Factory 338 Ultra Mag Chamber Length


New Member
Aug 27, 2001
Houston, TX
Does anyone know if the factory 338 chamber has sufficient headspace to use the extra 1/10" of a full length 300 or 375 case?

Assuming one lengthened the chamber (and didn't use the magazine), would 2900+ fps from a 300 gr. MK be possible?

Appreciate any info.



Steve Shelp

Well-Known Member
May 3, 2001
To give you a base line to go by I shoot a 338 Lapua Improved through a 32" barrel. this case has 120.5gr of H20 for water volume and I can go over 3000fps with it. 2900 is easy without pushing it at all and is where my accuracy load falls.

To give you a comparison the 338 Ultra Mag volume according to some others on this board holds 113gr of H20 and I believe Remington is making them with 26" barrels. Some others here have volumed the 300 Ultra and have come up with 116gr I think. So lengthening your chamber will give you more case capacity and end up somewhere aaround the 116gr mark, but the 26" barrel is going to hinder you some also. But you might be able to reach 2900 though. if not your going to come darn close.

Hope this helps.


[ 08-27-2001: Message edited by: Steve Shelp ]

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