BNM Custom Breech and Shroud kit
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BNM Custom Breech and Shroud kit
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Topic: BNM Custom Breech and Shroud kit (Read 1809 times))
TF89
Expert
Posts: 1016
Real Name: Dave
BNM Custom Breech and Shroud kit
«
on:
September 12, 2017, 12:46:00 PM »
Side bar: I have pictures, yet have not figured (or tried) out how to post them since the Photo Bucket issue. I'm going to be posting fairly soon (hoping at least) and that will have pictures
of the mods done to tweak the short falls of the design and cutting off 4" on length;). For this part of review, looks just like the pictures already out there.
I really like the Benjamin Discovery .22 platform due to its lightweight, small form factor of the stock and 2000 psi fill. Before changing over to the BNM kit I had this one set to shoot 800 fps with a 3.5% spread getting 22-24 shots with Crosman 14.3 premiers. The issue has always been around the need to quiet it down. I had an aftermarket solution, however that increased the overall length and would get raised eyebrows when people saw it. I began looking at other ideas, so in that end I had been eying two offerings, BNM and Crosmods. After a couple of years of eyeing the product and getting tired of the LDC, I decided to order a BNM kit.
I emailed Sergio a week after ordering as to status of the order, not having heard anything beyond the initial email letting me know that it had been ordered. He responded right away telling me it would be shipping the next day, turns out it was a few days later before shipping, kit arrived a little over 2 weeks after initial order.
Product arrived, well packaged and protected. The finish is really good, machining is great, close tolerances on the aluminum pieces. My initial impression was (still is) “Wow”, great job.
Before I begin this next part of the review I want to commend Sergio on the machine work of the breech, shroud and barrel bands was/is fantastic, seriously nice work.
(I ordered an extra band as I like two bands on the Discovery). Since I’ve mentioned it, I bought the bands with o-rings. I like how they secure the shroud, yet the downside for me it made taking the shroud off very difficult. So for now, have removed the o-ring. The barrel band ID is only a few thousand bigger than the shroud, so enough room for the air cylinder to expand and contract, yet not any slop.
It seems as if there are always somethings that could be improved and it is so in this case as well. There were a couple of areas where the tolerances were not up to par.
Listed in order of easy to remedy to harder.
1) The transport port bushing/sleeve had a larger OD than the actual ID of the hole in the breech. It would not fit until I reduced the OD by sanding/filing it down. The length was correct, just didn’t fit. The fix was to use a drill bit as a mandrel and while spinning the bushing use a file to reduce the OD until it just fit. I also added a slight bevel to the end so that fits in the barrel to ensure a good seal.
2) The bolt probe and cocking lug/bolt:
a) The probe body does not block the transport hole as noted in some past posts from a few years back. The finish of the bolt is nicely done. The probe was just a little shorter than I would have liked. Using the Crosman Premier HP which has about a .10” spacing (setback) between the inside of the pellet and the end of the skirt base. This pellet when pushed into place blocked about 35% of the port.
I contacted Sergio about this and once again, he responded quickly telling me that the probe cannot be longer as it will not clear the magazine. He is correct from the standpoint that the probe length has to be flush or inside the breech face because the magazine will not fit, however there is room for the probe to be longer than the one supplied. Since this kit is based on the Marauder, perhaps this is a common feature.
b) The hole tapped into the bolt for the screw/modified hex nut bolt was canted forward toward the barrel. This further reduced the bolt probes ability to push the pellet completely past the transfer port.
Overall the bolt probe was .074 short of the maximum length it could be. That may not seem like that much, however without that little bit extra, the pellet will partially block the port.
*NOTE* in limited testing this did not seem to affect accuracy or reduce fps surprisingly. So maybe I’m making a big deal out of nothing.
3) The probe stop bolt/screw mentioned above has a tendency to dig into the slot edge under the breech. The breech is aluminum and the stop bolt is steel. While the bolt was smooth (in action/use), there was a bit of grittiness from the stop bolt cutting into aluminum. I’m not sure how in stock form to get around that issue, perhaps with time the two parts will mate and ride smoother.
The bolt probe stop bolt and galling put a damper on my overall zeal for the KIT. Having said that I did come up with a solution which I will cover when I post the modifications I made to achieve my goal of a quasi-carbine.
*NOTE*
I have to say that perhaps it was just my BNM Kit that had this issue, I see very few posts talking about it, so maybe it was just my experience.
To wrap up this portion of the review and give a summary:
95% of the BNM shroud/breech/barrel band is top notch, the bolt cocking lug placement could stand some better quality control, at least in my case. While I’m not sure what the finish material is, looks like powder coat and is well done and sturdy, resists wear very nicely and has a nice even finish. The gun is quiet, maybe not as quiet as the aftermarket pickle. My barrel has been cut to 20” so a comparison of sound and fps is not fair.
The look seemed odd
at first yet has grown on me, fat shroud with skinny air cylinder.
Currently I’m getting the following shot count. From 1800psi down to 1050psi, averaging 750fps at 4% with a shot string of 28-30 Crosman 14.3 premiers.
I should mention that the bolt probe needs a lubricant, something like Krytox grease since the bolt probe is stainless steel and the breech is 7075 T6 (I think). I have been told that is what owners of the Marauder use to smooth up the action. From my experience it is a night and day difference. The cocking force is reduced and it is so smooth.
