338 Mega

[PapaSmurff]

Its a somewhat elongated wsm case with a 40 degree shoulder, low body taper and long neck. It has identical capacity as the 7 PRC in the 7 version at 84 grains and the 338 holds around 87 because of the neck diameter. OAL of the case is 2.150"

Ok, I have a fantastic update my friends. I was pressure/velocity testing with H4350 this afternoon when I had an idea: what if I changed over to large rifle primers instead of magnum rifle primers (I've read that this a lot of times helps lower the initial chamber pressures and therefore higher powder charges, yielding more velocity, and better ES is achieved). I'm posting a picture of my test of this using H4350 and 250 Bergers: the large magnum rifle primers are on the right and the large rifle primers are listed on the left side of the page in this picture. I couldn't go any higher because of pressure at 68.0 grains of H4350 using the magnum primers, BUT when I switched over Federal 210 Match primers I was then able to continue testing up to 71.0 grains without any stiff bolt lift (I probably could've went up one more grain to 72.0 before hard pressure signs). So then I decided to test the next powder (Reloder 19) with non-magnum primers this time. The results are incredible.. The velocities I got with RL-19 with both the 250 Berger and with the 270 ELD-X are much higher than I thought could be achieved without massive pressure. I'm posting 2 pictures below with these results from this afternoon. Starting accuracy testing development tomorrow afternoon using RL-19 (I used a 2 ft drop tube weigh RL-19.

 

[ruby76]

Ok, I have a fantastic update my friends. I was pressure/velocity testing with H4350 this afternoon when I had an idea: what if I changed over to large rifle primers instead of magnum rifle primers (I've read that this a lot of times helps lower the initial chamber pressures and therefore higher powder charges, yielding more velocity, and better ES is achieved). I'm posting a picture of my test of this using H4350 and 250 Bergers: the large magnum rifle primers are on the right and the large rifle primers are listed on the left side of the page in this picture. I couldn't go any higher because of pressure at 68.0 grains of H4350 using the magnum primers, BUT when I switched over Federal 210 Match primers I was then able to continue testing up to 71.0 grains without any stiff bolt lift (I probably could've went up one more grain to 72.0 before hard pressure signs). So then I decided to test the next powder (Reloder 19) with non-magnum primers this time. The results are incredible.. The velocities I got with RL-19 with both the 250 Berger and with the 270 ELD-X are much higher than I thought could be achieved without massive pressure. I'm posting 2 pictures below with these results from this afternoon. Starting accuracy testing development tomorrow afternoon using RL-19 (I used a 2 ft drop tube weigh RL-19.

Great results. I found the same thing in my 338 SS. I now use H4350 and F210M.

 

[elkaholic]

Ok, I have a fantastic update my friends. I was pressure/velocity testing with H4350 this afternoon when I had an idea: what if I changed over to large rifle primers instead of magnum rifle primers (I've read that this a lot of times helps lower the initial chamber pressures and therefore higher powder charges, yielding more velocity, and better ES is achieved). I'm posting a picture of my test of this using H4350 and 250 Bergers: the large magnum rifle primers are on the right and the large rifle primers are listed on the left side of the page in this picture. I couldn't go any higher because of pressure at 68.0 grains of H4350 using the magnum primers, BUT when I switched over Federal 210 Match primers I was then able to continue testing up to 71.0 grains without any stiff bolt lift (I probably could've went up one more grain to 72.0 before hard pressure signs). So then I decided to test the next powder (Reloder 19) with non-magnum primers this time. The results are incredible.. The velocities I got with RL-19 with both the 250 Berger and with the 270 ELD-X are much higher than I thought could be achieved without massive pressure. I'm posting 2 pictures below with these results from this afternoon. Starting accuracy testing development tomorrow afternoon using RL-19 (I used a 2 ft drop tube weigh RL-19.

Thats great info Jon! Ive been telling people for years to use std primers in the SS.SST, and Max because of the short burn column and easy ignition, but to be honest, Im a little surprised it still works with the MEGA! It might be only with the bigger bore MEGA because of faster burning powders, but it would be nice for someone to test the 7 MEGA. Ill be trying some in my Yukon you can bet!

