roll turn cartridge

[snow white]

Hi do you get more pressure on a crimped cartridge or a roll turn cartridge. Thanks for looking

[sitsinhedges]

The received wisdom is that a star crimp produces more pressure than a rolled turn over. Presumably this is because it is harder to open.

[Continental Shooter]

The received wisdom is that a star crimp produces more pressure than a rolled turn over. Presumably this is because it is harder to open.

 

[seeker]

Out of interest is this actual fact or ..?

I ask because was given a large box of mixed factory loaded 28 gauge cartridges, some rto, some crimp but with no printing. A quick sort and check showed many were probably the same basic case, wad, shot load, primer, powder but mixed rto/cr. Both chrono'd around the same, so i assumed similar pressures? Not terribly scientific but a reassurance check.

On reloading i only had the rto kit with me so , I cut back some damaged crimps, rough skived, loaded and used .. no difference.

I thought that the intro of crimp was to speed up the factory loading and eliminate a fiddly stage of the process (top card)??

Is the superiority of the crimp actual, or does It sit with the fact that the rto card leaves a doughnut hole in the pattern?

As an aside here's some data on the effect the depth of crimp can have on a load ... numbers for the intuition ? Reasonable to assume the effect is similar for rto... ?

So the rto/crimp question may not be the right question?

http://www.clayshootingusa.com/html/archive/aug_sep10/Cases%20and%20Crimps.pdf

Edited October 16, 2014 by seeker

[sitsinhedges]

Out of interest is this actual fact or ..?

I ask because was given a large box of mixed factory loaded 28 gauge cartridges, some rto, some crimp but with no printing. A quick sort and check showed many were probably the same basic case, wad, shot load, primer, powder but mixed rto/cr. Both chrono'd around the same, so i assumed similar pressures? Not terribly scientific but a reassurance check.

On reloading i only had the rto kit with me so , I cut back some damaged crimps, rough skived, loaded and used .. no difference.

I thought that the intro of crimp was to speed up the factory loading and eliminate a fiddly stage of the process (top card)??

Is the superiority of the crimp actual, or does It sit with the fact that the rto card leaves a doughnut hole in the pattern?

As an aside here's some data on the effect the depth of crimp can have on a load ... numbers for the intuition ? Reasonable to assume the effect is similar for rto... ?

So the rto/crimp question may not be the right question?

http://www.clayshootingusa.com/html/archive/aug_sep10/Cases%20and%20Crimps.pd

 

 

 

 

You ask the question 'actual fact?' then go on to make your own assumptions regarding velocity and breech pressure having a connection then more assumptions about overshotcards and do-nut patterns.

 

There are always ifs and buts, but in general rto's are supposed to result in lower pressures because the generally open more easily than a crimp meaning less pressure before they pop. A tighter crimp in any form will mean higher pressures.

[wymberley]

 

You ask the question 'actual fact?' then go on to make your own assumptions regarding velocity and breech pressure having a connection then more assumptions about overshotcards and do-nut patterns.

 

 

Don't think that that's a fair comment. Apart from a brief note of what he did and the reason for doing so, the bulk of Seeker's post is a series of more questions in addition to his first as highlighted by the question marks.

[Guest cookoff013]

 

You ask the question 'actual fact?' then go on to make your own assumptions regarding velocity and breech pressure having a connection then more assumptions about overshotcards and do-nut patterns.

 

There are always ifs and buts, but in general rto's are supposed to result in lower pressures because the generally open more easily than a crimp meaning less pressure before they pop. A tighter crimp in any form will mean higher pressures.

 

very true, but cannot ignore the original constituents of the load anyway. allow me to elaborate....

if i had 2 identical loads, lets say 1oz 1200fps classic load, at 7000psi, thats limp and thats with a normal components in a 2,3/4" shell, then the same components but 1/4" taller in compression wad and a roll turn finish will produce different numbers, whether that would be higher pressure or differential speeds. that i cant really argue, i cant even second guess much anymore because its been proved that the opposite can happen,

 

also wouldnt we say, if there is more room for the gasses to expand into, wouldnt the pressure be lower?

