338BR/338 Whisper noob questions

[MadRabbit]

Guys, I'm considering a build in .338W (338/7BR). I'm so new to this idea that I don't even know what to ask.

Here's what I'm looking for out of it: Longer range accuracy (500-600 yards minimum ideally- never opposed to reaching farther though), primarily subsonic suppressed shooting, and planning on using 300gr SMK's. I've combed these forums using every name I can think of for the cartridge, and really can't find very much info. I've read every thread I did find hoping to avoid being the noob that asks the same thing that's been asked and answered a million times already, but still haven't gotten what I'm looking for so here goes...

My primary reasons for choosing the 338W is 1) I already have a stripped 700 action with a .308 face waiting for a purpose in life. 2) Acoording to Cartridges of the World this seems to be suitable for my range/accuracy aspirations.

I'm thinking the bbl length should be somewhere in the 12"-16" range (I understand the SBR issues), and around a 1:7 twist.

I guess my two biggest questions are: Is this a suitable cartridge for the ranges I'd like to reach, or is something better suited for this (ie. 510W)? Am I in the ballpark on the bbl length and twist?

Any input is appreciated, just trying to use the action I have if possible. Thanks for any help you can provide.

[BWE Firearms]

First I would much rather sell you one of my 338 THUMPERS since it is the best cartridge that will ever be designed.:grin: But I do understand wanting to use the action you have. You never said what you are going to be using it for which can effect if it is suited for what you are doing with it. I would shoot a hog at 500 yards with our 50 THUMPER but until I do some more testing I don't think I would shoot one with our 338 THUMPER at this point, but the 338 is great fun to shoot steel targets at 500 yards.

In researching subsonic rifle cartridges I found that they all have close to the same drop which at 500 yards is about 23 feet. The limiting factor with subsonic cartridges is the amount of drop and not the range they can shoot accurately.

You are correct in barrel length, I would suggest to not go shorter than 10" for what you are doing and 14"-16" would probably be ideal. I use a 8" twist on my 338 THUMPER and have not had any problems with stabilizing anything.

As far as subsonics being a good choice for that you want to use it for its kind of up to you. If you can deel with the drop you should be fine.

[amafrank]

Despite thread jumpers trying to sell you stuff other than what you are asking about, the 338BR is a great cartridge and quite versatile. It will do what you want. As richard noted any .338 will have about the same ballistics if you're starting at the same speed. The advantage to the 338 BR is that it will fit your bolt face unmodified and is already pretty well tried and true. The .338 bullet has great ballistics and if you've got a scope with enough elevation adjustment you can get out there to 1000yds. There is also enough room in the BR case to load supersonic which gives you more possibilities. Thats a big advantage over other subsonic 338's. Depending on exactly what you want other cartridges might be just as good. The 510 is really neat but brass is expensive and harder to make. Its also a pretty large and long cartridge so mods would have to be made on the bolt and receiver to make your current rifle action work. It does do the job though and has the advantage of being able to find "fun" bullets like tracers, API and APIT and even spotter tracers though they require a special throating reamer be used. So the basic question is what do you want and what rifle are you starting with. From what you've posted the .338BR is an excellent choice.

Hope that helps and if I feel the need to sell you something I'll post it on the for sale boards where those posts belong.

Frank

[BWE Firearms]

I have to appologies for my earlier post. I ment the first line as a joke. I was not trying to sell you something you didn't want. I refer to my THUMPERS as I have more experience with them then other subsonic rifle cartridges.

Frank brings up a good point in regards to case capacity. You will be able to get good supersonic velocities with the 338 BR. With our 338 THUMPER we get about 2100 FPS before we run out of case capacity and the 338BR has a much bigger case volume.

[Spook]

I use a 8" twist on my 338 THUMPER and have not had any problems with stabilizing anything.

Mr. Hoffman, whats the heaviest bullet you've stabilized with the 8 twist and have you fired anything lathe turned or cast?

[BWE Firearms]

I have shot the 300GR Sierra Match Kings and the 300 GR. Woodleigh RN which have both stabilized fine and shot well. I just cast up some 220 gr from a Lee mold but I have not shot them yet. If anyone known of some heavier bullets they want me to try I'm game.

[BWE Firearms]

Spook,

What is the heaviest 338 bullets you have found. I have only foung 300 GR and 220gr molds for the cast. If you wanted some cast bullets let me know. They are not sized but they are cast up if you want somt to try.

