The 12.7 is likely Megapascals.In the U.S. we use PSI, Europeans may use pascal( Pa), kilopascals (kPa) or Megapascal (MPa) or they may use Bar.Bar is one unit of barometric pressure, 14.5 psi iirc.1 megapascal =145.038 pounds per square inch12.7 Megapascal = 1858 psi = 127 bar.I don't know about your regulator, but my regulator you turn it counterclockwise to increase pressure.Hunter
From only the DAR ll perspective, the twist is 1:18 or so and my 40g slugs keyhole and at 50m, you can see them spiraling away.
Rhett,Do you have a 26" .177 barrel? Finding one might be a little tricky. It seems Lothar Walther have some at 24"; so 26" should not be a stretch.https://www.lothar-walther.de/barrel-blank/airgun/standard-profile/74/airgun-blank-4-5mm-air-od-12-mm-l-605-mm?c=273https://www.lothar-walther.de/barrel-blank/airgun/standard-profile/77/airgun-blank-4-5mm-air-od-16-mm-l-605-mm?c=273The next question would be; can you get a barrel with a fast enough twist for slugs?You could contact LW USA and ask: https://www.lothar-walther.com/contact-formElse, someone is likely to pop up and tell you what they know from taking a similar journey. I think most small bore slug PCPs have been .172 caliber. So, centerfire barrel in that caliber can be had in faster twist rates, at 26". I know that NSA are making slugs in .177, so someone is shooting them with something. I think that the stock DAR 17" .177 barrel is suitable for 30 FPE. Mine was shooting 25 FPE out of the box, with pellets.Certainly, the 12.5 grain NSA slug should easily reach 950 FPS out of the stock DAR, with the hammer spring preload boosted a bit. If you need to "go to 11" with heavier slugs, you could also increase the reg pressure. The question is, is the stock barrel twist fast enough...EDIT: http://alfa-precision.net/airgun have 1:14.57 twist in 25.6" length:Barrel blank cal. .177 (4,5mm)4.5/16/370/650Cal. .177 (4,5mm) / OD 16mm / Twist 370mm / Length 650mm / F = 4.42 / Z = 4.59 / N = 12 / standard
Quote from: Firewalker on February 19, 2021, 12:29:15 PMFrom only the DAR ll perspective, the twist is 1:18 or so and my 40g slugs keyhole and at 50m, you can see them spiraling away. What caliber? Rhett is asking about a .177.Twist is directly connected to caliber. So talk about twist must include caliber. Less pedantically, also projectile length, more than weight. Technically; shape and position of CG. And tail shape...
By turning it in you've made the valve spring stiffer. The only thing I would double check is that you are not putting the valve spring into coil bind. Mine was set pretty close to that from the factory. 5 or 5.5 mm deep if i recall. Just something to be aware of.
A healthy amount of valve spring tension does help mitigate excessive dwell, and does so without much change in the amount of hammer strike necessary to knock it open. It also improves the valve's self-regulation characteristics, meaning the velocity is less sensitive to slight pressure variations...which is useful because no regulator is perfect.
For kicks and giggles, here is the napkin math for a barrel cal of .177.
I dont currently have any particular barrel in mind.I was thinking about the possibility of a lothar walther blank as I have seen others have good results with these in the past..24" would surely offer some benefits in efficiency and increased ability in the power department vs the stock 17" I would prefer 26" just to get the max length while still keeping the aol within reasonable measures. From my measurements with a 26" unshrouded barrelOal should be around 42" or similar to an mrod.As far as twist rates go I have no knowledge to speak of on the subject and was just gonna see what recommendations I could get from the more knowledgeable members here like yourself.I have seen a couple others talk about the alfa precision barrels you shared a link to and they do seem to be a viable option I just wonder if anybody has dealt with them before and how their results and experience ordering/ shipping was.
For kicks and giggles, here is the napkin math for a barrel cal of .177.Using the data provided by NSA, 12.5g, .178" dia, .234" long, BC .070 and by Berger's calculator, shot at 900fps, the minimum twist for ".177" is 1:16. Stability factor is estimated at 1.52 where 1.50 is the minimum factor for stable flight with this data. Using a tighter twist, such as a 1:14 twist gives a fully stable rating of 1.98.Bergers online tool can be used for any projectile as long as you have the data above like NSA provides. Just punch in the data and hit calculate.
Rhett,I am sure that a 24" or longer barrel would make it easier to reach high FPE than the stock 17" long barrel. That said, FPE gains are not linear. If you doubled the barrel length, you are likely to be disappointed - except about how quiet is. Eventually, the high pressure air in the barrel behind the projectile weighs more than the projectile; and then efficiency suffers... Bob Sterne has posted about the optimal barrel length for PCPs. They are expressed as so many calibers: 150 caliber length in .177 would be 26.55" long, for example.Also, unless you increase the barrel diameter, the increased flexibility of a longer barrel may make it harder to shoot small groups, and more tune or projectile fussy. That said, the DAR barrels are nice and stiff, and could probably be longer at the stock diameter. If you plan to use a shroud-less barrel and don't mind the weight, LW also make 16 mm diameter airgun barrels (as do Alpha precision).I found a bunch of posts about .177 slug barrels, with twist as a topic of conversation - see google links below. You might start with this post about a powerhouse .177 slug air rifle:https://www.gatewaytoairguns.org/GTA/index.php?topic=145128.0Alpha Precision barrel: https://www.gatewaytoairguns.org/GTA/index.php?topic=183408.0Slugs from a Marauder: www.gatewaytoairguns.org/GTA/index.php?topic=148177.0Slugs from pellet barrels: https://www.gatewaytoairguns.org/GTA/index.php?topic=148279.0Slug barrel. Has poly VS regular rifling discussion deeper in:https://www.gatewaytoairguns.org/GTA/index.php?topic=155749.0Here is a twist calculator often used on GTA:http://www.geoffrey-kolbe.com/barrel_twist.htmhttps://www.google.com/search?q=site:gatewaytoairguns.org+.177+slug+barrel+twist&rlz=1C1NDCM_enUS793US793&ei=CmwwYPSGJ8uz5gK5wrUo&start=10&sa=N&ved=2ahUKEwj0s9XkrffuAhXLmVkKHTlhDQUQ8tMDegQIBBA1&biw=1117&bih=533https://www.google.com/search?q=site:gatewaytoairguns.org+.177+slug+barrel&rlz=1C1NDCM_enUS793US793&ei=lWkwYL7YD5DG5gLQ45igDg&start=30&sa=N&ved=2ahUKEwj-9sa4q_fuAhUQo1kKHdAxBuQ4FBDy0wN6BAgEEDk&biw=1117&bih=533Quote from: RVaughn on February 19, 2021, 12:54:32 PMI dont currently have any particular barrel in mind.I was thinking about the possibility of a lothar walther blank as I have seen others have good results with these in the past..24" would surely offer some benefits in efficiency and increased ability in the power department vs the stock 17" I would prefer 26" just to get the max length while still keeping the aol within reasonable measures. From my measurements with a 26" unshrouded barrelOal should be around 42" or similar to an mrod.As far as twist rates go I have no knowledge to speak of on the subject and was just gonna see what recommendations I could get from the more knowledgeable members here like yourself.I have seen a couple others talk about the alfa precision barrels you shared a link to and they do seem to be a viable option I just wonder if anybody has dealt with them before and how their results and experience ordering/ shipping was.
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