Basically the .257 roberts from what the write up says.

http://www.gunsandtactics.com/shooting-the-25-45-sharps-cartridge

http://www.gunsandtactics.com/black-forge-weapons-and-the-25-45-sharps

Looks interesting, not that anything has a chance of supplanting the .223/5.56 round in the .mil / LEO universe.

I guess someone looked at the field of AR cartridges intended to improve on 5.56 and decided that the fact that .257" had been neglected among all the other standard bore sizes between .224 and .308 (.243", .264", .277", & .284") was an egregious oversight rather than a deliberate omission.

I said it was interesting, I didn't say it was particularly useful.   

Sounds like a solution for a non-existent problem.  If one of the other larger bore variants on the .223 case is not sufficient for the task, why think that the quarter bore will work magic?

Personally, I have some attraction to 6mm bullets and really like those little 55 grain Nosler BT's in my 6mm Remington varmint rifle (almost 4,100 fps sub MOA grenades), but, I've never given any consideration to the 6x45, so why the .257 variation?   Marketing hype.

The only  AR15 variation I thought worthy for my use was the 30RAR, and look how that turned out, even after the big, but short-lived initial push by Remington.

And I COMPLETELY agree with the "mildly offended" comment about commercial hijacking of the Sharps name and reputation.

Yeah. The 257 Roberts/+p was and still is an awesome round. It is an almost ideal deer rifle for much of the plains states IMO. It being super duper popular is a big ole fib for sure.

I was getting a slight chubby over the thoughts I had when I seen the title of the post. I was seeing a big sharps round loaded with smokeless and necked down to 25 caliber. Then I all deflated when I read what it really was.

  I would say that at ONE TIME the .257 Roberts was pretty danged popular, that is as was any necked/rimless cartridge in the 1940's/early 50's.

 

Might be moving a little off topic, so forgiveness sought.   The " Bob" .257 Roberts lost popularity for another reason:  The case size is an odd length. It is made on the excellent 7x57 Mauser case.   So is the 6mm Remington. 

This is a mid-size case, as far as length is concerned.   It will not work through a short action bolt gun.  Too long.  A regular full length standard action rifle is unnecessarily long, heavier and has longer bolt travel, and wasted magazine space.

There are only a few rifle manufacturers who continued to make bolt guns with a so-called mid-length action.  I have a rifle built on a SAKO L-579 action, a true mid-length action.  It is chambered in 6mm Remington (actually barrel stamped .244 Rem). The action is long enough to handle the 7x57 class of cases, without being heavier and having longer bolts and longer magazine well and magazine as would a full length standard action.   

These are no longer popular, due to the proliferation of short action rounds that perform just about as well, or perhaps better sometimes, especially the short action magnums which seemed to be in vogue for a while.

There are real advantages to these mid-length rounds.  They have the higher efficiency of the short action rounds, like .308, .243, .260, but have higher powder capacity and therefore greater velocity potential, especially when hand loaded.   But the x57 cased rounds seem to have gotten lost in the shuffle.  Pity.

You can make the mid length round work in a short action (I don't think Remington has ever offered the .244/6mm in anything but a short action), but you do lose some flexibility due to the inability to seat long/heavy bullets as far out as they ought to be to take full advantage of their case capacity.

Here are the 6mm Rem and the .308 Win from my desk collection. The OAL is pretty danged close with the 6mm just a couple mm longer.

There was very little the .257 Roberts could do that the .243 Winchester couldn't in a true short action cartridge.  The .25/06 bested it on the upper end of the scale and the .243 Winchester bested it on the lower end so it just faded from the scene except for a few diehard fans.

The "Bob" was and is a very good medium game cartridge.  It was capable, efficient and pretty forgiving for handloaders but it is an unlikely parent for a new AR 15 "wunderkind" like the 25-45 Sharps.   The 6.5 Grendel is as good or better than it could ever hope to be and is already an established round with factory ammo available.  I predict the .25-45 Sharps will become a game winning answer to "gun shop trivia" in relatively short order.

