Chamber size question

[wk4036]

I just shot a brand new Shilen Savage prefit barrel and noticed that the brass is expanding more than any of my other rifles.
This is a .308 parent case and the new Lapua brass measures .470 dia. right where the very rear of the chamber would be and above the case head the fired cases measuse .481 and will not go into my Redding "Neck" die without the die sizing a good portion of the case.
I noticed that my other rifles expand about .003 in this area.

 

[Eddie Harren]

Send it back.

 

[Rustystud]

That is the difference in a prefit and a better custom barrel is that the custom barrel only let's your web expand to .470"-.4704" (Palma/Match chamber) most prefit companies will cut their chambers to SAAMI spec. (.4714"- .472"). Most pre fit barrel makers will say the larger .200" line/web is within their specs. The .200" line /web on Lapua virgin brass is .4685" yes the case head is .470"-.473". The ID of both my Redding Competition die and my Dillon Carbide sizing die at the .200"/web is .466". We all know sized brass has spring back. The ultimate goal in reloading a competition cartridge is to get concentricity and don't over work your brass. The less you work your brass the longer it will last. Cases when fired grow in neck diameter, shoulder/body juncture diameter, web diameter, case length (from head to datum line), and neck length.
Nat Lambeth

 

[AckleymanII]

Sounds like PRE FITS are std SAAMI spec which would explain the bulge.

 

[shortgrass]

Sounds like PRE FITS are std SAAMI spec which would explain the bulge.

SAAMI specs don't allow that much "swell". Was the barrel installed properly using gauges?

 

[boltfluter]

Send it back. Shilen stands behind their products. At least in my experience.

Regards, Paul

www.boltfluting.com

 

[wk4036]

Sounds like PRE FITS are std SAAMI spec which would explain the bulge.

SAAMI specs don't allow that much "swell". Was the barrel installed properly using gauges?

Yes it was installed using guages and checked again

 

[shortgrass]

Sounds like PRE FITS are std SAAMI spec which would explain the bulge.

SAAMI specs don't allow that much "swell". Was the barrel installed properly using gauges?

Yes it was installed using guages and checked again

Send it back! Maybe include a couple of fired cases.

 

[wk4036]

Just checked with pin guages and its .483 just in from the radius on the rear of the chamber so i'd say its oversize.

 

[tenring]

Bought a Savage pre-chambered 6.5-284 barrel from PacNor bout 7 years ago. It shot terrible and my smith checked it, said it was chambered out of spec - send it back. I did and PacNor returned it saying they found nothing wrong. Sold it after 230 rounds.

 

[X Ring Accuracy]

Send it back. Shilen stands behind their products. At least in my experience.

Regards, Paul

www.boltfluting.com

Agreed

 

[wk4036]

Shilen agreed it was oversize and they are making a replacement.

 

[butchlambert]

That is the difference in a prefit and a better custom that only let's your web expand to .4685". You prefit company will say it is within their specs.

You were wrong this time Rustystud.

 

[fguffey]

This is a .308 parent case and the new Lapua brass measures .470 dia. right where the very rear of the chamber would be and the fired cases measuse .481 and will not go into my Redding "Neck" die without the die sizing a good portion of the case.

Very rear of the chamber, I have unsupported case head, I have case head protrusion. Before I install a barrel I invert a case and stick it into the chamber backwards. The first sign of pressure is case head expansion/flash hole/primer pocket expansion, and I have shell holders that do not have a tolerance for cases that have been hammered/fired with heavy loads.

Then there is the case head. the shell holder prevents the case head from being sized, the deck height of my shell holders is .125". So, the rear of the chamber is not much help if you did not measure the case head.

If my case head expands to .481" at the opening of the chamber I did something wrong.

I accept case head expansion, a good number for factory, new, over the counter case head expansions would be .00025".

F. Guffey

 

[hogpatrol]

fguffey, Do you have a photo of you taking that measurement. Are you using a CMM or optical comparator?

 

[fguffey]

Pratt and Whitney. For most it is an awkward gage. It started as an electronic gage, problem, I had no use for a gage that measured anything down to .000005". I replaced the electronics with a dial indicator.

F. Guffey

 

[Dusty Stevens]

Pratt and Whitney. For most it is an awkward gage. It started as an electronic gage, problem, I had no use for a gage that measured anything down to .000005". I replaced the electronics with a dial indicator.

F. Guffey

Hey i hear about those kind of measurements with calipers and mics!

 

[hogpatrol]

Pratt and Whitney. For most it is an awkward gage. It started as an electronic gage, problem, I had no use for a gage that measured anything down to .000005". I replaced the electronics with a dial indicator.

F. Guffey

Hey i hear about those kind of measurements with calipers and mics!

Hey, I bought a lathe. Now I'm a machineist AND a gunsmith. If I wiggle my electronic calipers they'll read to .0005. ;D ;D ;D

 

[fguffey]

Hey, I bought a lathe. Now I'm a machineist AND a gunsmith. If I wiggle my electronic calipers they'll read to .0005. ;D ;D ;D

Electronic? I have no reason not to believe you, the Pratt and Whitney gage weighs 35+ pounds, it sits on a case iron table. Accuracy depends on the type of dial indicator I have installed on the stylist. I also have vernier micrometers and height gages.

http://www.auto-met.com/mitutoyo/how_to_read_micrometers.htm

F. Guffey

 

[hogpatrol]

Guff, Take a photo of your setup and post it here. It'd be interesting to see another take on measuring. TIA, Hog