Why would anyone want to shoot slugs from a break barrel? The practical accuracy of a spring gun is limited by the platform, not the projectile.
The guys at my range who shoot sub-MOA at 300 yards with their .25 caliber FX's who shoot slugs; all same the same thing.Out to one hundred yards peleets are just as accurate as slugs. Longer than 100 yards is where the slugs shine. Since 100 yards is beyond the realistic range of springers,WHAT DIFFERENCE DOES IT MAKE!?I bet if the EMS does not sell well. Diana will cancel it, so no products next. :'(-Y
About a special slug barrel. I have been doing some tests and I do NOT think the EMS is the best candidate to shoot slugs. Slugs are too inefficient, especially in a long TP break barrel architecture. It has NOTHING to do with the rifling or the inside dimensions of the barrel. It has to do with achieving a reasonable ratio between cocking force and ME.My good friends at Predator sent me a sample of three tins of JSB KO's and I have been having some fun with them in the very limited time I have for my own amusement.Suffice to say here that for Break Barrels / Long TP guns the difference in ME is between -30% (WFTF Walther Century Varmint) and -20% (Hatsan 135) these are the differences in ME between the KO's and the JSB Exact Heavy, at the same weight/mass.In Sliding Compression Chamber / short TP guns, the difference in ME is between -20% (WFTF Ultra-Light Piston Walther LGU ) and 12% (Full power DIANA 52)An intermediate, and very interesting number is a loss of 16% in a short stroked WFTF D54; interesting because it means that there is a way to shoot the KO's at 720 fps to be WFTF FT legal and still get a decent trajectory (at least as related to the one I get out of shooting QYS 9.56's) the reported BC is 0.047, which is definitely interesting when compared to the best QYS's of 0.025.And all this with normal, standard barrels for each brand.Short range (out to 25 yards), the results are between good and very good in those guns that can deal with the 10.3 grs. mass, but longer range is where we split the men from the boys.... so to speak.
Hector,The original concept of the EMS really excited me. However, after cancelling all the flexible features for the home enthusiast, I lost hope!Changeable barrels, droop compensating shims, etc, Yea!!!!Cancel all that and what do you have?-Y
Walther Lothar .177 barrel at .182" groove diameter and .176" bore diameter is going to be more inefficient with a .1775" diameter JSB Knockout slug than it will be with a JSB Exact heavy. This because the oversize diameter skirt of the JSB heavy is meant to completely seal the gas pressure used to propel the projectile. Meanwhile, the JSB slug at .1775" diameter is 0045" undersize compared to the groove diameter. This means that building pressure will be allowed the escape past the slug resulting in a lower peak pressure....and at the same time reducing the total amount of gas available to propel the projectile to some extent. In fact, a JSB Knockout slug at 1775" diameter is just skating across the top 25% of the Lothar Walther lands. The bottom 75% of the lands are not engaged upon loading the slug. Not only does this possibly reduce spin imparted to the projectile (affecting longer range performance, performance in colder weather and performance at higher atmospheric pressure) but the projectile is also likely yawing down the barrel adding further to the inefficiency.
Tests show that the slugs DO get fully engraved (grooves included), and it is not a question of air escaping (which with a 0.001" clearance would create a labyrinth seal anyway).It is the simple friction equation where the friction is proportional to the surface.More surface, more friction.Deep seated slugs (to remove the swaging energy from the operation), end up yielding LESS muzzle energy, so it's not the rifling engraving what is being inefficient.Again: it is the contact surface/area.
I think slug barrel is the most likely. And when I say slug barrel I mean one that is intelligently designed. 1.) Removing the choke from a Lothar Walther Airgun barrel does not constitute the only change needed to make a slug barrel. 2.) We also need a much smaller groove diameter as LW air gun barrels come with groove diameters of either .182" (conventional rifling) or .181" (polygon rifling) for .177 and groove diameter of .221" (conventional rifling and polygon rifling) for .22 (which official spec is groove diameter .217"). While this large groove diameter is good for a large waisted bore riding diabolo pellets it is not good for a .217 slug which is ideally sized .0005" tight to the groove diameter. 3.) In order to reduce friction the land height on both the .177 and .22 barrels should be reduced from .003" to something far more realistic for a soft lead projectile with such a low spin rate. In comparison a .17 HMR only has lands .002" high and yet has to bite into a tough copper jacket bullet and spin it to a rpm almost 6.5x higher (due to 1 in 9" twist and 2650 fps velocity) than a 800 fps slug from a 1 in 18" twist barrel would be traveling at. 4.) Rifling twist should be appropriate for the expected speed of the slug. If the slug even with optimized tuning of the piston powerplant is never expected to reach a high velocity then rifling twist rate can and should be reduced in order to achieve optimum accuracy and secondarily reduce friction. See rifling twist calculator below to see how rifling rate requirement increases the closer the projectile is moving to the speed of sound. Rifling twist requirements also increases with lower temperature and higher pressure as well as distance. http://www.geoffrey-kolbe.com/barrel_twist.htm
Ballistic coefficient is for longer range. The effective range is limited by accuracy. Until this hurdle is overcome, it will be of no use to shoot further.
Hey Yogi, News flash. Everyone already knows that slugs are vastly superior to pellets at short range.
Quote from: UnderPressure on March 29, 2023, 08:22:15 PMHey Yogi, News flash. Everyone already knows that slugs are vastly superior to pellets at short range.Yea and the earth is flat and tomatoes are poisonous............ -Y
YOU can change the powerplantYOU can change the stockYOU can change the front sight for a KorntunnelYOU can set the droop or anti-droop YOU wantYOU can change the weight of the piston/guide assembly.
Quote from: c_m_shooter on March 27, 2023, 10:27:09 AMBallistic coefficient is for longer range. The effective range is limited by accuracy. Until this hurdle is overcome, it will be of no use to shoot further.No true. Ballistic Coefficient is for short range also. In fact, ballistic coefficient is so bad for many pellets that you will see wind drift measured in inches at ranges from 25 yards to 50 yards using just a 90 degree 10 mph crosswind ( which is classified as a "gentle breeze" according to Beaufort scale). That is, of course, outside the killzone of many animals. Even stepping up to a 26 fpe .22 ( JSB 18.1 grain pellets at 800 fps) still results in over 3 inches wind drift at 50 yards using that same 90 degree 10 mph gentle breeze. (see attached chart below from this HAM article---> https://hardairmagazine.com/ham-columns/the-external-ballistics-of-diabolo-pellets/ )Better to use a good slug.....ideally a boat tail slug like the one I attached in the second picture. The boat tail boosts the already impressive BC of a conventional slug at subsonic speeds by up to 50%.