Home Forums Reloading Big Game Rifles 708 loads using Horn 139sst

Plan on using big game, varget and h4350 for testing. I currently run the pharm load (46.2 big game under a 150 eldx with a LRMP). My question is what seating depth are you guys using for the 139 sst. With the 150eldx I found my sweet spot about .070 off jam.

If you measure factory ammo you will find the COAL is almost between .010 and .020" shorter than the cartridge dimensions shown in the loading manuals . I am sure this is so ammo will chamber in any gun. For hunting this is how I load my ammo.

Years ago I loaded ammo in my Savage 16 about .010" from the lands and my 708 shot great. However, while hunting pigs one afternoon I unloaded my gun ( a blind magazine model ) and when I ejected the cartridge the bullet stuck in the barrel and it threw powder everywhere. I was through for the day. What I think happened was there was some variation in the location of the ogive. At that point I started comparing factory ammo to hand loaded ammo and discovered that factory ammo is shorter than the Specifications shown in Reloading Manuals. Also all the factory ammo I have seen is crimped . I crimp all my ammo with a Lee Factory Crimp die.

Jambuster, that right there is why I never ever load hunting ammo closer than .020 if I can help it. Most times I can find a real good load somewhere between .040-.090 even with C&C bullets. My Sauer 101 in 30-06 likes the 150 Sierra PH best at .080 off as just one example of many.

My ammo is loaded and unloaded into rifles many times during hunting season, carried in vest pockets. A scuffed up case head, a piece of dirt or debris of some kind, any number of things and all of a sudden it's tight without a person knowing it. Less than .020 on a caliper is a cat whisker between the jaws. For me and hunting it's function, function, function, first and foremost or otherwise I figure it will bite me at the most inopportune time.

Same thing with crowding the mag length. I try to let .045 minimum. Just for me and my peace of mind knowing things will always work, if someone else wants to do it different, no skin off my back.

Did a small test loading from 46-48 grains of big game with a LRMP in .5 increments. Went and chrono’d those loads yesterday using my 2.185 bto (.065 off jam). keep in mind this in new hornady brass never fired and I’m also fire forming the brass. Velocity was 2700-2750 between all loads. Not much difference which I found strange. Shot 5 strings of 5 shots each load. 47.5 was the most accurate but nothing I’m happy with. Today I went out with another 5 strings. 47.5 with 2.160 bto, 47.5 with 2.170, 48 with 2.170, 48.5 2.185 and 49 with 2.185. 1 full grain past book max to see if I find pressure or better velocity. 47.5 with 2.160 shot 2780 and tighter group, 2.170 opened up a bit. 49 grains got me over the 2800 fps no pressure signs and not great group. Thinking these sst and my rifle prefer a bigger jump so gonna test that out next test day.

I do like to run my COL on the longer side but like stated above no closer than 0.020 but most of mine are around 0.050 -0.100 from the lands. Running long COL is overrated especially with hunting rounds and can cause problems in the field.

I load ssts in 3 rifles. Still working on one but the other 2 rifles would not shoot sst’s close to the lands. In one I know 0.060 off and other i think is around the same or there about. I shoot 708 xbolt with 139sst but I use varget/42 grs gives me 2775. I think last 5 shot group give me ES of like 3 using lab radar. Inch groups at 100. Working with big game/47.5 grs added another 100 fps but accuracy wasn’t great just decent. I think this gun likes the ssts but just don’t love them as it took a lot of effort just getting these one inch groups with varget

Thanks for that info. I’ll keep posting my results.

Got in the blind, went to load the same round I had chambered, ejected, repeat at least 10X. This time the bolt would not cam for any amount of money. Thought all of what you mentioned above. After repeated attempts, I removed the bolt, looked into the chamber, ran my finger up in there, found nothing. Looked at the bolt and there, perfectly paper punched, was a leaf the diameter of the breech face inset. It created a no-go situation. I even had packed up the gun in defeat, but then gave it another try.

Went out again today with more 139 sst. Tried a few strings with imr4350 for velocity and did a seating test with the big game.
The 3 strings with imr 4350, 45.5, 46, 46.5 grains. All shots were in the 2640-2700 fps range. I was kinda disappointed with the velocities and didn’t find anything accurate. Will do more testing. No pressure signs at all

Did 5 strings with big game and LRMP. 47.5 grains averaged 2800 fps and 48 grains averaged 2840 and a .6 moa group at 100yrds. The es/sd on the 48 grains was higher than the 47.5 but much more accurate. Getting close but not there yet. These sst seem to like a big jump compared to the eldx I normally shoot Gonna seat deeper. Will keep testing.

Don't know if the ogives are the same, but I'm loading 139 Interlocks on top of 43.5 Varget at 2.800. Getting 2842 from a 22" Montana. Dont know what the jump was (cant find it in my notes), but i could measure it again. Before heading to NY deer camp, I went to the local range and shot (3) 3 shot groups of .511, .490 and .427.

I could not get 139sst to group in my rifle. I adjusted powder and OAL. Best I could do was 1.5" groups, in a rifle that will print clover leaves with other bullets.

If you have 150eldx working well, I'm not sure its worth your time to mess with a lower BC 139sst.

If you are not happy with your 150eldx and big game performance, work up to ~41 of varget or ~40 of IMR-4064; both of these are crazy accurate for me at 2720fps from a 22".

Because I love to test and make new loads. Next I have Berger 168 vld to develop a load for. It’s a fun hobby that never quits teaching you.

Thanks I’ll give varget a try. Have a few lbs of that. Appreciate the info. Cheers