GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: Tdubya on March 16, 2017, 11:18:36 PM
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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 (http://s783.photobucket.com/user/tdubya48/Benjamin%20Discovery%20177/story)
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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
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Bnmcustom.com
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is your accuracy still good?
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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.
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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/ (http://www.bnmcustom.com/categories/)
Ordering one of these for my 2400 in about 3 weeks.... can't wait.
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You will love it!