I feel I understand the concept and can see the advantage ( accuracy + velocity ) for the first several hundred rounds. I also think that the portion of the throat/rifling that is P+'ed would suffer the effects of powder erosion at a faster rate than a non P+ throat and after a certain # of rounds you would just end up with a rifle with a long "freebore". Something like a Weatherby. Just my take on it.
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+P Throating
- Thread starter chetraguse
- Start date
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I haven't suffered from that but I don't shoot long, fast strings either.
Fiftydriver
Official LRH Sponsor
I designed and tested my Hybrid throat design at the same time Shawn was testing his +p throat design. Neither one of us knew the other was working on the project. both are nearly identical In theory and function.
basically, there is a conventional throat section in the bore that is roughly 0.0005" over nominal bore diameter. Then there is a section where a VERY SHALLOW leade angle transitions into the rifling. Then there is a length where the lands have been thinned so that the grooves are very shallow but the lands will still engrave the bullet body. After this section, there is another very shallow leade angle transitioning into the full height lands.
Shawns goal was max performance.
my goal was to get the then brand 200 gr wildcat 7mm bullet to survive the launch of my 7mm Allen Magnum rifles at 3300-3400 fps. We were having issues with the ogive of the bullet being ripped off after leaving the muzzle. Turns out this was a problem with the recommended twist rate from Lilja but thats a different story. Basically i needed the bullets to be GENTLY transitioned into the bore.
both designs accomplished their specific design goals as well as dramatically increase performance. This was possible because these throat designs gave all the advantages performance wise of a long freebore throat but with the accuracy of a short throat.
again, they are both nearly identical. They accomplish this because they make if VERY easy for the bullet to start down the bore which dramatically flattens the pressure curve and when loads are adjusted, you can use more powder to bring the pressure curve back up to where it normally was. More powder, more gas volume, higher bore pressures as the bullet travels down the bore but same peak pressures.
they offered accuracy because unlike a freebore throat, the bullets started rotating the instant they started traveling down the bore because they were being engraved by the shallow lands. Top accuracy extra 100-150 fps velocity compared to traditional throats, win win right……. Not exactly.
i tested my hybrid throat design in my 6.5 Allen Magnum, 270 Allen Magnum, 7mm Allen Magnum, 338 Allen Xpress and 338 Allen Magnum. In every test i gained 100-150 fps with same case life….
however, i also found that barrel life was dramatically shortened largely because of the very long section of throat with the very shallow lands. These eroded quite fast and soon, in as little as 300-400 rounds you basically had a freebore throat that was 1/2 to 3/4" in length. Velocity dropped off dramatically and worse yet accuracy really dropped. They were amazing until this happened and because of the length of the throat design, you simply can not set back and recut the throat….
these results were repeated with every one of my wildcats. shawn claimed his system showed zero barrel life loss. I consistently proved it and as such, i stopped offering my hybrid throat option to customers. Just not worth it. Instead i designed cartridges with enough engine to get the velocity i wanted without magical throats, just plain old fashioned, long lived accuracy throats.
in my professional opinion, these are the best way to cut your barrel life by 50-75%. Yes you will gain 100-150 fps for a while but then your barrel is worthless.
as mentioned, there were lots if heated debates on this topic. No debate for me, just offered my test results and they were not good so i dropped the option completely for my customers.
basically, there is a conventional throat section in the bore that is roughly 0.0005" over nominal bore diameter. Then there is a section where a VERY SHALLOW leade angle transitions into the rifling. Then there is a length where the lands have been thinned so that the grooves are very shallow but the lands will still engrave the bullet body. After this section, there is another very shallow leade angle transitioning into the full height lands.
Shawns goal was max performance.
my goal was to get the then brand 200 gr wildcat 7mm bullet to survive the launch of my 7mm Allen Magnum rifles at 3300-3400 fps. We were having issues with the ogive of the bullet being ripped off after leaving the muzzle. Turns out this was a problem with the recommended twist rate from Lilja but thats a different story. Basically i needed the bullets to be GENTLY transitioned into the bore.
both designs accomplished their specific design goals as well as dramatically increase performance. This was possible because these throat designs gave all the advantages performance wise of a long freebore throat but with the accuracy of a short throat.
again, they are both nearly identical. They accomplish this because they make if VERY easy for the bullet to start down the bore which dramatically flattens the pressure curve and when loads are adjusted, you can use more powder to bring the pressure curve back up to where it normally was. More powder, more gas volume, higher bore pressures as the bullet travels down the bore but same peak pressures.
they offered accuracy because unlike a freebore throat, the bullets started rotating the instant they started traveling down the bore because they were being engraved by the shallow lands. Top accuracy extra 100-150 fps velocity compared to traditional throats, win win right……. Not exactly.
i tested my hybrid throat design in my 6.5 Allen Magnum, 270 Allen Magnum, 7mm Allen Magnum, 338 Allen Xpress and 338 Allen Magnum. In every test i gained 100-150 fps with same case life….
however, i also found that barrel life was dramatically shortened largely because of the very long section of throat with the very shallow lands. These eroded quite fast and soon, in as little as 300-400 rounds you basically had a freebore throat that was 1/2 to 3/4" in length. Velocity dropped off dramatically and worse yet accuracy really dropped. They were amazing until this happened and because of the length of the throat design, you simply can not set back and recut the throat….
these results were repeated with every one of my wildcats. shawn claimed his system showed zero barrel life loss. I consistently proved it and as such, i stopped offering my hybrid throat option to customers. Just not worth it. Instead i designed cartridges with enough engine to get the velocity i wanted without magical throats, just plain old fashioned, long lived accuracy throats.
in my professional opinion, these are the best way to cut your barrel life by 50-75%. Yes you will gain 100-150 fps for a while but then your barrel is worthless.
as mentioned, there were lots if heated debates on this topic. No debate for me, just offered my test results and they were not good so i dropped the option completely for my customers.
How close in concept is yours to Dave's? He laid down the 45 degrees to 15, I did mine before his at 10 for the same bullet when they came out
Maybe different concept all together. Just curious.
Fiftydriver
Official LRH Sponsor
Totally different concept. These throat designs kind of start where yours stop, kind of.
bigngreen
Well-Known Member
Ya, Kirby wrapped that up with a bow on it. Seen a LOT of +P barrels quietly changed!!
Thanks
Nomosendero
Well-Known Member
Fiftydriver, I did not know but suspected, thanks for the info!
How does the old saying go
There is no free lunch!
I sent mine off after I started this. I talked to Shawn and my case had enough room for more powder so we'll see in couple weeks I guess.
Fiftydriver
Official LRH Sponsor
Be extra careful to keep bore cool. Never shoot more then three shot strings or better yet, only do practical field shooting which is find a target of opportunity, range, set up, dial in, take shot and record results. Shooting practice like this will get you a load of realistic practice with fewest rounds down the bore as possible, allowing your barrel to last as long as possible.
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