Weird .257 question

[YEMX]

I know that .257 (well- ANY big bore, really) benefits from a long barrel and high pressure...  But what I'd like to see is, what's the shortest .257 that's someone's built?  I mean, shortest AND effective?  I'm curious to see the possibilities.  The ONE caliber I haven't done (surprisingly) IS .257.  So I'd like to build one.  I tried doing a google search, but for some reason, I'm not getting the hits I'd like.  I refuse to believe with the close to or over 15+ years worth of .257 builds that there's no pistol, or carbine builds.  Not when there's been Quackenbush and Cothran pistols (probably carbines too?) built from .30 up to .45 (or maybe .50? I can't remember- people have done TOO MANY cool builds over the years to keep track of).  So if y'all could do me a solid, and let me know about yours or someone else's short big bore builds.  Looking at moderate power ones.  Not so much those stubby Crosman pistols (Although, those are REALLY cool!!!).  I want something for hunting. 

The really basic platform is this:

-7/8 size tube
- Cothran Powerhouse valve w/the larger exhaust port (.281")
- Cothran Rear cocking hammer
- Gen 1 Mrod trigger group

Anyhoo, thanks for reading my post, I look forward to y'all's replies!

[rkr]

.257 is long range airgun caliber with bullets to match. I don't quite get it why anyone would build a short range gun out of that caliber when we have .25 and bigger pellet guns or when you could build say low speed .45 bullet shooter with huge cavity bullets. .257 is an excellent compromise for relatively low operating pressure and good BC, not something that you can use with short barrel length. My .257 has 30" barrel and I don't really see the point of short barrel in that caliber.

[YEMX]

.257 is long range airgun caliber with bullets to match. I don't quite get it why anyone would build a short range gun out of that caliber when we have .25 and bigger pellet guns or when you could build say low speed .45 bullet shooter with huge cavity bullets. .257 is an excellent compromise for relatively low operating pressure and good BC, not something that you can use with short barrel length. My .257 has 30" barrel and I don't really see the point of short barrel in that caliber.

I'm well aware.  However, I'm wondering if anyone HAS built a .257 carbine, and what the performance is.

[rsterne]

All other things being equal (ie calibre and pressure), energy (FPE) is proportional to barrel length.... Essentially, half the barrel length gives half the FPE.... However, for a given calibre and barrel length, FPE is proportional to pressure, double the pressure, roughly double the FPE.... So, you can interchange barrel length and pressure in terms of their ability to produce FPE.... Once you take into account the mass of the air in the barrel, the edge in efficiency goes to the shorter barrel with more pressure....

Stay with the typical slug for a .257, the Lyman 257420 and it's variants (about 73 gr.), which is an excellent choice.... and use at least 3600 psi.... you should be able to get decent power with an 18" barrel.... about what you would get with a 24" at 2700 psi....

Bob

[YEMX]

All other things being equal (ie calibre and pressure), energy (FPE) is proportional to barrel length.... Essentially, half the barrel length gives half the FPE.... However, for a given calibre and barrel length, FPE is proportional to pressure, double the pressure, roughly double the FPE.... So, you can interchange barrel length and pressure in terms of their ability to produce FPE.... Once you take into account the mass of the air in the barrel, the edge in efficiency goes to the shorter barrel with more pressure....

Stay with the typical slug for a .257, the Lyman 257420 and it's variants (about 73 gr.), which is an excellent choice.... and use at least 3600 psi.... you should be able to get decent power with an 18" barrel.... about what you would get with a 24" at 2700 psi....

Bob

I kind of figured that's how the numbers would work out... 

So I'm probably going to either do a .250 slug, or perhaps a .30 slug... 

Has anyone tested the .30 hybrid slugs in the old smooth twist barrels?