257 Roberts Improved pressure question

[Zor]

I plan on building a Mauser in 257 improved and before I commit to an action I want to ensure that I can produce a good hunting round in a 117-120 grain bullet without producing enough pressure to push the limits of the action. I'm fairly novice in the reloading game, so any input is appreciated. I plan on a 24" barrel, but nothing about this build is concrete yet.

Thanks,
Zor

 

[rcmodel]

You can easily get 2,800 FPS with a 120 in a standard .257 Roberts at 45,000 CUP.

That will kill anything you should shoot with a .25 caliber rifle right there.

However, the .25 cal rifles are best loaded with lighter 87-90-100 grain bullets to take advantage of the speed and flat trajectory. With todays good premium hunting bullets, penetration is just as good as the old 120 RN bullets used years ago.

I really don't see much purpose for an ".257 improved" version, as they don't offer anything you can't get more of with a 25-06.

And the standard old .257 Bob ain't no slouch either when it comes to killing medium size game. It's been doing it just fine since 1930.

rc

 

[Zor]

Thanks RC. I'm looking into a Swedish M96 for a platform and all the Gustov's were supposedly proofed to 66,000 cup at the factory and I wanted to make sure I'm staying well under that. I'm using the Bob because it'll fit in the intermediate action length. I don't want the hassle of modifying it for the '06 case length. Any suggested starting place for loads? I've done plenty of plinking ammo for 223. and auto pistol stuff, but have yet to get into handloads for hunting. I've always heard that the Nosler Partition is the benchmark for a hunting bullet, so I have a box of them in 30 cal for my .308 and 300WSM platform rifles. Just haven't put anything together yet. Any bullet/powder advice would be great.

Zor

 

[greyling22]

I've got one. I like it. Recoil is pretty mild, brass is hard to find, and the regular roberts works well in it too.

attached are some links, load data, etc for the 257 ackley. It's kind of hard to find.

Unless you really want to reload an oddball caliber headed for oblivion I'm not sure it would be my choice of caliber though. It's a good round, but it has fallen from favor.

 

[41 Mag]

For your .257 AI powders, I would look hard at using nothing faster than one of the 4350's personally. While certainly not a 257 or even close to the AI version, with both my .243's and my 25-06's, the powders from 4350 slower in burn rate have always seemed to preform the best with 100gr and up weight bullets.

With your AI, I might also look into the mid weight bullets like the 110gr Accubond or the 115-117gr options as well. This should allow you to get a good velocity without pushing the limits and be able to use the same loads for both small and large critters.

Depending on which powder you go with you should easily be able to hit 3000fps with any weight bullet listed above, and stay well within your pressure limits. At this velocity there should not be much of an issue even using the Ballistic Tips, depending on the actual range and impact velocity. I found with my .243 and my 25-06 using the 95 and 100gr BT's, that if I kept the impact velocity around 2800 or less I didn't get the overly explosive results from them that many talk about.

I do agree that the AI's aren't always what they are touted to be, but hey I have a several of them, and have been happy with them all. It's your build, make it what you want it to be.

One tidbit, when you set out to pick your barrel, if you can, you might pick a contour which will allow you to leave a bit more length on your chamber profile. This will allow you a little room so that if you should decide to you could set it back and rechamber to a standard .257 later on, or vice versa, start with the standard and have enough to set it back for the AI version. I did this with my 25-06 AI, just in case I wasn't happy with the resulting performance, needless to say I believe it will simply stay this way for quite a long time,

 

[GooseGestapo]

My custom .257Robt is built on a LaCarouna (Spanish M98) action. These are notoroiously the worst M98 ever built. They were built by National Socialist in Spain during the 1938-39 civil war and heat-treating was "spotty". Some are brittle as china, and others soft as butter. I'm lucky in that mine is hard, but not overly....

It has more than enough strength for the Roberts. Just observe good loading practices and avoid loading beyond flattened primers, cratered primers, or sticky extraction and you'll be fine.

