Beeman Chief - Merry Christmas to Me !!!

[Ribbonstone]

Last time I tried this, Photobuck took a dump on me.

In case you get the urge to experiment....there is not a great deal of difference between a QB78S barrle and a Chief barrel; nothing that can't make it happen with a couple of stokes of a fine file.   Chief is on the top.



BUT it is the old smaller diameter barrel like the QB78Standard (not the 78D, AR2028, Qb79)....so your barrel band won't fit one of the fatter barrels.

The longer Chief loading platform is the main difference...but it's minor as the bolt probe crosses that space even at full cock.

Agree about the rinky-dinky valve retention scews...although they'll probably work at 2K, they don't inspire an abundance of confidence.

Does seem that 8 or 9 out of 10 of them have a bit of "bolt jump".  Never enough to unlock and puff gas in your face (at least not at standard speeds). Even the folks that never complained of it, but posted videos, can be seen to have it.  Does not harm, but it aggrivates folks.

The one at had has a bolt handle that screws into the bolt body.  After trying a few things, I just marked the bolt at 6 o-cllock and filed a little flat there...so the bolt actually locks a bit deeper...and the "flip" is nearly gone.

[rsterne]

I modded the gauge port and the inlet side of the valve this afternoon....



I milled three overlapping holes, offset, through the gauge block, and then removed the excess material with a Dremel.... the hole is about 7/32" x 1/2" and D-shaped with rounded corners.... There is still about 1/16" of material between the hole and the O-ring seat for the gauge.... The valve spring is larger than 5/16" ID, so I drilled the front end of the valve to that size.... The end of the valve, and both ends of the gauge block, are countersunk just to ease the flow through them.... I gained 2-3 cc's of volume, so I will use 141 cc (8.6 CI) for future calculations....

I carefully examined the valve attachment as well.... There is a steel backing block between the valve and the hammer, into which thread the flathead screw holding down the front of the receiver from the top, and the screw holding on the stock from the bottom.... That block in a QB is tight up against the back of the valve, so that those screws do some of the work in holding the valve.... In the Chief, there is a gap of about 1/16" between the back of the valve and the front of that block.... If you install the block and drop the valve in place, the back of the three tapped holes for the valve screws are flush with the back of the holes in the tube.... This means that the three valve screws are "on their own", holding all the force pushing back on the valve (1180 lbs. @ 2000 psi).... Those three 4 mm x 0.7 mm pan head screws look like they could be purchased at any hardware store that carries Metric, they certainly don't look of particularly high quality.... and the threads are in shear.... If the screws are at the minimum of the tolerance diameter at the thread root, that is only 0.118".... Assuming they are all taking equal load, I ran the numbers for three typical screw grades.... and the best SHCSs you can buy....

Grade 2 screws (74ksi UTS).... Safety margin, 60% shear - 1.2:1.... I REALLY hope Beeman isn't using cheap screws !!!
Grade 5 screws (120ksi UTS).... Safety margin, 60% shear - 2.0:1
Grade 8 screws (150ksi UTS).... Safety margin, 60% shear - 2.5:1
Metric Grade 12.9 screws (170ksi).... Safety margin, 60% shear - 2.8:1

This means that the screws should really be grade Metric 12.9 screws, which is basically the best SHCSs you can get.... The screws used are 5 mm long, so the proper McMaster Carr screw would be the following.... https://www.mcmaster.com/#91290a138/=1avzg91

I wish I had access to those screws, I would at least KNOW what they are, although they don't quite have the 3:1 safety margin I would like (and 3.5:1 is preferred).... I'm betting they are better quality than the pan head Phillips screws that Beeman use.... I could be wrong, of course, maybe Beeman had some special screws made, anything is possible.... One other advantage to the McMaster Carr screws is that the head is 7 mm diameter, which will be a far better fit in the 7 mm holes in the tube.... and way better than the 6.4mm head on the existing ones.... Incidently, in case you thought about shimming the backing block up to sit against the valve and share the load, I have a word of caution about that idea.... It could be done, if done carefully, so that the valve screws were still sharing the load.... HOWEVER, it would mean that you should not even remove the stock without degassing the gun.... If you make that block part of the load bearing system, then don't forget you did that.... I prefer having the proper screws to locate the valve, and then I can remove the stock and receiver without any concern about the valve anchoring system.... just the way it is supposed to work now....