[MadRabbit]

Glad to hear I'm not completely off base so far. amafrank, what are your thoughts in regards to barrel length and twist rate for the 338BR?

The project just moved ahead a step, the research continues...:smile:
Thanks guys.

[Spook]

Spook,

What is the heaviest 338 bullets you have found. I have only foung 300 GR and 220gr molds for the cast. If you wanted some cast bullets let me know. They are not sized but they are cast up if you want somt to try.

300SMK, 300 Lapua so far,260 Glenhill cast on hand in quantity but thanks. All three went very sub MOA in the rifles I've built. I am surprised that an 8 twist stabilizes the 300's @ your elevation (atmospheric density) as both JDJ and the Engineers at Berger told me to use at least 7.

I've been going with a 6.5 twist x 16.5 barrel in anticipation of shooting Lehighs lathe turned 338 and Hornady is about to give 338 shooters a nice surprise from what I'm told.
The lathe turned bullets make the subsonics really shine over distance if my other rifles are any indication.

Mad Rabbit it seems your thread is getting hijacked, sorry.
Where in CO are you?

[amafrank]

I think that anything over 16" doesn't really gain you anything other than a little safety in legal barrel length. Anything under means you have to register it as a short barreled rifle. So my opinion is 16" maybe + a quarter inch to be on the good side. As far as twist rate I've been looking at 1:7 or 1:8. The larger diameter of the .338 over the .30 cal will give it more gyroscopic stablity at the same rpm relative to the .30 cal but on the other hand those 300gr SMK's are mighty long. I think I'd have to say listen to Spook on this one as he's actually been doing some shooting and I'm still working on collecting parts to put one of these together. Its not always possible to simply compare other cals to come up with twist rates. Over spinning is less likely to give you problems as compared to underspinning too. I'd hate to knock the baffles out of a can if I wasn't a class 2 manufacturer. I hate to knock them out even being a class 2....
One piece of advice is to buy a good quality blank to have your barrel made. Its worth the cost to have a component you know is correct so you aren't chasing a number of unknown variables with a new rifle and cal.
Hope that helps

Spook,
I'd have to say that the heaviest .338's I've seen are the 300's too. The SMK's and some other round nose designs. . . I've been looking at having a mold made up for both the .338 and the .510 but not sure what design I want or weight. We've been shooting the 510 more but all the .338's have been in the Lapua.

Frank

[Spook]

10-4 Frank, me too. The Lehighs are waaay long and The scuttlebutt @ Hornady is a 285 gr., .338 that has the highest BC of any 338 bullet around which says "brass solid" to me...its gonna be long too.

You might want to give Glenhills in WI a call..his prices ar so reasonable for sized and lubed w/gas check that I couldnt see going through the trouble of casting my own.

[BWE Firearms]

MadRabbit,

I would also follow Spooks advice and go with a faster twist barrel then an 8" twist. I used the 8" twist because I was in a rush to get the prototype done and that is the fastest twist Shillen had in stock at the time. I did not think the 300 GR Match Kings were going to stabilize but they do.

As amfrank said its a lot different when you are a Class 2 manufacturer. If you destroy a suppressor in testing you simply build a new one.

Spook have you ever had a gas check come loose in a suppressor. I haven't used gas checks for that reason, and I have been playing with turning a rebated boatail on my .512 700gr cast bullets. I haven't been able to tell if it helps any but it doesn't hurt and it makes them easier to load.

[MadRabbit]

Don't sweat the hijack spook, this is all so new to me that I'm just basking in the knowledge being tossed around here, on topic or not. No hurt feelings on my end. :smile: Now on to the search for a .338 with a 1:6.5 or 1:7 twist...

[BWE Firearms]

Check with Shilen. I think they try to keep a couple of each of the faster twist barrels in stock. They were just out when I needed mine.

[alorton]

If you are looking for a .338 subsonic have you looked at the .338 Specter? Cases can be formed from 6.8 SPC or 10mm cases. While it won't give you the potential in supersonic, it comes in the lighter AR15 platform and if you just want to shoot suppressed subs there really is no disadvantage. Just a thought.

Heres the FAQ for the round at ar15.com:

http://www.ar15.com/content/page.html?id=559

[Spook]

If you are looking for a .338 subsonic have you looked at the .338 Specter? Cases can be formed from 6.8 SPC or 10mm cases. While it won't give you the potential in supersonic, it comes in the lighter AR15 platform and if you just want to shoot suppressed subs there really is no disadvantage. Just a thought.

