O
Old Gunner
Guest
I've seen some information on the rebated boat tail lately, it appears to be an old solution to excessive blow by when used in loose military MG bores.
I see the idea has been revived more recently, but I wonder just how much good it can do when bore and bullet sizes are a better match than the loose bore to bullet fit it was intended to compensate for.
One thing I wonder about would be a secondary shockwave effect.
When the older type tail planes of fighter aircraft were subjected to super sonic airflow, in terminal dives and early experiments, a secondary shockwave at the point where elevator and horizontal stabilizer met made control difficult or impossible. The All Flying Tail was revived from earlier aircraft such as the Taylor craft to deal with the problem. The Bell X-1 which had the two piece tail plane was adapted by locking the elevators and modifying the trim mechanism to give an all flying tail effect.
The all flying tail gave our Sabre Jets the advantage in trans sonic flight, the Mig 15 with the two piece surfaces could not manuver effectively when transitioning to super sonic in a dive situation, thus often augered in during a dogfight.
Since in the case of those aircraft the secondary shockwave tended to hold the craft on its previous course despite attempts to pull up, would the secondary shockwave generated by a rebated boat tail, or the similar wave generated by a deep crimping cannelure, tend to help hold the bullet on track?
An illustration from an British SAA manual shows such a rebated boat tail as being used by the .303 Mk 8 bullet (circa 1941 and perhaps from as early as the mid 30's )intended for extreme long range MG fire. So far I've not found any of this type bullet in those .303 cartridges of similar type that I've broken down for components. The FN boat tail .303 bullets from 1950's production that I have handy use an entirely different profile, with a very long tapered section, coming to a relatively tiny open base. Those bullets are nothing like any other BT bullets I've seen, perhaps an early VLD design. I'll try to post an image of one of these later.
I have run across mentions of a heavt BT bullet design experimented with when a magnum power level .303 Long Range match cartridge was designed for use with Cordite propellants. Cordite's extremely high operating temperature greatly increased thermal damage and gas erosion , so much so that the Mk 8 bullets could only be used with IMR 3031 instead.
The experimental BT Match bullet was said to have a flange intended to trap gases and expand to seal the grooves more effectively to hopefully eliminate blowby. It was not a sucess, probably due to difficulty in manufacturing, and the flange may have made a poor or uneven seal at the crown as the bullet exited.
Those Mk8 bullets illustrated in the manual appear to have been more a case of there being a belt at the bearing point than a true rebated tail. The diameter increasing slightly as the bearing surface begins and the thickened section ending where the taper of the boat tail begins.
I have a feeling that if fired from a bore with good fit to the bullet the fired bullet would have ended up with the belt swaged down before exiting the muzzle, the bullet in flight looking more like a standard Boat tail.
I see the idea has been revived more recently, but I wonder just how much good it can do when bore and bullet sizes are a better match than the loose bore to bullet fit it was intended to compensate for.
One thing I wonder about would be a secondary shockwave effect.
When the older type tail planes of fighter aircraft were subjected to super sonic airflow, in terminal dives and early experiments, a secondary shockwave at the point where elevator and horizontal stabilizer met made control difficult or impossible. The All Flying Tail was revived from earlier aircraft such as the Taylor craft to deal with the problem. The Bell X-1 which had the two piece tail plane was adapted by locking the elevators and modifying the trim mechanism to give an all flying tail effect.
The all flying tail gave our Sabre Jets the advantage in trans sonic flight, the Mig 15 with the two piece surfaces could not manuver effectively when transitioning to super sonic in a dive situation, thus often augered in during a dogfight.
Since in the case of those aircraft the secondary shockwave tended to hold the craft on its previous course despite attempts to pull up, would the secondary shockwave generated by a rebated boat tail, or the similar wave generated by a deep crimping cannelure, tend to help hold the bullet on track?
An illustration from an British SAA manual shows such a rebated boat tail as being used by the .303 Mk 8 bullet (circa 1941 and perhaps from as early as the mid 30's )intended for extreme long range MG fire. So far I've not found any of this type bullet in those .303 cartridges of similar type that I've broken down for components. The FN boat tail .303 bullets from 1950's production that I have handy use an entirely different profile, with a very long tapered section, coming to a relatively tiny open base. Those bullets are nothing like any other BT bullets I've seen, perhaps an early VLD design. I'll try to post an image of one of these later.
I have run across mentions of a heavt BT bullet design experimented with when a magnum power level .303 Long Range match cartridge was designed for use with Cordite propellants. Cordite's extremely high operating temperature greatly increased thermal damage and gas erosion , so much so that the Mk 8 bullets could only be used with IMR 3031 instead.
The experimental BT Match bullet was said to have a flange intended to trap gases and expand to seal the grooves more effectively to hopefully eliminate blowby. It was not a sucess, probably due to difficulty in manufacturing, and the flange may have made a poor or uneven seal at the crown as the bullet exited.
Those Mk8 bullets illustrated in the manual appear to have been more a case of there being a belt at the bearing point than a true rebated tail. The diameter increasing slightly as the bearing surface begins and the thickened section ending where the taper of the boat tail begins.
I have a feeling that if fired from a bore with good fit to the bullet the fired bullet would have ended up with the belt swaged down before exiting the muzzle, the bullet in flight looking more like a standard Boat tail.
