Marauder Project – .177 Tuning (Part 1)   1 comment

Greetings All,

The storms are moving in here in middle Tennessee. However, this morning I was able to get in a few hours of testing before the storm rolled in. On a previous post I received a comment with a link to the crosman site. On the blog I found one entry that went over what he did to get the “best” performance. (You can read it here.) I printed off the portion I was interested in and setup this morning.

Here is my helper this morning. He wanted to “help” me setup. 🙂

After reading over the post, I was a bit perplexed. The author notes the stroke adjustment is 4.3. How can I get 4.3 turns? I could convert the decimal into a fraction. I decided I would revert to my 1/4, 1/2, and 1 turn method; however, I now will deploy a new method of clock values. This will aid in a bit more fine tuning to get the desired result.

Clock value defined: This is a very simply method and is used as a reference in many tasks. If the Allen wrench is pointing toward the 3 o’clock position, that is my starting point for the adjustment. I move the adjustment to the 5 o’clock position and make a note. You get the idea now. A simple reproducible system.

Here the Allen wrench is in the “3 o’clock” position when I adjusted the metering screw.
Allen wrench in the 3 o'clock position

My goal for this tune is to have a 2000 psi fill and get about 20-30 consistent shots within 20 fps. Thus I begin by taking the action out of the stock and setting everything to “zero.” I call it zero not because of what the rifle shoots, but a reproducible starting point every time. For the hammer spring and stroke adjustments, I turned (as the Crosman post stated and my previous post state) the hammer spring (HS) and stroke adjustment (Sk) counter-clockwise until it stops. For the metering screw, I turned it right or clockwise until it stops.

With all adjustments set to zero, I moved them to the starting points indicated in the Crosman post. They are as follows: HS – 2.25; Sk – 4.3; PSI fill – 2000; Transfer Port Adjustment or metering screw (Ms) – 3. For the Sk, I just started at 4 1/4. For the HS, I started at 2 1/4 turns clockwise and the Ms is 3 turns counter-clockwise.

My current psi in the Marauder was 2200 psi. I shot the PSI down to about 2050psi. I am using JSB Exact Heavy pellets for testing. Here are the numbers:

868, 866, 873, 872, 894, (almost at 2000 psi), 900, 903, 906, 918, (at about 2000psi), 932, 943, 936, 932, 946, 944, 946, (~1900psi), 951, 958, Err, 948, 948, 952, 951, 946, 945, 945, 933, (~1700psi), 941, 935, 931,929, (~1600), 928, 926, 923, 917, 916, 906 (~1500 – 1550 psi). Total – 26 shots starting at 932 and ending at 923

This is a real good start. I want to bring down the velocity and try to make the hammer stroke more efficient. I refilled to 2000psi, swapped to Barracuda Match pellets and shot a 20 shot string.

960, 957, 959, 956, 957, (~1800 psi), 955, 955, 951, 952, 950, 949, 944, 941, 936, 934, 930, (~1650-1700psi), 929, 924, 922, 918, (~1600 psi).

According to ChairGun Pro, for 19.74 fpe, the H&N Barracuda pellets need to be at about 920fps. I decreased the Ms from 2 to 3 (2 o’clock position to the 3 o’clock position), refilled to 2100 psi (to see if the HS is correct), and began shooting. Here are the number and adjustments

955, Sk – cw 1/2; 951, Sk – cw 12 to 2; 955, 958, Sk – cw 1/4; 950, (1900), Ms – ccw 1/4, 933, Ms – 6 to 7, 929, 927, 926, (1800), 927, 924, 920, 917, 920, 912, 911, 910, 909, (1700), 905, 903, 897 (~1600psi).
Total – 20 good shots

After the last adjustments to the Ms, I noticed the clouds were getting darker. So I just finished out the shot sting and packed it up for the time being. I believe the only thing I am going to do next is back off the Ms until I get the average needed. The hammer stroke seems to be okay now and the fill pressure is close to 2000 psi.

With the next GOB match right around the corner, I am trying to get my Marauder ready for my first match with it. If the sun comes out later today I will try a bit more testing.

Until next time… “Live long and prosper.” -Spock

Blessings,
Jeff

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Posted April 24, 2010 by avv604 in Marauder

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One response to “Marauder Project – .177 Tuning (Part 1)

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