You can easily reach 3,100fps with 100gr bullets, and 2,900gr with 117-120gr loads without seeing ANY pressure indicators. My best accuracy however has been with the "classic" loads of 45.0gr of IMR4350 and 100gr bullet, or 48.0gr of IMR4831 (or H4831). These both get right at 3,000fps from a 22" standard Roberts barrel. 45.0gr of IMR4831 will give near 3,000fps with a 115gr Berger VLD hunting and a better whitetail cartridge/bullet dosen't exist, IMO.
Five for Five "bang-flops", and only one was a CNS hit. The rest were heart/lung hits, but exit wounds are the size of "footballs".....Do place your shots well to avoid excessive meat loss.......

I would just use the standard chamber (not AI) as dies will cost much less...

The standard 1/10" twist will stabilize any weight of commercially offered bullets. There were some custom 130gr bullets available some years back, but I never tried any. My experience with the 120's is that they are adequate for game up to elk and caribou. Even moose if that's all you've got.

I really, really like my .25's. My limited experience with 6.5's is leading me to believe there's little if any difference between them and the .25's and .270 with modern bullets.....

With a 115gr Nosler Partiton or 120gr Swift A-frame, the .257Roberts will leave you wanting for nothing more. I use the 117gr and 100gr Hornady's as they are much less expensive and work splendidly on whitetail deer. The Bergers and Sierra's are the most accurate.... (not dissing Speer's, just limited experience...).
My rifle prefers IMR4831, but it took me 29yrs of experimenting/chronographing to come to that conclusion....... H4831, IMR4350, H4350, RL22, and RL17 come very, very close 2nd place. H380 and H414 are splendid also.
The only powder my .25's have "gagged" on is Hybrid 100V. It's not "bad", but my lot# is MUCH faster than data indicates. Hodgdon's data says 48.0gr for ~45,000cup and 3,200fps. My lot number matches out at 44.0gr for 2,950fps, or, not as good as either H380 or H414......YMMV.

 

[Zor]

Thanks Goose.

I need to look if 257 improved dies are readily available and what the cost difference is.

Thanks guys.

 

[Zor]

Lee Pace Setter set 33$ from cheaper than dirt.

RCBS set 66$ from Midway USA.

Thoughts on the quality differences?

 

[greyling22]

You can't get a 3 die lee ackley set. You have to buy the alley sizing die and a Roberts die set for the collet die. I had to turn down the mandrel on my collet die to get the appropriate neck tension.

But lee dies are fine for the most part.

 

[Zor]

Pardon my inexperience, but what is the third die for? Most of my dies are just two dies, a sizer and a bullet seating die. I think I have a couple sets that include a neck sizer.

 

[greyling22]

3rd die is a neck sizer. A collet neck sizing die. works well with a fire formed case.

 

[Clark]

In 2002 I got 4 barrels and a reamer from Brownells, Lothar Walther 26" 2100 taper and put them all on Mausers in 257 Roberts Ackley Improved.

3 Were on VZ24s and one was on a Turkish Mauser KK type.

The VZ24 starts to change the bolt diameter and the abutment diameter with belted magnums at ~ 108 kpsi.

The primer pocket in 257 Roberts brass will get loose with one or two firings at 75kpsi.

So the brass is the weak link in the VZ24 - 257RAI marriage.

After brass has been fire formed, it is worth a lot more. It would be a shame to loose brass to loose primer pockets with a few shots.

I measure around the extractor groove with dial calipers. Then I fire the round. Then I measure the diameter at different spots all around the extractor groove. I find the load that is the threshold of any change in the groove diameter. The will be ~ 72kpsi. Then I back off 4% in powder charge.

Then I zero at 200 yards.
Then I see how much turret turning is needed and how close to point of aim I am at 300, 400, 500, and 600 yards.

 

[helotaxi]

^^^You realize that SAAMI recognizes 65k psi as the max safe pressure for any load in any firearm, right?

 

[Zor]

Wow Clark! That's what I was looking for. Although I don't know that I'll load hot enough to get those pressures, it's good to know that the action won't be the weak link. Do you have a favorite brass? Are all of those originally 8mm actions? If so what is your overall length. Also are these hunting or target rifles? If hunting, would you mind sharing some load info with me? I'm planning on a 24" barrel and taking deer, antelope and javalina with it. Thanks again for the info above.