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PostPosted: Sun Feb 24, 2013 12:23 pm 
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Location: Oshawa, Ontario
I wanted to have my hand at a big bore build, with a criteria of:

- making it .30cal
- NON-PAL(sub 500fps)
- decent shot count
- accurate within 30 yards
- clean looks

So I started with a donor QB78 in .22cal from Eric at Scopes and Ammo, completely stripped the components and cleaned up everything I could to make a smooth trigger and bolt action. Then I put aside the standard QB78 main tube replacing it with a PCP QB78 tube also from Eric.

I pulled one of my custom QB valves out from one of my other QB's that was too close to the 500 fps limit for my liking anyway and installed it in the new tube. I re-installed the "new" valve in my older QB for now in its stock form.

I found some JSB .30cal pellets from AoA (airguns of arizona) weighing in at 50.15gr with the hopes they would fit the bore of the .30 cal barrel I ordered 1 tin to test out. More on that later.

Then I needed to find a .30cal barrel, that was not easy to say the least... but another member had a barrel they weren't going to be using so I went and picked it up along with the custom made bolt handle. The barrel came as a "blank" another forum member was able to do the machine work to fit it to the QB breech as I have no access to a milling machine. After recieving the barrel back I started on modding the .22 bolt to fit an o-ring to seal the big .30cal chamber, rather than ordering a new bolt I added steel to the probe with the mig welder and turned it back down to proper fit on the lathe. Now to find an o-ring to fit, just dove in to the princess auto variety pack and the 3/8"I.D-5/16"O.D fit like a glove!!!

Which leads back to the pellets, I pushed a couple through with a jag to find very light rifling marks on the skirt nothing on the head, which I was expecting with the pellets averaging .300" heads, .307" skirts and the lands of the bore at .308". The next step was to test!!

I still need to figure out what if anything I'm going to do for a barrel band, for now its free floating from the o-rings out to the muzzle, and I'm waiting on a new tap to finish the muzzle brake then I'll post the final pics.

The barrel was a bit thinner than the origional QB78 barrel which measured out at 15mm the .30cal is .501" approximately 13mm, which worked out ok as the breech on the QB is sized to recieve at .500". So I slapped the o-rings on and assembled the rifle. once i gave everything a final check and worked the bolt several times to ensure proper operation (very smooth) I started to fill the tube for the first time with 850psi from a 48ci bottle. Then the moment of truth, no leaks found. Then I fired with no pellet, low and behold no leaks. I then loaded a pellet, I was expecting the skirt to expand a little to engage the rifling more positively but no such luck, still no leaks. I then topped the rifle off from my 22ci bottle from jdsairman with the regulator set at 1400psi there were more signs of rifling on this pellet, but still not the full engagement I would like.

That was it for Saterday night, too late to do any further testing, so i topped the tube back up to 1400psi and set the rifle in a safe spot to see if will hold the air over night to continue testing today.

Well I went out to the shop this morning to find what sounded like a full power shot!! (without a gauge hard to say if it lost any pressure at all).

I setup the chrony after topping up once again with the following setup:
- 1400psi
- 1*C
- JSB Exact .30 50.15gr
- muzzle 4 inches from the first sensor
- fresh 9v battery in the chrony
- 30 seconds between shots

I got the following results:

1- 483.3fps - 26.02fpe
2- 475.6fps - 25.19fpe
3- 457.5fps - 23.31fpe
4- 445.8fps - 22.14fpe
5- 421.5fps - 19.79fpe
6- 414.2fps - 19.11fpe
7- 404.1fps - 18.19fpe
8- 385.1fps - 16.52fpe
9- 376.2fps - 15.76fpe
10- 363.7fps - 14.73fpe
-----------
velocity avg- 422.7 FPS over 10 shots!!!!
energy avg - 19.90 fpe over 10 shots!!!
energy total was - 200.76fpe
largest velocity spread - 24.3fps
smallest velocity spread - 7.3fps
average velocity spread - 13.3fps

That did not empty the tube but I am not sure on the remaining pressure (again no gauge)

While that shot curve is not exactly ideal and there is a constant drop in velocity for a first test session I think it went well!! Further testing is needed to flaten out the velocity curve.

