Before a couple of weaks I red about it in a magazine, that I can't find again, but it was interesting!

In fact it was not a choke as in the smooth barrel, but a conical formed inside contour with
constant gain grade.
The most interesting was that this should cause
very higher speed with the same pressure an recoil.
The only "problem" was the special construction of the bullet - ribbed so that the bullet itself leaves the barrel without deformation.

Could anyone tell me where to find more informations?

koce

Something like this is fairly common in the Anschutz rimfires.

WE call them 17 extruders down here.... 22 rf with the muzzle down to .17.(maybe .19 can't remember) not too common but from my understanding will shoot most types of .22 rf ammo.

I think you're talking about the Black Star barrels of Houston. The pre-rifled blanks were bought slightly undersized and electro polished to a slightly "choked" bore. Factory specs were for .001 smaller at the muzzle.

I've never shot one, but understand some were magic and some were duds.

As a kid I used to think all rifles were choked because my first quality airgun (Feinwerkbau from Germany) was choked. I remember reading about the guns design and how important the choke was, and any thought of cutting the barrel shorter would ruin accuracy.
I'm not sure how a strong walled bullet would take to a choke. Pellets, cast slugs and 22 rimfire I can see, but what would be the advantage anyway??

Chevota, in THEORY, higher velocity at high accuracy. One of the issues with smokeless powder is that pressure rapidly falls off from peak levels as the bullet goes down the barrel. In THEORY, choking the barrel diameter down increases pressure down the barrel, which in THEORY can increase velocity.

What do we need then?

A gain twist, ratchet rifled, choke bored barrel! Yeah!

Well this thread went nutz in a hurry. A "choke" is a SLIGHT constriction at the muzzle for a few inches only, not a Swager/Extruder, and even different from the tapered Blackstar (though that IS an attmpt towards the same end in a different way). It is usually apparent that a barrel is "choked" when the muzzle is of a larger diameter than the rest of the barrel. This is because, when a barrel is contoured after being rifled (Particularly, but not limited to, button rifled barrels) the removal of barrel material allows the bore to "grow" just a bit. The "choke" at the end of the barrel causes the bullets final contact with the barrel to be of more exacting "as machined" dimensions. Thus helping to keep better accuracy.

[ 06-29-2002, 05:46: Message edited by: Vibe ]

There was one maker who claimed to produce a choked bore and perhaps, did. The problem was the choke was likely to be anywhere.
In the muzzle loading days, choked bores were common. the Choke was produced during lapping. The advantage was easier loading and theoretically improved accuracy. Harry Pope's barrels were produced with a constant taper from breech to muzzle and were unlapped. Regards, Bill.

koce, I believe what you are describing is the "taper bore" concept that was being touted in the 1930's by a German/American (I'm not sure exactly what he was) fellow named Harold Gerlich, who, along with a partner named Halbe originated a series of "super-magnum" small-arms rounds named HALGER (Halbe/Gerlich). One of these, the 280 Halger, seems to have been nothing more than a hot-loaded .280 Ross, and another, the .240 Halger, we would recognize as the 6mm Remington (although his was a hot-loaded 6X57mm Mauser, a round which dates from the 1890's and is, for all intents and purposes, identical to the 6mm Remington!!) In the mid-30's Gerlich came to the U.S., and tried to sell U.S. Army Ordnance on the concept of a taper-bore anti-tank rifle which had a final diameter of 20mm. I don't recall what the starting caliber was, but might have been around 37mm. This thing fired a slug that was 20mm with two relatively large rotating bands or flanges of original caliber, which would swage down to final diameter as the projectile travelled down the bore. The idea was to produce exceptionally high muzzle velocities by reducing the area the powder gasses pushed against as the projectile travelled through the bore, thus keeping pressures very high. The concept worked, and Ordnance did experiment with prototype antitank guns using the Gerlich idea. They were hard on bores!! I do not believe we ever issued any of these guns, but I believe the German Army used some of them in 20mm final caliber during WWII. (I may be wrong about this!!)

