Tuning m-rod .177 - I'd like to see if I can get NSA 12.5 slugs flying through it @900+

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jdanvers

jdanvers

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Jul 7, 2019
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South Central Upstate NY, United States
It's a Gen 2 with a huma in it - it's currently dialed up to 115bar and the gun tops out with AA 10.3's @mid 950's. I'm pretty sure 115 bar is actually to low as there is still a LOT of room to dial up the hammer spring ( and I have dialed it up ) but no appreciable bump in fps.

I'm thinking / guessing that in order to have it fling 12.5 slugs - both heavier and more contact patch with the barrel - I likely will need to see if I can get the 10.3 pellets zipping out of it 1050-1100'ish? Obviously I don't expect accuracy out of them at this sort of speed . . . ( I don't have the 12.5 slugs yet - going to place an order for a sample pack shortly ) I'm just hoping to preemptively "prep" the gun for when I do get them. If I can get the 10.3's moving at 1050 - how much slower do you guys think the 12.5 slugs will wind up being? Do you think I'll lose more than 200 fps? I'd like to have the slugs moving at least 900 . . . I should bump the reg up to . . . . 120? 125?

Bored . . . just something to do. {shrug shoulders} ;-)
 
you don't need to have slugs moving that fast to be accurate. My dream-tac compact shot the 12.5 slugs at 725 fps into a 1/2 inch hole at 34 yards, one of these days I'll find time to go out to a longer range.
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I'm not a major slug shooter but have begun playing with them a bit. IMO the speed is needed once you get beyond that short distance you note because the slugs are spin stabilized. Higher velocity means higher spin. And pellets function fine at those short distances. So to capitalize on the advantages of the slugs it seems one would need more relative velocity.
 
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you don't need to have slugs moving that fast to be accurate. My dream-tac compact shot the 12.5 slugs at 725 fps into a 1/2 inch hole at 34 yards, one of these days I'll find time to go out to a longer range.
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I'm not a major slug shooter but have begun playing with them a bit. IMO the speed is needed once you get beyond that short distance you note because the slugs are spin stabilized. Higher velocity means higher spin. And pellets function fine at those short distances. So to capitalize on the advantages of the slugs it seems one would need more relative velocity.
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believe it or not that’s not true. To be accurate short range the slugs need to be properly stabilized but once stabilized it’s good down range. Another way to put it is to get any accuracy at any distance pass 10 yards your barrel has to have enough twist rate for the slugs you shoot or spin the slug fast enough. Once proper stabilization revolution speed is achieved its fine done range, some inaccuracy is caused by harmonics but not destabilization of the slug. 


Generally speaking most airgun barrel doesn’t have fast enough twist rate for long slugs but usually short or lighter slugs are fine. Just try it and you will see what I mean. If you can get half inch group with slugs at 20 yards you most likely will bet half in group at 50 yards and 1 inch group at 100 yards, slug groups don’t open up like pellets down range. 
 
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I ordered up two sample packs of the 12.5's ( shipping costs more than a single pack so . . . why pay more for shipping than product? ;-) ) I'm going to turn up the HS on it until I get back to that mid-upper 950's range when they come in and see what happens with them. I've currently got it running 875-880 right now which is more or less the speed that works really well with the 10.3's for field target. I'll post back and let anyone curious know. 
 
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I don’t buy into the whole speed thing when it comes to slugs. Just try them in your gun first before you get desperate and start cranking things up. Here is why. I was testing slugs out of my Taipan. Shot some groups at 100 that were beyond belief. Ran to my chronograph and they were only going 737fps. Turned up my reg and put in a new spring. Tuned it to shoot them at 825fps. Guess what happened? Nothing. Same micro groups at 100yrds. There are quite a few things that go into whether a gun likes a particular slug or not. The last is speed.
 
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I don’t buy into the whole speed thing when it comes to slugs. Just try them in your gun first before you get desperate and start cranking things up. Here is why. I was testing slugs out of my Taipan. Shot some groups at 100 that were beyond belief. Ran to my chronograph and they were only going 737fps. Turned up my reg and put in a new spring. Tuned it to shoot them at 825fps. Guess what happened? Nothing. Same micro groups at 100yrds. There are quite a few things that go into whether a gun likes a particular slug or not. The last is speed.
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"There are quite a few things that go into whether a gun likes a particular slug or not. The last is speed."

