Gauntlet 22 carbine - need some help about barrel length

[mackeral5]

In my 14" barrel QB I recovered lost efficiency after 2 significant modifications.  Some of rsterne's QB builds have included something that isn't often talked about, but was a game changer for me in my QB journey--reducing the valve stem size.   Then of course you adjust the rest of the porting to match the resulting increase in valve throat area.  This allows more volume without increasing necessary hammer strike.  Of course this requires a new poppet, using your preferred poppet material.  Couple this with some form of an ultra light hammer, as in 20 grams or less.  Then you are set up to release the required air quicker and with less dwell.  I have run solid peek hammers, somewhere in the 15 gram range, with .210 valve throats up to 1700 psi.  At 1100 -1300 they don't require much hammer spring. 

I make my QB peek valve poppets/stems with materials from Amazon---3/8 peek rod and 2mm hardened drill rod.  Brass hobby tubing is used as a bushing.  I've used this combination to make 2mm stem/peek poppets and use them at pressures up to 3000psi---at this point thousands of rounds with no failures across 6 different guns.  Early on I was worried about potential failures but at this point  I have no concerns about stems failing.

Here's a link to the specific drill rod I'm speaking of.  This stuff is HARD.  :



Here is the brass hobby tubing.  In some valves it is simply a press fit, others require a little epoxy. 

[shorty]

Had to finally run a string with the shortened barrel (-5.5"). That puts it at a tip to tip of 18.5" and maybe minus an inch for where the pellet sits after the transfer port. Measured and re-measured.

Made a new hammer spring and leaves it at a .125" negative pre-load. Kissing the valve stem pushes it at 865fps with 14.3's so a good range with negative pre-load.

3000 psi fill and 1050psi end with the short barrel.
Shot #   FPS
1   793
2   810
3   797
4   791
5   808
6   798
7   797
8   799
9   795
10   809
11   799
12   804
13   808
14   802
15   790
16   798
17   800
18   800
19   810
20   792
21   793
22   804
23   821
24   815
25   813
26   808
27   801
28   807
29   801
30   809
31   815
32   804
33   805
34   803
35   821
36   809
37   796
38   795
39   808
40   807
41   800
42   810
43   812
44   824
45   805
46   812
47   809
48   806
49   814
50   808
51   802
52   802
53   816
54   799
55   796
56   810
57   803
58   808
59   804
60   818
61   803
62   829
63   829
64   816
65   827
66   822
67   816
68   826
69   815
70   819
71   812
72   811
73   811
74   810
75   817
76   819
77   821
78   813
79   802
80   819
81   801
82   798
83   808
84   812
85   819
86   815
87   821
88   821
89   828
90   832
91   811
92   827
93   823
94   812
95   817
96   818
97   824
98   838
99   827
100   828
101   837
102   841
103   838
104   836
105   835
106   828
107   842
108   829
109   824
110   824
111   817
112   814
113   809
114   811
115   800
116   800
117   792
118   793
119   781
120   789

I can really see how a harder poppet material would be advantageous but, I think I am sticking with this until something fails. It's just stupid quite at 20 fpe up to 26fpe. It's not until you lay on the preload over 900fps when the tone changes.

I am a happy camper....

[darkcharisma]

thanks Mac for the info on stem size reduction. i did something similar by boring up everything in the valve including reducing the poppet brass enclosure. i am sure stem size reduction will also help.

 shorty thats a great shot string, i might have to do something similar. you could have just reduce the hammer/valve  stop block, would have been a simpler mod and keep the same spring strength.

[mackeral5]

Had to finally run a string with the shortened barrel (-5.5"). That puts it at a tip to tip of 18.5" and maybe minus an inch for where the pellet sits after the transfer port. Measured and re-measured.

Made a new hammer spring and leaves it at a .125" negative pre-load. Kissing the valve stem pushes it at 865fps with 14.3's so a good range with negative pre-load.

3000 psi fill and 1050psi end with the short barrel.
Shot #   FPS
1   793
2   810
3   797
4   791
5   808
6   798
7   797
8   799
9   795
10   809
11   799
12   804
13   808
14   802
15   790
16   798
17   800
18   800
19   810
20   792
21   793
22   804
23   821
24   815
25   813
26   808
27   801
28   807
29   801
30   809
31   815
32   804
33   805
34   803
35   821
36   809
37   796
38   795
39   808
40   807
41   800
42   810
43   812
44   824
45   805
46   812
47   809
48   806
49   814
50   808
51   802
52   802
53   816
54   799
55   796
56   810
57   803
58   808
59   804
60   818
61   803
62   829
63   829
64   816
65   827
66   822
67   816
68   826
69   815
70   819
71   812
72   811
73   811
74   810
75   817
76   819
77   821
78   813
79   802
80   819
81   801
82   798
83   808
84   812
85   819
86   815
87   821
88   821
89   828
90   832
91   811
92   827
93   823
94   812
95   817
96   818
97   824
98   838
99   827
100   828
101   837
102   841
103   838
104   836
105   835
106   828
107   842
108   829
109   824
110   824
111   817
112   814
113   809
114   811
115   800
116   800
117   792
118   793
119   781
120   789

I can really see how a harder poppet material would be advantageous but, I think I am sticking with this until something fails. It's just stupid quite at 20 fpe up to 26fpe. It's not until you lay on the preload over 900fps when the tone changes.

I am a happy camper....

Very nice, well done!

[mackeral5]

thanks Mac for the info on stem size reduction. i did something similar by boring up everything in the valve including reducing the poppet brass enclosure. i am sure stem size reduction will also help.

 shorty thats a great shot string, i might have to do something similar. you could have just reduce the hammer/valve  stop block, would have been a simpler mod and keep the same spring strength.

You're very welcome.  I've paid very close attention to Mr Sterne's posts over the years.  Especially the QB build based on dual 88gr cartridges being used as air storage, virtually everything in that build translates over into the low pressure/regulated QB's....