308win (.340") chamber question

[Forrest r]

Been thinking about buying a shilen bbl for the 308 puma rifle. This rifle is a hoot to shoot cast bullets in. Right now I'm using a 1 in 11 twist 301/308 bbl with a chamber cut specifically for the sierra 175gr match king bullets.

I've been looking at the shilen bbl's & more specifically their 1 in 14 twist 300/308 bbl's. The main reason for the bbl is to shoot cast bullets in and the 155gr match jacketed bullets as a secondary/jacketed mainstay. I measured 20/25 loaded 308w cases that had .311" cast bullets loaded in them. The necks measured .340"/.341".

My question is if anyone is using the the 308win chamber with the .340" throats???
http://www.shilen.com/chambers.html

Is their any noticeable difference in accuracy compared to a standard 308w chamber?

[Larry Gibson]

I've been shooting cast and jacketed in a 14" twist .308W Palma barrel for about 10 years. You will find it excellent for your purpose. Controlling the RPM, especially with cast bullets will enable excellent accuracy at normal cast bullet velocities and much higher velocities. I've successfully shot cast bullets in mine weighing 90 - 200 gr with excellent accuracy. While the 14" twist will handle many different bullet designs the 2 that give the best accuracy at HV are the Lyman 311466 and in particular the NOE 30 XCB bullet.

Yes, a tight neck with lightly turned necks that are concentric and give minimal clearance will give better accuracy, especially at HV. The .340 neck is the best option.

Larry Gibson

[runfiverun]

where are you getting brass that measures .0015? thick.

[Forrest r]

Thank you Larry, was hoping you'd post about the .340 necks. I read your post in another thread about the 14 twist being a good (do all) twist. It got me thinking about dropping $400 on a bbl. Sold some molds I wasn't using to fund the bbl. Just need to put the call to shilen in.

The last 3 batches of lc brass I've bought (over a 2 year period) have all given me .340"/.341" necks with a cast bullet sized to .311".

I never use the expander ball/primer pin setup that came with the rcbs dies. I de-cap the brass by hand and size the cases with the shoulders set back .002" from the fired cases (bbl specific) and no expander ball in the necks. This keeps the necks from getting stretched/thinned. After the brass is sized I check the oal for trim length then use a lee universal expander to bell the case mouth. I've done the 308w's this way for decades

[Outpost75]

Turn necks to 0.0130-0.0135 for .340 chamber neck, only trues the thick spots, allows .311 cast bullet with safe 0.0015 release clearance.

[Scharfschuetze]

Forrest,

I just measured a few LC M118 unfired rounds, and all necks measured .340" across. That measurement is probably applicable to M80 ball also. Given that, GI ammo if fired in your new barrel may be a very tight fit.


where are you getting brass that measures .0015? thick.

I also measured a few LC 82 Match cases for their actual brass thickness at the neck. The average thickness was: .0155"

When the 7.62 NATO was still required by the Palma rules, many of the top shooters were using 1 in 14" twist barrels for the 150 grain SMK and the 155 grain Sierra Palma bullet. That proved to be the best twist for these bullets and it and provided stability and accuracy at the 800, 900 and 1,000 yard ranges that we shot the Palma matches at. That 1 in 14" twist will also shoot M80 Ball (147 gr FMJ) very well, probably better than anything else will, although as mentioned above, that .340" neck in the chamber will be awfully tight with GI ammo if you ever shoot that.

Looks like you've done your homework for a good combo barrel for both cast and lighter jacketed bullets.

[Forrest r]

Thanks to everyone for the help and insight. Larry did the leg work I just happened to be paying attention to what he posted.

[runfiverun]

guess I better pull that box of LC brass out of the cabinet and measure it.

[tomme boy]

Want to confuse you more? Get a .298"x.0307" barrel made. That was what the Brits had to use their bullets for Palma that were .307" That is why the Palma is limited to 155gr also. I had a Rock Creek M24 barrel that was tapered from 308 at the chamber to 307 at the muzzle and it was a AWESOME shooter. Rock creeks barrels are actually a gain twist rifling also but they don't tell may people this. It is only a 1" gain over 12" IF I remember what Mike told me years ago. But whatever the twist you ordered, it started out 1" slower till it met the advertized measure.

A little OFF TOPIC but useful info! LOL

[Scharfschuetze]

That was what the Brits had to use their bullets for Palma that were .307"


That's interesting and probably why the British Radway Green 7.62 NATO had such a bad reputation for accuracy.

By the way, I just had dinner with a British NRA range master in Wool, in the South of England last month. We talked about a lot of shooting things, but never got around to Palma shooting. Next time I'm over there...

[tomme boy]

A bunch of the Parker Hale barrels came about 10-15 years ago. They were all the tight bore barrels and a bunch of people did not know what they had. There was a reamer made just for that barrel. Or you had to ream the chamber then the throat separate with a modified reamer.

Larry might remember more about that???

[Forrest r]

A bunch of the Parker Hale barrels came about 10-15 years ago. They were all the tight bore barrels and a bunch of people did not know what they had. There was a reamer made just for that barrel. Or you had to ream the chamber then the throat separate with a modified reamer.

Larry might remember more about that???

Actually this is where the 308 project is going.

1. Rebarreled the rifle and did testing along with ordered a 3/4* throating reamer and made bump dies.
2. Rebarreled the rifle with a 301/308 bbl to see what affects the 301 had on cast bullets (simulate lapping a choke in the bbl)
3 Rebarrel the rifle with cast bullet friendly chamber and twist.
4. Order new bbl with with tested chamber/twist and send in bumped bullet & 3/4* reamer to have bbl throated.

It's nothing new to have a bbl's chamber cut then throat the bbl to a specif bullet. Typically they get rid of the freebore by doing this. Then they simply use a throating reamer that matches the angle of the bullet being used. Using a bump die does 2 things. Takes any voids out of the cast bullet and trues the bullet to the bore. A standard 311413 bullet, the top bullet was chambered in a standard 308 chamber. The lower bullet was ran thru a bump die and chambered in a the same 308 bbl used on the 1st bullet. The bbl had the 3/4* throating reamer used in it.
http://i162.photobucket.com/albums/t242/forrestr-photo/riflingleademarks_zps5d0d19fd.jpg (http://s162.photobucket.com/user/forrestr-photo/media/riflingleademarks_zps5d0d19fd.jpg.html)
Never bothered doing anything with a nose profile yet. Also you can clearly see the freebore/ball throat length on the bumped bullet. It's the distance between the end of the case mouth and the last grease groove where the rifling starts to engrave the bullet. By cutting the chamber and then using a throating reamer that rifling would of engraved the whole length of the bullet.

Same thing the brits or any other custom bbl mfg had done for decades.

Ordering the bbl today, that puts me 1 bbl closer to the end product.