 

what goes on in a shell is very complicated, first the primer goes off, then the powder charge starts to burn (its quick), the pressure starts to rise, the cardboard obturator pushes against the fibre wad, which compresses and in turn compresses the shot. the fibre wad also flattens out because you`ve just put 7000psi through it !

maybe all the powder is burned up into gas? (different loads and all). the crimp pops open and the gasses behind the obturator and the wad keep the wad squished, driving it down the bore. and hopefully into some unsuspecting pigeon.

some of the factors that effect pressure are "the physical volume of powder" "physical volume of gas created" and the "volume in which it can do so." ie the compression section and or the shot volume.

 

in a plastic wad it is very much simmilar but the plastic wad has a different obturator, and the shot is enclosed in a reduced friction medium, with plaswads i get lower pressures and higher speeds, and i did do a like for like loading, the fibre came back toast. i severely toasted that. which makes me think, that the fibre wad reduced the volume compared to the plastic counterpart.

 

@ seeker, a chrono is the last thing you`d want to evaluate pressures, in shot shells.

 

i think your evaluation of RTO is slightly suspect but i will say that it is very hard to compare all variables.

 

@snow white and the seven cartridges

different cartridges produce different pressures. if i had a high pressure load it may not change at all the pressures due to RTO. and if i had a bad low pressure cartridge it may respond in any way (low to high or even low - to low !)

[snow white]

Hi just chrono ten 20 bore cartridges used vectan a1 16.7 grains. obulater disc 14 mm fiber wade 28 grains lead card roll turn.worked out at 1211 feet second.

[sitsinhedges]

Hi just chrono ten 20 bore cartridges used vectan a1 16.7 grains. obulater disc 14 mm fiber wade 28 grains lead card roll turn.worked out at 1211 feet second.

 

That's in the ball park of what I was getting from some factory 28gram 20 gauge loads and is fast enough to do the job nicely without too much recoil.

[snow white]

Would I get a faster cartridge if I up the powerd to 17/grains or would it be dangerous

[super sharp shooter]

 

Would I get a faster cartridge if I up the powerd to 17/grains or would it be dangerous[/

 

It would make it faster but depending on the pressure it could become over pressured.

[turbo33]

Hi just chrono ten 20 bore cartridges used vectan a1 16.7 grains. obulater disc 14 mm fiber wade 28 grains lead card roll turn.worked out at 1211 feet second.

What case length Snow White and how deep was the roll?

[snow white]

Hi 65mm case length and 9 mm roll turn

[snow white]

Well answered my own question there is very minimal difference in crimp or roll turn put ten of each over chrono today

[turbo33]

Thanks for posting Snow white, interesting findings Your next mission is to pattern them so we can see the effect of the card on the shot I personally quite like the roll turn finish, bit like the old days

[Old farrier]

Hi

Got some roll turnover cartridges with a hard clear plastic (card ) in the end that are supposed to dissintidrate on fireing

Just a thought could you get a larger load in a rto than crimp given that the fired length of the cartridge are the same

If so the supposed lower pressure from a rto would be of benifit

Just a thought

All the best

Of

[snow white]

If weather doesn't get to bad will pattern some crimped and roll turn in the week.

[turbo33]

If weather doesn't get to bad will pattern some crimped and roll turn in the week.

 

Well done, would be interested to see the results

[Continental Shooter]

It is scientifically proven that a star crimp takes a lot more to undo than an RTO due to the resistance opposed by the crimp to the forwarding column (wad + lead) and the efforts needed for this to open it. it also goes without saying that an 8 star crimp take less effort to undo than a 6 star crimp (in fact there is a potential reduction in pressure to the tune of 40-60 bar).

