.308LN (Long Neck)

[Marlin Junky]

I'm going to do this .308LN thing but I'm wondering which of the following two approaches to take.

The first approach would be to have my .308LN reamer cut with a long throat (like the way Remington throated '06 700's decades ago) for LFN type boolits (I know they handle HV well) while the second approach would be to have the reamer cut with a more conventional throat that will probably be more compatible with the bulk of factory cut molds. My goal of this .308LN project is to go HV at 1MOA; however, the fastest I've pushed Lyman/RCBS/SAECO type boolits so far is about 2200 fps (I don't currently own a platform that'll do any better with "factory molds").

Any suggestions on throating such a chamber? I'm also open to tips on how to handle HV in a standard .308 chamber (if that's even possible).

Oh yeah, as far as barrels are concerned, I'm considering a "30 Tight" Krieger with .3075" grooves... am I going wrong here? I realize the "30 Tight" starts at 1:12" and goes slower from there; however, this'll be a 150-200 grain boolit platform.

Thanks,
MJ

P.S. For those not familiar with the '30 Tight' terminology, a '30 Tight' is bored .298", not .300".

[nicholst55]

An interesting project. I don't have any experience to draw on at this point; all of my cast work with .30 has been in the mid-teens to date - 1600-1800 FPS or so. I'll be watching this thread with interest!

Luck!

[mike in co]

i missing something here.
why go slow twist and why go under bore??
just dont see the reason if moa and hv is the goal ?

why have to under size your boolits?

why not a std krieger in a 12 or 10

[Marlin Junky]

Deep grooves and a snug bore are the goal especially if you're using bore-riding style boolits. To get taller than .004" lands and cut rifling you need to go with a '30 Tight' and 1:12" is better than 1:10" for HV, especially if your boolit bearing surface is on the short side.

MJ

[shooter93]

Bore dimensions won't matter unless you have an undersized mold now. If not then the mold can be cut to whatever diameter you desire. I generally make a couple dummy rounds with the cast bullet I intend to use, getting the loading dies first if it's odd enough. Then I have the reamer made to the dummies using minimal expansion room for brass, a bit larger for a hunting gun, and throated with a 1-1/2 degree leade with the bullet just touching the lands. 1-1/2 degrees seems to work pretty good for both J and cast bullets. For cast only I may even try 1 degree. You might as well have the transistion from the chamber, the step down, made much less than 45 degrees, and the reamer cut to keep your brass length maximum length. This would mean ofcourse you'd have to be dilligent about brass trimming but I believe it's also conducive to using PP bullets too.

[Marlin Junky]

why have to under size your boolits?


Most factory molds today struggle to cast over .309" in 50/50. What do you mean by "under size your boolits"? I'll only be truing them up in a .3085" die to shoot through .3075" grooves.

MJ

[Dannix]

Why going tight Marlin Junky? Want to shoot heavy stuff too? I thought I remember reading at 6mmbr that you wanted to only go as tight as you needed for the weight you wanted to shoot. fps wise though, iirc the difference between the min and max twists for a given bullet weight, the fps was ~70fps.

Edit:

To get taller than .004" lands and cut rifling you need to go with a '30 Tight
So, and I'm totally green in the area, but why can't you get a tall rifling at, say, 1:14?

[303Guy]

I can understand the bit about moulds casting undersize but how does the 30 Tight affect the chamber size (only the neck is important) from a neck grip and expansion on firing? I would think it more important to size the chamber to suite the case and throat for cast and paper patching. I have a rifle with seriously worn bore and throat that can be reloaded without sizing the neck. That leaves very little neck expansion on firing. (It also requires somewhat oversize boolits to fit the throat).

For j-words I would think the 30 tight would be advantages. For cast I would rather have more grooves than deeper rifling because of boolit distortion and base feathering which may affect accuracy.

[Marlin Junky]

I thought I remember reading at 6mmbr that you wanted to only go as tight as you needed for the weight you wanted to shoot.

You've got me confused with someone else.



Edit:

So, and I'm totally green in the area, but why can't you get a tall rifling at, say, 1:14?

30 Tight is available from Krieger in 12, 12.5, 13, 13.5 and 14" twists.

MJ

[Marlin Junky]

...how does the 30 Tight affect the chamber size...?

