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Question for you .338 guys!

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Old 09-08-2006, 11:42 PM
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Join Date: Jul 2001
Location: San Antonio, Texas
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Question for you .338 guys!

I will soon be starting another project, a .338-300RUM. I will be purchasing the reamer myself and was curious if you guys could give me any direction on throat diameter, length, and angle. I am planning on having the neck diameter be somewhere between .362"-.360". OH! should the neck be tapered toward the case mouth? If so how much? Will be using either the 250gr or 300gr SMK. Rather go with the 300gr.
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Old 09-09-2006, 06:58 AM
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Location: Pennsyltucky
Posts: 2,624
Re: Question for you .338 guys!

went through this a while back and i can give you some numbers. when you push rem or fed brass out to 338 and put a bullet in it, the neck of a loaded round will measure 365. can't speak for nosler brass but i would be surprized if it was much different. my chamber has a 368 neck and i'm gonna try them first without turning any off the necks because i don't think this makes much if any difference in accuracy.i'm fairly sure Shawn has his necks around 372.

i think 362 would be too tight and 360 simply out of the question. neck thickness of less than .012 is not enough for bullets and cases this size. a .012 wall thickness would make a loaded round of 361 or 362 and i like around .003-4 clearance. 365 would be the minimum i would consider.

as far as tapering the neck area i don't think it's needed.
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Old 09-09-2006, 07:44 AM
Join Date: Jun 2007
Location: North Idaho
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Re: Question for you .338 guys!

I would concur with Dave. I even go as far as to run factory spec neck (.372"), I am not a detail reloader unless I see a serious benefit. I have seen dramatic improvements in accuracy by checking how good your dies are and how streight they size the neck. I have seen little improvement in tight necking a rifle of these calibers.
Shawn Carlock

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Old 09-09-2006, 09:51 AM
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Re: Question for you .338 guys!

I would agree with Dave and Shawn. I am not a huge fan of tight necks either. I played with them quite a bit a long time ago when that was THE THING to do.

Now if your trying to cut 100 yard groups of 0.15" to 0.1", like the BR shooters are doing, that may be another story, that not what we do here on LRH. In fact most of us will seldom shoot at 100 or even 200 yards, groups at long range are what counts and to get that you need quality, consistant ammo and a properly built rifle.

Dies are critical and well worth spending what you have to to get a good match grade set. Do not cut any corners here.

You want bullet run outs of no more then 2 thou and preferrably under 1 thou.

As far as the chamber design, I am pretty standard. I use a 1-30-00 angle and have my reamers cut to 0.0005" over bullet diameter. Be careful here though. If you want to use a specific bullet say, a 250 gr SMK or a 300 gr SMK, order some in and put a mic to them. Do not just go off the nominal 0.338" diameter because it will bite you in the rear most of the time. Get the actual bullet diameter off the actual bullet and then add the 1/2 thou to that number.

If you will want to try multipule bullets, measure them all and cut the throat to the largest diameter.

One good example is comparing a 300 gr SMK to a 225 gr Accubond. The accubond generally runs a full thou smaller then most conventional cup jacketed bullet. Just something to keep in mind.

As to the taper in the neck, there is a reason for it, really nothing to do with the performance of the rifle though. What it allows you to do is have the reamer sharpened down the road much more often then a true cylinder neck design.

This is because, since there is a slight taper on the neck, when you send the reamer back to the reamer maker for resharpening, they only have to set the reamer back a small amount to get a totally clean and fresh neck from the resharpening.

In the straight cylinder design, if you happen to have the neck diameter reduce with wear, the reamer will need to be set back the entire length of the neck to get it back to original specs.

Now in your case you will not be using this reamer alot I would not imagine anyway so this is not a huge concern for you. Were you a gunsmith using this reamer over and over, I would say get the tapered neck.

In my opinion, the majority of the accuracy produced by the rifle, assuming all else is machined as it should be will happen in the throat and at the crown.

Alot of guys make a big fuss about tight chambered and such but in the overall picture for LR shooting, this means very little.

That is not to say you do not want the body of the chamber to fit the cases well because you do, but this is more for increasing case life then improving accuracy.

Good Luck,

Kirby Allen(50)
Kirby Allen(50)

Allen Precision Shooting
Home of the Allen Magnum, Allen Xpress and Allen Tactical Wildcats and the Painkiller Muzzle brakes.

Farther, Faster and Flatter then ever before.

Web Page: www.apsrifles.com

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Old 09-09-2006, 09:58 AM
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Re: Question for you .338 guys!

I think the standard leade angle of 1' 30" works fine. NEck diameter depends on how much clearance you want to run and how much you have to neck turn to get the neck walls the same thickness all the way around if you care about that sort of thing. I tend to believe that a uniform release of the bullet under pressure is a good thing no matter what caliber you shoot. If it only makes .010" difference in your group, then you might not care but I want all the accuracy I can get.

Both the 338 thunder and the 338 moag run about 1 and three quarter thousandths clearance. This is surely a bit tight for big game rifles, but my thunder is cleaned and checked regularly for foreign debris. It is not treated in the same manner as my other big game rifle.

The neck diameter on the 338 thunder is .367" THis diameter cleans up the neck perfectly. I don't know if the 300 ultra brass is the same way. It sounds thinner.

The tapered neck idea is not beneficial or necessary.
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Old 09-10-2006, 08:49 PM
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Join Date: Jul 2001
Location: San Antonio, Texas
Posts: 244
Re: Question for you .338 guys!

First off. Thank you all for the responses, they were all helpfull.

Fifty Driver

You being a gunsmith I thought you might be able to answer this question. I already have a 270-300RUM floating pilot reamer.
#1 is it possible?
#2 would this be advantageous, {financially that is} vs. buying 338-300 reamer"
For me to get the appropriate pilot for the new .338 barrel and purchase a neck and throat reamer, use the 270-300 reamer {with .338 pilot} to cut the chamber and use the neck and throat reamer to finish. The 270-300 reamer is carbide and has been used only once!

Also I had planned on [already have the brass] using 375RUM brass and necking down to .338cal, so neck turing will be a necessity. No big deal, already turn necks for the 270-300. Now to the actual neck diameter, lets say .002-.003" clearance and turn necks to .365" so the reamer should be ground to .367-.368". Sound about right?
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Old 09-11-2006, 05:58 AM
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Join Date: Feb 2004
Location: Pennsyltucky
Posts: 2,624
Re: Question for you .338 guys!

TX, i'll let Kirby answer the reamer question but if it were me,i'd just spend a little more and get a 338/300 reamer instead of buying a neck and throating reamer.

as far as neck clearance, i'd stay with .003-4 thousands on a loaded round, .002 on a hunting gun is a little snug.

the main advantage of using 300 brass is that you can use other brass like federal or nosler that has a little better quality than remington.
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