338 Remington Ultra Mag load data desired

Dave King

Well-Known Member
May 3, 2001

Just back from Oklahoma where I broke in my new 338RUM. I used some 'pull-push' loads and shot very well. I used the Remington factory 'hunting' load of 250 Core-Lokt, pulled the factory bullet and replaced it with the 250 Sierra GameKing (I didn't have any 250 MatchKings). The BC on the 250 Core-Lokt bullet should be about .420 according to my 'back-figured' BC. The Sierra 250 GameKing has a BC of .570 or there-about. I checked the bearing surface and diameter and felt safe with the 'pull-push' load.
The factory Remingtons have 90.0 grains of some powder and I get 2903 from the 250 GameKing. There seems to be some room for improvement in the velocity arena and the case was not nearly at 100% load density.

BTW, I used 4 rounds for velocity checks to get a ballistics chart (41 yards into a backstop on the scope installation day). I then drove to Oklahoma and used three rounds for the 100 yards zero. My next round was at 900 yards on a 19 x 36 silhouette from SWAG (guessed) data (2/3 the normal 308 come-ups) as I had left my ballistics sheet in the room. I had a miss, high, came down 2 MOA for a center mass hit (21 MOA). My next round was a POA/POI hit at 1000 yards with a 3 MOA come-up.

I fired an additional 10 rounds to get the short range data, backing down from 700 to 200. I played a little on the shorty (19x18) targets at 400 and 500 yards.

George Gardner was there with his 338 Lapua Mag, it's a good deal 'bigger' than the 338RUM. He was shooting 300 grain MatchKings at just over 2900 fps and hitting the steel pretty hard.

Now.... I need to get serious and load some proper bullets. I know I won't get 338 Lapua Mag speeds but I need to reload some decent rounds for 'plinking'.
Who has some load data with 250's or 300's and Reloader 25 or other appropriate powder?

Before there was any published data I did some testing on H-1000, RE-25 and IMR-7828.
I used Speer, Nosler, Sierra Gamekings, Hornady and Swift 250 grain bullets and accuracy and velocity considered, I settled on Reloader-25.
Depending on powder lot, seating depth and bullet I ended up between 91 and 94 grains.
The rifle was a stock Remington 700 BDL-SS (26inch barrel) in a HS Stock and a Timney trigger. With the typical long factory throat, and the bullet set out as far as the mag would allow it was still a .090"jump to the rifling.
I don't do the long range thing. Yet. I ain't good enough! I settled on the Nosler and 93 grains of RE-25. Accuracy is less than an inch at 100 and velocity is 2950fps.
I have never been able to get much over 2950 without pressure signs. I did hit 3000 with one lot of H-1000 but it was a hot load and accuracy wasn't there.
The gun wants to shoot, using Sierra or Hornady bullets and seated way out towards the rifling I shoot several several sub half inch three shoot groups. Smallest was .187".
Anything I can answer, let me know, Joe.

Thanks for the data confirmation.

Here's what I fired today.

Sierra 250 GameKing
Fed 215M
Remington Case
Neck sized once fired cases
Rem 700 action
27.5 inch Pac-Nor barrel
Leupold Vari-X III 3.5x10 M1 Long Range scope
100 yards.

89 grains of RE25, 2883 fps (cold bore shot)
90 grains of RE25, 2864 fps
91 grains of RE25, 2970 fps
92 grains of RE25, 2972 fps
93 grains of RE25, 3037 fps
94 grains of RE25, 3082 fps
95 grains of RE25, 3132 fps slight extractor mark
96 grains of RE25, 3159 fps extractor mark

All rounds fired and plotted onto one target, 4 into .493, 7 into .917 and one (as always) flier. Sweet spot seems to be 92 and 93 grains so I'll go for 92.5 at an estimated 3000 fps.

Today I shot again for more data.

Now I have a mystery going, Darryl and Warren, what am I seeing here?

exerpt from an e-mail I sent...

More data today, RL-25 data but data none-the-less.