I agree with the first and disagree with the second. Speed is probably not first but it is far from last.
 
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I probably shouldn’t have said last because it just depends on the gun. My TJ barreled P15 would shoot VK slugs fantastic at 750fps. When I bumped them up to 880 they shot like crap. Had to switch to a larger diameter slug of the same weight to get accuracy back. Why? I believe it’s because I got reckless with my air delivery chasing speed and blow by finally bit me. If I was able to hit the back of the VK really hard with air, which my P15 is not capable of, I may have been able to get them to seal up better in the 900’s somewhere. I think that’s where we sometimes get misled by the speed thing. My FX will shoot a slug with the exact same accuracy at 880fps and 935fps with the same slug. All I was saying is there are a lot of factors, don’t get hung up on speed. In some cases, guys may be using speed to mask another issue. Possibly a poor fitting slug in a pellet leade.
 
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I agree in that speed for it's own sake probably doesn't help anyone. But I don't necessarily view it as "getting hung up" on anything. Much as you noted for your FX, one of my favorite rifles showed no loss of accuracy until I approached 1000 fps. Shot count, however, fell from well over 2 mags at factory settings to barely 1 mag at the higher velocity. But the accuracy had not fallen off and shot count isn't a main concern of mine so the advantages (flatter trajectory, less time to reach target) outweighed the drawbacks, at least for me. I did lower the velocity slightly on that gun to make sure I got a full mag of consistent shots but it was unrelated to any loss of accuracy. Seems there is a balance for each shooter's needs and each gun/projectile combination. As to slugs, better spin stabilization, especially at longer ranges, might be seen as well. But again shot count might be lowered and some people might value the shot count over any possible increase in distance stabilization. Different strokes, few absolutes.
 
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Ok so ... my sample packs showed up today and naturally it was a cold and generally crappy day. ( low 20's and a bit breezy ) I'm gonna crank the hammer spring back up nonetheless per previous posts in this thread and run a few over my chrony that I have upstairs in a spare room. I do that, load 3 or 4 into a magazine, cock it and. .... click. "Huh?"

Check the guage - bone dry - empty. No air. {sigh} (lol) Must have sprung a leak from drinking with it last time.

Well .... this presents "opportunities" that I wasn't going to pursue out of laziness BUT since the thing was stone dead I figured I may as well pull it apart and throttle the regulator up some more and put the heavier OEM hammer spring back into it.

Readers digest: regulator @128'ish, hammer spring dialed up just one turn, 905fps with the 12.5's. I did go out into the back yard and quick tested at 25 and 50 yards and ... looks promising. ;-) Weather supposed to be better later in the week ... I'll play / test with it more then.
 
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Previous post was Saturday the 6th and what was going to be a simple test to see how fast they would have gone @the previous tune turned into a rebuild due to an apparently bad / leaky o-ring. Anyway -- it held air overnight so guessing the leak issue is resolved. It seems to be topping out @905fps and while yesterdays shots weren't bad - they weren't spectacular either. As I can't get it to go any faster and not wanting to dissemble it again - degassing and pulling the reg up / upping it to 130 (or more?) - I figured I'll start ~slowing~ it down a little and see what happens as that is something I can do with it right now. I backed it off to 890. It was at 905 yesterday.

{shrug shoulders}

It's a nicer *looking* day out - clear and sunny - but still cold and a bit of a swirling breeze - mid-20's temperature. I know - these ain't great and could certainly be better - I think there is potential here for this little gun and these slugs. I'm going to buy a box of 'em - I've still go 50'ish left of the samples to play with - but based on the very little play I've had with them so far - I think I can get 'em dialed up and shooting pretty consistently and accurately. With any luck I'll find a happy speed @less than 900 and I can be "lazy" (lol) and not have to fiddle with it. Who knows - I may have the throttle it up on the reg and get it above the low 900's . . . we'll see. Supposedly temps going to be in the upper 50's - possibly even hitting 60 later on this week. Fingers crossed.

mrod_50-60-yd_12.5_nsas-2.1615134389.jpg
mrod_50-60-yd_12.5_nsas-1.1615134390.jpg



 
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