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Popsbengo

Bullet Jump

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I came on this whilst browsing and was intrigued  https://precisionrifleblog.com/2020/04/15/18-shot-bullet-jump-challenge/

I've run some comparison tests at 100yds and found some surprising results (to me)

.308 155 Lapua Scenar 24" 1:11" barrel.  I was seating 10' jump and reasonably happy with my grouping considering my rifle has fired just under 3000 rounds and groups have opened up since new

I tried some 10' increments from not quite touching, outwards.  (My lands have been found using the drop bolt method and the Honady gauge - on repeated tests - the Hornady being 2' longer).

Barrel was cleaned and two fouling shots taken to set the chrono' up.  Cooling time between strings.

All rounds in Lapua once fired, fully prepped and batched, 43.5gn N140 powder weighed to gnats gnacker,  BR2 primers.  3' Neck tension and felt very similar in an abour-press die.

5 shot group at 10' jump = .55" (this was my "standard setting" to date)

didn't shoot 20' jump

5 shot group at 40' jump = .50

5 shot group at 60' jump = .36" - optimum

5 shot group at 80' jump = .38"

5 shot group at 100' jump = .76" (but I pulled one a tiny bit so I reckon~ .70 ) - this is a COAL of 2.810" (allowing for the meplat) which is .308 standard.

The best result was 60' jump with not much in it out to 80' jump.  100' was opening up as was 40'   Obviously the Mv increased a small amount due to seating depths.  If I play with charge weight at the seating depth I may get a touch better.

I shall repeat with 185gr Juggernauts and see where that goes - I'm hopeful

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I too recently read this blog that came from testing alot of combinations which the consistancy was better on way more jump..!!

This is all well and good if you get a long freebore throated or otherwise the bullet is sat real deep taking up powder room..

It's worth a trial even if you have to download it so much to avoid high pressures.

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If you seat to manufacturers spec length it's not taking up any more powder space than it should. Only in very special circumstances to I even care what the distance to the lands is, having loaded all my ammo to the spec by the manufacturer.  I have a four 300 AAC Blackouts -two bolts and two autoloaders. In all of them,110 grain Nosler/Noviesky ballistic tips will shoot well under MOA in a chamber throated for 240 grain bullets. Don't know what the 'jump' is but it must be considerable. 

Just one example.~Andrew

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I was thinking of my 7mm saum that's throated for 184gr hybrids set around 10 thousanths jump.

Another 50 or 60 jump will put the bullet back in the donut area on the case I expect...

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Seating depth tuning is a vital part of any load development.

However, some bullet shapes respond better to it than others and there isn't really a book of rules for which do and which dont so you need to test to know. Testing at 100yds is often far enough unless your struggling to split things in which case 200 or 300yds is certainly plenty.

Ive seen some bullets that have been far more seating depth tolerant than others so they seem to shoot equally as well close to the lands as they do various increments away from the lands, if they dont suit the barrel they also shoot equally as bad and nothing you do in moving them seems to improve the accuracy.

Then there are bullets that clearly show seating depth nodes, the accuracy comes in when the seating depth is optimised then it drifts out again either side of optimal, Ive seen 5 thou matter and 10 thou takes the node into its inaccurate place. If you then continue past the point where the groups have opened up they will usually become smaller again as a different optimal node is found, this can repeat every 40-60 thou or so. Of course its always best to find the node nearest the lands just to increase the case capacity or keep the pressure down a bit assuming this longer length will fit in and feed well from the magazine if used.

Every load I ever develop will have both the powder charge then the seating depth optimised in that order.

 

 

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Al,

Is there a trend in which bullets are more sensitive? To me they would be the ones to avoid 🤔

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A good rule of thumb Terry, is Ogive shape. Tangent will happily jump from anywhere, Secant is always jump sensitive. Its a broad rule, but generally correct.

The reason I shoot sierra's in anything, where possible.

