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megasupermagnum I think I saw where MSM2019 says that Mylar wraps increase pressure. It must be significant. I trust what he says, as he has test experience. Mylar is extra durable for protecting your barrel against very hard non-toxic types of shot, but certainly not necessary for protecting your lead shot from being abraded against the barrel - polyethylene is good enough for that. Again, if I want to do that (which is seldom, with today's good selection of wads with integral shot cups) I use simple strips cut from thicker polyethylene material I find here and there -- heavy duty bags, for instance. They look and work the same as Olin's Mark 5 sleeve in their old Winchester and Western shotshells.

Also, if you use the thick Mylar sleeves (.010") from Ballistic Products Inc, or others, it is almost impossible stuff to work with, in my experience -- very stiff and non conformal to the inside of your hull, and such material takes up a surprising amount of shot space. I believe that is one reason (besides bore friction, I assume) for the noticeable pressure increase. You'll notice BPI only sells the thin stuff now -- .003" thick. When I can't somehow find or use an appropriate heavy-duty shot cup for loading HeviShot or ITX13, etc, (which again is seldom), I use strips cut from Mylar file folders or old overhead projector slides -- same stuff, just cheaper and more easily available.

Joined: 11 Dec 2017 Posts: 77 Location: South Dakota

I'm fairly sure Mylar is a brand name of polyethylene. I believe they are one and the same.

I've heard of the pressure increase, but I've never seen the data that shows it. For the most part now wraps are considered extra protection. Obviously a wrap inside a shot cup would have no effect on the pressure. Used as a standalone wrap, I just don't know. Data I see worked up with them doesn't seem all that different than plastic wad data. I have to think the different wads we use with wraps, like gas seals and nitro cards, have a larger effect.

I use the .007" thick mylar from PR. They conform perfectly. I don't know if I have ever used the ones from BPI or not. The stuff from PR is extremely springy, not stiff, but always wants to be flat. They are very easy to roll slightly, stick in the hull, and then they conform perfectly.

Where I use mylar is buffered loads, specifically turkey or buckshot loads. The buffer I use, PSB buffer, is very rough on hulls. In both cases a significant portion of the shot is outside a regular lead wad, and I actually prefer to use nitro cards, felt wads, and gas seals myself, as they offer a better platform for buckshot, plus more internal room. Without a wrap, that buffer can dig into the hull and tear it up. I'm not sure the wrap does anything for patterns. I shoot a lot of muzzleloader, and some of the best patterns I get from them is nothing but a nitro card. No cushion, no wrap, just a nitro card or two. I've tried plastic wads in all my muzzleloading shotguns, and they always produce mediocre performance. I don't believe the wad cup is the miracle some people believe.

Mylar: https://en.wikipedia.org/wiki/BoPET

Polyethylene: https://en.wikipedia.org/wiki/Polyethylene

These two materials are only distantly related, are formed in methods different from each other and are quite different in chemical composition and structure, and thus have quite different properties and uses. Polyethylene is low in strength, hardness and rigidity, but high in ductility and impact strength and low in friction. It creeps readily under load. It typically feels a bit waxy.

Mylar (a trade name for BoPET - stretched polyethylene terephthalate) is a polyester film that is heat set (crystallized) under tension. It is hard and high in strength, and very chemically and dimensionally stable. It is naturally smooth and shiny, unless it has been purposely micro-roughened as some file folders are. Mylar displays a high coefficient of friction against smooth surfaces -- like the inside of a shotgun barrel, for instance.

Once you have the two materials in your hand, the differences in character are readily apparent. To be "floppy", Mylar has to be extremely thin (Mylar balloons or the wrapping on your spiral cut ham), but in any thickness, it doesn't tend to be "stretchy" like polyethylene. Once it gets to be .003" thick or so it is a pretty stiff sheet - again, compare a file folder made with Mylar to a polyethylene bag of the same thickness -- quite different properties. Remember old computer floppy discs? Mylar coated with an iron oxide magnetic recording surface. Tough stuff! It is easy to cut yourself with a fairly thin piece of Mylar, but I venture to say you'd never do that with polyethylene 10 or 20 times thicker and sharpened to a knife edge -- it's just too soft.