Temp 80
Humidity 100
Wind none
Rifle Tac-Ord 338 RUM
Barrel PacNor Polygonal 27.5 inch 1x8
Scope Leupold Vari-X III M1-LR (3.5 x 10 )
Chrony @ 8 ft
Target Distance 100 yards
Primer Fed 215M
Powder RL-25
Case Remington once fired and neck sized
bullet runout - minimal .001
OAL 3.650 (Same OAL for the Sierra 250s)
Bullet Sierra 300 HPBT

#1 80 grains RL25 2403 fps (Cold Bore)
#2 81 grains RL25 2416 fps
#3 82 grains RL25 2452 fps
#4 83 grains RL25 2491 fps
#5 84 grains RL25 2506 fps
#6 85 grains RL25 2548 fps (slight "extractor" mark)
#7 86 grains RL25 2627 fps
#8 87 grains RL25 2636 fps
#9 88 grains RL25 2673 fps
#10 89 grains RL25 2688 fps

I don't know why I have the "extractor" mark on the 85 grain load, I've examined the other loads and I see ever-so-slight extractor marks on the 87 grain load but nothing on the others (I use a 3x, 5x, and 8x jewelers loupe). There is some cratering around the firing pin on the cases but I believe that's due to the looser fit of the Speed-Lock firing pin I have.

I'm a bit perplexed by the powder requirement when compared to the 250 Sierras. I expected to get nowhere near the starting load of 89 grains of RL25 for the 250 when finishing off the big 300s. I believe I'll load several more cases for the 300 load test, I'll use 90, 91, 92 etc until I feel the need to pull the trigger from a distance with a string.

The 300s sit a fair distance into the case, the boattail is below the level of the shoulder at an OAL of 3.650.

Accuracy.... I nearly wet myself!!! I mentioned to you yesterday how I shoot onto one target and plot the hits in an attempt to limit my range trips for accuracy loads. Well, today I began plotting the hits (1.5 MOA low and .5 MOA right from my established 250 grain zero) and ALL rounds impacted essentially on top of one another, so much so that I couldn't distinquish one hit from another. Final group-- .863inches for all 10 rounds of 10 different powder weights. It's just a round raggity hole, I'm pretty pleased.
BTW, today I shot at my usual spot, a farmers field into a bank for a backstop. Shot from the bipod and sandsock, much more natural and comfortable.

I believe I'll be able to get 2700 without a problem but not much more as I'll be on a compressed load. Perhaps the RL22 is the better way to go for the 300, I could perhaps get another 4 grains of powder into the case if I'm thinking correctly.

I'd guess that the powder quandry is that the RL25 is better suited to the much heavier bullet in the larger .338 bore rifle, although RL22 could offer more usable powder it may cause some pressure curve problems. Maybe I should try the RL22 in the 250s.
Dave you may find that, the 300 gr will be your best compititive bullet to use.
At 2700 FPS in the 27" barrel that, is doing just fine.

To bad the throat in you rifle is not extended enough to seat the bullet out further.
A friend of mine at Williamsport has a 340 Weatherby imp. and with his 34" barrel,puts 92 gr of 25 in with the 300 gr bullet. He is doing VERY well with it too.
My load in a 340 Lilja IMP (340 case) rifle I use to shoot was also 90 to 92 grs of 25 or 5010. It did quite well with either powder.

Why extractor marks half way up your test list of powder?????????? Excess head space with THAT case? Bumped the shoulder back to far? I did run into a batch of 300 gr bullets that were just a bit OVERSIZE in the diameter. I measured some that were .3380" and went up to a few that went to one or two that were .3385". Talking to Sierra folks, I found that the allowable limits are to be up to .3384" on that bullet. You may have had a slight pressure problem from a slightly bigger diameter bullet. This happens more then one realizes. It's still a puzzle but, an answer can be found.

I think RL25 may be the way to stay with the 300 gr and experiment a bit more with the 250 gr and RL22

Good luck and your doing fine
Just a suggestion for you.... I've had much beter grouping and chrono numbers using 210 primers over the 215 primers in my 338 Lapua Improved. Have fired the 210 primer as low as 40F. In really cold weather I don't have the experience/data. In my 338 Yogi case I've had better luck using H1000 over R25. R25 SD was close to 40-50fps min/max variation. H1000 is low to mid teens.

Granted the RUM is a little different shape case and different volume so this isn't a 1-to-1 comparison. Just thought I would throw this out for your information.

have you water volumed aany of your cases? If so I would be curious to know what it comes out as. My case is 120.5gr of H2O. This is with the water being level with the top of the neck and an inverted primer cup seated in the primer pocket.