Nothing worse than a bullet that is 5 thou sensitive, its as much use as tits on a boar.

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1 hour ago, baldie said:

A good rule of thumb Terry, is Ogive shape. Tangent will happily jump from anywhere, Secant is always jump sensitive. Its a broad rule, but generally correct.

I found Hornady ELD-M 178gr  absolutely impossible to get a good enough load development in my .308.   However, the .338 285gr  shoots very well indeed out to 2000yd - definite legs on Lapua 300gr

I would be interested in an explanation as to why secant shapes appear more sensitive than tangent

 

 

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This is where the hybrid was a compromise between the 2 bullet types apparently but I'm not sure if its 5 thousanths sensitive..

I've not measured throat wear on my 1 in 8.25 saum barrel since I developed the load or checked if the accuracy has deteriorated.. 

It served me well at the Brits and a league match after so I've no need to want to check it...

My option for a sierra f open bullet is the 183 but it's the vld type so it's in the sensitive type unlike the 180gr smks, I've not tried either.

The 180gr smks could do well with the long jump explained in the blog.

I'm not sure the same as you pops why..

Laurie may explain things if he sees this thread.

Somewhere along the line I got mixed up on comparator measurement for my 6.5x47 with 139gr scenars.. it's done 2000 shots and throat has grown..

Once I found the I'd miss measured I gradually moved the bullet out and out and found it still likes the same measurement as it did 1900 shots ago..

I think there is some theory on the time the bullet spends in the barrel and the bullet leaving the barrel at the optimum for the harmonics..

It may not be to do with the bullet jump as we think of it as but to do with its position shortening or lengthening the time the bullet spends in the barrel 🤔.

I've not got enough time to find all these things out 🤣😂

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5 hours ago, terryh said:

Al,

Is there a trend in which bullets are more sensitive? To me they would be the ones to avoid 🤔

Its all about accuracy Terry and what level you want.

Ive said this before on other topics to do with accuracy but the amount of regurgitated dogma there is surrounding rifle accuracy is amazing and so thorough testing is needed to be able to draw your own conclusions that you can rely on.

Ive seen tangent ogive bullets that wouldn't shoot very well in a barrel, yes they would be consistent and not very jump sensitive but maybe the best they would produce was average five shot groups sizes of say 0.5" and that doesnt interest me. Clearly a 0.5" 100yd average is good enough though for certain applications so you have to set your own standards.

Then Ive seen secant ogive bullets that were as fussy as hell but when you found the sweet spot they were far better performers and 0.250" aggs were very common. Moving in 0.005" increments shows accuracy nodes and you see the group size shrink until its reaches optimum and then grow and shrink again and this continues like a wave anywhere from in the lands to as far as 0.160" away. Ive never seen a need to be 0.160" away of course as a general rule but sometimes small bullets on long free bores make that happen without sacrificing case capacity.

I would also say sometimes Ive seen tangent ogive bullets producing the best accuracy but they have still needed very fine seating depth tuning to find this, move 10 thou in one go and you've jumped past it. I tend to work in 5 thou increments and also in zones. For example touching to 40 thou out is zone one, then 40--80 thou out and then 80-120  thou out. Almost always I will find the accuracy I want in the first zone somewhere if the chamber has been throated to suit the bullet.

Ultimately I think you choose a bullet to suit your application regardless of ogive type and start from there, test it thoroughly and see if it gives you what you want, if it doesnt then move on to another providing the powder is showing suitable stability.

Something I dont buy into is the need to chase the lands during a barrels lifespan providing you never change the barrels length, I have never seen enough evidence with my own testing to suggest it matters and so this negates the issue of small incremental seating depth changes being a ball ache. As well as my own testing I know a very successful long range benchrest shooter who consistently won throughout the whole life of his barrel and he never changed the seating depth throughout the lifetime of the barrel. It started at 20 thou off and when I replaced it the bullets were jumping about 140 thou.  