It doesn't... how did I even imply it does?



For cast I would rather have more grooves than deeper rifling because of boolit distortion and base feathering which may affect accuracy.

I'm sure there's a happy medium somewhere (number of grooves vs. groove depth) but I don't know where that happy medium lies. I do know that going from a shallow grooved M70 in 30-06 to a deep grooved 336 (both with 4 grooves) meant I was able to shoot better groups with the smaller 30-30 case at 400 fps faster. I'm pretty sure Krieger barrels are available in 4, 5 and 6 groove configurations so there are several options especially if one includes the possibility of a .300"/.308" 6-groove barrel.

MJ

[303Guy]

... how did I even imply it does?Oh no, that was a question out of interest - you did not imply it in any way.

Perhaps my own experiences are due to the effects of an oversize throat and not groove depth (making them irrelevent to your quest).

Have you considered a very shallow leade angle begining at the chamber throat transition? Boolit design would change somewhat and it may not be a good idea for cast anyway. It means essentially that the leade is the throat (and that standard molds might not work at their best - I don't know).


... why go slow twist?My understanding is that a slower twist is better for lighter boolits and higher velocity. If a 1-in-10 twist 303 Brit will stabilize a 245gr cast then a 1-in-12 twist 308 should stabilize a 200gr cast just fine. I think the velocity limitation with faster twists has to do with the rifling shear or thrust forces on the boolit.

[excess650]

MJ,
You have me curious. What action are you using?

[felix]

The only advantage of tall lands is that they allow a lesser quality of lube for the same accuracy over many more shots. ... felix

[Dannix]

Was using the general 'you' there. As in 'for a body who wants blah, do such and such', not you personally. I didn't notice your specified bullet weight range. 1:12 indeed looks like the best compromise for you considering you want to shoot heavier boolits too. When I saw HV, I was, incorrectly, thinking light weight 30s.

Somehow I read need to go with a '30 Tight' AND 1:12" instead of need to go with a '30 Tight' [break/period/stop] 1:12" is better than 1:10" for HV, which really confused me. :oops:


This going to be for target or hunting? You planning on HP boolits for more 'dwell time' if the later?
:coffee:

[Larry Gibson]

MJ

Quite frankly I think you are on the right track. The majority of cast bullet weights I shoot for "accuracy" in my match .308s are 150 - 180 gr so I would opt for a 13 -14" twist barrel. However if 200 gr cast are definately in the mix then a 12' twist would be the way to go. That does somewhat limit HV with regular cast bullets of current commercial design. I would use the LBT .30 cal 154 gr bullet or the 311466 seated with the GC at the base of the neck to just kiss the leade of the throat for chambering. I also would use a tight neck reamer so case necks could be turned for minimal case neck expansion (.001 - .003 max) on firing. One last thing not mentioned here is barrel length; I would use a minimum 26" but would prefer 28 - 30" length for the same HV with slower accelleration than obtained with shorter barrels. I am able to do things with accuracy at HV using my 27 1/2" .308W S&L Palma barrel having a 14" twist that I can not do even with my 26" barreled 12" twist match rifle.

Larry Gibson

[Marlin Junky]

I think the velocity limitation with faster twists has to do with the rifling shear or thrust forces on the boolit.

I agree, which is why I'd like to try a 12" twist on "factory dup" loads with cast (and PP for that mater). I've heard of some having success with Lyman 311284 pushed out of a long barrel 30-30 with a 12" twist and knocking over long range silhouettes so I'm pretty sure a 1:12" twist .308W (or LN) will be fine for my stabilization requirements.

MJ

[Marlin Junky]

The only advantage of tall lands is that they allow a lesser quality of lube for the same accuracy over many more shots. ... felix

That in itself is a big plus but I think there's more to it than that. When I started shooting cast through my Pre-64 M70 (30-06) I was almost convinced the reason I couldn't achieve a decent level of accuracy (with any number of shots) beyond about 1900 fps was due to the 4-groove configuration coupled with the relatively tight (with respect to cast boolits) 10" twist. Then I started shooting the same boolits through my 60 year old 336 into tiny groups at over 2200 fps. Basically, the only difference I see between the two barrels (sans the external contour) is that the Marlin has deeper grooves.