Heres the FAQ for the round at ar15.com:

http://www.ar15.com/content/page.html?id=559

338 W in an AR-15? You Bet! magazine capacity suffers somewhat but its definitely doable :smile:

[i8asquirrel]

This is all new to me what is the parent case for 338 whisper & 338 thumper? I have a 300 whisper that I love and I'm building a bolt gun in 300 whisper.......I must have been in a hole some where,,,,,I have never heard of either of these two rounds.:eek:

[Spook]

This is all new to me what is the parent case for 338 whisper & 338 thumper? I have a 300 whisper that I love and I'm building a bolt gun in 300 whisper.......I must have been in a hole some where,,,,,I have never heard of either of these two rounds.:eek:

http://www.quarterbore.net/forums/showthread.php?t=4512

First post, lower pic, third cartridge from the left...338BR.

[BWE Firearms]

Here is a thread on the THUMPERS. The 338 THUMPER is designed for the AR platform.

http://www.quarterbore.net/forums/showthread.php?t=3655

[i8asquirrel]

DArn it.........there goes the bank account..those are sweet.

[love2shoot]

hmmm.......looks like I gotta sell some things....seeing a couple potential future projects.......

for a 338 sub....pardon my stupidity as I am just starting to educate myself on this caliber potential.......wouldn't a 308 necked up and shoulder moved back work? and yes, I am thinking possible mag fed in a semi auto......thinking on a 308 ar10 style rifle. just not overly impressed with the durability of 6.8 bolts....both from personal experience and lots of friends who use the caliber also.....only reason I might consider it in a ar15 is the fact that it would be at lower pressures then a standard 6.8.

other potential project I am considering is a semi auto variation of of richards 50 thumper. using a 300 wsm but cut back a little further then he did. It does not look like the really long 750grn projectiles would fit in a magazine, but some of the lessor ones I believe could work.........

[Grimjaw]

for a 338 sub....pardon my stupidity as I am just starting to educate myself on this caliber potential.......wouldn't a 308 necked up and shoulder moved back work? and yes, I am thinking possible mag fed in a semi auto......thinking on a 308 ar10 style rifle......


I think that would be 338 Federal, loaded subsonic.

[Romeyo]

Hi folks!

I'm just curious, has anybody ever had problems shooting 338 300smks/scenars, or similar bullets, with "slow" twists?

I'm asking because there's a formula (millers twist rule) you can use to pretty reliable predict bullet stability.

According to that formula even a 1 in 10 twist would be sufficient to stabilize a .338 300gr smk.
That formula gives you a gyroscopic stability factor (Sg) that needs to be 1.0 or higher to proper stabilize a bullet. In general you're looking for that Sg to be greater than 1.4 because of imperfections of the bullet, load and because of changes in atmospheric conditions.
Military uses a Sg of 1.5 to 2.0 because of the extreme conditions you might find on a battlefield.

Overstabilisation (Sg of 2.0 and higher) might (and will) cause precision problems because twist magnifies the symmetrical imperfectness of a bullet causing shot groupings to open up.
However, I have to agree with amafrank: understabilisation will likely cause much more problems than overstabilisation, especially if you're worrying about baffle strikes.
Some bullet/twist combos however tend to tumble at the first one to two hundred yards before flying stable causing bad precision or maybe even keyholing at short distance but very good results at long ranges.
Thats because bullet stability INCREASES during flight because of the bullets ability to maintain rotation is greater than to maintain speed.
However this adds drag to the tumbling distance (decreasing BC) and might cause baffle strikes, but can be corrected by using a faster twist.

Using this formula (there are downloadable excel sheets aviable) the Sg of a 300grain .338 SMK (1,7in bullet lenght) @ 1050fps in standard atmospheric conditions using a 1 in 10 barrel is 1.45.
1 in 8 twist: Sg 2.27
1 in 7 twist: Sg 2.97
1 in 6.5 twist: Sg 3.44

To me 1 in 8 seems to be perfectly fine, thats why I wanted to know if anybody experienced bad precision, keyholing of baffle strikes with that combo?