Something I do think is very underestimated is the barrels preference for a a particular bullet based on bearing surface length, shape and diameter. Ive built a lot of 6.5 x 47s and I remember one month I had four guns coming to completion at the rate of about one per week and they all then went into load development about a week ahead of the next. All barrels were Bartlein, all were 8 twist, all were ordered at the same time and came as part of the same batch. All were chambered the same with the same reamer and all had the same freebore. The first three guns shot 140gr Berger Hybrids into 0.250" aggs (at least 4x5shot groups) one even a bit smaller at .0.220", optimum powder charges and seating depths were all very close to one and other in the 40.0 to 40.3 gr range of H4350 and the seating depths were within 10 thou from longest to shortest when optimised. All three guns were using the same batch of powder, primers and bullets yet the forth gun with the same barrel and broadly the same stock configuration wouldn't shoot these Bergers for toffee. A switch to Hornady ELDM saw that gun instantly come alive and it was up with the other slightly more accurate Berger load as the best. All testing was consistent and identical as much as we could achieve and it left me scratching my head for a while. Ive seen similar things enough times since with different cases and calibers to know that there is something going on at a very minute dimensional level with bullet to barrel fit that only thorough testing will show.

Berger say that the 'Hybrid' ogive design gives the best of both worlds in terms of being unfussy regarding seating depth and good BC performance but it hasn't been my own findings. In 105s, 140s and 180gr I find seating depth changes of 5 thou can show significant changes to group size and with two 5 thou change so 10 thou in total the group sizes can half. They are a good bullet but by no means any easier to tune than any other bullet I have tried. I like Sierra bullets as they are very consistently made when you measure them closely and then I have also use a few makes of American competition bullets. No single bullet brand stands out, its much more about finding what the barrel likes.

This of course bring me back to the first point I made which is it all depends on the level of accuracy you are looking for.

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Very interesting Al 👍

I must agree regarding received wisdom or  "regurgitated dogma" as you say:  I'll listen to anyone (almost) but I always reserve the option to make my own findings

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9 hours ago, Popsbengo said:

I found Hornady ELD-M 178gr  absolutely impossible to get a good enough load development in my .308.   However, the .338 285gr  shoots very well indeed out to 2000yd - definite legs on Lapua 300gr

I would be interested in an explanation as to why secant shapes appear more sensitive than tangent

 

 

i would guess at the different bearing lengths, or possible one type has a similar angle to the rifling leade.

Secants, while sometimes have the accuracy edge, are known to travel transonic usually worse thanTangent. however the tangent gives up BC to the secant. Both important things to consider when its seriously long range. My favourite bullet in .308 is the scenar 167. Its a tangent bullet, doesn't have a wonderful bc, and is basically a glittery brick. It does go transonic/subsonic very well though. I've used it from a 20" AI at 1000 yards, and scored very well with it. Barrel length not suitable for such a range, but it works with that particular bullet.

Ideally though, you would have a cartridge that came nowhere near transonic, at the range you are shooting at.

I do think that seating depth, is married to barrel time/harmonics.

If you see two separate sweet spots, say 0.100" apart, that could well be the difference in the muzzle end, doing one full revolution, harmonically.

I dont know, I dont have the equipment, or the knowledge to measure such a thing. A barrel tuner would probably show such a thing up though.

On the .338 subject, I've almost always run Scenar 250's and 300's, until I happened upon a 500 box of the 250 SMK's. Hell, the gun went from a half inch gun, to a quarter inch gun, simply down to the shape. no mean feat in a 338, where recoil and shooter fatigue, usually prevent tiny groups.

For all my shooting, i search for a half inch 100 yards load, that isn't fussy on seating depth, doesn't walk when it get hot, and will hold it further out.

Shooting tactical comps, CSR, gonging etc, will rapidly see a tiny accuracy advantage at 100 blown into the weeds , when you are up and down, off obstacles, running etc. The minuscule group chasing is time better spent, actually shooting.

