no other reason, it just isn't right..
No flames intended, but the rifle is "right", your thinking isn't. Many factory rifles are designed with long throats - it's called reducing liability. Doing so allows the rifle to bleed off pressure on firing. This prevents or delays pressure spikes from rupturing the cartridge case.

Despite long throats, you can still get accuracy out of factory barrels. While groups MIGHT be inferior to what you'd get if using a shorter throated chamber, your barrel can probably shoot perfect scores (i.e., score of 200 out of a possible 200-20x) on an F-class target (10 ring = 1 MOA). However, the x-count (1/2 MOA ring) may be lower. Still, a 20 shot, sub-1 MOA group at 1000 yards is acceptable by most people's standards. If you want custom rifle performance, be prepared to pay for it (see below).

Don't forget, today's factory barrels get hammered out (literally) by the thousands, and cost less than $100 each to make. If you want a great barrel with a special chamber profile, it won't be cheap. The combined cost of a top-of-the-line barrel and chambering job is around $500. A dedicated 1000 yard target rifle can easily exceed $1200, and that's before any type of sighting system is added on.


Just curious, is there a reason why you want to stay with the 168 grain Sierra bullet? It's a fine bullet for 900 yards and less, but goes unstable in flight somewhere around 1000 when fired from most .308s. Sierra's 175s and 190s are much better choices for long range - even at 500 and 600, they're ballistically better than the 168. (Less wind drift.)

While I'm not a gunsmith, I do know some about a few .308 chambers:
The "M852" reamer was specifically designed for use with the 168 Sierra. However, chamber dimensions are fairly generous, and the bullet never touches the rifling. This is because the M852 reamer was designed for use with M14 (semiauto) rifles. With an M14, loading a round so the bullet contacts the rifling is a bad thing, as it can literally blow the rifle up.
It is possible to use the 95 Palma chamber to shoot 168s, as 1000 yard target shooters have used such chambers to shoot 175 grain Sierras. Even 190 grain Sierras can be fired through this chamber - the secret is to not get greedy for speed. Why can one chamber shoot so many different bullet weights? It helps that most of Sierra's sub-200 grain MatchKing projectiles have similar ogive profiles. The difference is then how much of the projectile extends into the neck of the casing.

11-29-2008, 05:55 PM
No flames intended, but the rifle is "right", your thinking isn't.

OK, then help me out. This isn't going to be a F-Class gun. I'm going to shoot 100-200 Varmint factory class at the local club. At least that's where I'm starting. I knew the rifle isn't going to have match grade accuracy, but like everyone else, I want to squeeze as much accuracy out of it as possible. If I have to live with the throat in this gun, give me some suggestions on a bullet/powder combination to at least start finding a load it likes. I just don't want to end up with twenty bullets and powders on my bench that won't get used. I know the Bergers are out. That's what I'm breaking it in and fireforming brass with because that's what I had on hand. They need to be jammed and a .250" jump isn't going to get it with those. Should I just plan on seating everything to 2.800" and tweak loads by varying the charge until I get the right combo? There are so many weights and types of bullets available, I'm not sure where to start looking.

Asa Yam
11-29-2008, 07:22 PM
This isn't going to be a F-Class gun. I'm going to shoot 100-200 Varmint factory class at the local club. At least that's where I'm starting...
For starters, try a different bullet.
Out to 200 yards, a flat based bullet probably shoots better than a boattail due to manufacturing tolerances (it's easier to make a good flat based bullet). Oddly enough, some lighter weight bullets (125 to 135 grains) have shorter ogives (noses), but engage the rifling sooner, OR;
Shoot longer (heavier) bullets, but at lower muzzle velocities (~2300 FPS) to reduce recoil.

Russ Rosene
12-13-2008, 12:27 PM
I have a 40x .308 with the mile long throat as noted above. I put a single shot follower in and seat 168 MK or larger to the lands. If you are shooting off the bench ignore the mag and find what length your gun/load likes.

As for powders, one of things I like about the .308 is that it is not picky and tends to have 2-3 speed nodes that shoot well. I tried 4064, BLC-2, RL-12 & 15, H322, W748, W760 [Varget had not been released yet] with bullets ranging from 168-190gr and found when I looked at my notes [good thing I took some] that H414 give me the best agg across the board [100-500yds]. Good thing too since I had 16lbs in my powder locker. 49gr, start a couple of grains below anybody's recommendations. Watch primers and bolt lift. Safety safety safety!

One thing I would like to point out is the load in my gun will probably NOT shoot as well in your gun. You will have to experiment. I load at the range to speed up the process and I only look for vertical as the coarse load [powder] indicator. Then I adjust seating, neck tension, etc to tweak further.