MJ

[Marlin Junky]

Was using the general 'you' there. As in 'for a body who wants blah, do such and such', not you personally. I didn't notice your specified bullet weight range. 1:12 indeed looks like the best compromise for you considering you want to shoot heavier boolits too. When I saw HV, I was, incorrectly, thinking light weight 30s.

Somehow I read need to go with a '30 Tight' AND 1:12" instead of need to go with a '30 Tight' [break/period/stop] 1:12" is better than 1:10" for HV, which really confused me. :oops:


This going to be for target or hunting? You planning on HP boolits for more 'dwell time' if the later?
:coffee:

Substitute 'one' for 'you' next time to avoid confusion.

It's going to be a hunter that drives tacks, or I'll rebarrel it. May HP for long range varmint destruction but for meat hunting, I probably just draw back the noses to air cooled hardness after HT'ing to BHN 25-30.

MJ

[Marlin Junky]

MJ,
You have me curious. What action are you using?

I prefer a stainless short action Savage but will use my stainless M77 short action if necessary.

MJ

[oso]

"Any suggestions on throating such a chamber?" - MJ
Would it be worthwhile talking to Mike Bellm about this?
I'm having luck with a 358 LN (358 Bellm rimless, based on 30-06 case instead of 444 Marlin) using a 358 Win chamber altered as you propose for 308 Win.

[Marlin Junky]

"Any suggestions on throating such a chamber?" - MJ

I'm trying to decide whether to throat it for LFN's... that was the purpose of this thread.


Would it be worthwhile talking to Mike Bellm about this?

I don't think Bellm is much of a lead-head. I did communicate with him quite some time ago and got the impression one can learn more from Jesse O. (Bellm's barrel guy) about cast boolit chambers and such.



I'm having luck with a 358 LN (358 Bellm rimless, based on 30-06 case instead of 444 Marlin) using a 358 Win chamber altered as you propose for 308 Win.

I'd use the 8x57 case instead of the '06 case if it's on a short action 'cause you need to work it less. How long is your .358 chamber?

MJ

[oso]

"I'd use the 8x57 case instead of the '06 case if it's on a short action 'cause you need to work it less." MJ
Use whatever case you'd prefer for your 308 LN.
Actually I prefer the final result for my application using .270 Win cases than 30-06 or 8x57 cases.

My chamber is 2.140"/54.5mm to the throat, then 0.07" to the rifling.

[376Steyr]

If it was my rifle, I'd start with a conventional throat, experiment with that for a while, then buy a throating reamer.

[Larry Gibson]

MJ

Attached are picures of the 308CBC along side a standard 308W and the 30x57 along side a standard 8x57 and '06.

Larry Gibson

[Good Cheer]

Just something to ponder...
In about 1982 I was going research on how to create the perfect wheel weight deer rifle.
As a test bed to help develop data I had a 788 in 7-08 altered to have a long neck. Used a 30-06 case run full length into 7-08 die. Gas cutting was a problem but it worked with the big long heavy 7mm that RCBS had. The man that did the alteration only lengthened the neck in the existing chamber.

[GabbyM]

Just something to ponder...
In about 1982 I was going research on how to create the perfect wheel weight deer rifle.
As a test bed to help develop data I had a 788 in 7-08 altered to have a long neck. Used a 30-06 case run full length into 7-08 die. Gas cutting was a problem but it worked with the big long heavy 7mm that RCBS had. The man that did the alteration only lengthened the neck in the existing chamber.

By gas cutting are you talking about in the throat area? Can't understand that one as I always heard a long neck helped quite a bit with throat erosion reduction. As in the 6mm REM is a far better round than a 243 WIN due to its longer neck. Savage / Stevens 7mm-08's with 11 1/2” twist barrels look like they'd be boolit shooters.