As far as accuracy goes I don't have the space here at home to properly check that out so I'll have to wait until I get a chance to shoot at some distance.

The scope I have mounted on the rifle I've called "QB.30" is a Leapers Bug Buster - 4-32 Mildot AO (SCP-432aomdl2)

As promised here are some pics:
Image
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QB.30 PCP w/ Leapers Bug Buster 4x32AO Mil-Dot
QB78D .22 w/ Leapers 3-9x40AO Mil-Dot
QB78 .22 Custom HFT Stock w/ Leapers 3-9x40AO Mil-Dot
Crosman 1100
Crosman 2240
Custom 2050
Brass M2250
Tanfoglio 1911


Last edited by gt403cyl on Sun Feb 24, 2013 1:53 pm, edited 2 times in total.

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PostPosted: Sun Feb 24, 2013 12:54 pm 
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Location: Kingston, ON
One word:
Beauty!
:drinkers:

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PostPosted: Sun Feb 24, 2013 1:13 pm 
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Location: Coalmont BC
Very nicely done.... well thought out and executed.... You need a little less hammer spring preload to get a proper bell-curve on your shot string.... and perhaps once that is done a slight increase in fill pressure to get the velocity back up to the mid 400s if necessary.... The combination of the two should increase your efficiency somewhat....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Sun Feb 24, 2013 1:14 pm 
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Location: Rocky Mtn Hse Alberta
Very nicely done!

love it :)

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PostPosted: Sun Feb 24, 2013 1:57 pm 
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:wink:
rsterne wrote:
Very nicely done.... well thought out and executed.... You need a little less hammer spring preload to get a proper bell-curve on your shot string.... and perhaps once that is done a slight increase in fill pressure to get the velocity back up to the mid 400s if necessary.... The combination of the two should increase your efficiency somewhat....

Bob


thanks for the kind words everyone :wink:

thanks for the info Bob, right now its a stock QB78 hammer spring, I guess the easiest way to remove preload would be to cut a coil at a time and see how it does?

Jeff

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QB.30 PCP w/ Leapers Bug Buster 4x32AO Mil-Dot
QB78D .22 w/ Leapers 3-9x40AO Mil-Dot
QB78 .22 Custom HFT Stock w/ Leapers 3-9x40AO Mil-Dot
Crosman 1100
Crosman 2240
Custom 2050
Brass M2250
Tanfoglio 1911


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PostPosted: Sun Feb 24, 2013 2:17 pm 
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Location: Markham , Ontario
Looks good Jeff. Hopefully the pellets will work .


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PostPosted: Sun Feb 24, 2013 3:41 pm 
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Nice job Jeff. I always wanted a bigbore QB but barrels are so hard to get. I would really like to hotrod that QB lol.. Maybe one day I will make one.



George.


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PostPosted: Sun Feb 24, 2013 3:48 pm 
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Location: Coalmont BC
Maybe just half a coil at a time.... and have a spare spring handy for when you go too far....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Sun Feb 24, 2013 4:04 pm 
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Location: Oshawa, Ontario
magnumair wrote:
Nice job Jeff. I always wanted a bigbore QB but barrels are so hard to get. I would really like to hotrod that QB lol.. Maybe one day I will make one.George.


Thanks George, I have no doubt you could do some really nice things to the QB, believe me, id love to have a matching set but I will be waiting to find a smaller bore .30 barrel.

rsterne wrote:
Maybe just half a coil at a time.... and have a spare spring handy for when you go too far....

