Improved TM1000 & EV2 Breach Seals

[Boomer_Mikey]

I’m always looking for ways to improve my guns… my side lever operated TM1000 didn’t pass the breach seal tissue paper test and a little experimenting resulted in this simple solution.


(R) Stock TM1000 breach seal (L) my o-ring replacement

I’ve been fitting thimbles on my benchrest rifles to permit indexing them for the best possible accuracy. The EV2 barrel is normally equipped with an o-ring inside to seal the bolt probe… the trepanned groove in the barrel isn’t difficult to machine; however, it does take time and IMO doesn’t help accuracy as the tolerances used in the EV2 are somewhat sloppy.

I decided to use my improved TM1000 .177 breach seal design to seal the EV2 barrel and eliminate the o-ring inside the barrel and the associated issues with replacing it. This permits me to use tighter tolerances in a barrel or thimble to control barrel/pellet run out resulting in improved accuracy potential.



(R) Factory barrel (L) Custom EV2 barrel with thimble… notice the smaller hole used to feed pellets with improved fit for improved accuracy potential.


Modified EV2 bolt and probe fitted with a Delrin o-ring breach seal body. The probe has been re-shaped for improved air flow.



Boomer

 

[Pete Wass]

Efficiency?

Nice job on these mods. I got to wondering with regards to thimbles if there is some efficiency lost in the air having to find the hole in the barrel ? Might not feeding the air through the bolt be a better way to push pellets?

Thanks,

Pete

 

[Boomer_Mikey]

Yes, I do

IMO air still has to flow from a cylinder and valve below the barrel and make a couple of turns to get to the back of the pellet, no gains there. Guns that feed air directly from the rear through a bolt or rotary breach improve air flow efficiency to the pellet without the probe in the way and simplify barrel/caliber changes.

Rarely do you find a barrel that has the bore centered in the barrel blank (I haven't seen one yet) and it takes a lot of work to turn down the blank to run true with the bore and sleeve it back up to the receiver's barrel shank size to install a thimble on center with the bore to allow indexing. Guns that feed air directly from the rear through a bolt or rotary breach don't need any extra work like that for indexing; just a good leade and crown cut on the centerline of the bore.

The Chip Smith Sumo, USFT and Thomas actions are great for those of us that like to test/play with several barrels.

Guns with side ported barrels in most cases have smaller receivers and less bulk. I find it difficult to control myself calling those huge bulky guns butt-ugly compared to my EV2 and I can help the air move a little better through the thimble and across the probe by adding some streamlining features to the probe and thimble as well as adding o-rings to eliminate air leaks improving consistency and extreme spread numbers.


Boomer

 

[Pete Wass]

Thank You

IMO air still has to flow from a cylinder and valve below the barrel and make a couple of turns to get to the back of the pellet, no gains there. Guns that feed air directly from the rear through a bolt or rotary breach improve air flow efficiency to the pellet without the probe in the way and simplify barrel/caliber changes.

Rarely do you find a barrel that has the bore centered in the barrel blank (I haven't seen one yet) and it takes a lot of work to turn down the blank to run true with the bore and sleeve it back up to the receiver's barrel shank size to install a thimble on center with the bore to allow indexing. Guns that feed air directly from the rear through a bolt or rotary breach don't need any extra work like that for indexing; just a good leade and crown cut on the centerline of the bore.

The Chip Smith Sumo, USFT and Thomas actions are great for those of us that like to test/play with several barrels.

Guns with side ported barrels in most cases have smaller receivers and less bulk. I find it difficult to control myself calling those huge bulky guns butt-ugly compared to my EV2 and I can help the air move a little better through the thimble and across the probe by adding some streamlining features to the probe and thimble as well as adding o-rings to eliminate air leaks improving consistency and extreme spread numbers.


Boomer

Great explanation.

Pete