Duplex Loads

[Freebore]

Just curious.....has anyone ever experimented with duplex loads. Back in the late sixties while working on a 22/308 Imp (not mine) we developed some duplex powder charges using compressed loads with powders of two different burning rates using a slower burning base charge, and a faster main charge (not mixed together). The idea was to develop a load with a burning rate that would work well in the overbores, and give good high velocity without high pressure or sacrificing too much barrel life.

At the time the buzz concerning duplex loads was hot in the wildcat development circles, but seem to drop off, I have not heard of any work in this area for many years.

Just curious if anyone has heard or seen any info on this type of experimental loading.........thanks

[LDBennett]

Many new powders have been introduced since those days of wildcatting. Those new powders do what the duplex loads were suppose to do. In general Duplex loading is very dangerous and should not be attempted. I would suggest to forget Duplex loading and leave the blending of powders to powder companies who have the facilities and the tools to test powder blending for pressure.

LDBennett

[muddober]

The idea of duplex loading has always been in my view the recipe for disaster. The 454Casull when first introduced utilized of all things a triplex load as I recall was made up of a little Bullseye being the first to be put in the case, then some Unique and then topped off with 2400. I like reloading and have even experimented a bit making up loads of my own but duplex or mixing of powder has always been a little over the top for me.

Ron

[JLA]

A good friend of mine and I load our black powder cartridges with about 3 gr. of green dot under our heavily compressed charges of BP, thats the only form of duplexin I have ever attempted. As LD pointed out, powder companies ahve a powder for EVERYTHING now a days. So duplexing outside of doing what I have just described is begging for disaster...

[TranterUK]

I have tried many special loads over the years from mixing shot sizes to sabot discarding but would never try a duplex in a centre fire rifle or pistol cartridge.

The pressures you could be producing may result in a catastrophic failure. Without safe conditions and pressure measuring instruments, it's not somewhere to go.

[Freebore]

In response to my original thread, let me remind all, that I was not promoting the use of duplex loads, nor asking for any data. While working on the 22/308 Imp project back then we did in fact use a number of duplex loads and were able to safely push a 48 gr projectile to well beyond the 4000 fps limits of that day.

Let me clarify that the people involved were not just your average shell stuffers, but in fact some highly notable members of the shooting society. A well thought out process was the rule of the day and loads were actually fired in a bench gun, not in an off the shelf model.

I appreciate everyones concern for saftey as there is no real data or reference material readily available. Again, I do not support or recommend the use of these loads without a lot of product knowledge and support.

Thanks......

[LDBennett]

Freebore:

While your efforts with duplex loads may have included "experts", no expert can measure pressure created by those duplex loads without the proper pressure measuring devices that all reloading manual editors use to develop published loads. Did you have pressure measuring equipment? If not, you were toying with danger. Any results you may have gotten for this gun were only for this setup and are not applicable to any other. I sure hope you guys didn't allow the data to be passed on to other reloaders.

For all you other reloaders out there, in general, a reloader should only use published reloading data from reliable sources (not some guy on the internet or a fellow shooter at the range). And then, the loads should be developed from a starting load level (approximately 10% below the Max load) with the components specified in the recipe, as a starting point.

Safety first! Duplex loads are a bad idea, in my opinion!

LDBennett

[Freebore]

In reality, while working up any new load one should be aware that even published data is just a reference mark and not any guarantee, actual determination is derived by observing basic signs of pressure problems. I have loaded rounds considered OK from some popular reloading manuals and observed early signs of excessive pressure right from the start.

Its important to remember that each component used in the process is a variable and different from what was used to develop published data. Along with components, temperature, humidity, and actual case capacity are extremely important to qualifying any round at any given time.

In all loading procedures, when developing new loads I depend heavily on my case head gauge (and have for many years), this tool is the first line in looking at pressure conditions. Knowing what case head expansion to expect regardless of other signs is an extremely important concern. The basic rule is under .0004" for low pressure cases (30/30, etc.) under .0006" for mid-pressure cases (22/250, .270), and under .0007" for large magnums.

In the case of the 22/308 Imp project, I don't believe anyone else even knew the round existed as it was chambered from a custom made reamer made for this particular project. Just for the record though, the final conclusion was that an ulta high velocity round could be developed, unfortunately barrel life was extremely short (100 -150 rounds).

Thanks to all for your views and comments

[JLA]

DAMN!, whats the point if you have to rebarrel and start over every 150 shots. Most of us shoot that much in a day at the range...

[Freebore]

I believe this is why you do not see any 22/308 Improved chamberings around. I did see (some time ago) a 22/308 chambering but was not in an Improved version. The Improved version has about 10% more capacity with hardly any taper and a 40 degree shoulder (actually doesn't look much like a 308 case after renecking and fireforming).

As for barrels, the project did included a prominent barrel manufactuer and a few gunsmiths, overall it was just experimental work. The barrel failure was due to throating errosion (which greatly affected accuracy). I'm sure powdered down a little, this would have been a nice varmint round, but there were/still are so many hot rock 22's around (like you said), what would be the point.

[JLA]

I guess I could see the recreation of working on a project like that if its what you enjoy doing. I mean, One of my most beloved hobbies is Pontiac Fieros, How many people do you see driving one of those things, let alone shelling out more than 500 bucks for one. But I have 2, and am in the process of acquiring 2 more, and both of them most likely will cost me a couple guns, which is my other most beloved hobby. But yeah, I can see where sending a .22 cal bullet downrange at 4000 + would feel rewarding, but then again so would being able to drive from your house to the store in a Fiero without overheating...

[LDBennett]

I have a garage full of vintage motorcycles, both street and off-road that I restored myself, over the last 15 years.

It is neat to drive around on a 43 year old BSA 650 twin or go off-roading on a 36 year old 500cc Triumph. They are not absolutely stock but slightly modified to really modified, not for looks but for purpose. But talk about a sink hole for money! I got about six good guns in each of just those two and many more in the race bikes. But it kept me out of trouble for all these retirement years.

LDBennett

[Freebore]

Hey....if you enjoy doing what you like to do, then I would say its money well spent

[JLA]

100% agreed