recomended jump, 338 scenars, smks, b408s

[learjet]

hey everyone im just beginning load dev for my 338 rum, and wondered how far off the lands are u guys seating ur match 338 bullets. this is my first 338 rifle, and im wondering if the 338s are as picky as some other bullets are.

my first attempts were seated .100 off the lands, b408 Lock Bases, w various charges of h4831ssc, cci250s(which i have had here for years). these shot just over 1 moa, and before i start swappin powders, primers etc i thought id see what everyones using for jump. kinda pricey to start closin it in, and testing, so i figd id ask

thx

 

[Lt. Arclight]

Re: recomended jump, 338 scenars, smks, b408s

Most of us load to magazine length. Touching the lands can give a safe load-pressure signs.

 

[learjet]

Re: recomended jump, 338 scenars, smks, b408s

thx. like i said my first 338. my 308 likes .30 off, my 223 likes them a bit closer, and my wsm doesnt care. in the interest of saving ammo on load development im tryin to learn if my .1 jump is excessive for the 338 based rounds, or weather some folks are gettin decent accuracy there. like to not toss too many of these Lock Bases down the tube at that length if theres no point. and yep, thats about all i can get outta my mag atm

thx again

 

[guther]

Re: recomended jump, 338 scenars, smks, b408s

Mine shoots best at no more than .0040 off the lands. It shoots the best at .0020 off. Sierra 300 gr match kings in .338 Lapua Imp. I tried shooting the closer and father than this and got negative results. This is most likely typical that other folks will tell you as well.
Guther

 

[Lt. Arclight]

Re: recomended jump, 338 scenars, smks, b408s

Guess what, there is no easy,cheap way to develop a load. That's another cost that few care to include when they start shooting 338RUM or 338LM.

A valid point is "most" of our 338LM our tactical rigs and magazine fed. If you are stuck with 3.620 coal due to the mag-that's what you use. My AI with a Bartlein 1/9 barrel shot today well with .5 moa at 300 yards with at least a .035" jump to the rifling.

I have fired over 5K rounds of 338LM and learned that bullets stuffed tight into the lands WILL give you overpressure signs. They aren't match rifles-they are exceptionally accurate but if you are chasing the lands,you'll end up chasing your tail because the throat is going to be moving forward as the throat erodes.

You failed to give ANY info other than your stick is a 338RUM. Is it a stock rifle with a factory barrel,has it been rebarrelled?What is the length and twist? Have you figured what your absolute max COAL is? and are you feeding it one at a time or through a detachable magazine? And what do you expect? 1 moa? .5moa?

There aren't alot of guys shooting the RUM as do the 338LM or variants of other 338 wildcats.

Why are you shooting Lapua lockbases when 250SMK's are cheaper and just as accurate.Scenars need to be seated longer to get the ogive forward-whereas the Lockbase's ogive is substantially forward compared to the SMK's and Scenar and will contact the lands loaded shorter. Its more important to use a bullet comparator than measuring the coal. Reloading the 338 isn't any different than any other round- you have to learn what it likes and what it doesn't and that costs money and barrel life.

Another mistake guys make is developing long range loads on how they group at 100 yards. A waste of time ,IMO. Get a load that shoots consistent at 300 and then back up.

If it is a stock rifle-it is only capable of so much. Guys just don't get actions trued and new tubes chambered because they like to spend money. My advice, get Sierra's manual and go from there. Powder Valley has PLENTY of bullets. Good Luck.

 

[learjet]

Re: recomended jump, 338 scenars, smks, b408s

ty again guys. my rifle is a savage rum w a 1 in 10 28" mcgowen barrel. still a work in progress, as my Stockade stock hasnt arrived yet. my friends 338 lapua likes .050 off, and i have no intention of crammin them into the lands. my personal experience w 338s before this one is zero. just lookin for a starting point. max col atm is about 3.62, but i could, if i feel the need, have a longer magbox made by a sheetmetal guy. id rather not, and dont plan on it atm. i decided to start w the Lock Bases for the very reason you mention, gettin them a bit closer to the lands while staying within the length of the mag. got a comparator -

the 100yd issue is something i need to consider. but the 3hr drive to mifflin can be tough to schedule.

hopin for .5ish moa at some point

thx for the info again

lear

 

[Lt. Arclight]

Re: recomended jump, 338 scenars, smks, b408s

learjet,before you do anything with seating depth,you first have to make up a dummy round or use a stony point tool to determine where the rifling in the barrel starts.

At that point,using a bullet comparator you'll know exactly where the rifling starts-this of course changes as the throat erodes. Provided the chamber is cut correctly you'll only have to adjust your load for velocity-the accuracy should still be there.

Its about a 2/1/2 hour drive to mifflin for me. I do have 300 yards 22 miles from my home.

 

[learjet]

Re: recomended jump, 338 scenars, smks, b408s

ive done the dummy / comparator measurements, hence i know im .1 off @ 3.6col. ill forget about the seating depth for awhile, and just work w std load dev techniques, and work @ longer ranges whenever possible. ill get some chrony data as well.

we hit mifflin once a month or more whenever our schedule allows. the 100yd+ ranges closer to here are awful expensive so i havent joined any. can do 300 here on the farm, but im a bit paranoid, i dont shoot anything but vmaxes & rimfires. i try to be a good neighbor hehe. ill pm u next time we plan a mifflin run, we enjoy meeting other LR shooters gettin help, and passin on some where we can. we were just up there last friday, the range is in good shape, although the brush is gettin a bit thick betw 5 and 600.

 

[AKAce]

Re: recomended jump, 338 scenars, smks, b408s

.338 EDGE and .338 RUm that I load for both like to be .005 - .010 off the lands. In my talks with Shawn @ Defensive Edge, he has stated the same. My Savage will run 3.890 in the Box mag .