Odd Settings Due to Stroke "Drifting"

[Lammy1000]

After tightening #42 screw for the second time to stop hammer stroke from drifting and before I retighten # 42 "harder"(advice from Crosman engineer), I am going to leave stroke @ 0 turns where it naturally drifts to and reduce hammer preload to 1. My original conservative tune was 2H, 2S and 1.25 valve. Now it is 1H, 0S and 1.25 valve. This seems goofy having that much stroke and so little hammer spring preload...any predictions (I do not yet own a chronograph).

Please, if anyone can think of a permanent solution for preventing the hammer stroke f/drifting. I thought that retapping for a larger set screw (#42 is a 6-32) might allow for a better bite, preventing movement of this setting.

[Supercharged86]

.... My original conservative tune was 2H, 2S and 1.25 valve. Now it is 1H, 0S and 1.25 valve. This seems goofy having that much stroke and so little hammer spring preload...any predictions (I do not yet own a chronograph)....

Hey Lammy, Not goofy at all, in fact this is exactly how "The A-team" recommends setting up the Mrod. except they chose to use a wide open VP. However, without the chrony you'll have no idea of the results. The premiss of their instructions is to select a fill point, then with a max stroke setting (which you have) increase the hammer spring pre-load one turn at a time until you reach the desired velocity (for a given fill pressure).

Sorry, no answer for your drifting settings. Mine is still dead on since last adjusted in March and several hundred of shots later.

Steve

[Lammy1000]

My 1H, 0S and 1.25 valve settings are working great. 40 shots without a poi change and velocity is high enough to out-penetrate my RWS 34 spring gun. Uses only 16 psi/shot. The .177 caliber really helps in terms of efficiency.

[Supercharged86]

My 1H, 0S and 1.25 valve settings are working great. 40 shots without a poi change and velocity is high enough to out-penetrate my RWS 34 spring gun. Uses only 16 psi/shot. The .177 caliber really helps in terms of efficiency.

What pellet are you shooting and the fill pressure? I'll test the settings and give you an approximate velocity. Steve

[Lammy1000]

Thanks Steve! I am filling to 2200 psi and shooting Crosman Premier 7.9's. Can't wait to see what you get for velocity.

[Supercharged86]

Thanks Steve! I am filling to 2200 psi and shooting Crosman Premier 7.9's. Can't wait to see what you get for velocity.

Hey Lammy, Sorry for the delay. Here's what I came up with, 2200 fill pressure (on my SCBA, 2150 on my Mrod), if I remember correctly the stock gauge was off by a good 100 psi (lower) compared to my SCBA gauge. Anyway...

HS 1, ST 0, VP 1.25 = 745 fps

HS 1, ST 0, VP 1.75 = 850 fps
HS 1, ST 0, VP 2.25 = 930 fps

HS 1, ST 1, VP 1.25 = 755 fps
HS 1, ST 2, VP 1.25 = 745 fps
HS 1, ST 4, VP 1.25 = 740 fps

HS 2, ST 0, VP 1.25 = 745 fps
HS 2, ST 1, VP 1.25 = 745 fps
HS 2, ST 2, VP 1.25 = 755 fps

HS 3, ST 2, VP 1.25 = 750 fps

Although, 745 fps came up on various settings, the difference would likely be seen with the extreme spread over 20-40 shots. Cheers. Steve

[Lammy1000]

Steve, Thanks so much for doing these tests. I am surprised that the changes in hammer spring preload and stroke did not effect velocity much, while the VP had a significant effect. This may not be a surprise to those with alot of tuning behind a chronograph.

I am thinking of backing out the VP to 1.75 from 1.25 for settings of: HS 1, ST 0, VP 1.75. Velocity of 850 fps may be even better for accuracy? Would you guess that a bell curve of velocities is occurring at these settings?

Update: the change in VP to 1.75 has a significant impact on poi of impact at 55 yards. I was needing 9/10 ths of a mildot hold over. Now, poi is slightly above the crosshairs. This is ~2" difference. This gun really is alot of fun.

[n0tzl]

Hi Lammy,

I added another setscrew to lock the original one, like Crosman did on the transfer port, thats worked to keep the stroke setting in place over hundreds of shots and many adjustments. I had just as much problem with the spring adjustment backing off but filing the ends of the spring smooth and a couple dabs of silicone grease seems to have cured that.

Dan

[Supercharged86]

Steve, Thanks so much for doing these tests. I am surprised that the changes in hammer spring preload and stroke did not effect velocity much, while the VP had a significant effect. This may not be a surprise to those with alot of tuning behind a chronograph.

I am thinking of backing out the VP to 1.75 from 1.25 for settings of: HS 1, ST 0, VP 1.75. Velocity of 850 fps may be even better for accuracy? Would you guess that a bell curve of velocities is occurring at these settings?

Update: the change in VP to 1.75 has a significant impact on poi of impact at 55 yards. I was needing 9/10 ths of a mildot hold over. Now, poi is slightly above the crosshairs. This is ~2" difference. This gun really is alot of fun.

Lammy, Although, the spring pre-load and stroke length will effect velocity especially if it's drastically changed (one test result I didn't add above, HS 0, ST 6, VP 1.25 = 714), these adjustments are designed to make a given fill pressure work more "efficiently". The adjustment to the VP will certainly have the biggest effect on the overall velocity and the POI, as you experienced. Increasing the velocity to 850 will certainly improve some aspects of your shooting; longer distance trajectory, increased energy (fpe) for hunting purposes but will not necessarily improve accuracy. In fact, depending on the pellet can sometimes worsen the results. Regardless of the settings, there will be a bell curve (more pronounced if your initial fill pressure is several hundred pounds over your peak tune pressure). Hope this helps. Steve

[Lammy1000]

Steve, thanks for your feedback. I believe that 850 fps is close to the sweet-spot for many pellets. Certainly driving a pellet too fast is detrimental to accuracy and I read that Crosman premiers were designed for top accuracy at 800 fps. Olympic match guns are the most accurate air guns with muzzle velocities of 550 fps.

To cut to the chase, do you think that my settings of 1 H, 0S and 1.75 V at a fill 0f 2200 psi is a good solid tuning? I am using ~21 psi/shot and get 30 rounds without a noticeable drop at 55 yards. Admittedly, I have not performed extensive accuracy testing at this tuning like I did at the lower velocity tuning (~750 fps). Hopefully, 850 fps will yield excellent accuracy too.

Dan - I do have another 6-32 set screw that could be used to jam screw #42, but since blue loc-tite did not work, I believe this set screw was not torqued enough. Hopefully my 0 stroke setting will not have to be changed.

Lou