I know that the 300 Rum is larger but here is some thing to compare to. I checked an unfired 27/300Rum, water even with the top of the neck and got 112.6, unfired 300 rum came in at 113.5, and a once fire 300 was 116.4.

Like you said, the 300 RUM and 375 RUM cases are longer than the 338 RUM, by .1 inch I believe. (I believe this was to accomodate the 338 bullets in production with cannelures.)

I'll check the water capacity of a case this evening.
Another load test tonight in the 338 RUM.

Temp 80
Humidity 80%

I tried 90 grains of RL25 over the Fed 215M primers and the big 300 grain Sierra MatchKing. (Load Density 100%)
OAL 3.650 (magazine limited)

Four rounds over the Crony:
2712 fps
2709 fps
2729 fps
2735 fps

Avg: 2721
ES: 26
SD: 12

No pressure signs on any case, first round was cold bore.

I tried the 300 Sierra MatchKing on a crop damage deer at 200 yards, pretty devastating.... it was a bang-flop proposition.

BTW, water capacity for once fired cases, 111.3 grains (water to top of case, primer in backward)
seeinng how you've got the first venison of the season we can all come to your place for steaks right?

Thanks for the info on the water volume. that 111.3gr H20 is just about the same as a standard 338 Lapua Mag volume. I've measured both Norma and Lapua, 338 Lapua brass, right out of the box and it measures roughly 112gr gr H2O before fireforming to my imporved case. I guess R25 is working good for you with those numbers. keep it up.


Yeah... it's the first venison... but we'll be having hamburger and not steaks!

Thanks for the info on the Lapua 338, I didn't check any I have here.

You might find it interesting to mote that I use my 338 Lapua dies to neck size and seat the bullets in the 338 RUM. I reset the sizing die to neck only and the seater I didn't need to change for the 250's, but I needed to run the seater in 1 5/8ths turns to seat the 300s to 3.650.

I received a 338 Rem Ultra as a gift from my wife a few weeks ago. It was very nice of her to hear me say that I was interested in getting one, then to go out and get it for me. Anyway, I mounted a scope on it, worked the trigger down to 2 1/2 pounds and then reloaded a few rounds for it. I had some H870 sitting around to start with and one hundred 300 grain Matchkings.

Here is the data;
Remington 700 Stainless Sendero 26" bbl
Tasco 20x42 Sniper Scope (need a better scope!)
ProChrono@15 feet

300 Sierra MKHP
COL - 3.775" (.010 off the lands)
New re-sized/trimmed Remington Cases
Fed 215GM
Hodgdon H870
100 yds.
Altitude 8800 feet/Temp; 70F - 85F/slight breeze from any direction (mountains)

88.0 gns 2233 fps (cleaned barrel)
89.0 gns 2365 fps " "
90.0 gns 2420 fps " "
91.0 gns 2465 fps " "
92.0 gns 2495 fps (cleaned barrel)
93.0 gns 2485 fps
94.0 gns 2565 fps
95.0 gns 2610 fps

88 to 92 gns went into 2.8"@100 yds. (I would expect from being cleaned after every round fired)

93 to 95 gns went in to .550"@100 yds (without being cleaned after every shot)

No pressure signs were visible on the cases. I cleaned the barrel after each of the first five rounds then after each three shot group.

98.0 gns - 2575 fps
- 2611 fps
- 2594 fps
Av - 2593 fps S/D - 54
group size .880"@100yds.

99.0 gns - 2649 fps (slight ejector mark)
- 2597 fps (slight ejector mark)
- 2674 fps (slight ejector mark)

Av- 2640 fps S/D - 42
group size 1.250"@100 yds

100.0 gns - 2674 fps (ejector mark)
- 2611 fps " "
- 2549 fps " "
Av- 2611 fps S/D - 38
group size 1.760"@100 yds.

99 and 100 gns is over max as the velocity fell off but the pressure increased. Accuracy went away pretty fast also. Looking at the data I would expect 93 to 95 gns to be the sweet spot. This rifle has no brake on it and it recoils very heavy. In fact it was very hard not to flinch as the charge and velocity increased. I may have to put a brake on it to survive the recoil. It kicks much harder than my 340 Weatherby in a Win Mod 70 Sporter.

I'm not sure I trust the Standard Deviation that the chrono was giving me.

I will be trying Reloader 25 and 22 this weekend with both the 250 Gameking and the 300 MKHP. I'll post the data if you are interested.

Sorry for the long post.

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