Guess what.... There isn't a hope of me finding 4 mm x 0.7 mm short SHCSs locally, and McMaster Carr won't sell to Canada.... Rather than wait weeks to get someone to source them and forward them to me.... I am going to drill out the valve and fit three 10-32 low-profile SHCS, just like the whizzy mod you do for a Disco for higher pressure use.... Now this doesn't mean you can run more pressure in the Chief, we still don't know what the tube is made of.... In addition, the tube ID on the Chief is 22 mm (0.866") instead of the 0.745" on the Disco.... That means the Chief has 35% more force on the valve at the same pressure.... 2000 psi in the Chief is like 2700 psi in a Disco.... In fact, at 2100 psi, which is where the Chief (assuming a 1006 steel tube) has a 3.5:1 safety margin the three 10-32 low-profile SHCSs, with their 140ksi UTS, will only have a 3.7:1 safety margin.... That suits me just about perfectly.... I will have to drill the holes in the tube out to 5/16" for the larger screw heads, but that will decrease the stress in the bearing area.... While I am at it, I am going to drill the hole in the top of the tube to 5/16" as well, in preparation for a larger OD Teflon transfer port....

This project is finally starting to see some direction....

Bob

PS, Ribbon, RE "bolt jump".... Mine didn't have it stock, but as soon as I increased the preload it did.... and the more preload, the more it jumped up.... Seems pretty obvious to me that the hammer cocking pin is hitting the back of the cocking slot in the bolt when you whack the valve harder and it opens further.... I'm pretty sure that is why some guys have Disco bolts jumping up as well.... they have increased the hammer spring and/or preload to try and get more power.... the pin hits the bolt, and the lack of friction of the handle in the cocking slot allows the handle to jump up.... In a Disco, you can shave a little of the back of the bolt (not so much that you can't cock it though).... In the Chief, you might have to mill the slot in the bolt a bit longer (if possible).... Pardon the drivel, I checked the Chief, and the cocking shoulder on the bolt when locked is flush with the front of the slots in the receiver and tube, and the hammer hits the back of the steel backing block inside the tube before the cocking pin hits the front of the slots.... the way it SHOULD be.... My apologies to Beeman.... 

or file a groove in the receiver or bolt handle, to allow it to lock better....

RBS

[Hoosier Daddy]

Fastenal has branches in BC... www.fastenal.com 

Branch Code: BCKEL
Hours: Monday - Friday 7:30am - 5:00pm
Phone: (250)491-4424
Fax: (250)491-4462   
#1 801 Dalton Road
Kelowna, BC CAN V1X 7X3



Branch Code: BCCHA
Hours: Monday - Friday 7:30am - 5pm
Phone: 604/793-0645
Fax: 604/793-0823   
Unit 5&6, 7949 Venture Place
Chilliwack, BC CAN V2R 4H5



Branch Code: BCKAM
Hours: Monday - Friday 7:30am - 4:30pm
Phone: (250)314-0018
Fax: (250)314-0218   
1365A Dalhousie Drive
Kamloops, BC CAN V2C 5P6



Branch Code: BCABB
Hours: 7:30AM to 5:00PM Monday to Friday
Phone: (604)557-0440
Fax: (604)557-0441   
1- 30465 Progressive Way
Abbotsford, BC CAN V2T 6W3



Branch Code: BCVER
Hours: Monday - Friday 7:30am - 5pm
Phone: 250-260-7044
Fax: 250-260-7045   
2709A 43rd Avenue
Vernon, BC CAN V1T 3L2

[rsterne]

Thanks for that, I'm still 3 hours (each way, without snow) from the closest Fastenal, but I will check their stock and shipping charges.... I have decided to go with the overkill of the 10-32s, rather than the best Gr. 12.9 - M4s, which are still not at 3.5:1 safety margin at 2000 psi.... I'd sooner be safe than sorry....

Bob

[canadian_shooter]

Congrats on the Chief. I am happy with mine and am looking forward to what you do with yours. I was trying to explain the preload adjustment in another post a while back and am pleased to see you have this also. Happy New Year!

[Ribbonstone]

From the weather reports...am guessing you have a good bit of shop time.

Am reading with interest....may go ahead and change the screws to something a little better.  Not to increase fill pressure, but because those phillips head screws just look "wrong".

So long as you have yours apart (assume you still do), what's your estimate of actual air volume?

[WesBob]

Here's Bob's calculation for the reservoir volume from earlier in the thread:
"The reservoir, from the back of the fill fitting to the front of the gauge port, is 13-5/8" long x 22 mm (0.866") diameter, and there is about 1 cc additional volume inside the fill fitting.... I would calculate the reservoir volume to be (132 + 1 + 2 + 3) = 138 cc, and will be using that for any future calculations.... Note that this is almost identical to a Disco, and they run the same 2000 psi pressure, so they both have the same volume of air available.... enabling direct shot count comparisons.... "

[Ribbonstone]

OK...correcting for 138CC's (where I estimated 155cc's). 

