When did Benjamin begin the Gen 2 M-Rod?

[Bicycleman]

Thanks, Bob.  I am going to check mine tonight.

[K.O.]

Green Mountain Has 10 lands and grooves...Crosman 6 and is supposed to be slower twist...

[bnowlin]

Thanks, Bob.  I am going to check mine tonight.

When I say indent it looks like someone slid a barrel inside a shroud and he is right about the lands and grooves being 10.
Bob

[vdwb]

Green Mountain Has 10 lands and grooves...Crosman 6 and is supposed to be slower twist...

+1 to K.O., yup 10 as opposed to 6.

[K.O.]

Have read of being a tighter choke but know no specific diam mentioned...For that matter bore and groove specs...

the new .22 barrel available in the custom shop they say is 20 twist and not choked..

back when Bob was designing the BBT .25 40g for Mrod and L.W.  I said that the G.M. barrels on mine were .250 bore and .252 groove...I think nobody else spoke up...well I now think I was close to right but  think the bore is closer to .2497+ and.2498 and .252 groove...  the choke on one seems to be .2493-.2494 ish what I was calling .2495 back then... the other seems to be choked to ~.2488... would love to know how they are choked...The L.W. choked section shows a tapered O.D. indicating it is a swaged  choke... while the GM the O.D. stays parallel...  The .2488 barrel likes lubed H&N Grizzly... the .2493 choked barrel does not... the Grizzly mic to .2495... So there does seem to be some variation over the two years... probably two  different buttons at different life/wear..?

[Bicycleman]

Do these pictures help to determine what manufacturer made this barrel?
My eyesight is not good enough to be able to count lands and grooves.
But I would like to know which barrel this one is.

[vdwb]

Bicycleman,
Hard to tell without removing the air stripper/shroud spacer. You can ‘slug’ the barrel and count the lands and grooves.

[Bicycleman]

That is an 'Ah Ha" moment.  Thanks Dennis.

[AlanMcD]

And while you have it off, you could drill out those vent holes in the mount a bit and the gun will be noticeably quieter . . .

[HunterWhite]

I just shoot a pellet into a bucket of water.
I can count grooves this way. I can measure the size, but not very well.

Hunter

[mtsheron70]

And while you have it off, you could drill out those vent holes in the mount a bit and the gun will be noticeably quieter . . .

Do you mean the holes visible in that last picture?  What diameter would you drill them?

[bnowlin]

3/16 is a goo number at an angle down.  Be easy as they are hard to come by.
Bob

[Bicycleman]

On a previous thread, someone had mentioned something about drilling some holes at the other end of the shroud.  Anyone here actually try that?

[bnowlin]

On a previous thread, someone had mentioned something about drilling some holes at the other end of the shroud.  Anyone here actually try that?

Yes sir did all mine years ago.more air flow down shroud. less noise
Bob

[Bicycleman]

Good to know, Bob. 

[K.O.]

I forgot... here is a thread about the new Barrels... and a pic of the lands and grooves that I snagged from it...reply # 68...

  https://www.gatewaytoairguns.org/GTA/index.php?topic=159630.60

pic is thru an optical comparator... can see the bore is about .250 and groove is about .254 and bore groove ratio is about 25/75 on the new Crosman barrels... The Green Mountain Barrel bore groove ratio is more like 50/50...Mrod .25 G.M. muzzle pic in this thread reply # 79... also muzzle pic of an XL 725 barrel (not choked)...

 https://www.gatewaytoairguns.org/GTA/index.php?topic=110616.60

differences  with slugs can be more significant than pellets IMHO...