Need more velocity from my 22 Cal Benjamin Marauder with MDS Hammer and TSS

[FuzzyGrub]

I was told not to use the steel, factory hammer with the aluminum tube..

Absolutly correct! 

I would not try the Hill Aluminum hammer, either.  It may or may not be harder than the aluminum tube, but given cost of tube it is not worth finding that out.    MDS is the way to go. 

[bear air]

Rocker1 will get you squared away. He has a vast knowledge of the Marauder platform.

[Fred J]

Here are the shot strings, for your viewing pleasure. The top string had an average velocity of 864 fps with JSB 18.13 gr pellets, while the bottom string had an average velocity of 853fps. The only setup difference between the two strings was the bottom string had 1/4 turn less preload. The meter valve (flow) was set at 6.5 turns out (full open). Both stings were done with a 2,900 PSI fill pressure, and shot down to 2,150 fps. I wish that I had fill the Mrod to 3,000 PSI: I think I would have have 2-4 shots in the string within 2% of the extreme spread.

[bear air]

That looks darned good Fred.

[triggertreat]

32 shots averaging 30 FPE with still a low ES is very good for a .22 cal Mrod.

[Fred J]

Here's an update regarding my 22 cal Marauder: I was finally able to achieve 28.2 fpe and 40 shots with 2% extreme spread. I am still using the MDS hammer with about 7 grams weight added to it, bringing the hammer weight up to 52 grams. I replaced the 10.5 lb outer spring on my Twin Spring System with a 15.5 lb spring from Hill. The TSS is adjusted to provide 0.020" hammer free flight. Finally, the transfer port was enlarged to 0.161". I am filling the rifle to 3,000 PSI and shooting down to 2300 PSI. If I shoot the rifle from 3,000 PSI down to 2350 PSI I can can keep the ES down to 1.42%. No modifications were made to the valve.

I am planning to use this rifle for 100 yard benchrest competition at my local air gun club. The original 177 cal rifle was given to me by my old boss. The rifle struggled to shoot 1" groups at 30 yards. It has be converted to 22 cal. The 22 cal Crosman barrel was polished with JB Paste (30 passes). It now can shoot 1" groups at 100 yards with JSB 18 gr pellets (light wind), if I do my part.

[cjk]

Wow Fred, sounds like you did a *(&^ of a job tuning! 1" at 100 yards... NICE!!!  What club are you shooting with? I live in East troy and work out of Burlington.

[Fred J]

Bagerland Air Gun Association in Bristol, Wisconsin. We have a group here who want to start 100 yard benchrest competition.

[triggertreat]

Fred, when I was reading over your setup, I thought I was reading over mine.  They are very similar with custom MDS hammer weights and TSS springs while using a stock valve.  Your tune is very similar as well but mine is setup for 30 shots at 31 FPE within a 2% ES.  Mine also has a MMHF barrel and a lightweight reservoir tube.

I am wishing the best at the 100-yard range.  That will be a good challenge in .22 cal.

[Motorhead]

Remember to check Transfer choke screw ... 5 turns CCW from bottomed out is wide open