 

[PapaSmurff]

Thats great info Jon! Ive been telling people for years to use std primers in the SS.SST, and Max because of the short burn column and easy ignition, but to be honest, Im a little surprised it still works with the MEGA! It might be only with the bigger bore MEGA because of faster burning powders, but it would be nice for someone to test the 7 MEGA. Ill be trying some in my Yukon you can bet!

I have 4 sets of 270 grain ELD-X's ready to start accuracy testing with tomorrow afternoon 71 through 74 grains of RL-19. Will continue to post my results as things progress.

 

[PapaSmurff]

Ok, I have some more updated results: I was having a difficult time getting the accuracy that I wanted on a consistent basis, within normal operating presssures, with the 270 ELD-X or the 250 Bergers. Some groups were turning out fantastic and some were turning out not so fantastic. Also when I went to resize my brass I noticed that it was very difficult to resize (a clear sign that I was running my loads at very high pressures..). Therefore I backed off my powder charges and started finding consistent accuracy with about every bullet I have been working with. That being said, the 270's are just too heavy of a bullet for this cartridge unless you use the long throated reamer that Rich offers. I chose to use the medium length reamer and then uni-throat another .130" which I thought would be plenty, and it is except I had forgotten how much Hornady's always seem to like A LOT of jump. Most of my accuracy loads with Hornady ELD's in most calibers I have loaded for, seem to wanna jump around .100". If I seat the 270 ELD's that far down in the case I will only have enough powder capacity and the pressures will be too high for me to get much more than the 2,600-2,650 FPS velocity range with them. However my throat length is plenty long enough to push the 250 Bergers anywhere from 2,700-2,800 fps with acceptable pressures. So now on to my progress in the next post.

 

[PapaSmurff]

After all the testing I've done so far (around 200 rounds) I think I came up with a cool idea for this cartridge that I don't think anyone else has tried just yet perhaps. My Ruger rifle will handle an overall cartridge length in the high 3.4" range. So I tried some Cutting Edge .338 caliber 250 grain single feed Lazer bullets in it. Even though they're single feed, the cartridge overall length that I found best accuracy at with them is 3.445". Since they're single feed bullets, most of the bullet is forward of the seal tight band, not behind it so the bullet shank doesn't protrude down into the case farther than the neck shoulder junction for the boat tail/ogive junction of the bullet; therefore not taking up precious powder capacity. Anyways, I finally have consistent 1/3"-.4" accuracy results group after group at ranges up to 725 yards with 72.0 grains of Reloder 26 and a cartridge overall length of 3.445" yielding a velocity of 2,700 fps and single digit ES with the single feed 250 grain Cutting Edge Lazers. I can easily load them up to around another 75-100 fps by adding a couple more grains of powder but the accuracy wasn't consistent at velocities above 2,700 fps. The Lazers look awesome when loaded up in the the 338 Mega case too! Posting several pictures below: picture of some of the Lazers loaded up for testing, picture of my sight in single head shot on 200 yard target, grouping of 3 shots on my 300 yard target that measures around 1" center strike to center strike, and also another 3-shot group on my 725 yard target that measures 2 3/4". I think I've got a pretty good feel for the 338 Mega now and if anybody is interested in building one and has any questions then please feel free to PM me and I'll be happy to answer. It is a wonderful cartridge indeed for anyone wanting a 338 with true long range performance potential, but not wanting all the extra muzzle blast, recoil, heavier weight, longer action requirements, etc. of the 338 Lapua. Pictures from todays described above progress are posted below.

 

[Mike D Texas]