Guess I just didn't want to belive it....but I swear it takes a few more pumps to fill the Chief than the Disco (then again, I got the Disco running over a longer pressure range....so OK...I'll go with 138cc's as the Chief's volume)







That prretty well comes out to somthing like 1.4-1.5 FPE/cuin....which is didn't belive...way better than the simple tune that got put on this rifle.

[WesBob]

Nice! Good efficiency ☺️!

[Ribbonstone]

OK...it took like 7-8 years of pharthing around (and having to back up out of blind paths to start over) to get a Disco to get to about the same level of efficiency.



Less energy....much longer pressure range...so even though the efficiency isn't much difference, the Disco certainly has a longer shot count.

Yeah...guess I'm "lucky" to find that Chief's "the spot" so quickly.

But if seems too easy.

[nervoustrigger]

The more you practice, the luckier you get! 

[grand-galop]

Hey RIB!!!  You get excellent result with both rifle but since Bob`s new input, I think he is hunting for the same efficiency with  much more FPS and higher grains balance efficiency...  You did MASTER TUNING on both of your rifles...  Thanks for sharing...

[Ribbonstone]

On one (the Disco) was a lot of experimentation....on the other (Chief) was pretty much luck.

[rsterne]

I modded the valve today.... drilled the throat to 1/4" (originally 5 mm = 0.197")....



Then I drilled and retapped the screw holes to 10-32.... and milled a recess for a 5/16" transfer port, and then milled the exhaust port out to 0.210", angled at 10 deg. towards the seat to improve the flow.... then used a small spherical burr on the Dremel to fair it into the throat....



The throat area is slightly more than the exhaust port, and that in turn is slightly more than the bore if I use a 3/32" bolt probe, which is the plan.... I have yet to drill out the barrel port and make a transfer port.... The receiver will be drilled through 5/16" and I will be using a Teflon transfer port of that OD.... For the next tests I will be using a transfer port of 0.166" ID, which is 75% of the bore size.... but I can (and probably will) go larger at a later date....

Bob

[SpiralGroove]

Nice Bob,
I think I need to sell a few airguns and buy a mill .

[rsterne]

The next step was to fit the valve to the tube.... This involved careful setup to redrill the three valve screw holes and the hole for the port all at 90 deg. to each other and in the same plane.... All four holes were drilled to 5/16", to fit the heads of the 10-32 low-profile screws, and the new 5/16" OD transfer port.... Then the receiver had to be drilled out for the transfer port to pass through, and the barrel machined to accept the top of the transfer port.... Here is what the parts look like after this was done....



There were two additional modifications made to the receiver.... Note on the side, just below the notch for the loading port (above in the photo as the receiver is upside down) a 6-32 setscrew near the back of the notch.... There is a matching one on the other side.... These setscrews tighten against the sides of the back of the loading tray section of the barrel, greatly increasing the stability of the barrel in the receiver.... Also note that the M5 flat-head screw behind the transfer port is already in place.... It is trapped between the barrel and receiver, once the barrel is in place....

With the new Teflon transfer port, the barrel/receiver assembly must be lowered over the transfer port, which fits like a peg in the two holes shown in the above photo.... It will be about 0.010" longer than the space available, so that it is in compression when you tighten that flat-head screw.... The way this is assembled means you cannot install the receiver and then slide the barrel into place from the front afterwards.... I will admit that this was an unforeseen problem, but fortunately there was an easy solution....



The photo above is a top view of the barrel/receiver assembly.... Note there is a hole drilled in the barrel loading tray to allow access to the Phillips drive in the flat-head screw that holds down the receiver.... This enables you to drop the flat-head screw into the receiver, slide the barrel into place and fix it with the (now) three setscrews (the original M5 on top, and the two 6-32s on the sides at the back of the loading tray).... and then drop the assembly over the transfer port, tightening the flat-head screw (through the new hole in the barrel loading tray) as you lower it into place.... and finally using that screw to put the transfer port into compression to seal it.... I admit (sheepishly) that I was very lucky that this solution was possible.... otherwise I would have worked myself into a rather embarrassing corner.... Sometimes it is better to be lucky than smart....  .... Here is a photo of the barrel, modified with the new port, and showing the access hole for the flat-head screw....



