GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: Fred J on July 01, 2022, 04:03:14 PM
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I recently converted my .177 Cal Benjamin Marauder (with a MDS hammer and Twin Spring System) to a 22 Cal.
The problem I ran into is that I can only get 770 fps with 18.13gr JSB pellets when I use the MDS hammer (no provision for the stock striker) and the TSS (with a 12 pound spring) when I am maintaining about 0.040" free flight, and the meter valve opened 6 turns. I am getting 60 good shots with less than 2% ES, but I would like to get my velocity up to 850 fps with the 18 gr pellets.
I have no problem achieving 850 - 860 fps if I replace the TSS with the stock hammer spring turned in 4.5 turns), and the meter valve turned out 3 turns. I am getting 32 shots with an ES of less than 2%. I am using the MDS hammer in this tune. I thought of putting the TSS back in the rifle, and re-installing the stock hammer, but the stock hammer tends to bind during cocking.
Is there something I am doing wrong with the TSS? I am not real mechanically inclined, so I don't want to drill out the transfer port or replace valve components.
Thank you!
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Two things you can try one is putting some extra weight in the back of the hammer spring bore or open up the transfer port some.
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Thank you for your advice. I have a question for you: I recently ordered a new mds hammer from JSAR. I was surprise to see that I received a 'Buffered' hammer (see attached picture). I didn't send it back, because it looks real interesting. I have seen some pictures posted on GTA, and some of the guys think it is a Raptor hammer. I can't use this hammer with my TSS, since there is considerable pre-load on the TSS springs. Could I use this hammer in my gen II marauder? If so, how would I tune it? It look like one could adjust the size of the buffer by adjusting the space between the recessed striker and the end of the hammer.
I tried the buffer hammer out with the striker fully recessed with my stock hammer spring. Other than some vibration during the shot cyle, it seemed to shoot OK, except I was only able to achieve 720 fps with JSB 18.13gr pellets before the stock hammer spring became coiled-bound (3 turns in for the hammer tension). So I just put the buffer hammer away and used my old mds hammer with my stock spring, per my previous post.
I have a stock hammer spring, a 10 lb spring and a 12 pound spring. Any suggestions? No instructions came with the buffered hammer.
Thank you for your help!
I would be willing to experiment with this buffered hammer, but I have no experience with adjusting a recessed striker.
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Are you still using the 22 transfer port? If so you could step it up to the 25 cal one. It's a direct swap with the 22. I believe the 22 sits at .125 and the stock 25 is at .140. That will allow more air flow which will increase velocity but lower shot count. If your gun will shoot the 15.89gr pellets accurately that could be another option too.
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Thank you for your advice, Chris. I will try the 25 Cal transfer port. I have tried the 15.89gr pellets in my Marauder: They are accurate, but they don't buck the wind like the 18.13gr pellets.
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You could take out the gap between the spring and hammer . . .
While the gap is "ideal" from a bounce prevention standpoint, it is not any good to have it if you can't get your desired performance results. I ran into a similar situation with a .22 build that is using a lightweight hammer at only ~30 grams and a TSS (with a non-stock valve though), and I found I actually need a even a bit of pre-compression on the spring to get where I want to be, and the efficiency is still holding well. Remember, we are not trying to prevent "all" hammer bounce here, but bounce that leads to the valve opening again. A 0.04" gap might be ideal from a bounce elimination standpoint as it assures that the valve won't open again, but that 0.04" is costing you speed with your pellet too. And even some compression with the TSS leads to WAY less pre-compression and spring load than existed with the factory spring and end cap . . .
In the end, I think Travis's idea of a bit more hammer weight is the right answer for both of us, but I have not yet had the time or inclination to make a weighted shim to put in my hammer. I do have a regular JSAR MDS hammer at about 50 grams, and it leads to way too much dwell in my set up (but allows for gobs of power if I want it) so the ideal balance point is closer to the 30 grams for me. Probably a similar situation for you too . . .