Would I buy it again?
Yes most definitely, with caveat of knowing that I would have to do some tweaking. I don’t have the ability to build this on my own and this is a great way to get a nice looking, quiet multi shot, 2000 psi, lightweight air gun. Speaking of weight, without a scope, shortened by 4", two barrel bands, some additional work inside the shroud, ("edited as I got the name wrong") Hillairgun de-pinger and SSG, it tips the scales at 6.2lbs. The before stock Discovery with LDC weighed about 5 oz less. I think my stock is a bit heavier as the specs on the web state 5.2lbs for an out of the box gun.
As I have already mentioned my BNM semi carbine project will be forthcoming. I say semi because my original idea was to have the barrel be 18” with the shroud being even with the fill port cap. Ended up with a 20” barrel and the shroud out past fill cap by 2".
I really, really like it. Seriously this is my favorite gun.
*Update*
After a couple of thousand pellets and 6 months I still really like it and would buy again. The finish is holding up great and I have taken this this thing apart about 20 times, I'm a fiddler, what can I say
Regarding QC
I ask Sergio for another breech and bolt kit because of the galling in the slot and canted cocking bolt. I was thinking that the one I received was a fluke and a new one would work better. He sent me one another one and I unfortunately found the issue remained the same.
I feel that Sergio needs better QC on the bolt and locking lug bolt orientation and hole placement. As I mentioned the cocking lug was canted and needed to be spaced another .074 to give maximum pellet setting. The new assembly I received was even worse. The locking lug was canted and because the bolt handled hit the back of the breech, the length was .105 short. The actual Bolt probe has a great fit and finish and is certainly the correct length. The issue is the placement of the of the cocking lug or maybe bolt handle along with the cocking lug hole not being drilled 90 degrees to the bolt.
I also had to remove flashing inside some of the holes, not a big deal, just something to keep in mind. As I said above, I would buy again knowing that some cleanup might be needed.
«
Last Edit: September 14, 2017, 03:20:29 PM by TF89
»
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Benjamin Pistol (P-rod)
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KnifeMaker
GTA Senior Contributor
Posts: 8224
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Real Name: Michael
Re: BNM Custom Breech and Shroud kit
«
Reply #1 on:
September 13, 2017, 01:16:27 AM »
Thank You for the write-up Dave!
Having the same issue with the cocking bolt digging into the rear of the slot when closed. It digs in while reviewing it as well.
I can assure you that it is Not 7075 T-6. I have used a Lot of it, and can tell you that the bolt would have a hard time gouging it. Heck, even a good file will get flattened teeth when trying to file anodized, and T-6 heat treated 7075.
Back when I was co-owner of an Archery shop, and abefore the carbon shafts came out, many shooters were not happy with their arrows bending so easily.
We carried the top of the line Easton T-6 7075 shafts, and when making up arrows for them, I would take a 4 or 5" piece of one of their shafts and pitch it out onto the floor of the range. The soft, standard arrow shafts would hit with a light thud. The same length of 7075 would ring like a bell.
It has a very high RockWell Hardness. (And is very expensive) requiring carbide tooling to work when at T-6 hardness.
I was thinking of moving the location of the lug bolt forward a bit, and also machining the rear of the breech block a bit. This would allow the probe to both retract further, to miss the mag. and still push the pellet past the port.
Knife
Knife
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Central Texas
Lmgunner13
magna venandi
Sharp Shooter
Posts: 698
yes
Real Name: Phil
Re: BNM Custom Breech and Shroud kit
«
Reply #2 on:
September 13, 2017, 02:46:41 PM »
Thanks Dave, I have the BNM breech and shroud on my discovery in 22 also. I did not have any of those problems. Went together perfectly and has functioned flawlessly since I installed it back in May. I average 841fps with JSB 18.13 for 28 fpe over 20 shots. I do have a power adjuster and a stainless steel fluted hammer.
Phil
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Lumberton Texas
Hatsan AT44S 10 QE .25 (soon to be regulated)
PROD .22 Rocker1 LDC, .120 TP, ART TSS
Discovery 22 Boyd's Hunter stock, BNM Multi shot Breech and Shroud, Power Adjuster, 3000psi Mod, Stainless fluted hammer and pin.
Ruger Blackhawk elite 177 tuned
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Mean life expectancy for a gray squirrel at birth is 1-2 years; the average life span of an adult is closer to 6 years. Records for maximum life span are 12 years in the wild and 20 years in captivity. On my property the life expectancy is 30 seconds...
TF89
Expert
Posts: 1016
Real Name: Dave
Re: BNM Custom Breech and Shroud kit
«
Reply #3 on:
October 13, 2017, 12:21:35 PM »
For those that might be waiting for me to do a follow up as I mentioned in this review, well..... life has gotten very busy. The bigger issue is that I lost the write up I had almost completed and need to now recreate. I still have the pictures, etc, just not the words.
Dave
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Benjamin Pistol (P-rod)
Benjamin Discovery .22, BNM breech/shroud (35 FPE with 20" barrel)
Crosman 400
Crosman 140 with 2260 top end
Remington NPSS .177
Crosman 1322, 14” barrel, partial mods, flat top piston
Beeman P17
XISICO XS-12 .177 Prototype trigger
HW25 (1968)
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BNM Custom Breech and Shroud kit