Forming 257 Roberts from 6mm Rem brass.

[morcey2]

I've got a 257 roberts that I had built last year. Like an idiot, I wasn't buying up every bit of 257 Bob brass when it was available everywhere last year. I only picked up a bag of 50 because "I'll get more later." Now, there ain't no more later. Those 50 are currently loaded, but I have another bullet type I want to try.

I picked up a bag of about 200 once-fired 6mm remington cases. They range in quality from brand-new/never-loaded to reformed 280 and 30-06 cases. The reason I picked them up is that I'm having a 6mm built this spring. After sorting through them, I've got about 120 usable cases. Of these, I was going to form about 25 of them into 257 roberts to load with 115 gr ballistic tips & H100V. The 6mm has a slightly steeper shoulder angle and the 50 cases I've resized so far are about 0.015" shorter at the datum line (0.375" diameter insert in the hornady case length gauge) than the normal 257 Roberts cases. 1.775" v. 1.790".

Is this enough of a difference to worry about? I want to be able to blow out the shoulder and neck to the correct dimensions without stretching the case walls if possible.

Matt

 

[LAGS]

Personally, I cant see why you need so much .257 Rob. right now, and are willing to decrease your supply of 6mm brass if you are going to build a rifle for it later.
When you build your new rifle, you may be in the same Brass Boat and then can't find 6mm brass.
I say use what you have for its intended purpose and if you NEED More Brass, then find some 7 x 57 Brass and you can make either case out of it later.

 

[morcey2]

I'm only going to be using 25 of the 6mm, not the whole lot. That will give me about 115 of the 6mm, including 2 boxes of Federal Premium w/ NPs that I picked up on clearance last year. I have a bunch of 7x57, but it's all loaded right now. I have several 7x57 rifles that not only I shoot, but I loan them out some also. I want every 7x57-headstamped round to be just 7x57.

If that is still an issue, just consider it a purely technical question.

Matt

 

[greyling22]

you can find some 257bob on gunbroker, but 8mm mauser is cheaper.

 

[morcey2]

you can find some 257bob on gunbroker, but 8mm mauser is cheaper.

I've bid on a couple of auctions on GB to try to get some. Hopefully I'll win one of them soon. or ever. If someone has a brass stretcher, one of the LGS's has a bunch of 250 Savage brass. I have a 1893/1916 spanish action that would probably make a good 250-3000, but that's another story.

I have a bunch of 8x57 brass also, but I have a more 8x57 guns than any other. I tried forming one piece of PPU 8x57 and the neck ended up really thick. It was too large at the neck to even chamber.

Matt

 

[243winxb]

6mm Rem formed to 257 Roberts

The difference in datum to head is more like .0188" Its possible for a head separation to start forming. Another problem may be misfires, unless you form a false shouder.

 

[Blackrock]

Haha let me tell you of a trick I learned the hard way. Took two guns to the range. 6mm rem and .257 Bob. Laid all my gear and ammo out on the bench. Shot 3 rounds of 6mm and then 3 rounds of .257R. Then another 3 of 6mm and 3 through the .257R which did not hit the target, sounded different and oh crap those were 6mm I fired in the 257R.

6mm brass was a little sooty but fire formed to .257R now.
It can be done, the 6mm loads were 87g HPBT and 38.7g of varget.

 

[243winxb]

Like Blackrock said, that will work.

 

[John3921]

Kens Brass advertises that they have 7mm Mauser in stock. 7mm Mauser is the parent case for the Bob.

I've never ordered anything from them, they just popped up doing a google search.

I don't know if you'd have to turn the necks or not.

 

[Hanshi]

Although I no longer have a 6mm I do have several boxes of brass and loaded ammo and primed brass. I've used quite a few 6mm cases in the .257R and they performed admirably. Accuracy is excellent as is function and it was no trouble forming these cases. I prefer to go up a caliber than down a caliber or more; no shaving case necks that way.

 

[fguffey]

I've got a 257 Roberts that I had built last year.

This should be at post 11, I am sure someone has ask "When you decided to have a rifle built, what action did you decide to use?" For someone to give advise on forming and firing knowing what action is being used is more than 'nice to know'.

I use forming dies, my favorite is the 308 W, next is the 7mm08 and the 243 Winchester. When forming I choose to use 30/06 military cases because of the head stamp, manufacturer and year, no chamber designation. When forming a case for a chamber I determine the length of the chamber from the shoulder to the bolt face first, when forming the case I adjust the die off the shell holder to guarantee the case is long enough from the case body/shoulder juncture to the case head to compensate for the length of the chamber from the shoulder of the chamber to the bolt face. After forming the case must be full length sized to the final caliber.

There is a difference between full length sizing and the length of the chamber, that is the reason I adjust the die off the shell holder with a feeler gage.

