Necking down 338LM to 7mm

[dinmax82]

Getting a build started, going with an unimproved 7-3338LM first for the brass.

When I built my 6.5 GAP SAUM they said to neck down in small increments from either 300 or 7 SAUM.

I found this article from the old site http://www.6mmbr.com/thirty338.html and they go straight from 338 to 30. Seems like it'd be more prudent to do it in three steps with a bushing die.

How would y'all recommend I go about necking down a 338 to 7?

 

[Warren Dean]

LMAO!!!!!

 

[dkhunt14]

That's a lot of overbore. I would neck to 30 first, then down to 7. I don't like bushing dies to neck down. Matt

 

[Sniper338]

I wonder how much difference it really is between a 7stw volume and 338lm... or 300 nosler...

 

[dkhunt14]

I wonder how much difference it really is between a 7stw volume and 338lm... or 300 nosler...

The 338 Lapua is a pretty big case. I don't know the H2O capacity offhand. My buddy shoots 93 grains of H1000 with a 300 grain bullet. I shoot 104 of R33 with a 300 grain in my IMPROVED. It is a little smaller then a 338-378. Matt

 

[ballistic64]

I wouldn't think there would be much gain over the 7 RUM

 

[dkhunt14]

I looked it up online and guys say Quickload says 108 and guys that weighed say 113 to 114 grains of water. The Lapua case is thick and heavy and can run more pressure then a RUM case. Matt

 

[Sniper338]

Its each to their own. Thats qhat make it a competition!

 

[Dusty Stevens]

That may be comparable in barrel life to my 257stw. At 75rds the barrel looked like a 6ppc with 2500rds

 

[ebb]

This sounds very close to a 7mm Allen mag. My friend has shot this chambering for several years now and loves it. It is indeed rough on barrels, but if you want super performance you must give up something. I think he told me it will go from a 100yd zero to 1000 in less than 15MOA. When he sends it to the smith he sends 2 barrels at a time. You my want to talk to Kirby Allen.

 

[dinmax82]

If I can get 7-800 rounds I'll be happy.

I've seen the AM version and this should be simpler on brass. I want this version for the brass to start with.

Thanks to those that are helpful.

 

[dkhunt14]

If I can get 7-800 rounds I'll be happy.

I've seen the AM version and this should be simpler on brass. I want this version for the brass to start with.

Thanks to those that are helpful.

Maybe or Maybe not. Sometimes it is easier to neck down and fireform. I like the new version to not be a lot bigger then the starting case so fireforming is not that much different then formed ones. Your right with the size of the Lapua case you don't need extra capacity. Matt