Bob


Thanks bob already thought ahead for the backup spring, I need to fill my hpa bottles to continue testing, i will keep this thread updated

Jeff

_________________
QB.30 PCP w/ Leapers Bug Buster 4x32AO Mil-Dot
QB78D .22 w/ Leapers 3-9x40AO Mil-Dot
QB78 .22 Custom HFT Stock w/ Leapers 3-9x40AO Mil-Dot
Crosman 1100
Crosman 2240
Custom 2050
Brass M2250
Tanfoglio 1911


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PostPosted: Sun Feb 24, 2013 4:08 pm 
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Location: Coalmont BC
BTW, I'd back up about 3 feet from the first Chrony sensor.... It will eliminate any spurious readings....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Sun Feb 24, 2013 4:14 pm 
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Joined: Mon Sep 05, 2005 10:55 pm
Posts: 6845
Location: Rocky Mtn Hse Alberta
curious why the oring groove forward of the transfer port orings?

You may want a barrel band on the gun to protect that barrel from breaking at that groove. Personally I would have not oringed it but that would allow a bit of leakage likely. :)

Looking forward to groups with the pellets.....

Walter....

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PostPosted: Sun Feb 24, 2013 4:28 pm 
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Location: Oshawa, Ontario
Voltar1 wrote:
curious why the oring groove forward of the transfer port orings?

You may want a barrel band on the gun to protect that barrel from breaking at that groove. Personally I would have not oringed it but that would allow a bit of leakage likely. :)

Looking forward to groups with the pellets.....

Walter....


I had asked the machinist to replicate the origional QB78 barrel and thats what he did. I do plan on a barrel band its just a matter of making/finding one to fit the slightly thinner barrel. I have not tried to modify a stock qb band yet that is on my list of things to do.

as far as breaking... i guess its possible, but the o-ring grove I do like as a backup seal as the oring size was a "guestimate"

I would like to get the barrel band installed before testing accuracy

Jeff

_________________
QB.30 PCP w/ Leapers Bug Buster 4x32AO Mil-Dot
QB78D .22 w/ Leapers 3-9x40AO Mil-Dot
QB78 .22 Custom HFT Stock w/ Leapers 3-9x40AO Mil-Dot
Crosman 1100
Crosman 2240
Custom 2050
Brass M2250
Tanfoglio 1911


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PostPosted: Sun Feb 24, 2013 5:01 pm 
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Quote:
curious why the oring groove forward of the transfer port orings?
You may want a barrel band on the gun to protect that barrel from breaking at that groove
.
I would agree with that, no reason for the forward O-ring groove, and with the barrel wall only about 1/32" between the bottom of the groove and the bore, and it being so close to the fulcrum point at the end of the breech.... it could easily get bent at that groove, and then break....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Sun Feb 24, 2013 5:38 pm 
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Location: Oshawa, Ontario
rsterne wrote:
Quote:
curious why the oring groove forward of the transfer port orings?
You may want a barrel band on the gun to protect that barrel from breaking at that groove
.
I would agree with that, no reason for the forward O-ring groove, and with the barrel wall only about 1/32" between the bottom of the groove and the bore, and it being so close to the fulcrum point at the end of the breech.... it could easily get bent at that groove, and then break....

Bob


I did forward my concerns about the o-ring grooves depth and weekening the barrel in those spots before the machinist started on it. The grooves aren't as deep as the stock QB barrel, the thinnest the barrel got in the grooves if my math is correct is .100", 1/32" is .0312" while it still isn't as thick as say a .22 barrel would be once there is a barrel band on the rifle I don't believe it should be an issue.

Thanks
Jeff

_________________
QB.30 PCP w/ Leapers Bug Buster 4x32AO Mil-Dot
QB78D .22 w/ Leapers 3-9x40AO Mil-Dot
QB78 .22 Custom HFT Stock w/ Leapers 3-9x40AO Mil-Dot
Crosman 1100
Crosman 2240
Custom 2050
Brass M2250
Tanfoglio 1911


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PostPosted: Sun Feb 24, 2013 6:06 pm 
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Location: Coalmont BC
Hmmmmmmmm.... OD of the barrel where it inserts in the breech is 0.498".... Bore is 0.308", so that leaves 0.190" divided by two is 0.095".... less the depth of the O-ring groove which is usually 0.063".... leaves 0.032" by my calcs.... maybe a few thou more if the grooves are unusually shallow....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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