F. Guffey

 

[morcey2]

This should be at post 11, I am sure someone has ask "When you decided to have a rifle built, what action did you decide to use?" For someone to give advise on forming and firing knowing what action is being used is more than 'nice to know'.

I'm not entirely sure how the action is relevant, but I've read enough of your other posts to trust your judgement. It's built on a Yugo-captured K98 receiver using a A&B barrel.

I use forming dies, my favorite is the 308 W, next is the 7mm08 and the 243 Winchester. When forming I choose to use 30/06 military cases because of the head stamp, manufacturer and year, no chamber designation. When forming a case for a chamber I determine the length of the chamber from the shoulder to the bolt face first, when forming the case I adjust the die off the shell holder to guarantee the case is long enough from the case body/shoulder juncture to the case head to compensate for the length of the chamber from the shoulder of the chamber to the bolt face. After forming the case must be full length sized to the final caliber.

There is a difference between full length sizing and the length of the chamber, that is the reason I adjust the die off the shell holder with a feeler gage.

F. Guffey

I have used a feeler-gauge between the case and shell-holder on loads for a 7x57 w/ a very slightly undersized chamber to get a couple thousandths extra shoulder set-back and it worked quite well. It's weird when every case you measure is 0.003" shorter in the middle of the shoulder after firing than before.

But that's a different rifle.

On the 257 front, I was able to score 50 winchester cases on Gunbroker. I'm paying out the nose for them, but I need them and didn't plan ahead very well. And we all know what that means.... That midway, grafs, and everyone else will be flush w/ 257 Bob brass now that I spent the money. :banghead:

Thanks,
Matt

 

[fguffey]

I'm not entirely sure how the action is relevant, but I've read enough of your other posts to trust your judgment. It's built on a Yugo-captured K98 receiver using a A&B barrel.

Thank you, a friend called, he built 5 magnificent rifles, problem, he fire formed cases for the first build. He had 5 of the first 10 cases suffer incipient case head separation. I suggested he could have checked that problem before he left the shop, I suggested I could have fixed the problem long enough for him to form his cases had I met him at the range. He did not use a Mauser action.

It's weird when every case you measure is 0.003" shorter in the middle of the shoulder after firing than before.

I can measure from the center of the shoulder to the case head when determining the length of the case from the shoulder to the case head. All the information available suggest using a diameter of .375" datum/hole. I do not find that necessary because I am comparing the case length of one case with the length of another case or the length of a chamber with the case when measuring from the usual places.

Drilling a .375" hole can be done with a minimum working knowledge of shop skills. A case that shortens when fired from the shoulder to the case head would be weird, the case length from the end of the neck to the case head can happen when the case body fills the chamber. the neck gets shorter and the case body lengthens from the shoulder to the case head.

F. Guffey

 

[morcey2]

A case that shortens when fired from the shoulder to the case head would be weird, the case length from the end of the neck to the case head can happen when the case body fills the chamber. the neck gets shorter and the case body lengthens from the shoulder to the case head.

I measured with the 0.375" insert in a Hornady case length gauge.

This particular rifle (7x57, not the 257 bob that started the post) wouldn't quite close on a go gauge but would chamber FL sized cases with a slight amount of resistance. I used a 0.006" feeler gauge between the case head and shell holder and that gave me enough extra room to easily chamber the cases with no resistance. I had done a set of cases for a load work-up and they seemed to measure shorter than before I shot them. I figured I had messed up the zero on the calipers or something so I did an experiment with the next set of cases.

They were resized the same way and loaded. I measured each case right before firing and wrote it down. After firing I'd set it aside to cool while I measured and fired the next round. After that round, I set that one aside and measured the previously fired case. I consistently got between 0.002" and 0.004" shorter measurements on each case after firing. I'm not sure what that means, but I only neck size them after that and it's proving to be an extremely accurate rifle. I originally bought it as a donor/project rifle, but I think it's staying as-is. I did do a chamber cast to make sure the neck area of the chamber had sufficient clearance and wasn't going to be causing pressure issues. It's a standard milsurp throat/leade. Larger than necessary and very long. One thought I had was that the shoulder angle in the chamber wasn't quite correct which may be the case, but I haven't measured that part in detail and it isn't obvious to the naked eye.

Matt

 

[fguffey]

but would chamber FL sized cases with a slight amount of resistance.

Before that:

It's weird when every case you measure is 0.003" shorter in the middle of the shoulder after firing than before.

F. Guffey

 

[fguffey]

Quote:
but would chamber FL sized cases with a slight amount of resistance.

Quote:
It's weird when every case you measure is 0.003" shorter in the middle of the shoulder after firing than before.

Morcey2, The bolt closing with slight resistance is the equivalent to a crush fit. When the case shoulder contacts the chamber shoulder the case body expands, when fired the case body fills the chamber and forms to the length of the chamber from the shoulder to the bolt face. After firing the case is sized, during sizing the case body diameter is reduced, reducing the case body diameter pushes the shoulder forward.

F. Guffey