There is a 5/16" diameter flat machined to accept the top of the Teflon transfer port.... It is machined down flush with the bottom of the O-ring grooves on either side of it, and breaks through into the sides of the O-ring slots.... If the O-rings were still needed, this would be a problem, but of course they are not needed now that the Teflon transfer port will seal directly against the barrel in compression.... I may still install them, they won't do any harm, of course.... but they really aren't necessary any more.... Here is another view of the new porting system....



Looking through the receiver and into the barrel port (on the left), you can see the oblong port machined into the barrel, and the way it blends into the 0.21" diameter circular shape at the TP parting face.... The port was machined with a 5/32" end mill, with the back of the port vertical and flush with the back of the 0.21" TP, and the front angling forward at a 30 deg. angle.... This makes the barrel port, at the borelilne, 0.17"W x 0.25"L, which gives it the same area as the 0.21" diameter round TP.... On the right, you are looking through the main tube, into the valve, and you can actually see right into the valve chamber, showing the vastly increased area for flow.... The only remaining job was to modify the bolt to thin the probe, the results of that are shown below....



Before starting changes on the bolt, I loaded a JSB 18.1 gr. Heavy pellet with the stock bolt.... The larger diameter but fatter probe pushed it just flush with the front of my angled barrel port.... However, because of the taper inside the pellet, and the smaller probe I wanted, I knew that the new probe would have to be longer.... It turned out that increasing the overall length of the bolt by just 1/16" was all that was needed.... However, the new, longer barrel port was so much longer that you could actually see the front O-ring on the bolt (there were two, tiny O-ring installed stock).... Before installing the new longer 3/32" probe (in a hole drilled in the end of the bolt), I machined off the bolt shorter, to remove the front portion of the front O-ring gland, leaving just the small diameter bottom portion of the gland intact.... The front of the bolt is now flush with the back of the transfer port, so that it will not obstruct the airflow in any way.... This leaves just the single rear O-ring in place to seal the breech.... I see no reason for two, that is a redundancy that I can live without (I hope).... I guess I will find out when I fire the gun for the first time.... If it does leak, I can always machine it to take a slightly thicker Metric O-ring, with more compression on it when in battery, to insure a seal.... The new, thinner probe seats an 18.1 gr. JSB Heavy just comfortably ahead of the new angled barrel port.... The area around it for airflow is still the smallest part of the porting system, but is the equivalent of a 0.200" diameter port.... compared to the 0.138" diameter of the original porting system.... This means I have increased the area of the ports by 110%.... so it is 2.1 times the area I started with....

Bob

[Ribbonstone]

BOB;
 
Am thinking that's a lot of work...and very good work...to just run it at 2K. Am I right in suspecting you might be thinking of 2.5K (although I have some reservations about the air tube's quality...I mean they are out of any lawsuit range...so it could be melted down Pinto bumbers).

I'll let you know if the little Phillips head screws take a dump on me at 2K...they don't nearly have as much "slack" in the tube holes as the 2K Disco or the 3K P-rod.

Then again, I'm not trying to get 50foot pounds out of her.

[nervoustrigger]

Note there is a hole drilled in the barrel loading tray to allow access to the Phillips drive in the flat-head screw that holds down the receiver.... This enables you to drop the flat-head screw into the receiver, slide the barrel into place and fix it with the (now) three setscrews (the original M5 on top, and the two 6-32s on the sides at the back of the loading tray).... and then drop the assembly over the transfer port, tightening the flat-head screw (through the new hole in the barrel loading tray) as you lower it into place.... and finally using that screw to put the transfer port into compression to seal it.... I admit (sheepishly) that I was very lucky that this solution was possible.... otherwise I would have worked myself into a rather embarrassing corner.... Sometimes it is better to be lucky than smart....  .... Here is a photo of the barrel, modified with the new port, and showing the access hole for the flat-head screw....

Bob, I got a chuckle out of that    Here's a picture of my QB79's loading tray...



Nice work, by the way.  I expect when you are done, it will be worthy of a "hail to the Chief" salute.

[rsterne]

Ribbon, sometimes the challenge is not all out power.... which will obviously be greater if I could up the pressure.... but seeing what you can get within the limitations you are handed.... I would LOVE to find out what the burst strength of the tube is, though.... now that I have far stronger screws mounting the valve.... The stock factory screws in my Chief were REALLY lose in the holes in the tube, which allowed the valve to slide back and misalign the port with the seal.... likely where my loss of performance was compared to your gun....

Jason.... I guess you ran into the same problem, and came up with the same solution.... *LOL*....

Bob

[Ribbonstone]

Yep...screws are a poor fit.  No worse than some others...kind of fit seen on Discos.  Will replace them..and maybe unalign the ulucky alignement in doing so.