Tuning High Reg. Pressure vs Low Reg Pressure

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Drumsnguns

Member
Jun 14, 2016
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North Carolina, United States
Recently I was starting to notice that my groups were opening up at what was once a very nice tune. I did the usual, barrel clean, check hammer stop, check HSTA, scope mount tightness, etc.

So I thought I'd re-tune. I was watching Dubber's video on tuning for slugs at high power.

Long story short, I went from the original tune at 120 Bar where I was originally getting very tight, sub-MOA groups out to 100 yd with NSA 38.9 slugs at 880 on PW-4... to a tune involving 135 Bar.

At 135 Bar started shooting groups at Max and went down to PW-1. I got my best sub-MOA groups at PW-2

Low and behold at PW-2 the slugs were flying at 884 fps...essentially the same speed at 120 Bar on PW-4 at 880 Bar.

Dubber mentioned that, in his opinion, it's better to shoot slugs with a higher reg pressure than a lower one.

I always thought it better to shoot at lower reg pressure for obvious reasons like air conservation, less stress on the gun, etc. He and the other SA guys shoot .22 and I shoot .25 so maybe apples and oranges?



Right now back at the original 120 Bar tune, I'm having trouble with that one consistent flier that lands from 1/2" to an inch or more from a very tight 4 shot group. It could be me but it is very consistent...almost every group. It's driving me nuts.

Target.1639940413.jpg
50 yards/ no wind/ 38.9 gr NSA@ 880fps

Curious if anyone has any opinion on all of this.

Thanks,

KP/ in NC
 
Yeah, for pleasant shooting (smooth shot cycle) and higher shot count before it falls off the reg, lower reg pressures are great. But they normally have to go up if going for power/velocity, and then you hope you have enough adjustability in the hammer spring pre-load adjustment to make sure the hammer can bang that valve open against the higher reg pressure. Or you then need to proceed with either a heavier weight hammer or heavier hammer spring.

You don't say what gun you are shooting (or I missed it), but if you are watching Dubber's videos I would guess an FX - Which model? Are you using a moderator, and if so have you removed it to see if you still get the flyer? Have you verified the barrel is tight in the block? I recently had flyer issues with a new-to-me DL Compact, and when I took off the shroud I noted that I could slightly wiggle the barrel. Tightened the barrel lock nut down and problem gone.

Just kind of thinking out loud...
 
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Hey guys 

Yeah, shooting an Impact MKII with the 700 mm Superior Heavy liner. Also have a Slug A liner that I might start experimenting with.

I’m also using the CF liner sleeve as well. 

Barrel tightness and other spots have been checked and everything seems good 

Am using the FX OEM moderator. I’ll check with and without next time the weather cooperates. 

My post was certainly wordy and might have gotten confusing so the message was:

I can get the same speed at low reg pressure and high reg pressure. Is there an advantage at shooting the same speed at higher pressure? 
I’m not going for high speed and power.

The slug seems to really like 880-885 fps which I would think is not that fast.

Thanks

I’m not sure what u mean by tensioning the barrel with the shroud. Could you explain that one please? Thanks. 



 
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Quite a few months ago I was contributing to a FX Impact topic. I can’t remember what the topic was actually about because there are so many of them but I stated something that I discovered that falls in line with this topic. When my gun was bone stock, I found bliss with a slug at 935fps at 120b. I did some mods and decided I wanted to find that magic tune at a higher reg setting for increased speed. After a ton of slugs I found bliss again. Walked downstairs to the chronograph and guess what? 935fps again. Again the gun went under the knife with a larger TP and a bottle reg. This time I based my tune with a reg setting in the 135b range hoping for finding magic in the 950-960fps range. After another couple pounds of slugs I found the perfect balance so I headed downstairs to the chronograph. Yep, 935fps again. As I modded the gun and increased my reg setting, the gun always started out faster than it previously did before the mods. Running the gun wide open at a particular reg setting was getting insanely fast. Backing the hammer spring down to the knee of the reg setting also kept producing higher velocities as I modded and increased the reg. But in the final stage of shutting down the valve to get the ultimate accuracy, I always wound up shutting the gun down to 935fps with that slug. Ironically I’m a million miles away from when the gun was stock but still shooting the same speed for the ultimate accuracy.
 
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Hey guys 

Yeah, shooting an Impact MKII with the 700 mm Superior Heavy liner. Also have a Slug A liner that I might start experimenting with.

I’m also using the CF liner sleeve as well. 

Barrel tightness and other spots have been checked and everything seems good 

Am using the FX OEM moderator. I’ll check with and without next time the weather cooperates. 

My post was certainly wordy and might have gotten confusing so the message was:

I can get the same speed at low reg pressure and high reg pressure. Is there an advantage at shooting the same speed at higher pressure? 
I’m not going for high speed and power.

The slug seems to really like 880-885 fps which I would think is not that fast.

Thanks

I’m not sure what u mean by tensioning the barrel with the shroud. Could you explain that one please? Thanks. 


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Tensioning the barrel with a spacer just a MM longer than the distance from the shroud to the block. When you tighten the shroud it puts tension on the barrel and really snugs things up barrel and shroud wise. Somebody was selling these in carbon fiber, better than my Delrin, but I don't remember who.