Member Joined: 02 Feb 2007 Posts: 371 Location: mpls mn

As for the lazer
i don't own one but have access to several

Joined: 10 Jul 2011 Posts: 30 Location: St.Louis, MO

I was gifted a few thousand 16 ga Alcan kwik serts a few years ago and quickly discovered that they have a potential flaw, the pedal breaks off when loading. I was loading some R-P new primed hulls and when seating the KS on top of the fiber wad the pedal broke off on one side. I was told they had been stored inside the fellows house so temperature swings would not have been a problem. I promptly trashed the remaining Kwik Serts because it reminded me of an encounter with a local gunsmith close to 40 years ago. He showed me a shotgun barrel that he had replaced with a Kwik Sert sized bulge on one side of the barrel. he surmised that the shot wrapper had stuck in the barrel and the wads passed by causing the bulge.

This is something to keep in mind when making your own Mylar shot wrappers. The pictures on Ballistic Products website show the wrapper used inside the shot cup.

The original advertising for the WW Mark 5 wrapper says it is made out of polyethylene.

Joined: 04 Mar 2019 Posts: 1845 Location: Central ND

Maximumsmoke, is spot on regarding Mylar.

Mylar is great stuff BUT because of it's stiffness and high coefficient of friction it has a tendency to raise chamber pressures well above what a similar sized piece of polyethylene will. Simply putting a Mylar wrapper inside a regular lead shot wad, with no other changes, will raise chamber pressures as much as 2,500 PSI.

I like Mylar. My favorite 16 gauge Bismuth loads use Mylar as a shot wrapper, but Mylar shot wrappers also require that powders like Blue Dot, Longshot and Steel be used.

Polyethylene and Mylar are two distinctly different materials and need to be treated as such. Never substitute Mylar for polyethylene, or blindly use a Mylar shot wrapper inside a lead shot wad.

What I have just posted is not a guess or a supposition, the information comes from some fairly extensive pressure and velocity testing. The testing was done using lead, buffered lead, Bismuth, buffered Bismuth, steel, buffered steel, Mylar in lead shot wads and Mylar used as a shot wrapper in direct contact with the bore.

mylar is TOUGH stuff , Used to use .004 squares to clean slotted equip where I worked - once it grabbed , the equip had to be dismantled !! For a quick sert sub , it is much easier to cut the OP and cush out of herters wads . All the parts are there and already shaped and easy to load - big capacity !.... Mark , does mylar have a similar effect when used inside a soft cup - a lot of the guys use it this way !?

Joined: 04 Mar 2019 Posts: 1845 Location: Central ND

16gaDavis,

I never tested it with a soft shot cup only, just inside the shot cup of a standard lead wad, but I can't see that there would be any difference.

I know folks use Mylar that way, because it has been presented by a reloading products company as OK....but it really isn't a top notch idea.

I have never seen an application, where Mylar was used as a shot wrapper, inside or outside a wad, that did not raise chamber pressure. It was always well over 1000 PSI and up to 2,500 PSI.

Joined: 11 Dec 2017 Posts: 77 Location: South Dakota

That's very interesting. I can fully understand why Mylar would have an effect outside of another wad. What I can't understand is why would Mylar have any effect at all if fully inside another wad? That's not something I've ever tried myself, as I consider it kind of a belts and suspenders situation, but I don't understand how it could effect pressure either. That is truly bizzare. To clarify, do you mean say a wrap inside a TPS wad ({mylar fully inside wad cup) with hevishot raises pressure, or are you talking some of the loads out there that use a standard 1 1/8 oz wad with a 1 1/2 oz load of shot, where a good bulk of the shot (and Mylar) is hanging out the top of the wad cup? If the first scenario, do you have any theory's why this might be?

Joined: 04 Mar 2019 Posts: 1845 Location: Central ND

megasupermagnum,

Yes to the TPS wad example. The TPS wad was never made for hevishot, it was made for target loads using steel shot. The Mylar is used to stop the hevishot pellets from rubbing through the TPS wad.

I positively know what effect Mylar has on chamber pressure, but I do not know exactly why.

This is my best guess.......Mylar, because it is so rigid, will make the outer wad petals create more friction than they would without the Mylar. Without the Mylar each pellet in contact with the wad petals would create a divot on the inside and exert force to that tiny area, dampened under acceleration by the polyethylene. With the Mylar the pellets act more collectively over a larger area and that increases the surface area of the wad petals(from tiny divots to the entire wad petal especially at the bottom of the shot column), which increases the friction which drives up the chamber pressure. Again that is my best guess and it is a WAG at best.