Again, only applies to me personally, and the disciplines I shoot.

 

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Some very interesting and useful information there chaps, especially as I’m about to start down this road with my AI in .308 & 6.5x47. Thank you. 👏

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Al,

So in reading you explanations & comments it is, as per a lot of thing, what your rifle (or more specifically you barrel( likes?

Also, and correct me if I’ve read this wrong, small increments could make a difference but in some cases (no pun) not.

Might go and revisit the 6 Dasher when the world wakes up again

T

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Another interesting one from a few weeks ago, was a customers 7 Rsaum i built on a Bat/bartlien.

The guy is a meticulous loader, and managed a super load at 100-800 yards. 

It wouldn't hold it together at 1000 and 1200 though.

Then he showed me his bullets.

Bergers, and the biggest pile of sh1t, i've seen in a long time. When the bullet meplat is at 45 degrees, and jagged, You really should know you are pissing in the wind.

Replaced with a Hornady tipped bullet, and he's now hammering the 1200 yards at Stickledown.

Just because the "top" shooters endorse them, doesn't mean they are any good.

Test for yourself !

 

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15 hours ago, baldie said:

 

Secants, while sometimes have the accuracy edge, are known to travel transonic usually worse thanTangent. however the tangent gives up BC to the secant. Both important things to consider when its seriously long range. My favourite bullet in .308 is the scenar 167. Its a tangent bullet, doesn't have a wonderful bc, and is basically a glittery brick. It does go transonic/subsonic very well though. I've used it from a 20" AI at 1000 yards, and scored very well with it. Barrel length not suitable for such a range, but it works with that particular bullet.

 

I remember a post you wrote a few years ago about the Scenar 167 and Viht N150 combination, which is the Viht accuracy load so I copied it in my AW.

The jump is huge but it works “out of the box”. 

That’s all I use in it now. Up to 600 yards I’ve not found anything to better it.

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4 hours ago, terryh said:

Al,

So in reading you explanations & comments it is, as per a lot of thing, what your rifle (or more specifically you barrel( likes?

 

Also, and correct me if I’ve read this wrong, small increments could make a difference but in some cases (no pun) not.

Two answers here Terry.

1. For sure there will be times when the very best results show you a barrel likes a particular bullet but I think with most good quality rifle barrels its more about recognising the times when it doesnt like a particular bullet, this saves lots of wasted time, money and heartache. These times of spotting the bad one will be rarer than the times it likes various bullets as barrels are generally good most of the time.

When I got into rifle building I used to read comments here and elsewhere about "I hope this new barrel is a shooter" or "I finally found a good load but I thought the barrel wasnt going to be a shooter"

This made me think that either the quality of rifle barrels and/or the quality of the machining that went into them was a bit of a lottery and that people expected the possibility that a £700-£1000 rebarrel job might not shoot. That really worried me as I wouldn't know what to say to someone if I had charged him for a duffer.

Now some 4yrs and 200+ re-barrels or gun builds later Ive only seen one barrel through my hands which I considered bad. Even then it wasnt dreadful but it was a real heartbreaker in the sense it would show great promise but would never maintain good enough consistency over 5 shot groups on a long range benchrest rifle. It was a made 'match grade' barrel from a company I hadn't previously used that I had bought to try out, after 400 rounds it still coppered terribly and just wouldn't hold together at 'match level' so was returned for a refund and Ive never had the confidence to revisit that company again. This barrel was tried out on my friends LRBR gun and we gave it everything, after 400 rounds it had been thoroughly tested. Other than that I have used barrels from Bartlein, Krieger, Brux, Sassen, Bergara, Walther and PacNor and without exception they have all shot well on rifles I have had control over the load development and Ive never had a single incident where I have needed to replace a barrel. One chap a while back wasnt sure of his barrel so I developed a load for him to prove the rifle was fine and then charged him for the load development. The guarantee I give every customer is that if I cant get the gun to shoot with a suitable bullet for his application I will replace the barrel FOC, when I do get it to shoot I give them the load data and they have to pay me for my load development time and materials. He was more than happy to pay for the work and also few tips on shooting more consistently at my range.

