N/A AR2078 custom bulk fill build

[JamieUK]

Just thought I'd share some details on a project I've just finished up....a 2078 bulk fill build.

Following an airgun lull I was looking for something to restart the ol' mojo, and remembered a bulk fill tube I'd come across 4 or 5yrs ago that was sitting on the shelf-

Basically a cylinder threaded either end, 1 complete valve (brass) and 1 valve body (S/S painted black for some reason).

The maker was trying to do a HPA build, but the valve was all wrong with its flat seat, 6.35mm throat and stem-

I did try it on Co2, but with the standard hammer spring maxed out it was horrific to cock, and only made 5fpe) so......it was modding time.....

I bored the brass body out and turned up a PEEK seat and delrin poppet (matched/ lapped at 45deg).....

.....and converted the other S/S valve body into a check valve/ fill port, with matching probe-

The insert in the fill valve was left long so I could use it as a fixing point for the end barrel support later on-

With this new valve a lighter hammer was required, so turned one up from oilon (similar to mds) with a PEEK striker face and S/S core, increased throw and weighing in at 30gr-

Running negative preload and aided by the new oversized cocking bolt, its now 1 finger cocking.....

......and producing upto 12fpe (at 18deg C) through a modded/ sleeved 20" .177 crosman barrel.

Also made up a fairly basic offset RVA to make things easier during the testing phase.....

.....and after some polishing and powder coating (light texture satin black, on my little tribostatic home set up) the action was sorted-

This just left the stock! I did strip back the original TH stock, only to find the most bland and unattractive lump of beech you've ever seen in your life, so following some work to the pistol grip, and a little sharpening up around the edges, it went of to a mates body shop for a lick of paint.....BMW/Mini 'Hot chocolate metallic'-

Absolutely over the moon with how this has come out, and after giving the crosman barrel a fair bit of attention, it stacks ftt's at 25m (bottom shot a sighter, then 5 or 6 in group above) -

Looking forward to some warmer weather and trying this out to 50m next.

Anywho, long post so sorry about that, and if you've made it this far......thank you

 

[OneAcreFarmer]

That is beautiful work sir.

 

[JamieUK]

That is beautiful work sir.

Thank you very much

 

[Treefrog]

That's good stuff, Jamie. Thanks for posting it. That's amazing accuracy from a Crosman barrel!

I don't think the QB/AR series of rifle get the kudos that they deserve. A basic and simple platform that works quite well, but lends itself to nearly endless improvement and modification. I've been a fan since Tim McMurray handed me my first QB-77.

Cheers,

J~

 

[JamieUK]

That's good stuff, Jamie. Thanks for posting it. That's amazing accuracy from a Crosman barrel!

I don't think the QB/AR series of rifle get the kudos that they deserve. A basic and simple platform that works quite well, but lends itself to nearly endless improvement and modification. I've been a fan since Tim McMurray handed me my first QB-77.

Cheers,

J~

Thank you

Totally agree you J, in a world of fandangled multishot PCP's (that I'm not knocking by the way!) the simplicity of the QB's are their biggest attraction. There is something nice about taking your time with a single shot bolt action....(and it helps when you HAVE to using Co2 )

There aren't many cost effective barrel blanks over here in the UK (I think the cheapest is a Silco HW blank) and ours laws prevent traders selling 'finished' barrels direct to the public (they have to go via an RFD, for a fee which sucks) so the crosman barrels are a nice option.

The bore needed a fair bit of polishing, like most cheaper barrels do, but in my experience (and to ruffle a few feathers) the finish is often the only real difference between a high end and cheap barrel....as long as the bore isn't oversized.....if that's the case then it's game over.

Thanks for looking and posting J

 

[Treefrog]

Your response is appreciated. I've long thought that the UK suffered from too much government regarding all type of arms. That's a bummer that more barrels aren't available there.

I had the opportunity to compare an original QB77 with a 2017 vintage QB78. The bore on the original 77 was extremely smooth, but the 78's barrel was rather rough. It's since been cleaned and polished, but is no where near the original standard. Accuracy improved a lot. That was the goal.

I also noticed the difference in out of-the-box velocity. The 77 was shooting at about 140-fps over what the 78 yielded. The large o-ring sealing the transfer port versus the restricted piece of plastic the 78 had was part of the difference. I think the bore smoothness may have accounted for the rest.

I've been experimenting with something called the BStaley mod as a means to reduce velocity and increase economy. It's been interesting to see how many useful shots a single cartidge can yield.

Cheers,

J~

 

[JamieUK]

I probably would have gone with the standard barrel had mine come with one, but it was purchased as basically just a bag of bits.

The BStaley mod looks like a good way to minimise travel and bounce for not much effort, so definitely worth a try. I see the figure of 300fpe per cart bounced around (25 shots at 12fpe) so it would be good to hear how you get on J

 

[Treefrog]

I posted a thread about my results with the 22 QB a while back. The idea was about controlling velocity instead of maximizing it like (almost) everyone else. I restricted the transfer port along with reducing hammer bounce.

At 65-degrees, a pair of cartridges yielded 93 useful shots (492-fps average for 716 ft/lbs total). A single cartridge yielded a surprising 55 useful shots, but at reduced velocity (451-fps average for 352 ft/bs total). Accuracy remained pretty much the same for both data sets.

I was set to experiment further, but hurricane Helene got in the way. Once all the downed wood is dealt with, I'll hit the basement and see what else can be done. 80 shots at a 400-fps average velocity from a single cartidge would be ideal for indoor shooting at ten yards.

Here's the original thread. - https://www.airgunnation.com/threads/an-economical-approach-to-co2-for-the-qb78-series.1310296/

Cheers,

Jeff

 

[JamieUK]

Those figures are looking really good already Jeff.

Restricting flow at the TP seal first was a wise move, and I can see why your now keen to look at limiting hammer throw. If your still running a standard hammer and spring there surely must be some further gains to be had