 
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Biohazard man hit the nail on the head for tensioning the barrel. A quick way to see if it helps is to get a piece of 1” pvc over the barrel and cut a bit longer than the space you have. Make sure cuts are square! I also think Matt’s comment refers to having almost no pressure leaving the barrel to disturb the slug once it’s out which to me would also mean not having a perfect balance or pressure and spring. More air in a shorter burst so you have the slug moving the same speed as the air behind it as it leaves. Exact pressure is kind of irrelevant 
 
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Vetmx 

ok now that is interesting! So where are you now? Higher reg pressure for that 935 magic sweet spot?

curious as to what cal. and slug.
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I stayed with the 128b reg setting only because if I decide to someday shoot a heavier slug, when I open everything back up to start the tune, I will have gas in the tank to push them. If lhandy’s shot count question was directed at me, I can’t answer that question. When it comes to slugs, not pellets, I have zero concern for shot count. If you do, you’re crippling yourself. But if I had to guess, it stayed real close. I just looked at my notes and I was at one point at 136b. My take is my gun, how I have my barrel system tensioned and choice of slug has one speed where it produces it’s best accuracy. Don’t get me wrong, if I didn’t overly scrutinize the gun, I could have been fooled into thinking the gun was really accurate at 945 and 954fps. Looking at my notes I see that I left the gun at these speeds for sometimes a week. But they eventually fell apart. The 935 tune does not fall apart. Lastly, all my settings and slug are worthless to you. It just doesn’t work that way with slugs, questionable gauges, and these 6 or 7 piece barrel systems. All of us have to write our own book about our own gun. FX may be marketing the M3 as a shortcut special, but it isn’t when it comes to slugs.
 
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I don't know if either a lower or higher reg pressure is "better", think it depends on your goal. I have observed that usually somewhere around 96-97% of the maximum velocity at a given reg setting yields the highest consistent velocity shot count. Obviously, you can back off on the reg and get a higher overall shot count, but the lowest ES count might be fewer. Of course, what little I think I know was discovered by blundering around, so don't count on it. 
 
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This picture is the most frustrating part of trying to shoot bullets out of a pellet gun. This picture is also better than what most guys see when they decide to jump on the bandwagon. The best slug advice I can give is don’t trust anything you see a guy post online. Video or words. When it comes to slugs, the guy who appears to be walking on water today will more than likely be swimming for his life next week when his gun won’t do what it did 5 days ago. Shooting slugs is a hobby within a hobby. Chasing them almost never ends. My goal is to have a grab and go slug gun. The Impact has all the tools to get you there but……all those tools are the fly in the ointment for a rock solid consistent gun. The guns ultra adjustability is what hurts it. One thing is for sure. Every Impact owner should have bloodwork done after 6 months to check the level of lead in his blood.
E1451EE8-9305-4924-82E9-65951D6FFD72.1639954961.jpeg

 
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I think it's easy to get too focused on a "balanced" tune, while maybe overlooking the most accurate velocity. Maybe it makes sense to play around with the HST until you find the best velocity, forgetting about efficiency for the moment. Once a speed is identified, then tune to it. None of my rifles have externally adjustable regs (I'm not an FX guy), so tinkering with the reg is labor intensive. Of course, if you're a Daystate fan (and I have a couple), then it's all kind of moot, as they seem phobic about owner tuning.

But here's something to consider. Say you're getting 900 fps at your current tune, and you find that 870 is your best speed. If your current tune gives enough good shots at that velocity, then maybe not worry about maximizing it, enough is enough.
 
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This picture is the most frustrating part of trying to shoot bullets out of a pellet gun. This picture is also better than what most guys see when they decide to jump on the bandwagon. The best slug advice I can give is don’t trust anything you see a guy post online. Video or words. When it comes to slugs, the guy who appears to be walking on water today will more than likely be swimming for his life next week when his gun won’t do what it did 5 days ago. Shooting slugs is a hobby within a hobby. Chasing them almost never ends. My goal is to have a grab and go slug gun. The Impact has all the tools to get you there but……all those tools are the fly in the ointment for a rock solid consistent gun. The guns ultra adjustability is what hurts it. One thing is for sure. Every Impact owner should have bloodwork done after 6 months to check the level of lead in his blood.<img src="
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" />//www.w3.org/2000/svg%22%20viewBox=%220%200%20210%20140%22%3E%3C/svg%3E
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I’m not sure about the larger calibers 22&177 are the 1’s I’ve shot the most slugs out of. My 22 maverick sniper just loves 27.5 gr nsa and shoots well every time I pick it up. It was also the easiest to tune of 2 mavericks and an m3. My 177 maverick was a royal pain in the butt to tune like you said shoots great today like crap tomorrow. Then I put a lw barrel in it and low and behold easy to tune and right on the money every time I pick it up
 
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Yep, a barrel system consisting of a bunch of parts is fun for some and great for projectile sales. But by simplifying one of the complexities of a FX you eliminated a weak area. I don’t blame FX for staying with what they offer. If they were to switch to putting real barrels on their guns, a lot of guys would then complain about their gun being a one trick pony. 
 
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Yep, a barrel system consisting of a bunch of parts is fun for some and great for projectile sales. But by simplifying one of the complexities of a FX you eliminated a weak area. I don’t blame FX for staying with what they offer. If they were to switch to putting real barrels on their guns, a lot of guys would then complain about their gun being a one trick pony.
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A lot of serious shooters see the weakness in the liner/sleeve system, but it has proven to be a marketing dream. And it's great for folks who like to tinker. I agree, I don't see FX making a fundamental change. 
 
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