Massive problem

[Handsome Rob]

Long story short:
I'm trying to work up a load for an old, 1947 Mauser that has been rebarreled to .257 Bob.
I've only been to the range with it 3 times now (2hr round trip)
First time shooting old factory ammo to dial in the scope. 120gn ammo into neat 1" groups, 100s into 1.5

Second to try some reloads. I didn't have a "recommended" powder but found a load for what I had (imr4064). 100gn Core Lokt bullets into 1.5" + groups. Not great, but showed potential. I loaded these instead of Partitions, simply due to cost difference. 

Yesterday. I got hold of a jug of THE recommended powder (imr4350) & loaded up the 100gn partitions I actually want to shoot. Terrible. Best 'group' was maybe 4" with zero consistency. Load range was 43.5gn to 45.5gn (no pressure signs anywhere, bullets seated to book length 2.770" LOTS of bullet in the case) 

Could a powder & bullet change really affect things THAT badly?

I'm probably going to pull the stock & scope anyway, then try another scope just in case, but just want confirmation that a load couldn't be THAT bad all by itself. Could it?

[Mike1000]

I would probably do a bullet seating length test first. Run a set of loads increasing the depth by .010" each time, beginning just off the lands at minimum powder. Once you have a seating depth, run a Satterlee test to find a decent powder charge at that depth.

I've been amazed at the difference seating depth and charge makes but I've never loaded for something that old mind you. You could also very well be right that something has come loose in the scope.

[MacGyver]

My first thought - and definitely my luck - would be that a screw came loose on my scope mount.

 

[gregintenn]

I’ve found IMR3031 to be THE powder for a 257 Robert’s. I would check to see if your scope mounts and rings are tight.

[deerslayer]

Also, for giggles, measure the OAL of a few bullets and don’t be shocked if they vary by a few .001s.  Some measure on the ogive for this reason.  

[peejman]

Got a chronograph?  I'm curious if there's significant difference in velocity. It's possible that bullet isn't stable at that speed. 

Edited November 4, 2021 by peejman

[Handsome Rob]

1 hour ago, peejman said:

Got a chronograph?  I'm curious if there's significant difference in velocity. It's possible that bullet isn't stable at that speed. 

I do, but I generally don't use it when I'm working up a load that's within normal parameters. I use it once I've found a load, but it's a magnetospeed & I don't want it throwing off my groups during testing. 

[leroy]

Ya might want ta slug the barrel n measure the od of the partitions carefully.  Big barrel/bullets on the small side.  Especially after the factory loads did OK.. m.

leroy.  

[Quavodus]

You could have a faster than normal twist. I think most .257 Roberts have a 1-10". At least that's what I remember. Heavier longer bullets might shoot better, I personally would shoot 115, 117, 120.  but, don't rule out a loose ring or base. 

Edited November 5, 2021 by Quavodus

[Mowgli Terry]

I've used H4895 and several flavors of 4350 with 100 through 115 grain bullets. Something is not right. I go along with tightening screws. I'd also add changing out the scopes. Start simple. Also, test the twist along the way. My two Roberts that I actively shoot do very well using heavier bullets and 4350. In the simple stuff check the length of your throat.

[Sunfish]

When you say the factory rounds grouped better makes me think that the reloaded rounds are not up to pressure. I will also tell you that old guns like old flat base bullets. In a 57 mm case I have had great results with AA 2520 and AA2700 with the heavier bullet weights  

[Mowgli Terry]

It would be great if you could let  us know how your work on the Roberts came out.  I did a no brainer on a Ruger #1B in 257 Roberts. I took some of my go-to loads for my varmint rifle to try the rifle out. The result was like you described. Horrible results on the best day. Finally, found the answer. Ruger had throated the  rifle for 100 gr.+ bullets. The COL 0f 3" was easily done. That Ruger is not a dual purpose rifle. That means my favorite 75 and and 87gr bullets would not work. It is a MOA rifle with the right cartridges.

When you are dealing with a built up Roberts you may find some interesting problems dealing with the way the gun was put together.  For example, my old Mauser is made up as a varmint rifle with short throat and 1:12 twist. How would that work with a 120 grain spitzer bullet? My rifle was not made as a dual purpose rifle. Hope your rifle works out.

[papa61]

I read and learn. Don't shoot 257 but the knowledge will translate. TGO people are great!

[Handsome Rob]

On 11/28/2021 at 10:41 AM, Mowgli Terry said:

It would be great if you could let  us know how your work on the Roberts came out.  I did a no brainer on a Ruger #1B in 257 Roberts. I took some of my go-to loads for my varmint rifle to try the rifle out. The result was like you described. Horrible results on the best day. Finally, found the answer. Ruger had throated the  rifle for 100 gr.+ bullets. The COL 0f 3" was easily done. That Ruger is not a dual purpose rifle. That means my favorite 75 and and 87gr bullets would not work. It is a MOA rifle with the right cartridges.

When you are dealing with a built up Roberts you may find some interesting problems dealing with the way the gun was put together.  For example, my old Mauser is made up as a varmint rifle with short throat and 1:12 twist. How would that work with a 120 grain spitzer bullet? My rifle was not made as a dual purpose rifle. Hope your rifle works out.

Thanks for the tips.

Unfortunately, medical circumstances have forced me to have to part ways with the rifle, for now. 

I did fully dismantle & reassemble the entire rifle, just to be 100% sure of all my torques, scope & mounting bits.

With hindsight, I'm 99% certain that by loading to SAAMI length, rather than loading to the chamber/mag length was my main issue. Not the powder or bullet. I did load up some further test rounds with the exact same charge ladder, but loaded to .010 off the lands. That gave me a COAL (if my rememberer is right) of 2.89", rather than the SAAMI spec of 2.77. I was 100% confident that one of the higher end loads would get me exactly what I was after.

I've saved them & all my loading gear in a safe place though.... as soon as I'm paid up with the doctors, I'll be buying another. I feel a Kimber 84M in my not-too-distant future.

Edited November 30, 2021 by Handsome Rob

[Mowgli Terry]

Hope you are a Doctor free shortly. Right, load to rifle. Sounds like your rifle is throated out for the heavier bullets. Also, check that twist. A slow twist could be spoiling your best efforts.  A notable of a bygone era said the 257 Roberts was the most useful caliber ever designed.  Good luck and best wishes. Stay safe.

[Handsome Rob]

Thanks Terry, I appreciate it. 

I'm doctor free now, but unfortunately it'll be a minute before I'm rid of his billing office!

[Mowgli Terry]

7 hours ago, Handsome Rob said:

Thanks Terry, I appreciate it. 

I'm doctor free now, but unfortunately it'll be a minute before I'm rid of his billing office!

The more things change to more they are the same. Different Doc billing office is the same. Keep us updated on the progress with the Roberts.

[slickshot223]

Rob, I think your issue is more with the seating depth than the loads! As suggested find out the throat length and back of about .020" ,think you will find a load somewhere close to that load length!! Let us know!!