Ive gone to the length of telling this story because I believe people give up on barrels as 'bad' way too often when it is actually their own load development shortfalls or their shooting technique that is the problem. I talk every week with guys about load development and its clear that at least 50% dont really know what they are doing and even others who do still dont do it thoroughly enough to achieve the levels of accuracy and consistency they want. Half inch groups are perfectly adequate for a vast number of shooting disciplines and as was said earlier misses are more down to shooter error and gun control. Of course there are times when half inch is no good and then we get into the quarter inch world or less where the fist benchmark is 3 shot groups but the final word in my experience is 5 shot groups. Load development is very much the difference at this level and the shooter must be at a level where he can trust his technique so as to rule out flyers as human error and call them for what they are, harmonic shortfalls. The number of shots that get marked on load development targets as pulled and shooter error never ceases to amaze me, if I pulled that many shots I would never be able to differentiate between  myself or the load. My favourite are the 3 shot groups I see all the time published online which I call 2 & 1s, two shots touching or through the same hole and the other 1/2" away and put down to a pulled shot when these are classic harmonic issues most of the time. If it were shooter error it wouldn't happen as frequently as it does.

2. Everything comes down to testing. Even with tangent ogive bullets I will still carry out just the same level of seating depth testing as I would with secant or hybrid ogive, In fact if Im honest most of the time I haven't checked what kind of ogive they have because I know my testing and the holes in the target will tell me everything I need to know. There will be odd exceptions but broadly speaking most of the time every load Ive ever developed will show its sweet spot between just touching and 40 thou off the lands if you work in 5 thou increments over this 40 thou range. Sometimes SAAMI reamer specs and case/bullet combos mean you cant get into this range and so cant start 20 thou off but that doesnt matter, just load to within 50 thou of mag length and make that your reference point, you can then cover 20 thou either side just the same.  If possible every load I work up starts with the bullets 20 thou off the lands or this nominal mag restricted reference length and every powder charge test is done at this length, there is no need to change this at this stage. Once Im happy with the right powder in terms of stability I will then load up a number of rounds long say 50 thou longer than my reference length and I take a hand press to the range along with calipers to measure CBTO.

I will start with a clean barrel and fire 3-4 sighters/foulers at the same reference length off the lands and Im expecting group sizes to be the same as the average they showed on the powder charge testing. Then I will go longer or shorter by 5 thou and see what happens with a 3 shot group. If the group size stays the same or shrinks I will then go another 5 thou in the same direction and again if it stays the same or shrinks I will follow that trend until it starts to get bigger. If I dont get what I want on say moving towards the lands then I will go to the other side of my reference length and work away in the same 5 thou increments. Its very rare not to find the optimum for that bullet with that process covering a 40 thou range in 5 thou increments.

Some people are fixated about being near the lands but its not necessary other than to maximise case capacity. I tend to work things freebore wise to ensure they can seat their bullets with the bearing surface to boat-tail junction clearly above the case neck to shoulder junction where donuts can occur as donuts can cause havoc with repeatable seating depth. Some calibers have very long free bores yet they can still shoot tiny with huge jumps. Like I said at the beginning, I see seating depth nodes that repeat every 60-80 thou so load your bullet to the length you want or can and then cover a 40 thou range from there, if there isn't a sweet spot and you feel you have shot well then thats the time to start looking at a different bullet.

Sorry for the lengthy post guys but its not easy to answer these kind of questions in a few sentences.

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Disclaimer

I should add that my comments in this thread refer to rifles I have built and where I have had control of the entire process.