 

This also allow for less powder to be used as the compression helps the powder burning better and, in general, generate more forward power (due to the initial effort made by the gas to push the load forward) than and RTO, hence why no manufacturer uses and RTO anymore these days..

 

Another factor to take into account is the depth of the crimp, both on RTO and Star crimp: 1 mm deeper could increase the pressure of up to 100 bar,again, due to the difficulties in opening the crimp.... that's why is so important (although unknown to most) to know the exact measurement of the finished shell.

 

For that, and other reasons, you should never replicate a factory shell, never mind chopping and changing cases/wads/crimp

 

Also, the wad is of primary importance as Cook said....a plastic wad will help retain the gasses, hence increase the pressure and use the full power generated by the pressure to open the crimp, also, the column (wad+led) that the pressure need to move is important, hence why you need to chose the right wad for the load as, if the majority of the weight is higher it will need a different effort to to move it than if it is lower.

 

I know most people reload just for fun or because they've got a safe load from somewhere/someone, but reloading is a very precise science dominated by the physical laws of internal ballistic (which in turn is formed by many other physical rules) and you cannot play with them or assume anything. Reloading is also affected by many external factors that needs to be factored in when assembling a shell: primes (can differ in power from batch to batch, etc) powder (different batches of same powder produce different date, etc), wad (different wads fiber/plastic are affected by humidity and conservation status, etc), crimp (star vs roll, 6 crimps vs 8 crimps, etc). Any of this can have negative effects on your load and unbalance what you believe to be a safe recipe.

 

You might not blown your gun and very occasionally happens these days that someone blows off a limb (thanks to the guns mainly) but it should never been approached so superficially as to say, i got some shells and nip&tuck here and there and they were fine....because they weren't! you just got lucky, and should in no way mention that on a public forum where people my thing is ok to do so ....some day someone can really lose a limb doing that and thinking it was fine!

 

Also, the fact that 2 shells have the same speed, it doesn't mean that they have the same pressure and it shouldn't be i no way reassuring. High pressure doesn't mean high speed as well as low pressure doesn't mean low speed.

 

Thanks,

[biketestace]

It is scientifically proven that a star crimp takes a lot more to undo than an RTO due to the resistance opposed by the crimp to the forwarding column (wad + lead) and the efforts needed for this to open it. it also goes without saying that an 8 star crimp take less effort to undo than a 6 star crimp (in fact there is a potential reduction in pressure to the tune of 40-60 bar).

 

This also allow for less powder to be used as the compression helps the powder burning better and, in general, generate more forward power (due to the initial effort made by the gas to push the load forward) than and RTO, hence why no manufacturer uses and RTO anymore these days..

 

Another factor to take into account is the depth of the crimp, both on RTO and Star crimp: 1 mm deeper could increase the pressure of up to 100 bar,again, due to the difficulties in opening the crimp.... that's why is so important (although unknown to most) to know the exact measurement of the finished shell.

 

For that, and other reasons, you should never replicate a factory shell, never mind chopping and changing cases/wads/crimp

 

Also, the wad is of primary importance as Cook said....a plastic wad will help retain the gasses, hence increase the pressure and use the full power generated by the pressure to open the crimp, also, the column (wad+led) that the pressure need to move is important, hence why you need to chose the right wad for the load as, if the majority of the weight is higher it will need a different effort to to move it than if it is lower.

 

I know most people reload just for fun or because they've got a safe load from somewhere/someone, but reloading is a very precise science dominated by the physical laws of internal ballistic (which in turn is formed by many other physical rules) and you cannot play with them or assume anything. Reloading is also affected by many external factors that needs to be factored in when assembling a shell: primes (can differ in power from batch to batch, etc) powder (different batches of same powder produce different date, etc), wad (different wads fiber/plastic are affected by humidity and conservation status, etc), crimp (star vs roll, 6 crimps vs 8 crimps, etc). Any of this can have negative effects on your load and unbalance what you believe to be a safe recipe.