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I took Travis's and Alan's recommendation. I put a 1/8" brass shim in my MDS hammer, which brought the hammer weight up to 58 grams, and added preload to the TSS (1.75 and 2.0 turns in). When I shot the rifle with 0.04" free flight the rifle shot at 22 fpe (750 fps with AA 18.13 gr pellets. So I had to put some preload on the TSS to get the velocity I was looking for (865 fps). Here were the results:
MV 6.0 turn out
2.0 turns of spring preload
AA 18.13 gr pellets
Fill pressure: 2900 PSI
Shot down to 2150 PSI
High Vel.:869 fps
Low: 855 fps
32 shot with an extreme spread of 1.61%
Average FPE: 30.04
MV 6.0 turn out
1.75 turns of spring preload
AA 18.13 gr pellets
Fill pressure: 2900 PSI
Shot down to 2150 PSI
High Vel.:859 fps
Low: 842 fps
35 shot with an extreme spread of 1.98%
Average FPE: 29.28
My goals for this tune was to get 40 shots with an extreme spread under 2% and an average FPE of 30. I'm happy with the 30 fpe, and I think I could have reached the 40 shot goal if I revised my ES to 3%, but I am more interest in power than shot count for this rifle, since this rifle is used for pesting and bench rest competition out to 100 yards.
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The Light weight MDS hammers were ORIGINALLY designed for REGULATION CONVERTED rifles. If using with a standard non regged M-rod it likely is too light !
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Assuming a stock OE valve, what is the hammer weight for the .22 and .25 Marauder?
James
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Run your metering screw out 5.5 turns and make sure the set screw does not run it back in. You can also pull your trigger group off so you can work/see the gap better. Maybe 0.030" gap. You can also cut one coil off of the 12.5 lb. spring to increase the spring rate. A 15 lb. spring will also help if you can find the right diameter. I use a .25 cal valve spring which has a slightly lighter spring rating than the .22 cal valve spring has.
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My hammer was 73 grams without the Striker, 78 grams with Striker.
Hunter
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Fred,
I am running a Rocker1 MDS hammer in my .25 because of the aluminum air tube.
Same speed as with factory with same settings.
40fpe..
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Does anyone have a link to Rocker1 MDS Hammers? Thanks!
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I am also running a Rocker1 MDS hammer in my 177. I am using 58 gram because the 39 was too light.
Email Rocker1 to let him know what you want.
Go to members at the top of the page, search for Rocker1.
Hunter
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Thank to everyone for your help!
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Fred,
I am running a Rocker1 MDS hammer in my .25 because of the aluminum air tube.
Same speed as with factory with same settings.
40fpe..
I too have an aluminum tube and I have the factory hammer, a Tim Hill aluminum hammer (and valve) and the JSA MDS (Delrin and stainless steel). I am trying to figure out what hammer and valve (Hill or OE).
Can I use the aluminum Tim Hill hammer in the aluminum air tube?
James
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Does anyone have a link to Rocker1 MDS Hammers? Thanks!
Just send a PM to Rocker1.
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Jesse, the train of thought behind the aluminum hammer on aluminum tube is it will gall the tube. Fred you could switch to a stock 25 cal port it is .140 versus the stock 22 at .125. Or if you really want to open it up and pump some air out Hill has a nice .160 and then you could open the barrel port to match it. Mine are all regged which is a completely different animal but I have some that I have the barrel opened to .160-.170 and use .160-.140 transfer ports. I have found that slightly undersizing the TP to the barrel port helps snap the valve shut a little quicker helping a lot with efficiency.
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I would have thought 58g would be enough for your 22/30fpe non-regulated application. As Keith said, a heavier spring to get some gap back, to gain some efficiency. It might make cocking more difficult, but there are always trade-offs. BTW, the 32 and 35 shot at 30FPE and under 2% Es is pretty good. An OEM 22 could get 30 shots at 30FPE, but with 4% Es.
David (Rocker1) can make the MDS hammers in an assortment of weights, within limits, striker or no striker, recessed striker, peek striker, cored or non-cored, flat sides or round, pocketed deeper or larger.
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I was told not to use the steel, factory hammer with the aluminum tube..
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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.
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Rocker1 will get you squared away. He has a vast knowledge of the Marauder platform.
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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.
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That looks darned good Fred.
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32 shots averaging 30 FPE with still a low ES is very good for a .22 cal Mrod.
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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.
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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.
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Bagerland Air Gun Association in Bristol, Wisconsin. We have a group here who want to start 100 yard benchrest competition.
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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.
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Remember to check Transfer choke screw ... 5 turns CCW from bottomed out is wide open