Discovery BNM breech/shroud install and review

[Tdubya]

Installed the BNM breech/shroud kit on my .177 Discovery. Kit comes with Aluminum  breech, bolt, shroud (with baffles), band for shroud, and one Marauder .177 magazine. Also includes the necessary screws, seals, and extended transfer port for the breech riser.  Install went fairly smooth. Only challenge was getting the transfer port properly aligned. And the magazine was difficult to insert. A little sanding and polishing of the extrusion that the magazine slides around and all was well. The mags don’t snap in like on the Marauder. You just press the mag in until it is flush with the breech extrusion that fits tightly into the magazine slot. So don’t remove too much material. Doesn’t take much sanding to get it to fit nice and snug. There are a couple of good youtube videos that are very helpful.


There are several color combinations to choose from. I selected plain aluminum breech and band, with a metallic red shroud. I like it! The breech had some machine marks, but you could probably polish out if they bug you.


I was a bit concerned about a post that I read that claimed a loss of 50 to 100 fps due to the extended transfer port. So I took before and after chrony readings.  Turned out just the opposite (see numbers below). Actually had a substantial increase in fps with no loss of usable shots. However, I did install a power adjuster that I had originally purchased for a 2240. I used the stock spring and had the adjuster as far back as possible to get a fair comparison. I think this adjuster’s spring socket  may not be as deep as the stock cap. That plus the adjuster’s included spring follower may have provided more preload than stock.  Anyway, the first 10 shots were surprisingly consistent, especially the stock string. The consistency did suffer some with the new breech.  Due to necessary extended transfer port?


All in all, VERY pleased with the results.  No more frustration loading those .177 pellets! 


Here are the chrony numbers and a few pics.


Benjamin Discovery   3/14/17         
                                   BNM install / plus power adjuster (at lowest setting)
  before   after   psi
1          987                         1042   2000
2          990                         1047   
3          987                         1047   
4          985                         1055   
5          988                         1054   
6          991                         1052   
7          988                         1052   *
8          987                         1052   *
9          988                         1052   *
10          989                         1044   
      * = shot not registered on chrony   


average   988                          1049.7   
deviation   1.6996731         4.3982319   


11          983                           1053   
12          977                          1038   
13          977                          1035   
14          971                          1026   
15          967                          1016   
16          957                          1006   
17          952                           998   
18          941                           986   
19          936                           979   
20          928                           966   


average   958.9                 1010.3   
deviation   19.145350         28.249090   


21           917                           959   1200
22           912                          940   
23           901                          929   
24           888                          905   
25           880                          888   


average   899.6                 924.2   
deviation   15.630099         28.119388   




Second AFTER string. Slightly filled past 2000 psi
   after 2nd string   psi
1          1051   2200
2          1057   
3          1054   
4          1055   
5          1056   
6          1063   
7          1067   
8          1063   
9          1057   
10          1060   


average  1058.3   
deviation   4.8773854   


11          1058          1700 psi start
12          1053   
13          1047   
14          1039   
15          1028   
16          1018   
17          1012   
18          1002   
19           991   
20           977   


average   1022.5   
deviation   27.297741   


21           868         1200
22           843   
23           815   
24           787   
25           754   


average   813.4   
deviation   44.958870




PICS
http://s783.photobucket.com/user/tdubya48/Benjamin%20Discovery%20177/story

[KnifeMaker]

I have not been able to find the maker of this breach, or it being sold. Every link I have tried leads to a dead page.

Knife

[darren]

Bnmcustom.com

[Smokehogan]

is your accuracy still good?

[Tdubya]

Accuracy still great. And it is a lot quieter.
Maybe not as quiet as my .22 Marauder, but definitely backyard friendly now. I'm sure tuning for lower power and more shots will quiet even more.

[imadunatic]

I have not been able to find the maker of this breach, or it being sold. Every link I have tried leads to a dead page.

Knife

http://www.bnmcustom.com/categories/

Ordering one of these for my 2400 in about 3 weeks.... can't wait.

[Tdubya]

You will love it!