How Much Magazine Tolerance Needed?

[LynnJr]

I am wanting to put together a 338 Norma Ackley Improved on a Remington ultra mag action with a PT&G bolt and I want to run a magazine instead of going single shot.
My load with a standard 300 grain Berger OTM is 3.602 inches long and with a 256 Flatline that would be about 3.655 long.

I see magazines at 3.715 and 3.850 inches long. Is that 3.850 mag too long considering most of the taper is taken out of the Norma Improved case?
How much clearance is too little and how much is too much?

[ar15barrels]

You typically need about 0.025" for straight walled cases and more like 0.075" for tapered cartridge cases.
The more tapered the case body is, the more the stack of cartridges turn into a banana inside the magazine.
As they stack like a banana, there needs to be extra length for them to move up as a group.
Extra magazine length is not an issue unless the bullet tips can get caught under the receiver.

[LynnJr]

So Randall you would go with the 3.850 magazine?

[ar15barrels]

It sorta depends on what it takes to run that longer box.
Do you have to cut the feedramp behind the bottom lug seat to get those longer cartridges up out of the box?

[LynnJr]

Constructed of heat treated steel
Coated with a black Teflon finish
Long action magazines are available 338 Lapua
Long action magazines are available in three different cartridge lengths, 3.715", 3.775" and 3.850".
3.715" is used on many factory rifles and the MDT TAC-21 long action chassis (100-008-333)
3.775" is compatible with Remington long action Police rifles
3.850" is compatible with Savage 110 FCP HS Precision .338 Lapua
Polymer followers
Made in USA
AICS style magazines, fit AICS stock and other AICS compatible bottom metals.


This is from a Brownells and and it sounds like 3.775 is the limit without lengthening the feed port. The 3.715 seems to be the standard length and since this is a 338 Norma Improved and not a 338 Lapua Improved 3.715 is all I would need.
It does limit me from switching to 338 Lapua or the I down the road.
I am so used to shooting single shot rifles that this magazine stuff gives me a headache.

[diver160651]

Constructed of heat treated steel
Coated with a black Teflon finish
Long action magazines are available 338 Lapua
Long action magazines are available in three different cartridge lengths, 3.715", 3.775" and 3.850".
3.715" is used on many factory rifles and the MDT TAC-21 long action chassis (100-008-333)
3.775" is compatible with Remington long action Police rifles
3.850" is compatible with Savage 110 FCP HS Precision .338 Lapua
Polymer followers
Made in USA
AICS style magazines, fit AICS stock and other AICS compatible bottom metals.


This is from a Brownells and and it sounds like 3.775 is the limit without lengthening the feed port. The 3.715 seems to be the standard length and since this is a 338 Norma Improved and not a 338 Lapua Improved 3.715 is all I would need.
It does limit me from switching to 338 Lapua or the I down the road.
I am so used to shooting single shot rifles that this magazine stuff gives me a headache.

I use all CIP- for interchangeability.

You can use either CIP or standard with LM cartridge loaded to book COAL; but the magwells are mag specific. It might be worth a bit of feed ramp work for your UM -- BUT; If you're loading at high pressures, other actions would make me feel safer if I was pulling the trigger or your spotter.

Not that "you" may want to chase the lands someday or find something like an MTAC etc in the future, but those might benefit from having the extra room, as does a recoil or drop induced round shift.. CIP is more flexible http://www.milehighshooting.com/accu...-cip-magazine/

CIP- is the longer listed length and typical how it is referred. Many customs, chassis and bottom metals, use CIP.

[LynnJr]

Diver
Thanks for your post as I never even considered recoil or drop and I have thrown my rifle at a buck or two after missing the shot.
I haven't decided on which bottom metal yet mainly my concern was getting those long solids and a 5 round capability with the least amount of issues.
The Norma Improved I am using has very little taper and those rounds always tend to pop out of magazines.