Question about duplex load

[jray57]

I got my breech plug recessed and started to try some duplex loads. The first was one which seems to be highly recommended- 10gr VV110 under 60 gr H4198. I tried this load with BCR sabots and 300 gr Rem .458 also with RCR and Hornady 300 gr .452. Both loaded with good (stiff) resistance, the RCR/.452 being somewhat harder. Accuracy was acceptable with the .458s but not with the .452s. On inspection of spent sabots I found that quite a few of the BCR had "mushroom" or inverted bases and the rest had very open bases. Of the RCRs I could find there were also "mushroom" cups and exaggerated open bases. The sun was too bright so I didn't bother with the chrony. I have never experienced this with single powder "book" loads that have been tested to the high limits. My question is that the good accuracy experienced in using this duplex but with the obviously stressed sabots should I back down on the load and if so how? Do I reduce both powders by the same percentage or reduce the main charge only? And how much reduction is possible/recommended before pressures become too low?

[Dave W]

You can tweak the load by adjusting the ratio. IIRC 10/60 shoots to approx. 2450fps, 9/61 will probably take approx. 20fps off the 2450fps, 8/62 another 20fps off the 2450fps, etc.

11/59 will probably add 20fps to the 2450fps, 12/58 will probably add another 20fps, etc.

10/55 in theory will probably shoot to approx. 2350fps and be a little easier on sabots. The only way to know for sure is to shoot and time the loads.

[youp50]

Fairly common for 458 dia to out perform 452s.

In my stock 50, I duplex with 4759/4198. Petals can be missing, sabots flared. They have been well used. Keep them in mind if you have accuracy issues. Otherwise a stressed sabot causes me no concern

I expect sabots to 'toughen up' after things cool down. If they are holding together well enough in the heat, they will be ok in the fall.

[Richard]

jray............that 10/60 duplex is one I put together a couple of years ago. I mainly shot .458, 300 gr. Remington's with it + Harvester black crush rib sabots. Never had any problem with blowing sabots. I generally look at the skirt on the sabot. If the serrations around the outer edge of the skirt appear fairly even, then NO problem. IF, you start getting bigger chunks of plastic missing here and there, then you might be stressing the sabot. Like Dave W indicated, just play with varying the two powders.
Richard

[deadeer]

I just recently recessed my breechplug also, and I shot the 10/60 duplex today (n110-H4198).It timed at 2520fps with 300 rem/bcr. My gun usually likes 67 gr H4198 at 2350fps, but with the new plug it clocked only 2219fps avg for several groups! Whats up with that? It still grouped good, but the group really fell low on the target. 70gr H4198 shot 2400fps with good groups, as well as 5/65 duplex (n110-H4198) for 2460fps. I want the insurance of a duplex this year after misfiring on a 140" deer last year (luckily got reloaded and scored) but will not go thru that again!
Thanks, Jay.

[chuck41]

Duplex is more trouble to use than single powders, but that added insurance against a "Click-Fooosh" when you're expecting a "Bang" is worth a whole bunch.

[Richard]

You know...................Duplex loads for hunting should be no problem at all. The way I look at it, you get to your hunting location (lets say, by car or truck or maybe staying at a cabin or lodge) and with still warm hands, you load your duplex load..........easy enough? (how many times do you take a second shot at a deer with a ML? Maybe a "coupe de gra'?) or finishing shot? OK, so lets say your load is 5/65 N-110/H-4198 which shoots at say 2450 fps. Now, you know 70 gr. of H-4198 will give you about the same velocity? So, maybe carry an extra duplex in your possibilities bag but also carry a few straight 70 gr. 4198 loads. Now, if you need that finishing shot or some type of follow up shot, just reload with the straight load. If you have time or in fact, missed with the duplex, then you have time to put the duplex back in and continue hunting! Seems like a no brainer to me?
Richard

[deadeer]

;)Excellent idea Richard!

[boarhog]

Deadeer,
I have been thinking about why recessing your BP would result in a 130 fps slower average speed. I suppose that any change in the chamber area could change the burning characteristics of the load. Seems like I remember reading something about Roy Weatherby's claim that the radiused shoulder on his cases improved efficiency, and increased speeds. I don't know if his claim could hold up to independent scientific testing. I would be interested to see a test of recessed, and non recessed BPs, on the same day, same temp, same load, etc.

BTW, I bagged a big doe last season with 10/55 N-110/H-4198 under a 300 gr Barnes OR. Seems like I remember the load averaged just about 2300 fps. Perfect performance!

[Dave W]

Aug 10, 2010 1:23:44 GMT -5 boarhog said:

Deadeer,
I have been thinking about why recessing your BP would result in a 130 fps slower average speed. I suppose that any change in the chamber area could change the burning characteristics of the load. Seems like I remember reading something about Roy Weatherby's claim that the radiused shoulder on his cases improved efficiency, and increased speeds. I don't know if his claim could hold up to independent scientific testing. I would be interested to see a test of recessed, and non recessed BPs, on the same day, same temp, same load, etc.

BTW, I bagged a big doe last season with 10/55 N-110/H-4198 under a 300 gr Barnes OR. Seems like I remember the load averaged just about 2300 fps. Perfect performance!

Did it. OEM plug was slower, more so with slower powders. Others mileage may vary.