Brocock Compatto .25

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Well it is a year and a half later now. I took the Compatto apart today and voided my warranty by removing the Transfer port power adjustment and drilling it out to 11/64". I replaced the spring with a stock spring from a .25 Marauder (tried a 12 lb spring but it just wasted more air) and adjusted the hammer striker screw to a position 2mm recessed from the hammer face. With a fill of 220 Bar and JSB 25.4 grain pellets the first shot was 834 fps for 39.24 ft/lb. Second shot was 824, Third was 805, Fourth was 795. There is a lot more tinkering to be done before I am satisfied but it is a start in the right direction. I did discover that the .25 DOES NOT HAVE the SLING SHOT HAMMER system. This was unfortunately misrepresented to many people as having the slingshot system which is only on the original .177 and .22.
What it really needs is a bottle conversion and a balanced valve like the one I put in my Marauder from Jefferson State Air Rifles ...................I'll probably tear it down to see how the valve might be improved and while I am at it port and polish the entire transfer port area.

Thurmond
 
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"T3PRanch"Well it is a year and a half later now. I took the Compatto apart today and voided my warranty by removing the Transfer port power adjustment and drilling it out to 11/64". I replaced the spring with a stock spring from a .25 Marauder (tried a 12 lb spring but it just wasted more air) and adjusted the hammer striker screw to a position 2mm recessed from the hammer face. With a fill of 220 Bar and JSB 25.4 grain pellets the first shot was 834 fps for 39.24 ft/lb. Second shot was 824, Third was 805, Fourth was 795. There is a lot more tinkering to be done before I am satisfied but it is a start in the right direction. I did discover that the .25 DOES NOT HAVE the SLING SHOT HAMMER system. This was unfortunately misrepresented to many people as having the slingshot system which is only on the original .177 and .22.
What it really needs is a bottle conversion and a balanced valve like the one I put in my Marauder from Jefferson State Air Rifles ...................I'll probably tear it down to see how the valve might be improved and while I am at it port and polish the entire transfer port area.
Thurmond


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Thurmond,
The FAC Brococks are rated to 240bar fill, so filling to 240 might get you that bell curve. Otherwise, if the regular hammer acts similar to the slingshot you need to just slightly turn the screw in (shorten hammer stroke). With my .22 (it has the SSH) once adjusted I get a 25-27 shot curve starting at 908, peaking at 935 and back to 900. If I turn the hammer striker just an 1/8 turn out the string will start at 930 and decline. I've noticed the Brocock is VERY touchy with adjustment.

Oh, and your bottle conversion, as I'm sure you know, is known as the Bantam - likely my next gun in .177, Beech HI-Lite
 
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Thanks BTB, I have several ideas as well as a mini lathe and mill. It definitely needs hammer and valve work. Hammer will be first since it is easiest. I'll try 240 bar. I did not have a tank with that charge level and humidity is currently too high to run my compressor outside. I have a regulator too I can try but I cannot get the breech end of that stubborn air tube. I have tried everything in the book. I have considered making a drop down bottle adapter (like JDS Airman's Marauder adapter) and hacking the tube off. Kind of a tinkerers Bantam Sniper Regulated Edition. ;)

Thurmond
 
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And another year has gone by. Best shot count with the original air tube and JSB 34 grain at 40 ft/lb was 1 magazine from 240 Bar to 100 Bar.

Great things are in store for this Compatto:

24" Heavy Lothar Walther .25 Polygonal Barrel machined for the Compatto and threaded 1/2-20 for a moderator (Original barrel is 17")

Shorten Tube and add a custom bottle adapter block with gauge and foster fill port.

Add a 500 cc Carbon fiber Bottle

Lane Regulator set for a 60 ft/lb gun (pressure and large plenum)

JSAR will be doing the machine work!

Hopefully it will be done in a month or two and I can begin tweeking and testing once again.

Edit: My Compatto arrived at JSAR Monday the 19th of March. They tell me about 4 to 5 weeks depending on workload. They have to design and produce the bottle block with foster and gauge ports, machine the barrel blank (lead, breech seal, transfer port) and thread the muzzle end for a moderator, shorten the existing tube, machine the tube for the bottle block attachment and mount it. Can't wait to see the results. They usually turn out some very special items. I wish Travis would come up with a balanced valve for it as well. ;)

Edit Update: In two days it has been at JSAR for 2 months and no date of completion in sight since it is waiting on an unchoked LW Poly Barrel (no ETA). I don't think it is very high on their priority list (if it is even there at all) since they are busy bringing the Raptor to market. Possibly it "might" be done in another couple of months (I HOPE)! Surely before Christmas 2019! lol

At this point I am kind of starting to lose interest in the project due to delays.
 
