brown dog

That sounds far too quick; this is a 6br going three times faster at shot exit

That's very quick - and being a mS faster than avg vel calculates (0 to 324 m/s over 16") , would imply that it must be reaching mv speed well in advance of 16".... did it give a bespoke pressure/vel time curve?

My calculated barrel times won't be that far out ... start vel (0) and MV are knowns, as is barrel length. A simple approximation would have assumed constant acceleration the whole way, but I've improved on it with an assumption that acceleration for .22lr takes place from 0" to 16" and that , from that point, vel is constant... which is likely to better approximate reality, certainly close enough for govt work. ...on that methodologically, it'll be in the parish. I think 🤔😂 To my mind, the only variance QL could introduce would be nuances that challenge my working assumption to treat acceleration as being constant from 0" to 16".... but I'd have thought such nuance would introduce differences likely to be in microseconds, rather than milliseconds. Best gross-error idiot-check would be to confirm my 16" barrel, barrel time: Start 0m/s end 324m/s, distance 16" 😊😊

I used his macro. You have to adjust barrel length and then node number (to find values matching your barrel time).

Why? 16, 17, 18, 19 all show identical delta; so 17.5 midpoint to my eye ? If you include the 20 too, (which I don’t because it marks the start of rapid change into the next values) then midpoint 18?

If someone has 'real' match ammo velocities and barrel times, it'd be interesting to rerun that; I'd be keen to see if any of the output is sustained by QL approximations ...that said, it's worth noting that I picked the Tenex published midpoint mv ... so it's probably a good representative value for finding an mv-tolerant sweetspot barrel length

Remembering those aren't real, but based on the (valid and necessary) assumptions described in the photo, I think my values will be close enough and 'within tolerance'. Using Long's OBT calculator to identify node times against barrel times: So... taking my valid-assumption-based barrel times as 'close enough', ... we can see the following: 16-19" barrels all have roughly the same low value for muzzle disruption with match ammo ... meaning 17.5" would be a safe 'forgiving of variance' midpoint to pick 20" is nice... but right on the edge of the wheels falling off...so unforgiving of variance and likely to be the most frustrating- sometimes good sometimes seemingly randomly bad 21"-24" have more muzzle disruption and are therefore likely to be consistently less forgiving ... (perhaps that's why longer match barrels are choked, to overcome muzzle disruption at this length?)

Right. I'm bored, so some fag packet maths to try to show what I mean. QL barrel times for .22lr could make this more meaningful.... but, until someone has the QL approximations, here's my best approximation (with a valid assumption on .22 acceleration form described in the first photo): so,

😂

Just noticed, long has some OBT calculators here: http://www.the-long-family.com/optimal barrel time.htm We're working back to front with .22lr... is anyone able to give a barrel time value for .22lr match at 1" intervals 14" to 24"?

😂😊

Allan, the wave is travelling at the speed of sound in steel, not in air. I'll look it up, but gets to the muzzle when the bullets barely left the chamber

Thinking on.... that's sort of what a tight fitting limbsaver is ?

Yup, if the Al tube is holding a damping material, to my mind. Is that yours?

Would batch to batch mv variance be significant enough to change barrel time enough, if your barrel length is at a wave relectivity sweetspot? There'd probably be a bit of 'forgive' either side, much like the charge variance forgiveness postulated for OCW ? I think the clamp could work, but it'd need to be a damper... If 'hard' , I think it'd risk it's own reflectivity, refraction on far side etc? A clamp applying a wrap of shock absorbing material could do it?

😂 my point was, if this doughnut theory is correct... 22 Match ammo is all the same mv (give or take) So... it should be possible to work out which barrel lengths will have shot exit when the doughnut is away from the muzzle. So, made up numbers, 16, 17.5, 18.25, 19, 23.5 could all be optimal lengths ... with other lengths less optimal, and some lengths positively to be avoided. At a doughnut-optimal length, the tuner could then be employed to do whatever voodoo it's doing. ... just spitballing.! I just got rid of a cz455 precision that simply didn't want to shoot... it had every ingredient that should have made it work, but it just didn't want to..it was 'unforgiving' and would just randomly throw shots out of a group that otherwise felt good, and sounds much like Allen's finnfire .... what if both barrels were at a lengths that mistimed the harmonics of the donut? In contrast, I replaced it with a cz452 cut to 17".... and it wants to put every bullet in the same hole. ....this is not to be confused with 'optimal mv length' where 14" seems to be the value that's routinely trotted out, I'm focusing on the harmonics of the doughnut... and timing shot exit to take place when the doughnut is away from the muzzle as it reflects back and forth along the barrel ...if there's any value in the doughnut theory🤔😂😂

