Question regarding how sabots are measured and proper grove vs bore fit.

[TF89]

This is actually my first post on this forum.  I have owned a Knight American .50 call that I bought from a pawn shop about 9 years ago.  It has sat unused, until last weekend when I took it to a NRA Basic Muzzleloading class.  It is in great condition and the barrel and bore are almost perfect.   It is a hoot to shoot.

The barrel bore is .500 (top of the lands) and the grooves OD is .510. 

Here is my question(s) and I have been searching the Internet for days for an answer.  I'm sure it is out there, just unable to find it.  There are two aspects, where are sabots measured and are they supposed to completely seal the grooves?

I did find some information that shows that most people with the bullet in the sabot measure at the largest diameter, which seems to be just past the where the petals start.  All my sabots are from Harvester, black crushed rib H15045BR, black smooth and red crushed H250455RR and the base of sabots are .502 or less.   Since my groove OD is .510, the barrel is not completely sealed.


As an example when I load a Hornady XTP .452 300 grain bullet and a Harvester crush ribbed (black H15045BR) sabot.  It is fairly tight fit when seating in the bore, however, with the breech plug removed and looking down the bore I can see light around the grooves.  So the lands are are snug, however the sabot is not creating a water tight seal.

Is that normal?  Are there sabots that do completely seal the barrel?

Thank you,

Dave

[Rainier10]

@Sabotloader is one of our resident muzzle loader gurus. I’m sure he will chime in with some good info. Lots of other members here to help as well.

  Welcome to the forum.

[Smokepole]

I shoot Harvesters with .452 XTP's exclusively in my .50 Optima..  Real snug fit, but I've never looked down the breech for light.  They are plenty accurate.  A good seal is made once you pop a cap.  Great combo. 

[GWP]

Biggest thing is if it fits 'tight' to 'very tight', and the accuracy is good, you are doing well. Like the other fellow stated, when it fires, the base of the sabot should seal up against the bore.

[Sabotloader]

This is actually my first post on this forum.  I have owned a Knight American .50 call that I bought from a pawn shop about 9 years ago.  It has sat unused, until last weekend when I took it to a NRA Basic Muzzleloading class.  It is in great condition and the barrel and bore are almost perfect.   It is a hoot to shoot.

The barrel bore is .500 (top of the lands) and the grooves OD is .510. 

Here is my question(s) and I have been searching the Internet for days for an answer.  I'm sure it is out there, just unable to find it.  There are two aspects, where are sabots measured and are they supposed to completely seal the grooves?

The most important part of the sealing process is accomplished by the cupped sabot base.  The sabot body itself will not seal until ther bore until the rifle is shot and the force of the powder throws it forward. As it travels up the bore it will compress and obturate to the bore aiding the sealing process.

I did find some information that shows that most people with the bullet in the sabot measure at the largest diameter, which seems to be just past the where the petals start.  All my sabots are from Harvester, black crushed rib H15045BR, black smooth and red crushed H250455RR and the base of sabots are .502 or less.   Since my groove OD is .510, the barrel is not completely sealed.

You may be correct with your measurements but again the sabot and the powder cup will swell with the force of ignition.

As an example when I load a Hornady XTP .452 300 grain bullet and a Harvester crush ribbed (black H15045BR) sabot.  It is fairly tight fit when seating in the bore, however, with the breech plug removed and looking down the bore I can see light around the grooves.

This very typical until the round is shot - once this happens the sabot forms an air tight seal.

  So the lands are are snug, however the sabot is not creating a water tight seal.

Once again you are absolutely correct! if you want to seal the barrel from moisture prior to shooting it has to be sealed at the muzzle with something like a 'Muzzle Mitt"

Is that normal?

This is normal! you may find a sabot that would completely seal the bore but it would be a real bear to load if you could load it.  Also remember not all ML bore are not completely concentric all the way down the bore.
 

Are there sabots that do completely seal the barrel?

Thank you,

Dave

There could and might be but they are not designed to completely seal the bore prior to ignition. After ignition, and if you are using the correct sabot they will seal the majority og the gas behind the sabot.

Just my 2 cents....

[pd]

To the OP: You just got a whole lot more than 2 cents' worth from SabotLoader.

Welcome to Hunt Washington.

[TF89]

That was a great explanation and thank you for the detailed information and how important it is to work at keeping any moisture at bay.  I'm used to the PB world and sealed cartridge's. 

Thank you all for the impute.

Dave