.22 Benchmark 2 Groove Barrel

[Sighters]

I have recently dusted off my BM barrel to see how it will do in 20 fpe. Was deadly at 28 fpe. Not related to the speeds but it seems that after about 50 shots with 16 grain JSB pellets at 750 fps the accuracy is not too good until I use a pull through to clean out the barrel. Once the patches comes out clean the accuracy is fine again.

Should I try to polish the barrel? I have a Weirach .177 barrel that I never clean with a pull through. Only felt pellets and may I add that after 50 shots the felt pellet is hardly stained. This barrel was polished with a fine diamond paste.

Gert

 

[therealld]

polish Benchmark

I polished mine. Though they ARE already lapped and polished as made, I have still found a bit better result after a bit more. For sure the last few inches was not lapped much from the maker as much as the rest, and for low power like sub-20fpe, I think it best to cut several inches off, since its tapered down so tight on that end.

 

[Sighters]

I polished mine. Though they ARE already lapped and polished as made, I have still found a bit better result after a bit more. For sure the last few inches was not lapped much from the maker as much as the rest, and for low power like sub-20fpe, I think it best to cut several inches off, since its tapered down so tight on that end.

Barrel is 26" at the moment. I will probably cut it to 19 or 20". Seems to me this excessive length is also making the air consumption too much.


Gert

 

[therealld]

Gert

Its not so much the length, but the tapered bore .... the longer it is the more drag. I found 28" to be great for 30fpe, but prefer 22" for 20fpe.

My unregulated open class gun gets well over 40 decent shots with the long barrel beginning with 1550psi and working down to 1250psi.

 

[Sighters]

Its not so much the length, but the tapered bore .... the longer it is the more drag. I found 28" to be great for 30fpe, but prefer 22" for 20fpe.

My unregulated open class gun gets well over 40 decent shots with the long barrel beginning with 1550psi and working down to 1250psi.

Thanks for the info. Will chop it today and chamber to go into my Walther LG300.

Gert

 

[crb]

Exactly what do you use to do the chambering? A specific reamer or a 22 cal RF reamer ran in short or ?

ETA, as for polishing what I use in my RF chambers is Flitz. After using a split arbor to eliminate any burrs and cross land tool marks left over from the reamer I then use Flitz to give it a high polish.

 

[therealld]

Benchmark leade

Exactly what do you use to do the chambering? A specific reamer or a 22 cal RF reamer ran in short or ?
------------------

For my USFT's, which thumb-seat, I do this:

I've had good results with a tiny hooked boring bar set at a slight angle in the cross slide of my old lathe ... I run it in some with it not cutting, then bring it in to cut a bit as I draw it out of the bore, if you get what I'm saying. I then finish up with really fine (#1200) wet or dry wrapped in a tapered roll, spinning it cw a bit, then ccw. Use sharp tool and good oil.

I also have a decent air grinder spindle, and have used it to grind a tapered leade ... get the barrel centered really well and truing slow, then run the grinding wheel around 50,000 rpm, advance it into the bore about 1/8" inch with no contact, then slowly bring it into contact and run it back and forth (again, the slide is set for around 2 degrees) to create about a 2" degree per side tapered leade. Keep checking with the pellet of choice til it just goes in nice, then polish with the 1200.

 

[crb]

One very nice thing about using 22 cal bbls is that the Hawkeye borescope works great in that bore. You can't use it in a 17 cal which has really put me off on messing with 17s, whether firearm or air. I have no confidence in a chamber I can't look at with the borescope.