However, if you plan to use that extra long VLD bullets turned from solid copper alloy bars you better have a fast twist.
For calculation I chose a .338 295grain SP bullet from GS Custom Bullets (South Africa)(I chose this particular one because it's the heaviest/longest .338 solid i found) and did the same calculation:
1 in 10 : Sg 0.62
1 in 8 : Sg 0.97
1 in 7 : Sg 1.26
1 in 6.5 : Sg 1.47
(standard atmospheric conditions)

On their homepage you'll find a datesheet that contains smililar information, however beeing more "optimistic": http://www.gsgroup.co.za/338295SP142.html so seems that my calculations are not that far off, and after all on the safe side.

What's also confused often is the fact that muzzle velocity doesn't influence bullet stability that much. Bullet stability is mostly influenced by the bullets shape (lengh and "meat" at the outer diameter) and barrel twist.

I got this knowledge by reading books like applied ballistics for long range shooting from bryan litz (berger bullets chief ballistician), which I would highly recommend to anybody interested in the subject. Its a VERY interesting and easy read (you're not overkilled by euqations, formulas and thelike).

I know that there's always a difference between theory and praxis, however I often got the feeling that theres much mystic and many misinterpretations about whats going on when shooting a gun just because people are afraid of a tad science an math ^^


Btw: I would also be interested in how hard it would be shortening .308 brass and necking the case down to .338 instead of necking up 7mmBR brass?

[amafrank]

one thing the books don't teach is that books are great for theory but don't always work in real life. Once you get below the speed of sound the stability rules change. This is the reason why everyone is suggesting twist rates that seem a bit faster than recommended by millers formula. Also realize that the spin rate of the bullet is directly affected by the velocity and that will affect stability. So now in the real world we use the formula to get in the ball park and testing to dial it in. 1 turn in 10 will not work with the subs and 300gr bullets. Also note that once a bullet tumbles its gone. It won't tumble for the first hundred or two hundred yards and then suddenly be stable. It may wobble or nutate slightly but no tumbling. Many publications have covered the yaw or nutation of a bullet as it clears the muzzle and this behavior is one of the reasons that .223 suppressors are not recommended on barrels less than 10" in length for full auto use.
Overstabilizing is bad for artillery and bad for long distance shooters because the bullet (or shell) nose doesn't tip and follow the trajectory of the projectile. In long range shooting that causes a flow across the projectile which will create drift due to the Magnus effect. It can also cause the fuses on artillery shells to fail due to impacts not being on the nose....newer fuses seem to have made up for a lot of this but it can still happen.
For us in the shorter range world of subsonics none of those overstabilizing issues will really be a problem. Our big worry is overspinning a weak jacket. For the most part I've not seen any issues there either. I've fired 110gr plinkers through my 30-221 with an 8" twist at 2500fps and not blown up the bullet. All of these are the reasons I suggest that over is better than understabilizing.

Frank

[Romeyo]

Alright thanks! I know that there's always a difference between practise and theory. But since I'm quite interested in ballistics and whats going on I wanted to know why people are leaning toward those 6.5twist barrels and where/why theory is failing. I guessed that those formulars get inaccurate when coming to the trans- and subsonic range. Thanks for clarifying!

Any comment on shortening and necking down .308 brass in stead of starting with 7mmBR brass?

[amafrank]

One of the main reasons everyone is using BR brass...either 7mm, 6mm or 30 cal, is because the benchrest brass is more consistant in thickness and also because it uses small rifle primers where the .308 uses a large rifle primer. The smaller primer is giving more consistant pressures in the benchrest round....not sure how it fares in the subsonic range. You can use .308 brass for making 338BR but you will have to neck turn the brass for it to work. The case is much thicker in the body than the neck needs to be. When you use the BR brass its already cut to the shorter length. Normal .308 brass is 2.005 long and the BR brass is 1.55" + or -. So you can see that the .308 cases will need a bit of trimming and they will be cut down into the thick part.

Hope that answers the question

Frank

[Romeyo]

Lapua makes .308 palma brass that uses small rifle primer pockets, a smaller priming hole and "lapua quality" tolerances, they're cheaper than 7mm Rem BR brass and also readily aviable. So why not giving it a chance? I don't mind neck turning since It won't have a bad effect on accuracy I guess :wink:

Only thing I'm worried about is case forming. Is it as simple as running a proper shortened (and lubed) .308 palma case through a .338BR (full lenght) sizing die and then neck turn and trim it?

Trimming and shorting would be done on a leathe, so no real issue.