Yes, Larry
that's exactly what I was asking for,
but it was not in english, so I was not sure how is it all called.
It was interestig for me if something like this
was made with any hunting cal. and would it really
cause all what was thougt?
Is there some research data on this experiment?

koce

koce, I doubt if anything as radical as say, a reduction in caliber from 37mm to 20mm was ever tried in small arms, but I believe I recall that Elmer Keith described some similar experiment having been performed at a U.S. Army arsenal during WWII using, I believe, the .50 Cal Browning machinegun cartridge as the original diameter. I believe there is any excellent industrial and scientific museum in Munchen (Deutsches Museum??) that has a lot of arms and firearms. They might have some info concerning the German Army's use of Gerlich's concepts during WWII. The U.S. Army Institute of Military History at Carlisle Barracks Pennsylvania might also have info on this subject. I am not certain how one would go about requesting the information from them, however.

koce, go on Google, and search for Gerlich Taper bore rifle.... I got some responses: See below:

The German SPzB41 used the Gerlich taper-bore ... While the PAW designation marks this
weapon as a recoilless rifle weapon its design was that of a ... www.feldgrau.com/weap.html - 18k - Cached - Similar pages

DML 1/35 Sd.Kfz. 250/11 w/Panzerbusche
... special "taper-bore" weapon, 2.8cm (1.1in) heavy anti-tank rifle ... Three different taper-bore ... All relied on what is commonly known as the Gerlich principle. ...

www.internetmodeler.com/2000/apr2000/ first-looks/dml_sdkfz250.htm - 22k - Cached - Similar pages

Miscellaneous Questions #2
... Most of the Gerlich rounds used a bullet ... In an 8� or so pound rifle (sighted ... dimensional anomalies (tight spots, loose spots, reverse taper to the bore ... ome.sprynet.com/~frfrog/miscellb.htm - 41k - Cached - Similar pages
A Cartridge Collector's Glossary
... common is for a.50-caliber magazine rifle. ... TAPER BORE - A experimental design of
gun whereby the bore ... objective is to create higher velocities (see Gerlich ...www.cartridgecollectors.org/glossary.htm - 53k - Cached - Similar pages
THE SEARCH FOR HIGH VELOCITY
... of these is the Conjay Firearms sniper rifle ... a developmental blind alley; the cone,
taper or squeeze-bore gun ... first developed to prototype stage by Gerlich ...
www.quarry.nildram.co.uk/highvel.htm - 31k - Cached - Similar pages

I Guess there were some rifles!!!

"The problem was to achieve and sustain a high velocity over battle ranges, which required a large calibre at the chamber end of the gun, for maximum interior ballistic efficiency, but a small-calibre projectile for optimum exterior ballistics and penetrative power. The first attempt to achieve this was a developmental blind alley; the cone, taper or squeeze-bore gun.

This was first developed to prototype stage by Gerlich in the 1920s, who demonstrated examples at Woolwich in 1932. A cartridge case, apparently based on an extended .303" (7.7mm) necked out to 9.25mm, fired a 95 grain projectile with an emergent calibre of 7mm at a muzzle velocity of 4,880 fps. The British showed interest and continued to experiment for some years, but the only service weapon using this principle was the 2-pdr Littlejohn.

The Germans were the first to introduce taper-bore weapons. They required entirely new gun barrels, with a calibre which reduced from the chamber to the muzzle, and a tungsten shot of muzzle calibre, fitted with flanges of chamber calibre. As the shot proceeded down the barrel, the flanges were squeezed into the shot, leading to the nickname "squeeze bore". Anti-tank guns of 2.8/2.0, 4.2/2.9 and 7.5/5.5cm bore were introduced. The velocity champion was the 2.8cm PzB 41, with a 28mm cartridge reducing to 20mm at the muzzle, which achieved a muzzle velocity of just under 4,600 fps. These weapons were highly effective, but doomed in German service because of the tungsten shortage (steel shot would disintegrate on impact at these velocities)." (FROM A BRITISH SOURCE)

The British adopted the same principle with the Littlejohn adaptor, which consisted of a squeeze-bore extension added to an otherwise conventional 2-pdr armoured car gun. Again, it led to a great increase in performance with the around 4,200 fps muzzle velocity, but was unpopular because of the necessity to remove the adaptor before full-calibre HE shells could be fired. In the event, the special shot was sometimes fired without the adaptor (effectively becoming APCR) which worked quite well at short range. Examples exist of a Littlejohn HE shell experimentally produced for the 2-pdr, but this was too small to be worthwhile.

It's a bad day when you don't learn anything new!!!