After all the testing I've done so far (around 200 rounds) I think I came up with a cool idea for this cartridge that I don't think anyone else has tried just yet perhaps. My Ruger rifle will handle an overall cartridge length in the high 3.4" range. So I tried some Cutting Edge .338 caliber 250 grain single feed Lazer bullets in it. Even though they're single feed, the cartridge overall length that I found best accuracy at with them is 3.445". Since they're single feed bullets, most of the bullet is forward of the seal tight band, not behind it so the bullet shank doesn't protrude down into the case farther than the neck shoulder junction for the boat tail/ogive junction of the bullet; therefore not taking up precious powder capacity. Anyways, I finally have consistent 1/3"-.4" accuracy results group after group at ranges up to 725 yards with 72.0 grains of Reloder 26 and a cartridge overall length of 3.445" yielding a velocity of 2,700 fps and single digit ES with the single feed 250 grain Cutting Edge Lazers. I can easily load them up to around another 75-100 fps by adding a couple more grains of powder but the accuracy wasn't consistent at velocities above 2,700 fps. The Lazers look awesome when loaded up in the the 338 Mega case too! Posting several pictures below: picture of some of the Lazers loaded up for testing, picture of my sight in single head shot on 200 yard target, grouping of 3 shots on my 300 yard target that measures around 1" center strike to center strike, and also another 3-shot group on my 725 yard target that measures 2 3/4". I think I've got a pretty good feel for the 338 Mega now and if anybody is interested in building one and has any questions then please feel free to PM me and I'll be happy to answer. It is a wonderful cartridge indeed for anyone wanting a 338 with true long range performance potential, but not wanting all the extra muzzle blast, recoil, heavier weight, longer action requirements, etc. of the 338 Lapua. Pictures from todays described above progress are posted below.

I love the CE Lazer bullets. That are proving to be ridiculously easy to tune in every rifle I have tried them in.

This is from my 338NMI with the 275 Single feed Lazer. The seal tite band sits perfectly about .010 ahead of the case mouth when touching the lands. This was a fireforming load with N570 at 2914fps.

Of course it could be the rifle because I've never gotten ABLR bullets to shoot that good so easily.

Again fireforming and touching the lands.

 

[cmcshooter]

I have lurked and never posted, but Rich suggested I share all my data for the 338 Mega. I'm including all my powder tested, charges, and velocitiese. I'll also include a chart that might be close to accurate for energy and velocities, etc. My final loads for the 250 Berger OTM and the 250 SBD2 are at the end. FYI, I am on my 18th firing for my first 16 pieces of brass. This is exceptional brass life given the performance I'm getting out of my final loads. Hope this helps.

338 Sherman Mega
ADG Sherman 300 Mega Brass CCI 250 Primer
Case Length after Necking up=2.147 Case Length after Fire Forming-2.137
Fire Formed with 64 gr. RL19 (2540 FPS) with Spear 225 gr. Bullet jammed at .020"

Final Neck tension is .004 (364 bushing)


Pressure Testing
250 Berger OTM (.010" off lands) RL26

75 gr.	2886
75.5	2892
76	2917
76.5	2955
77	2918
77.5	2928-No pressure but load feels compressed but not pushing the bullet out.

250 Super Bulldozer 2 H4350

65	2707​
65.5	2708​
66	2738​
66.5	2753​
67	2770​
67.5	2772​
68	2789​
68.5	2794​
69	2820​
69.5	2854​
70	2861​
70.5	2864​
71	2909​

250 Super Bulldozer 2 N550

68	2892
68.5	2914
69	2918
69.5	2939
70	2943
70.5	2963
71	3003-Pressure Signs

338 Sherman Mega 1000 Yard Data (250 Super Bulldozer 2)

Muzzle Vel	1K Vel	1K Energy	1K MOA	Supersonic (roughly)
2770	1869	1939	24.6	1900
2800	1891	1986	24.0	1900
2850	1931	2072	23.0	1950
2900	1973	2159	22.1	2000
2950	2013	2249	21.3	2050
3000	2053	2341	20.5	2100

Here are my final loads, but at least the info above can let you see the ballpark velocities for a few different powders with two different bullets.
338 Sherman Mega (250 Berger OTM)
250 Berger OTM
ADG Brass
Case Length=2.139"
Shoulder set at 1.767" with E-420 Gauge
Ogive=2.265" (.110" Off Lands)
CCI 250 Primer
68.5 gr. N550 @ 2940 fps


338 Sherman Mega (250 SBD2)
250 Super Bulldozer 2
ADG Brass
Case Length=2.139"
Shoulder set at 1.767" with E-420 Gauge
Ogive=2.283" (.090" Off Lands)
CCI 250 Primer
67.8 gr. N550 @ 2860 fps

 

[PapaSmurff]

I have lurked and never posted, but Rich suggested I share all my data for the 338 Mega. I'm including all my powder tested, charges, and velocitiese. I'll also include a chart that might be close to accurate for energy and velocities, etc. My final loads for the 250 Berger OTM and the 250 SBD2 are at the end. FYI, I am on my 18th firing for my first 16 pieces of brass. This is exceptional brass life given the performance I'm getting out of my final loads. Hope this helps.