I do remember two instances of guns that just wouldn't shoot well and both had reputable match grade barrels fitted, one of them I re-chambered for the chap FOC as an experiment and the other was a rifle belonging to a friend which i didnt build or have anything to do with.

In both cases the rifles had been bedded which might not have been right, they also might have had ignition problems which are really hard to identify or quite possibly they were just bad barrels. Each rifle shot in the half inch range at 100yds but groups shapes were inconsistent and generally they weren't nice.

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All very interesting. 

With regard to chasing the lands once a precise load is found I also tend not to revisit my loads until the barrel is what I expect to be half way through it's useable lifespan and then if necessary retune the load. Which makes me wonder about all the jump to the lands etc, is it that dimension that really makes the difference or are we actually adjusting chamber pressure and or optimal barrel time?

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39 minutes ago, MJR said:

All very interesting. 

With regard to chasing the lands once a precise load is found I also tend not to revisit my loads until the barrel is what I expect to be half way through it's useable lifespan and then if necessary retune the load. Which makes me wonder about all the jump to the lands etc, is it that dimension that really makes the difference or are we actually adjusting chamber pressure and or optimal barrel time?

I think distance to the lands is irrelevant other than to give a reference point to work with. Its all about barrel timing and minute changes in chamber pressure and MV. Before you can explore that properly though you need to be sure your powder is stable and is giving repeatable barrel harmonics.

The truth is it doesnt really matter if we know what exactly is happening so long as we have a reliable and repeatable method of finding whatever our desired levels of accuracy are, Im happy I know how to find mine.

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3 hours ago, Big Al said:

The truth is it doesnt really matter if we know what exactly is happening so long as we have a reliable and repeatable method of finding whatever our desired levels of accuracy are, Im happy I know how to find mine.

Amen to that.  Sound advice 

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5 hours ago, Big Al said:

I think distance to the lands is irrelevant other than to give a reference point to work with. Its all about barrel timing and minute changes in chamber pressure and MV. Before you can explore that properly though you need to be sure your powder is stable and is giving repeatable barrel harmonics.

The truth is it doesnt really matter if we know what exactly is happening so long as we have a reliable and repeatable method of finding whatever our desired levels of accuracy are, Im happy I know how to find mine.

But then surely if a bullet was jammed it would create higher chamber pressure and hence a different barrel time. Surely there must be a corelation somewhere. 

And how are the factory loads explained such as gold medal match that seams to shoot in any reasonable 308? 

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When I bought my rifle I had some Remington Premier Match SMK 168gr given to me to "see how good it is"  - it was so far beyond crap!  So bad I thought my new very expensive rifle was a duffer.   I tried some Random Green and it was pretty good for RG.  Some ammo/rifle combos are just not happy bunnies.

Jamming causes higher starting pressures but does that result in faster bullet acceleration (evidenced by higher Mv) thereby reducing travel time ?? 

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3 hours ago, MJR said:

But then surely if a bullet was jammed it would create higher chamber pressure and hence a different barrel time. Surely there must be a corelation somewhere. 

And how are the factory loads explained such as gold medal match that seams to shoot in any reasonable 308? 

Yes I would expect a jam will up pressure and then differing amounts of jam will created differing pressures as well. As for a correlation? possibly/probably I dont honestly know. I would really wonder if anyone really does know as ultimately it goes back to what I said earlier, so long as we have a system that lets us get to the levels of accuracy we need consistently then does it really matter if we understand the whys?

What I do see is people trying to simplify a process or look for some kind of magic way to save doing the hard yards. Thats fine if 0.5moa at 100yds is your target and repeatability over a wide temperature range doesnt matter. Our opinions probably differ on the performance of the gold medal match in a number of different rifles goes but again it doesnt matter if our applications are different.

Its the same with pet loads or these magic calibers that are supposed take no load development and they will shoot almost anything, all well and good in your average hunting gun but not the kind of stuff Im interested in.

 

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