As long as the loading data was developed using the Mylar there is no issue.

There are a lot of people using Mylar inside wads without the load being tested, that's OK with me, because I don't have to shoot their reloads in my shotguns.

Joined: 11 Dec 2017 Posts: 77 Location: South Dakota

Seems kind of odd they would name a wad tungsten propulsion system, when not intended for tungsten shot. Laughing

Way back when I first started loading steel shot, I remember the multi-metal being the latest and greatest wad, and I used a number of them. I scarcely remember the TPS wad being called something else, but I can't remember what it was. The MM was also much thicker/stiffer than the TPS. I gave up on both long ago anyway, and never loaded hevishot. I came to prefer the SAM1 wad from Reloading Specialties. It's too bad they never made a 16 gauge version. Despite the kind of odd appearance, and sometimes questionable wad slitting (some batches were great, some looked like they were cut by a monkey), despite all that, I never found a better performing wad for steel. They were also some of the thinnest, although I never had rub through become a problem, even shooting the huge stuff like BBB and T shot.

Your theory on why a Mylar wrap would do anything is as good as any. I know set back is a factor. I believe in the manual, RS recommends you do NOT use an overshot card underneath the shot inside their SAM1 wad. The idea being that the card prevents set back, and raises pressure. Felt wads are perfectly acceptable to take up space if needed, but they also compress. I was always sure to have at least an 1/8" felt wad, as if you shot them with nothing, it was rather typical to find half a dozen shot stuck in the recovered wad.

Have you worked for a company that pressure tests ammo, or do you have pressure testing equipment yourself? I've got the Pressure Trace II system, which is basically the homeowner version of pressure testing. They warn to not use it to work up data, but it has proven very accurate. I know you made up a bismuth load, as I plan to do myself. Have you done anything more off the wall in 16 gauge? I've got some 1 3/8 oz loads ready to be tested when I get around to it. I'm a low velocity, high payload guy. Just for fun I mocked up some loads in a federal hull. I found the Federal 2 3/4" 16 gauge hull could easily hold 1 5/8 oz of lead shot with powder, gas seal, 1/8" felt, and 1/8" nitro card.

Without starting an "ideal for 16 gauge" war, have you done anything like that, or even lighter at high velocity?

Joined: 04 Mar 2019 Posts: 1845 Location: Central ND

megasupermagnum,

When Precision Reloading Inc. was located in CT, I did all the ballistic testing from 1992 until 2001, when I left the company. (I actually worked there longer than that.)

No I don't have access to any piezo test equipment now.

The ONLY reason I strayed from lead wads was the only wad for 1 1/8 oz. lead loads and heavier loads was the Remington SP-16 which is not a good match in any hull except the Remington SP (RGL). (I know I know it fits the long gone Winchester CF)

One thing lead to another and I dropped messing around with 16 ga. lead loads using a gas seal, felt wad and Mylar wrapper and spent more time with those components and built Bismuth and Steel loads. Just when I had time to to go back to developing the lead loads, Tom Armbrust (who we borrowed the 16 ga. test barrel from) needed his barrel back. So that ended the 16 gauge load development. Not long after that I left the company.

None of these loads are what I consider 'off the wall', they don't use any components that haven't been used. It is just the easiest way to build loads that seal, perform and pattern well, when you don't have wads for the application.

IMHO, there are now some real possibilities with wads that both PRL and BPI carry, but neither company seems to want to spend time building the loads. I get it that there isn't a lot of ROI for the 16 but.......

Joined: 04 Mar 2019 Posts: 1845 Location: Central ND

Now that I am retired and have time and a place to pattern and velocity test, I am thinking about working on those lead loads.....probably a nice 1 1/8 oz. load and a buffered 1 1/4 oz. load for turkey.

I will have Tom Armbrust or Precision Reloading do the final P & V testing for me.

Joined: 08 Feb 2009 Posts: 1311 Location: Western WA

Joined: 04 Mar 2019 Posts: 1845 Location: Central ND

Brewster11,

It's more fun doing the work myself and any mistakes I make will give me more information then if I have someone else do the work for me.