I'm mildly offended by the crassly commercial use of the Sharps appellation for a cartridge that isn't really suited to hunting bison.

I do wonder how it would run with a load of FFg driving a paper patched bullet though. 

The real 25-45 Sharps:

You can make the mid length round work in a short action (I don't think Remington has ever offered the .244/6mm in anything but a short action), but you do lose some flexibility due to the inability to seat long/heavy bullets as far out as they ought to be to take full advantage of their case capacity.

Here are the 6mm Rem and the .308 Win from my desk collection. The OAL is pretty danged close with the 6mm just a couple mm longer.

Jesse,

What do you know about the action length of the Remington 700's ancestor, the 722 (from 222 to 257 Bob) and the 721 (270 win, 30-06, and similar)?

The 308 was designed 10 years before the Remington 700.  Is it a case where the 'old' short action by many gun makers was a little bit longer, but once the 308 came on the field and become so popular so quick that it defined what was going to be considered the short action from then on?

I know that Sako used to sell just actions, and these were available in 5 lengths.  #1 was for 222 and 223 length cartridges, an extra-short if you will. #2 was standard short action #3 was midsize 7x57mm and kin #4 was standard (30-06 length) and #5 was 'magnum' length (real magnum 375 H&H long, many of the cartridges we associate with magnum like the 338 winmag are actually sized to fit the standard length action

Fair enough.   I don't claim to be the definitive expert on the subject, just someone who has had more than a passing interest in hunting rifles since the 1960's.   I was speaking more to the claim made by the developer of the 25-45 Sharps than to any objective measure of popularity for the various cartridges.   We have had a national love affair with the .30 caliber since long before I was born regardless which flavor you choose and I had graduated high school before I ever saw a .257 Roberts in person.  Its a fine round and the rifles that chamber it are generally a joy to handle and shoot but on its best day it really never approached the widespread appeal of the .30 calibers, contrary to the claim made in the advertising copy for the 25-45 Sharps.

I agree that the "Bob" is a superior cartridge to the .243 Winchester on elk sized animals but if I were afield after elk I wouldn't pick either caliber as my first choice.  Likewise for black bear - neither cartridge is ideal for heavily muscled animals even if the shot is placed at relatively close range with surgical precision.  The .243 Winchester was and is capable of handling any deer sized game providing you choose the proper bullet and operate within the cartridge's limitations.  It is a flatter shooting round with slightly better ballistics until you get to the 90 - 100 grain bullets where the .257 Roberts begins to overtake it.   Both are efficient cartridges and the difference between them on a well placed shot is primarily academic IMO.

I believe the .25-08 was called the .25 Souper back in the day and yes, it is apparently a very good wildcat but none of the .25's are as popular as I think they deserve to be.  They have long been overshadowed by the .270's and the various 6.5's and 7mm's.  The .257 Weatherby is as close to a "death ray" as I know with 115-120 grain Nosler Partitions but the .270 Winchester probably outsells it 10 to 1 .  Go figure.   

   

Two of the best shooting rifles I have ever personally fired were owned by the same guy who would not part with either of them.  Selfish clod.       One was a .25/06 built on a post war FN Mauser action with a Timney trigger, a 24" Douglas barrel, and an old Weaver K6 that refused to die.   The man could shoot that rifle into one hole all day long at 100 yards and took an impressive amount of game with it.  That rifle even made me look like a marksman.   The other was nearly identical except for the stock and scope but chambered for the 6.5/06.  It was the older rifle of the two and had a Kahles scope on it, which I had never heard of at the time but if anything it would outshoot the .25/06 especially at long range.  He referred to it as his "mountain gun" and routinely put rounds into tight cloverleafs at 200 yards.   I got to shoot that one as well and it was an object of lust for a long time.     He kept them both because, according to him, he never found any other rifle which would outshoot either of them and couldn't make up his mind which one he liked best.  Neither rifle had the recoil or the muzzle blast of the .270 Winchester and both were pretty much a one shot, DRT proposition in his hands.   Ever since then I've had a lot of respect for those two calibers.  At this point my hunting collection doesn't have either of them represented but you never know - maybe someday.