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 Post subject: QB-AR soft screw heads
PostPosted: Thu Sep 06, 2018 3:01 pm 
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Joined: Wed Oct 17, 2007 3:27 am
Posts: 2585
Location: Winnipeg, Canada
Started a couple of nights ago to change out the bbl on my pcp'd AR.

I had a lot of trouble with the factory screws that were left on the gun. The worst was the breech screw under the barrel loading tang.
Ended up drilling and hammering in a torx bit to use as an extractor.
The drill had to come out again for the bbl band screw- simply drilled the head right off.

Said it before, and I'll probably say it again. Cross-head/Phillips screws got no place on a gun- not even the butt plate. :axe:

Got lucky on the breech retainer screw. Found a box of Unbrako SHFH 10 x 32 x 1/4, and they are a direct fit.
I dispensed with the star washer- it's not needed on a screw that is properly tightened. The bbl band screw has a temporary nut and bolt set up for now. I'm going to have to look for a custom bbl band for it- something that comes with an improved screw head.

Hopefully tonight sight in and test. The last "D" bbl I had here in .177 was a very tight shooter. Lookin for a repeat of that :mrgreen:

-D.S.

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PostPosted: Thu Sep 06, 2018 8:39 pm 
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Location: Caronport, Saskatchewan
Looking forward to your results!

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PostPosted: Fri Sep 07, 2018 2:39 am 
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Location: Winnipeg, Canada
Leak and function tested tonight.
No leaks on the firing cycle and everything is operating as it should.

Ran her up to 2000 psi with the Hill pump. She's running a bit on the hot side- 900-955. No curve there. Same old nose dive strings.

At 3000 psi, 1020 to 1070, again with the diminishing string.

Odd that I'm getting such flat strings in .22, and not .177 :? Haven't changed anything on the gun. I'm going to have to back off on the hammer- that's too hot for precision work. I'll get the shim off the spring guide and see what happens. Will have to be on the back burner for a while though, until I can get a new bbl band in. I don't think that band screw and nut are gonna stand up to one more tear down....
I was too tired to do full string counts- just did ten shots each at the shown tube pressures...

With some luck, I'll get it out to the gravel pit this week-end for a rough sight in...

-D.S.

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PostPosted: Fri Sep 07, 2018 8:20 am 
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Was pretty tired last night. Numbers above were taken with the 10.5 gr Crosman ultra mag field/target domes.

-D.S.

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PostPosted: Fri Sep 07, 2018 7:31 pm 
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Location: United States
Interesting problem w/ the drop in 177. I'm scratchin my head but I do have some thoughts: Since the 10.5 Cros pel is likely a good bit harder to push than the 22 you used, I wonder if that's the cause? Like the pellet not moving as quickly would hold the valve is open longer. Or if the increased breech pressure is causing a leak, or more of a leak, and venting excess air. I'm just not sure which way would cause more, if many, air loss. I wouldn't think either of those would cause much difference but it's all i got. So I thot maybe try a lighter JSB to see if it changes? I dunno but looking fwd to you finding out bc now I'm curious.

I have that screw prob w/ most stuff made in china. Same on japanese motorcycles so i always wondered how they tighten the bolts w/o leaving marks since removing/reinstalling Hex, Allen or Phillips always left obvious marks. Often phillips were so soft you're lucky to get them out normally so you're forced to buy better ones. Soft bolts worked great when buying a used japanese bike bc if the bolts were marked I didn't buy it.
I like Torx myself, but it's not like you can get them at the local hardware store.


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PostPosted: Sat Sep 08, 2018 1:05 am 
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Location: Winnipeg, Canada
It has been a while since the tuning for .22- about 3 years. I really hemmed and hawed over the caliber change. The .22 bbl is actually one of the better ones I've come across, and it will likely end up back on the gun if I can't get the .177 to group.

To be honest, I wasn't expecting that much of a gain in velocity. In .22 with the 18 gr jsb heavy, I was getting in the the 740-780 fps range with a 17 shot count on the string before velocity drop had an effect on p.o.i. I was actually hoping for mid to upper 8's.

I think I'm going to try a smaller dia. transfer port to slow the gun down. I have some fuel system vacuum hose that is the right outside diameter, and a lot smaller inside diameter than the ice maker poly tubing I'm using. There ain't much of a shim on the hammer spring- just a thin washer that worked well for .22.

It's just going to be a question of time to get into the gun...

-D.S.

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 Post subject: Oh Yeah!
PostPosted: Tue Sep 11, 2018 4:53 am 
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Location: Winnipeg, Canada
I couldn't quickly come up with a transfer port throttle that I liked, so I went the other way, and dremelled off 2 coils of the stock hammer spring. I couldn't find my thin washer shim in there- probly took it out on the final tune for .22.

I got a curve :mrgreen:
A hail mary hundred and ten yarder of a long bomb of a curve :rolleyes:

Filled to 3 K, and got a 45 shot string from 792.1 to 977.2, and then back down again. Shot #45 was 715.2 and had that hollow, nearly empty tube sound that I've become intimately familiar with.

Good news is the gun is easier to cock, and easier to reassemble. I've stayed with the cock on closing- it seems far smoother than the other way around, which I experimented with briefly, with an equally brief stab at an R.V.A.
I'm not gonna need a 3 K fill at all for .177. I'm guessing a good start point would be around 2.2-2.4 K, with a likely more or less level 25 shot string.

Gun sounds less like a 3" .410 bore, and more like a .22 LR shooting CCI subsonics, which does wonders for the migraine situation.

Still have to test the bbl for group, and there's still a possibility I'm going to have to dial her down a shade further.
For now, I've got a workable starting point. That's the sort of good news I like to associate myself with.

Here's a quick informal shot of the beast:

Image

3K D.V. tube with the .177 "D" bbl and Bushnell Legend 4-12 X 40mm A/O.

If I go back to the .22 bbl on this rifle, I'm going to have to order in another stock hammer spring.

-D.S.

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PostPosted: Tue Sep 11, 2018 11:53 am 
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Location: Caronport, Saskatchewan
It's a beaut!
Glad you are making some progress, and on the migraines too =).


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PostPosted: Wed Sep 12, 2018 5:10 am 
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Location: Winnipeg, Canada
Curiosity got the better of me with this bbl.
I filled to 3 K again, and used the front of the curve~ the first 14-15 shots are in the low to upper mid 800's, so I used that as a bench mark.
There's still less than 125 shots through the bore. These usually shoot-in around the 350 or so shot mark. I may take some degreaser to the bore to hasten the process.

Here are the first few shots for group with the new barrel.

Image

5 of the crosman 10.5 gr ultra mag at 12 M.
Getting close to the bottom of the tin on these. There's a lot of lead flakes in this tin. Not great. Gun can't seem to settle in with these.

Image

5 of the JSB 8.44 gr domes. Gun wants these to group.

Image

5 of the 8.2 gr Meisters. Coming down the home stretch now :wink:
This is a good omen. I think the polymag predators are going to do very well out of this bbl, just based on what I've seen before in bbls that like the meister.

Still have a bit more work to do on the rifle yet.
I'm going to trim one more coil off the hammer spring- knee of the curve is still kinda hot velocity wise.

The trigger needs more work yet- still a shade on the gritty/heavy side, but a far cry from factory stock.
I've been spoiled rotten with decent triggers this summer. :lol:

-D.S.

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