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The Compatto is finally back after 3.5 months but I am battling a leak at the bottle adapter to plenum tube interface. I have some urethane 90 durometer o-rings on order and will polish the interior surface where the o-rings mate against the inner tube surface as it looks quite rough from the machining process which was used to shorten the tube and the holes made to secure the bottle adapter screws. I am currently loosing about 100 psi per hour. I used an electronic EdGauge and it reports that I am using 50 psi per shot. I have collected no other data due to time constraints. Preliminary shooting shows a fair increase in the number of shots. I estimate 30 with JSB 34 Grain. I traded my poly barrel blank for one that is not choked and initial slug testing is one ragged spot (I shoot painted disk not paper) at 80 yards. My measurements were spot on because the original stock fit without modification with just about .1" of clearance between the bottle block and the front of the stock. I did switch to a .35 liter CF bottle from a .5 liter bottle to balance the guns look a bit better. With the .5 liter bottle a 2" extension is needed for the moderator to clear the bottle. I knew it would be needed from the beginning so no surprise there and I do have one that DonnyFL made for me last year about this time. The factory barrel had a step machined just in front of the breech for attachment of the factory shroud. I was ask if the new barrel needed this step machined and I responded NO do not make a step there BUT the barrel came back with a step machined which is useless since the factory shroud is 6" too short for the new 24" barrel plus the step spoils the line of the new barrel. I had planned on bluing the barrel since it is still in the white but now to cover the step (miss step is more like it. lol) I plan a piece of CF Tube to cover the entire barrel and provide tension to the barrel similar to the system the JSAR Raptors use. Current CF Tube in the PIC is just for Temp use as it is 3 pieces and not one piece as will be used in the final iteration. The apparent barrel droop is an illusion caused by 3 pieces of misaligned CF Tubing!

1562468603_19165435055d2160fb918902.11281694_P7060200.JPG

 
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The Compatto is finally back after 3.5 months but I am battling a leak at the bottle adapter to plenum tube interface. I have some urethane 90 durometer o-rings on order and will polish the interior surface where the o-rings mate against the inner tube surface as it looks quite rough from the machining process which was used to shorten the tube and the holes made to secure the bottle adapter screws. I am currently loosing about 100 psi per hour. I used an electronic EdGauge and it reports that I am using 50 psi per shot. I have collected no other data due to time constraints. Preliminary shooting shows a fair increase in the number of shots. I estimate 30 with JSB 34 Grain. I traded my poly barrel blank for one that is not choked and initial slug testing is one ragged spot (I shoot painted disk not paper) at 80 yards. My measurements were spot on because the original stock fit without modification with just about .1" of clearance between the bottle block and the front of the stock. I did switch to a .35 liter CF bottle from a .5 liter bottle to balance the guns look a bit better. With the .5 liter bottle a 2" extension is needed for the moderator to clear the bottle. I knew it would be needed from the beginning so no surprise there and I do have one that DonnyFL made for me last year about this time. The factory barrel had a step machined just in front of the breech for attachment of the factory shroud. I was ask if the new barrel needed this step machined and I responded NO do not make a step there BUT the barrel came back with a step machined which is useless since the factory shroud is 6" too short for the new 24" barrel plus the step spoils the line of the new barrel. I had planned on bluing the barrel since it is still in the white but now to cover the step (miss step is more like it. lol) I plan a piece of CF Tube to cover the entire barrel and provide tension to the barrel similar to the system the JSAR Raptors use. Current CF Tube in the PIC is just for Temp use as it is 3 pieces and not one piece as will be used in the final iteration. The apparent barrel droop is an illusion caused by 3 pieces of misaligned CF Tubing!

1562468603_19165435055d2160fb918902.11281694_P7060200.JPG
Click to expand...

Doubtful that 90 duro orings will make any difference in a static seal. Smoothing and polishing should help. When I got my Kral sear from JSAR it wouldn't even go into the gun due to the "rough" finish. I polished it up and it works great now. Shame to pay high $$ for stuff like that only to have to fix it yourself.

Gotta wonder why it is leaking in the first place? Didn't they leak test it before shipping it out?
 