Martin

[amafrank]

Lapua makes .308 palma brass that uses small rifle primer pockets, a smaller priming hole and "lapua quality" tolerances, they're cheaper than 7mm Rem BR brass and also readily aviable. So why not giving it a chance? I don't mind neck turning since It won't have a bad effect on accuracy I guess :wink:

Only thing I'm worried about is case forming. Is it as simple as running a proper shortened (and lubed) .308 palma case through a .338BR (full lenght) sizing die and then neck turn and trim it?

Trimming and shorting would be done on a leathe, so no real issue.

Martin

you pretty well got it. cut to near proper length, run through the sizing die(lubed), trim and neck turn. Should be good.
The Lapua Palma brass will also be thicker most likely, since you're cutting it down from the .308 length. That cuts down the case capacity so you probably won't get as much powder in the case as you could with the BR brass. You'll have to work up loads for that particular brass too since it will give different velocity than the BR brass but thats pretty much required anyway. I also don't know how important it is to have the small rifle primers so maybe cutting down 308 brass would be fine...


Frank

[Romeyo]

Alright, sounds good. I'm not really worried bout the reduced case capacity since those subsonic loads doesn't require all of the aviable space inside the case even with deap seated bullets, do they?
And since a friend of mine got quickload for some years now I guess creating starting loads won't be too hard, although I guess that most "7mmBRcase" loads would work too (at least subsonic loads) just creating slightly more pressure and speed.

Martin

[d-mon]

High Romeyo,

For making your 338 br cases from 308 cases, try the following method:

Full lenght size the 308 cases in a 338 br dies with out the expender.
Then trim down (with a lathe or dremel first then case trimer, maybe with a .300 pilot at first because of the neck thickness).
Then you can use a K&m expender back to 338 that will make the neck snug fit on the K&M 338 pilot of their neck turning device.

Once that is done, you can load straight away.
I use that method for my 300 whisper brass with great results.
Good luck
ND

[Spook]

or,.... you can cry once, buy Lapua 6BR brass, trim it to length and have brass you'll be able to pass down to future generations.

Going the reform route...you may or may not be successful. I had a bad experience reforming Lapua 7.62 X 39 into a 22 cal shorty....it was almost like the brass in the body of the case had memory...

You might want to read up on annealing.

I cant say I didnt have fun wasting a few hundred cases. :smile:

[Romeyo]

Memory brass... now that would be cool. No more resizing ^^ Who knows, maybe in 10 Years all cases are made out of some super durable, reloader friendly memory polymer...

So you think annealing might be necessary before running the case trough the resizing die (and maybe even in between running a case multiple times through that die before ever comin to dersired specs)?
Well, I got a propane torch in my workshop, lets see if i'll need it...
Thanks for the 6mmBR brass tip. I'll try it if .308 palma brass protests against my plans..

Martin

[Spook]

Memory brass... now that would be cool. No more resizing ^^ Who knows, maybe in 10 Years all cases are made out of some super durable, reloader friendly memory polymer...

So you think annealing might be necessary before running the case trough the resizing die (and maybe even in between running a case multiple times through that die before ever comin to dersired specs)?
Well, I got a propane torch in my workshop, lets see if i'll need it...
Thanks for the 6mmBR brass tip. I'll try it if .308 palma brass protests against my plans..

Martin

Well...since you asked me what I think. I think you'll never be able to make brass as good as you can buy...using the approach you've described...and you're handicapping any edge you might've gained on accuracy... by using 6BR brass.
It'll be interesting to hear what your conclusions are at the other end. Best of luck with it.

[Romeyo]

I might try out both techniques to find out if its worth going the 6mmBR way.
How many cal. expenders would you recommend for the necking up process? 7mm, .30 (and .338) I guess?

I think I'll be able to share results somewhen in may to june since I'm just doing research at the moment because of lacking the money for such a project right now (unfortunately it's not the only expensive hobbY I got :rolleyes: ).
However I already got a promising "baseline"... a Savage SS target action :smile:

Martin

[Spook]

I go to 30 then 338 . If you get 7mmBR brass it goes in one jump with a 10% loss.

[amafrank]

I've just expanded and sized a bunch of 7mmBR cases with a CH4D die/expander and it works quite well. I haven't lost any yet but I expect to. I'm going from 7mm to .338 in one swipe.
I finally got a barrel blank ordered. Now I just need to decide whether to use the Mk X Mauser action or maybe just finding a CZ or Rem 700 action.

Frank