338 Sherman Mega
ADG Sherman 300 Mega Brass CCI 250 Primer
Case Length after Necking up=2.147 Case Length after Fire Forming-2.137
Fire Formed with 64 gr. RL19 (2540 FPS) with Spear 225 gr. Bullet jammed at .020"

Final Neck tension is .004 (364 bushing)


Pressure Testing
250 Berger OTM (.010" off lands) RL26

75 gr.	2886
75.5	2892
76	2917
76.5	2955
77	2918
77.5	2928-No pressure but load feels compressed but not pushing the bullet out.

250 Super Bulldozer 2 H4350

65	2707​
65.5	2708​
66	2738​
66.5	2753​
67	2770​
67.5	2772​
68	2789​
68.5	2794​
69	2820​
69.5	2854​
70	2861​
70.5	2864​
71	2909​

250 Super Bulldozer 2 N550

68	2892
68.5	2914
69	2918
69.5	2939
70	2943
70.5	2963
71	3003-Pressure Signs

338 Sherman Mega 1000 Yard Data (250 Super Bulldozer 2)

Muzzle Vel	1K Vel	1K Energy	1K MOA	Supersonic (roughly)
2770	1869	1939	24.6	1900
2800	1891	1986	24.0	1900
2850	1931	2072	23.0	1950
2900	1973	2159	22.1	2000
2950	2013	2249	21.3	2050
3000	2053	2341	20.5	2100

Here are my final loads, but at least the info above can let you see the ballpark velocities for a few different powders with two different bullets.
338 Sherman Mega (250 Berger OTM)
250 Berger OTM
ADG Brass
Case Length=2.139"
Shoulder set at 1.767" with E-420 Gauge
Ogive=2.265" (.110" Off Lands)
CCI 250 Primer
68.5 gr. N550 @ 2940 fps


338 Sherman Mega (250 SBD2)
250 Super Bulldozer 2
ADG Brass
Case Length=2.139"
Shoulder set at 1.767" with E-420 Gauge
Ogive=2.283" (.090" Off Lands)
CCI 250 Primer
67.8 gr. N550 @ 2860 fps

Very good write up and impressive results. I could get quiet a bit more velocity with my 26" Ruger semi-custom rifle chambered in 338 Mega as well, but I just couldn't seem to get the consistent "under half MOA" group accuracy until I dropped back to around the 2,700 FPS mark with whatever powder I chose. Very possibly could be my particular rifle just doesn't like the higher nodes however. Will be picking up my second 338 Mega (a semi-custom Bergara build) at the end of July. Anxious to see how well the load develop goes for that one.

 

[Reemty J]

Could you show the cartridge in a photo compared to another known caliber/cartridge, say a 338 win mag? Thank you

 

[cmcshooter]

Could you show the cartridge in a photo compared to another known caliber/cartridge, say a 338 win mag? Thank you

You bet. Left to right: 7 rem mag with 168 Berger VLD, 338 Mega with SBD2, 338 Mega with 250 Berger OTM.

 

[elkaholic]

You bet. Left to right: 7 rem mag with 168 Berger VLD, 338 Mega with SBD2, 338 Mega with 250 Berger OTM.

Thats a good comparison because it sheds light on the difference in the 7 MEGA and the 7 RM. The MEGA will blow the doors off of the RM and do it in a mid action if you want to,

 

[Reemty J]

What parent case is it based off? Looks like a short fat efficient case.

 

[elkaholic]

What parent case is it based off? Looks like a short fat efficient case.

Its a WSM case head but its .060" longer than a WSM and is "Shermanized" as people like to say now. Simply means low taper, longish neck, 40 degree shoulder. Ackley but more of it, and not necessarily formed from a salami parent without modification, which the MEGA fits.