 

You might not blown your gun and very occasionally happens these days that someone blows off a limb (thanks to the guns mainly) but it should never been approached so superficially as to say, i got some shells and nip&tuck here and there and they were fine....because they weren't! you just got lucky, and should in no way mention that on a public forum where people my thing is ok to do so ....some day someone can really lose a limb doing that and thinking it was fine!

 

Also, the fact that 2 shells have the same speed, it doesn't mean that they have the same pressure and it shouldn't be i no way reassuring. High pressure doesn't mean high speed as well as low pressure doesn't mean low speed.

 

Thanks,

The best reply iv read in ages,

And that's why I love reloading !

[Paladin]

I totally agree with Continental Shooter.

I've pulled the old proof sheet set up dropped the same amount of powder as the last batch, and failed proof. Batch numbers are put on powder for a reason. It's a good job that proof guns are not like shotguns.

When loading an over shot card and a roll turnover on a commercial loading machine you can still run at full speed, it makes no difference it's not fiddly at all.

[Continental Shooter]

Hi,

 

I've been reloading for the past 20-25 years and i can tell the changes each powder went through during these years.

 

Powders like the Vectans (A1 and AS more then any other) GM3 and some old B&P are the ones that have become more unstable and subject to changes.

 

Also, powder manufactured for commercial use (including this for the NS factory shells) is of a totally different composition of the one sold to private reloaders in that it is manufatured to suit specific needs: hence why on the NS site you can load 27gr with Vecatn A1 on 20 bore.

 

Vectan A1 is for loads of 24g-26g (being 26gr the one you MUST proof), however, in the past, this powder was slower and could have accepted 27 gr in certain cases (very low power prime, RTO, etc).

 

To give you an example (A1 2010):

 

20/70 Fiocchi 616 Z2M 19 1,15/1,18 gr 25,0 gr # 7.5 S 60 mm Pmax: 615-621, V0: 385-390 m/s

 

A1 (2014 Batch) with lower powder prime

 

20/70 Fiocchi 615 LB6 + 21mm 1,25 gr 25,0 gr # 7 S 60 mm Pmax: 719-726 bar, V0: 404-411 m/s

 

However the same load, with the same batch of A1 with a tighter crimp:

 

20/70 Fiocchi 615 LB6 + 21mm 1,25 gr 25,0 gr # 7 S 59,5 mm Pmax: 835-842 bar, V0: 402- 409

 

Same **** happened with GM3, once it was more progressive and allowed for a certain degree of playing: i remember using it indifferently for 23-28 gr loads in 20 bore, but nowadays i wouldn't go above 25 ... 26 top!

 

So, beware of factory sourced loads or certain manufacturers... best for me are the american powders (Hogdon, IMR, etc - I personally favour IMR 800X) as they've been consistently produced for decades and they satisfy reloaders from Alaska to Texas.

 

Also, some old trusted powder like Tecna N or Sipe N or S4 N which, despite undergoing some transformation throughout the past few decades, have not lost their basic characteristic and you can still safely reload recipe from 15-20 years ago with very small (and acceptable) variations in data.

 

Another manufacturer that hasn't change much in the past decade or so is Vithavouri...good consistent powder in my books.

 

That said, i still reload A1 (although you will need to ascertain whether is A1, A1 SP or A1 x32 as they will all have different burning and reloading characteristic) therefore, once i finish the batch i have, and buy a new one, i benchmark it against a trusted and well known load which will give me an idea of how the new batch is (more progressive, less progressive, the same) and from there, i can adjust the shell to bring it to the usual values.

 

hope this helps,

[rbrowning2]

Study 2 at this web site is an interesting read re the science of velocity/pressure.

 

http://www.claytargettesting.com/index.html

[Continental Shooter]

very good reading,

 

Thanks,

[super sharp shooter]

Some good info there.

Edited October 29, 2014 by super sharp shooter