[felix]

Minimizing turbulence is the name of the game. That's a factor of both neck angle and length together with the diameter of the neck. However, for a gun shot every day a longer neck helps in selecting the projectile of choice. A projectile will be continually seated out further to maintain the same pressure curve that shoots. ... felix

[358wcf]

Seeing the later comments and photos reminded me of a plan I shelved a few years ago to build a cast boolit shooter for "extreme hunting accuracy" with acceptable velocity in 30cal. that would work through a standard short bolt action such as a Rem700. I played with running the standard 308 case through my 300Savage trim die to form it to 300Sav, leaving the neck the full 308Win length. The plan was to reduce the case capacity to improve loading density, while leaving a very long neck, similar to the 30-30 to totally enclose a long, heavy cast boolit and give some flexibility in seating depth. The slightly steeper shoulder angle from the 300Sav might be a bit of an improvement over the standard 308Win as well.
The project was shelved due to obligations such as kids, putting them through college, and life in general. Today, I might just pick up that plan again, and run with it. Stealing ("collaborating") further ideas from you younger fellows might help more than a bit, as well.
Thanks for sharing your thoughts and ideas, and good luck on YOUR project- I wish you success at every turn!

358wcf [smilie=1:[smilie=1:[smilie=1:

[Good Cheer]

By gas cutting are you talking about in the throat area? Can't understand that one as I always heard a long neck helped quite a bit with throat erosion reduction. As in the 6mm REM is a far better round than a 243 WIN due to its longer neck. Savage / Stevens 7mm-08's with 11 1/2” twist barrels look like they'd be boolit shooters.

The gas cutting was happening in the case neck, behind the entrance to the rifling. It was an interesting configuration to work with. The case looked like a miniture long neck beer bottle. So it was named the 28 Long Neck. The inside of the barrel could look like it was hot dip galvanized and it'd still be printing 2" groups at a hundred yards.
Over the years since then I've pondered getting a 7mm again with a decent neck length. Maybe something like a 7-30 Waters but with the neck twice as long., like a 32-40 necked down to 28. The stingy necked 7-08 works pretty good with the old 280473 though.

[Marlin Junky]

Seeing the later comments and photos reminded me of a plan I shelved a few years ago to build a cast boolit shooter for "extreme hunting accuracy" with acceptable velocity in 30cal. that would work through a standard short bolt action such as a Rem700. I played with running the standard 308 case through my 300Savage trim die to form it to 300Sav, leaving the neck the full 308Win length. The plan was to reduce the case capacity to improve loading density, while leaving a very long neck, similar to the 30-30 to totally enclose a long, heavy cast boolit and give some flexibility in seating depth. The slightly steeper shoulder angle from the 300Sav might be a bit of an improvement over the standard 308Win as well.
The project was shelved due to obligations such as kids, putting them through college, and life in general. Today, I might just pick up that plan again, and run with it. Stealing ("collaborating") further ideas from you younger fellows might help more than a bit, as well.
Thanks for sharing your thoughts and ideas, and good luck on YOUR project- I wish you success at every turn!

358wcf [smilie=1:[smilie=1:[smilie=1:

I too thought of using .308 brass in .300 Savage dies; however, the gain in neck length didn't impress me. Granted a .360" long neck is better than a .300" neck but a 1/16" gain in neck length isn't worth my trouble. I'm looking for a 1/2" long neck where possible.

MJ

[Marlin Junky]

The gas cutting was happening in the case neck, behind the entrance to the rifling. It was an interesting configuration to work with. The case looked like a miniture long neck beer bottle. So it was named the 28 Long Neck. The inside of the barrel could look like it was hot dip galvanized and it'd still be printing 2" groups at a hundred yards.
Over the years since then I've pondered getting a 7mm again with a decent neck length. Maybe something like a 7-30 Waters but with the neck twice as long., like a 32-40 necked down to 28. The stingy necked 7-08 works pretty good with the old 280473 though.

Using QuickLoad, I put an RCBS 7mm-145-SIL in a .30 Remington case, seated to 2.7" COL (.329" seating depth) and stuffed it full of H4350 (37.2 grains). The result was 2339 fps from a 22" barrel at 37.3K PSI. A couple more grains of W760 approaches 2500 fps but it'll cost you another 6.5-7K PSI. With HT'd WW metal and the right barrel, the .30R case necked down to 7mm sounds pretty cool... unless you're not interested in a short bolt action. Obviously, you'll have to work out the bolt head, etc. issues with your gunsmith and who knows how long Remington will continue to produce .30R cases. They are available through Midway, etc. but you'll pay about 1/2 buck each for them... which I personally would prefer to turning the rims on 30-30 cases.

MJ