.308 - short throat

[Jackpine]

I just assembled my first rifle. It has a model 12 action and Shilen barrel. A friend measured the chamber with his Stoney Point gauge. Using 175 gr Sierra Match Kings the COAL would be 2.69 at the lands. I chambered a 168 gr. Federal Gold Medal Match rouind and when I extracted it there was a scuff mark that ran halfway around the bullet.

This is my first custom barrel. Has anyone else seen a throat that short? I suppose on the positive side I won't have to worry about loading too long for the magazine. But it does cut into case capacity.

The rifle will be used to learn long range shooting, out to a 1000 yards. I was planning on using 175 gr SMK or 178 gr AMAX. Will the short chamber hurt me?

[Grit #1]

Scuff mark could be where the round went up the feed ramp or scraped the side of the action on the way out. Ejector plunger pressure.
Best regards,
Grit

[ellobo]

Try this to get the true distance to the lands with your favorite bullet. With a fine tooth hacksaw split the neck of a cartridge case half its length. Insert a bullet so it extends further out than the expected distance to the lands. Chamber the cartridge and see how far into the case it is pushed by the throat. Back off accordingly to get the distance off thel lands you want.
Make sure there is some tension on the bullet before you chamber the round.
El Lobo

[Jackpine]

El Lobo, that is what the Stoney Point gauge (Now Hornady OAL guage) does.

Grit I think you are right about the ejector pressure.

I took the gun over to the local gunsmith yesterday. He noticed that the scuff mark on the bullet does show any signs of the rifling, it is continuous around half of the bullet. He is wondering if there might be a burr in the throat.

I'm going to borrow my BIL's inspection camera that he uses in his plumbing business to see if I can get a better look inside the chamber.

[Jackpine]

No luck with the camera. Too big to fit in the chamber and not enough resolution to make out anything from the end of the barrel.

I did try one more thing. I neck sized a case so I had enough neck tension so it was difficult to push the bullet into the case. I painted up the bullet with a magic marker and then pushed the cartridge into the chamber with a wood dowel. Then I used the dowel to push the cartridge out from the muzzle. The COAL was 2.76, and there was a scuff mark visible all around the bullet and no signs of hitting the rifling.

Now I'm thinking it is just a very tight throat. Maybe it was a worn reamer? Should I be happy with a throat that tight? Just load to 2.8" and go with it? I would have to make sure that I had enough neck tension so the bullet wouldn't stay in if I extracted a live round.

[Jackpine]

I spent some more time playing with dummy rounds in the Savage and a couple other factory guns that are in the safe. Looking at the SAAMI .308 chamber drawing I am pretty sure the throat is closer to .308 than the .310 that is spec. I am assuming that isn't normal for custom barrels. It makes it impossible to use a gauge to find the lands.

So I called Shilen and they said to ship it back along with a dummy round that I would like to shoot in it and they will check out the chamber.

So the next question is what length should I load the dummy round to. Should I load it to the max magazine length? I was thinking about swapping out the Savage bottom metal for Accurate Mag. Anyone know how long I can go?

[Jackpine]

Summer is too dang busy. It took me awhile to find the time to get the gun taken apart and load some dummies. I sent the barrel back to Shilen and I had it back in about a week and a half. They did a chamber casting and measured the throat diameter at .30815. They said that was good to go. I put the rifle back together last night. Hopefully start on some handloading soon.

[Apache]

If the cartridge is not centered with the bore it will leave scuff marks on the bullet also if you have a tight chamber.....have you checked run out on the cartridge?

[Jackpine]

I went back and edited my previous post. Thinking one thing and typed another. The throat was .30815, not .3085.

I get light scuff marks all around the bullet when I just push the bullet in (not using the bolt).

[memilanuk]

Most custom (non SAAMI) match reamer prints that I've seen show the freebore dimension as something like .3085. .30815 does seem *awful* tight...

[stangfish]

Either contact your reseller or Shillen.

[Jackpine]

Either contact your reseller or Shillen.

I did send it back to Shilen, they are the ones that told me the throat diameter.