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Doubtful if it was leak checked. The pressure tube had not been degreased or honed and had enough chips from the machining process to cover a dime. I used some 1200 grit last night and followed up with some diamond grit emery cloth. Much better now but still losing 200 PSI per day. I used some spray leak checker and did not see any indication of a leak so the next thing to do is check the valve since the metal chips were in the pressure tube.

Mine was the last custom work they will do because the Raptor is taking most of their resources for now at least!
 
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Unfortunately I do not have the skill set for my mini lathe and mini mill to accomplish everything I would like to do with them. I am learning slowly though since all I have for instruction is the internet due to my Rural location far from the 21st century! lol

I am still losing air at a much reduced rate but I cannot find the leak. Tried aerosol liquid leak checker recommended by Ernest Rowe, Tied a rubber "bladder" over the muzzle. I just can't seem to find the leak. The leak at the adapter has been repaired by polishing the inner wall of the plenum tube.
 
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I wouldn't trust the "balloon" on barrel method either. I had a QB one time that leaked very slowly at valve due to a new peek poppet and it didn't show with balloon. I removed the barrel, put the leak tester in the TP and could only see the bubbles with a 7x loupe and not the naked eye. I burnished the poppet at it stopped.

The trouble with having stuff done by someone is knowing who to trust. When a business is also a "sponsor" negative reviews can disappear. Not saying it happens here on AGN, but I am not allowed to post on certain websites due to posting negative (but 100% truthful) stuff about a "tuner".
 
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Yea, Next step is a total tear down but I have a tractor to fix first unfortunately! I highly suspect there is a tiny metal fragment in the valve poppet. 

Edit: 24 hour monitoring shows an 18 psi / hour loss which is much better than the 100 psi / hour initial loss when received but still not good enough .... 0 is good enough ;) !

Edit 11 July 2019 I tore down the entire gun late this evening when I got home from a trip to town 80 miles away. I found one tiny metal chip across the o-ring where the pressure tube interfaces the breech block. I also cleaned out the valve seat and cleaned and did a tiny amount of silicon grease lube to the poppet shaft and associated parts. So far 2.5 hours have elapsed with zero loss in pressure. In fact the pressure is reading higher due to temperature increase in the room where the gun is sitting. I think it may be leak free now! If no leak in a 24 hour period then I will begin to characterize and tune it for 34 to 52 grain slugs!

Edit: Update. I woke up this morning to find that the pressure was at 2540 which was a loss of 765 PSI overnight :( 

Found that the o-rings on the adapter block had extruded during the night to the point of a leak at pressures above 2540 PSI. Need less to say I am not particularly pleased about this development but Matt at JSAR will get me fixed up even if it takes another bottle block!

Yep I have now renamed this gun the Brocock "Extruder"! O-Rings that is ..... flowing elastomer .... leaking air :(



19 July 2019. The Bottle Block is back in Oregon since it is just too loose a fit in the tube and even extrudes 90 durometer urethane o-rings in 12 hours at 230 bar of pressure. I have no doubt that the tolerances would have been fine IF the pressure seen by the tube was regulated to 3K or less but that is NOT where this gun was modified to operate best!

I did get my barrel shroud "stiffener" installed (500 mm of CF Tubing). It uses an elastomer bushing to provide tension to the barrel (like the Raptor as it is the same bushing but cut down to fit my gun on my Mini Lathe).

Now at 4 months since beginning the last round of modifications and I still do not have a working gun! Oh the endless joys of prototyping! :( lol

On the bright side though the little I shot it before the stiffener was installed and the bottle block returned to JSAR for rework or replacement showed Exceptional Accuracy like several top end guns with slugs and pellets!
 
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Just to provide closure for this thread: JSAR made me a new bottle block that fit very well and it has now been leak free for over 4 months. The gun shoots very well ... much better than I expected from the stock valve setup. Hole in Hole at 66 yards. The regulator I used is an Altaros from an older AirForce gun that I converted to non regulated. The regulated pressure is about 1800 PSI and I get a LOT of shots from the 350 cc bottle filled to 4350 PSI!

I have been waiting for FX to ship me a Chrony for several months now so I can do some chrony work on the gun. Still has not been shipped though so I am still waiting to finish the characterization of the gun. The gun is shooting very flat though so I am estimating based on flight time to target that the velocity for 34 grain slugs is around 875 fps or so from the 24" poly unchoked barrel!

All in all I am pleased with the conversion!
 
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