Duplex Post by RB

[edge]

dougsmessageboards.proboards.com/index.cgi?board=smokeless&action=display&thread=348

Jan 29, 2009 11:39:00 GMT -5 rbinar said:

8-)For some time I have been getting inquiries about duplex loading. Since so many of you have questions I thought I should try to answer them all at once. Or at least most of them at once.

Duplex loads have to be broken down by caliber. The caliber most in need of a duplex is the standard 50 caliber rifle. The reason for that has been repeated time and again but let’s consider the fact that NO 50 caliber rifle regularly shoots a 250 grain bullet. It is unheard of because of it’s slight weight. Most 50 caliber rifles never shoot a 300 grain bullet. The average weight bullet is between 435 and 600 grains.

The common duplex is 14/61 with the booster powder being N110 and the primary powder H322. Many shoot this load because it’s fast (2600 to 2700fps) and accurate. You are allowed to move up a grain or two to 15/60, 16/59 and down to 13/62, 12/61 in search of best accuracy but I suggest you stay in this area unless you consult with some one who can develop a custom load.

In the above load using Imr-4759 or Xmr-5744 as a booster is permitted if you can’t find N110. However go easy, it might be best to start with less and work up if you substitute.

All I have to say extra about duplexes with a 250 grain bullet is that loads of less powder are possible. If you're recoil adverse but still would like some extra speed loads of 70, 65, or 60 grains would work. If 2500fps was your perfect speed a 65 grain duplex would shoot a 250 grain there with little temperature sensitivity and safe pressure. I’m not suggesting a load just a concept. I will help you with the load if you need it.

Lately I’ve heard of 300 grain bullets being used in duplex loads. In the past I’ve not recommended that, even now I have reservations but will accept this: the load I’ve seen suggested is a very good load. I’ve seen a 10/60 load suggested with 5744 and 4198. If the timed speed is correct (2450fps) it is very near the ideal pressure for this amount of powder.

What I don’t want to happen is a speed war started with 300 grain bullets. They kick and most can’t take near what is offered for a full single powder load. I help some shooters go to very fast speeds but it’s not with duplex, so why bother?

Still there is always the need for temperature stability and this new load would be just that. Add the fact it is immune to misfire and I can see the attraction. But still I believe one 300 grain duplex is enough if you have a speed you have to go let me know and I’ll tell you how to get a broke shoulder errr... safely.

I have more thoughts on duplex in 45 and 40 caliber but I will add those as the post progresses

[edge]

Jan 29, 2009 14:53:18 GMT -5 rbinar said:

Ok let's progress a bit. The next subject is duplex in smaller calibers. This reply is for the 45 caliber bore.

First let's talk about sabots. A lot of powders will shoot sabots to considerable speed. H4198, N130, and RL7 will load to about 60 grains a little more in the cold a little less in the heat. The limit is not the powder but the sabot. Warm weather reduces the maximum speed these powders will shoot without sabot disruption. They reach 2600fps even in our summer.

There is still the choice of slower powders such as H322, Xmr-2015, N133, 10X, Benchmark all able to make sabot bursting pressure. Some of these might get the 212 grain sabot/bullet to 2800+fps.

This brings up the question why duplex sabots in 45 caliber? The answer is not the same as in 50 caliber. Though the bullet is still unusually light weight it is a lot closer to normal weight than the 250 grain bullet in 50 caliber. So we have a number of powders in a usable working range.

Normally I see duplex loads in 45 as super tuned attempts to get maximum accuracy. If you need to devise such a load for your rifle it's up to you. I'll suggest this: try a single or two and see how sabots work in your rifle. If your accuracy is such that you've got to try again then a duplex might be the trick. With a good barrel I think most of you will be satisfied with a single. On occasion a duplex might also be used on a special load, maybe machined sabots or such but even then it may not be necessary.

Only sabot-less 45 shooting remains. Here again you can go as fast as you like with a single. 45 caliber bullets can be theoretically shot to 3000+fps in this manner. But I prefer a rifle that will kill the game and not maim the shooter. All the powders mentioned for sabots will work and some slower than that as well. So there is no lack of selection.

If you have or have used a sabot-less duplex in this caliber it didn't come from me, well maybe indirectly. There is some debate about how fast the pressure gradient affects engraving but I have found plenty of accuracy in singles. I’m still not to a full opinion if I think sabot-less duplexing in this caliber is necessary at all. But I respect those with another opinion because, "I've been wrong before".

[edge]

Jan 30, 2009 20:30:47 GMT -5 rbinar said:

Jan 30, 2009 19:56:53 GMT -5 ewc said:

And the .40 stuff...

I thought someone might ask that and it's appropriate you were the one.

All 40 caliber shooting is sabot-less. Actually Judd, Steve, Chuck and a few that names escape me have done a good job so far with little input on my part.

It is known that singles will shoot to speed with powders up to the 75 grain loading level. Current speeds at that level seem to be in the 2700fps range.

It is also known a wide range of duplexes will shoot also. Duplex loads in the 85 grain weight are good to near 2900fps. Also it should be of no surprise that the right load will be able to make 3000fps within a very limited pressure range. So I would say the state of duplex in 40 caliber is well advanced. The only trick is to be sure and use a proven load.

Care must be taken not to make the combined powder speed so quick it is wrong for the load contemplated. At 85 grains about 2900fps is a rather mild pressure and this can be seen by vent life at this load level and speed. However to shoot faster one must be careful to use more powder and that would have the effect of shooting with a combined powder speed that's even slower than the 85 (was it 87?) grain load.

The fear I have in this caliber is not development. If proper caution is used it can and I hope will go smooth. My fear is single powder loads will be forgotten with negative consequence. Many might not shoot 40 because they feel it is a "duplex" caliber whereas the truth is 40 caliber is less in need of duplex of any.

Single powder development in 40 caliber is stopped for the time being and that just in it's infant stage. From Judd's results with 4895 and a few others I can tell that a VERY wide speed range is available in the 40 caliber (from 2200 to possibly 3000+fps) with single powders. No other caliber can use as many powders at optimum pressure as the 40. Powders from H4198 to Imr-4895 are already known to work well at load levels from 45 to 75 grains.

I'm content while we play with the optimum duplex at around 3000fps, however let's not decide duplex is an "automatic" in this caliber. The numbers of simple, accurate singles are enormous and it would be a shame to ignore that.