First experience with duplex

[ChrisChampion]

Well I tried duplex for the first time in my 50 cal Savage over the weekend and my results were a little disappointing. My goal is to get a couple of different loads, (either duplex or singles), that shoot very accurate at 2500-2600 fps with a 250g bullet. Once I find the speed level I want then I will tweak for best accuracy.

All loads listed below were shot with 250g Shockwave & MMP HP12 sabots. This combo loads snug in my gun (40-50lbs loading pressure). Temp was in the low 20's. I will eventually try to tweak a load to shoot with the 250g Barnes Spitfire TEZ flat base and Harvester red crush rib sabot. My .50 Savage sports an OEM Savage breech plug with a RW vent liner. I shoot my gun with a fouled barrel and plug and do not swab between shots. Plug, barrel, and vent liner had apx 20 shots on them.

Here are the loads I tried:

65g Duplex
20/45 (SR4759/H322)...Ave 5 shot velocity was 2382 fps
25/40 (SR4759/H322)...Ave 5 shot velocity was 2394 fps

Velocities of both 65g duplexes were pretty consistent. Extreme spreads were less than 30 fps for each.

70g Duplex
22/48 (SR4759/H322)...Ave 5 shot velocity was 2486.

Velocities of the 70g duplex was very erratic extreme spread was about 161 fps (2396-2557).

Accuracy for all the duplex loads varried from about 2" to 3.5" for 100 yd 5 shot groups. Not what I'm looking for. And of course the speeds were at least 150 fps slower than I expected.

After getting these readings I switched gears and shot a few 44g single loads of SR4759 with the same bullet/sabot combo for comparision and only got a 2204 fps average. I expected around 2300 fps with this load, but had never shot it over the chronograph before. I have a plastic jug of 4759 and recall that the new lots in the plastic jugs give slower velocities than the old metal cans. As replies to my earlier post about 4759 velocities indicate that is what most others are seeing.

I then shot the following singles:

65g N120...Ave velocity was 2461
66g N120...Ave velocity was 2504
72g H4198...Ave velocity was 2484
74g H4198...Ave velocity was 2575

The 65gr N120 load was the most accurate of the day putting 6 shots in a 1.5" group at 100 yds. Nothing else shot under 2" at 100 yds.

I questioned my chrono readings so I shot my pet load of 67g H4198 300gr Barnes Original, Harvester BCR sabot a few times and got my normal 2385-2410 fps readings. I also shot a few 150g 30-06 rounds and got just under 2900 fps, also what it normally shoots so I know the chrono was giving me good numbers. I am also very anal about measuring powder and was even more so this time as when I measured out each powder for the duplex loads I measured each booster and primary charge twice to make sure I was right on the money.

I'm not giving up on duplex loads. I think I'll wait until I can get some N110 before trying it again however.

One thing to add. If you are thinking about trying duplex, before you do, please do a lot of research and get some advice from those that have done it before and know what they are doing. My reasons for trying duplex are simple. I want to shoot 250g bullets faster than I can with book powders; I want to do it with the most accuracy I can get; and I want to do it with the least amount of recoil. Alot of guys on this board shoot it and have great success with it. Loading two powders down the bore instead of one was not that big a deal and only takes a few extra seconds at the bench. You have to be careful in your measuring and loading techniques whether you are using a single or duplex. It was fun trying something new and I still have all ten fingers to show for it.

[SW]

I'd try the proven 14/61 VV-110/H-322.

[richard]

Chris: Here are a couple that have worked good for me......

10/60 N110/n120 for 2579 fps
16/59 N110/H322 for 2565
22/48 N110/H322 for 2525

By the way, should the powders get mixed up or you load them in reverse, no sweat, they will shoot just fine. Maybe a tad slower but not by much.
Richard

[DW]

For the 70gr duplex I found a 18/52 ratio the best with the OEM plug and the regular unbonded SW/SST. With N110 as the booster speeds were around 2535fps, but I was not shooting at those temps, probably around 60*.

[RBinAR]

8-)Chris I should have sent you a PM however I'll answer here instead.

The duplex loads you show look promising but they are too slow (bullet speed wise). I know I suggested these levels but the bullet has to make 2500fps with 65 grains of powder to have consistent ignition.

One thing bothers me. That's the fact you show a load that has 5 grains more booster and a bullet speed that's only 12fps faster. That should not happen.

Another concern but not as bad is the 70 grain load is only 2486fps. It should be nearly 2600fp for best accuracy and consistency.

Here's what I'd suggest. First stay with the 70 grain load for now and add more booster in 2 grain increments.If you have to shoot 26/44 or even 30/40 that's ok but get the speed up.

Another thing I'd like to ask is what kind of weather are you having while shooting and how many shots are you firing?

Also you are using a magnum primer right? You need as much energy in ignition for cold weather as possible. Also clean that breech plug where it has NO crud build up. Drill bits are required to do that the plug can hide crud and it's hard to know till it's drilled out.

Since your groups are not too bad I'd think it's only a matter of finding what speed your rifle wants. That's likely faster because most duplexes shoot accurately with speed.

[ChrisChampion]

Thanks RB.

I'll work on the 70g load with higher amounts of 4759 until I can get some N110.

Based on what you told me and what I've read I was surprised about the minor increase in spead despite the 5gr booster increase too.

Weather was in the low 20's, about 65% humidity, shooting into a 10-15 mph headwind.

I started with a plug, barrel, and ventliner that had 20 shots already fired from the day before.

I fired 30 shots total counting the single powder loads. My gun has always shot best on a fouled plug. I'm going to try my next session with the plug fouled but if I can't get any accuracy out of these loads I'll try drilling it out for the next time.

Using Fed209a primers...thats all I ever use.