257 roberts imp brass problem???

[SweaterDood]

This is a common issue with “improved” wildcats, especially older ones. The change in case taper is what generates issue. These dimensions are not standardized and the die/chamber combination can cause issues. On top of this the differing manufacturers of brass can have differing external dimensions to begin with. It is best to take cases fired 2-3x, (neck sized only!) And send them to a die maker or for custom dies that match the chamber.

I ran into a similar issue, but for me it was caused by brass dimensions. I have a bulge at the .200” line from where WW brass is smaller than the Hornady brass used to have dies made. I was not able to source more Hornady after my initial lot, and did not verify external dimensions of WW against my reamer. Not a big deal, I just know to throw brass in the trash after 3 firings, from loose pockets.

 

[wildcatter]

Get some Lapua 8x57 Mauser brass, run through a 308 win die just enough to size the neck then full length with 7x57 Mauser die finally a 257 AI Roberts die. I did this for my 6mm Remington AI then fireform them with 13grains of bullseye and case filled with cream of wheat or I used corn cob media and sealed them with zest bar soap. Paraffin or bees wax will work as well. Then turn your necks to fit your chamber with a loaded round.

You will have the best brass a available for a 6mm AI or Remington, 257 AI or Robert's, or 7x57 AI or Mauser. I was shooting .250" groups and after 5 firings I am sure 100 rounds will be more than needed to wear out a new barrel. Nosler and federal are no better than Winchester or Remington and primer pockets won't take the top end loads, Lapua will take more than your primers will. Been where your at but will never go there again! The 8x57 Mauser brass from Lapua is the best you can get for these cartridges!

Just remember you have to turn the necks when you neck down brass especially taking it down this far. It thickens the neck the smaller you size the necks down. Using the fireform method I do, I don't have to turn till I have a fired case. This is a very hardy case, and will last with heavy loads! Which is the main reason I Improve the cases I use it in!

 

[std7mag]

Gee, and here i am using 7X57 PPU brass, thinking i was fine.
F/L to 257 Roberts, fireform & done.

 

[wildcatter]

Many are fine with Federal or Norma, I just expect better,,, much better! I wouldn't go thru the work if it was not noticeably better. Plus I know it last more than three times the firing at the pressures I run. It just depends on how good your fine with!

 

[SweaterDood]

Many are fine with Federal or Norma, I just expect better,,, much better! I wouldn't go thru the work if it was not noticeably better. Plus I know it last more than three times the firing at the pressures I run. It just depends on how good your fine with!

What is the diameter at the 0.200” line on the Lapua 8x57 brass? Measurement can be on virgin or FF brass, but please indicate which. Thanks in advance.

I don’t want to spend $150 on brass to find out that it won’t help me...

 

[clowdis]

Sounds like the easiest fix is to have someone turn a little off the end of your sizing die. If you purchased a prechambered barrel how did you check the headspace? Most (but not all) prechambered barrels are sent with a short chamber that must be finished up at installation. Maybe the chamber is still .005 short?

 

[wildcatter]

What is the diameter at the 0.200” line on the Lapua 8x57 brass? Measurement can be on virgin or FF brass, but please indicate which. Thanks in advance.

I don’t want to spend $150 on brass to find out that it won’t help me...

.4703" with fired 8x57 JS Lapua brass, my Remington 257 Roberts head stamp measures .4714". Be careful as they sell rimmed 8x57 JRS mauser as well and that has a rim. the JS is what you want! Midway is your best bet finding it most times.

not a waste at all. the most durable brass I have found, and super consistent, you won't find that with any other brass manufacture!

I would have tried the 30/06 but requires more work with the longer case. I had three ruined cases out of the first 100, and those were at first start, after that no bad cases, and all dies I used were standard RCBS or Reading FL dies.

 

[SweaterDood]

Thank you for the info. It is greatly appreciated. If the Lapua brass starts at a slightly larger diameter, then I will have a simple, high quality solution.

I have WW and Rem brass. Both measure 0.468” unfired. The 0.002-3” growth in the case head diameter is a big problem. Even quality brass like Lapua wouldn’t handle a chamber mismatch like this. This is what I am referring to as a waste, not putting the quality of Lapua brass in question.