My nuance on that, was that I read it as saying 'don't have shot exit when the doughnut is at the muzzle' ... which, as you say reflects up and down the barrel at the speed of sound in steel. And from that, since we can't tweak barrel time through charge or seating manipulation in a rimfire, means that some barrel lengths will be optimal for a match round, and some will be not... each step length aligning with when the doughnut is away from the muzzle. I didn't pick up on a gas/pressure change.. I'll reread, but that strikes me as so infinitesimally small (volume change vs overall volume) that I would struggle to buy it as an idea

I agree, there's a slight conflation of waves, I'm not sure I follow how transverse nodes affect longitudinal waves, but... I quite 'like' the thinking g about longitudinal waves effect on the muzzle condition, and I'm quite struck by the observation that the bullet has gone before transverse can 'really get going'.... perhaps less so in a rimfire so... given that we can't adjust barrel time via charge weight on a rimfire, how else might we 'tune' the timing... with a chosen round, change barrel length to suit the round's barrel time... for tgt rounds all just Subsonic, that would suggest there are optimal barrel lengths to hit each reflected wave sweet spot, and by extension, there will be barrel lengths that won't shoot as well...by his theory, that could be calculatable and would apply irrespective of barrel weight etc... so (made up numbers) for match ammo, 17", 18.5", and 20" could all be optimal, with any value in between less optimal. So....on a fixed sub-optimal barrel length are the dampers achieving their main effect via transverse or longitudinal damping? Would a better effect be achieved by matching barrel length to a particular round? Or put another way, if Long's theory holds water, for a rimfire with match ammo... barrel length does affect accuracy. (And I'm not sure where that all leaves tuning weights which clearly, empirically also have an effect! 😂🤔)

Just read this.... any thoughts? "I tried them before and turned to something similar. Instead of using the limbsaver deresonator, I got better results with the following procedure:Hang the rifle from the buttplate. In a quiet environment, tap the barrel with your index finger along its length, and listen to the tappping noise with your ear close to the barrel, although not touching it.What you are looking for is for a spot that makes a dull noise about 6 inches from the muzzle.Mark the spot with a texter.Next, keep tapping towards the chamber end and look for the spot where the noise is the loudest. Mark with a texter.Keep on tapping back to the chamber end looking for another dull noise point. Mark with a texter.Then I use a product called megasorber which are adhesive sheets of a very efficient polymer that converts vibration into heat. On the other side of the adhesive sheet, you have a layer of aluminium foil which acts as an heat sink to dissipate said heat.http://www.megasorber.com/soundproofing-products/vibration-dampeners/constrained-layer-damping-sheet.htmlI cut a 4 inch long section of that sheet and stick it with its mid section on the spot on the barrel that you marked as the one with the loudest vibration in a way as to surround completely the circumference of the barrel.This will really subside the travelling wave mentioned on http://www.the-long-family.com/OBT_paper.htm.I felt a good improvement in accuracy on about 20 out of20 of my target rifles that I did this procedure to.The point which makes the loudest tapping noise is the one where the amplitude of that travelling wave is the highest allowing the damping to work at its best.That frequency that you are trying to dampen is shaped like a donut that travels down the barrel at about 20 000 fps, disturbing the bullet according to the obt article 8 times on a 24 inch barrel. If you manage to dampen 40% of that vibration at each pass, the projectile will only meet that donut once and at 20% of the amplitude.Really worked for me."

🤔 I'd have thought so.

😂😂

Yep, my point was at unit / bn level; ie no scaley/engr/log etc regt ever deployed as a formed NI inf bn; but was normal-jogging for RA / RAC. We sometimes backfilled with non-capbadge or attached capbadges, eg, in the COP pic, a Cfn and a couple of Cpls (probably from regtl wksp) are part of the pl. Bruin line made me laugh!😂😊

RA and RAC deployed in NI inf role all the time throughout the 'troubles', and when doing so, delivered all the same inf capabilities/roles; so if a COP was part of that particular deployment's ORBAT, a COP would be formed, just as people would be roled/trained for low risk search etc. RA and RAC were pretty unique for deploying in inf role, as everyone else deployed 'in role' .. ie engrs went in engr role, loggies in log role, scaleys in scaley role etc

Your google-fu is weak, grasshopper: https://www.snipershide.com/shooting/threads/new-caldwell-radar-chronograph-velociradar-labradar-competitor.7050337/