Barrel twist for subsonic, heavy 30 caliber bullets???

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  • Last Post 31 August 2011
mtn_runner posted this 22 June 2011

Hi Folks

I inherited a 'home sporterized' M93 chilean mauser in 7x57 that is pretty much a disaster.  Timney trigger that was added at some point doesn't work, one piece scope mount that has been welded on to the action, bolt bent by who knows how, etc.  It is a mess, but despite all of this, I have shot a couple of deer with it and they were very dead and good eating.

I would like to rebuild this mess into a good low velocity 30 caliber carbine for heavy cast bullets and I am working with a local gunsmith to see what we can do.  We are thinking that rebarreling in a .308 winchester caliber might be the way to go.

My question is, what is the best rifling twist for a 200 - 220 grain bullet traveling at between 900 and 1200 fps?

I am thinking about an 18 inch barrel that is threaded on the end for useful attachments.

Appreciate any suggestions

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jr460 posted this 22 June 2011

1 IN 10

1000 yards easy

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James Ball posted this 22 June 2011

1-10 for a barrel as short as 24in.If you can get one 26in or longer go 1-12 you can always shoot it 1300fs or faster

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mtn_runner posted this 22 June 2011

Ok,

so 1 in 10 seems to be the way to go.  Any comments on barrel maker?  My last year's midway catalog says that I can get an Adams and Bennet 30 caliber barrel with a one in ten twist for about 80 bucks.

Lija, Douglas, Hart, Kreiger, etc offer the same for +$250 bucks.

Given that this is a bit of a 'ghetto job' with the messed up home gunsmithing to date on the reciever and bolt, is there any reason that I should not go for the cheap barrel?  On this action, would be putting one of the 4 star barrels be like casting pearls before swine?

Comments on the cheap Adams and Bennet barrels, good or bad experiences would be much appreciated.

Regards ...

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TomG posted this 22 June 2011

I'd be real interested in the rational you used in deciding to use a 30 cal sub sonic bullet for deer hunting. Your power level is going to be about that of a 357 magnum handgun and the dia. is such that with no expansion, your going to be chasing a lot of deer through the woods with holes in them. 

I've used probably 8 or so Adams and Bennet barrels for various guns.  My experience is that they are about on a par with factory quality barrels.  Some shot quite well and some were just minute of deer.  I've been using them on my prairie dog guns in lieu of burning up $300 blanks.  By hand lapping them before chambering, they will usually shoot way under 1 MOA.   I would think that an un lapped one would be perfectly adequate as far as accuracy for killing deer.

As far as twist rate goes, you first need to decide what bullet you want to use and then make some calculations to find the ideal twist rate.

Tom Gray 

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mtn_runner posted this 22 June 2011

Tom,

Thanks for the note.  I have no intention of using a subsonic .30 cal for deer hunting.  Mainly I hunt deer with my .54 cal muzzleloader and deal with elk with my .348 winchester (with NEI 250gr cast bulets).  I can't see chagning this recipe in the foreseeable future because it has been consistent for a few decades.

What I do want to do is create a low cost, accurate and quiet rifle that can deal with some of the wildlife problems around here.  I've had some expressions of interest from the local rich folk who are moving in around here and have no shooting experience.

Regards ...

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linoww posted this 22 June 2011

1-10 works fine with the 225g FN bullets @ 1000-1250 and also a pointy 190 in my 30-06.I'll check the bullet length for you.

George

"if it was easy we'd let women do it" don't tell my wife I said that!

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Ed Harris posted this 23 June 2011

The recipe which has worked well for me is a boltgun chambered for the Lapua version of the 7.62x39 cartridge, which has a gradual forcing cone of about 1 degree with no cylindrical ball seat, and a .3114 diameter forcing cone entrance. I use a pull-off .30-'06 match barrel of normal .30 cal. .300 bore x .308 groove dimensions and ten inch twist, which came off somebody's heavy barrel match rifle, cutting off the '06 chamber, setting it back to 22 inches and rechambered. This will adequately stabilize #311299 or #314299 subsonic with very good accuracy, and the bullet can be seated out with the GC located at the base of the neck.

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

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TomG posted this 23 June 2011

Ahhh, now I see where you're going.  Around here we call it micro game management.  The three S principle.  Shoot, shovel and shut up. 

As far as being certain that you have enough twist, I'd recommend going to the JBM website and using his little twist/drag program.  All you do is put in the dimensions of the bullet you want  to use and it's alloy and it will calculate the stability factor for you.  Just stay around 1.4 or above and you'll be fine.  I've used it lots of times and it always proves to work out very well.  Use the bullet drag and twist program.

http://www.jbmballistics.com/ballistics/calculators/calculators.shtml

The older I get, the more I think about safety. (I'm currently nursing two cracked ribs, Owww) Going sub sonic with a large capacity case can get you into the realm of Secondary explosion effect where large pressure spikes can occur with a less than full case of slow powder.  I wouldn't go there unless I had to.  

If feeding isn't an issue, I'd go with a 35 Rem. or 7mm BR where you have the correct size head dia. for the bolt and as small a case as practical.  The magazine can be modified to feed them if you want to mess around with it.  The long, RCBS 7mm SiL bullets shoots well in a 7 BR case.

Hope this helps.   Tom G.

Ps:  My Michigan deer gun is a Marlin lever action shoulder buster in 45-70.  An LBT 350 gr. WFN bullet works perfectly.  Never had one get away from this gun. 

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tturner53 posted this 23 June 2011

.308 Win. on a '93? There may be strength issues.

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raytear posted this 23 June 2011

J.D. Jones has his Whisper line of proprietary cartridges for shooting heavy for caliber bullets at sub-sonic velocities. You might check his outfit for specs. I think it is SK Industries or something close to that.

Also, as someone else said, a Model 93 Mauser is not strong enough for .308 Winchester loads, by a long ways!  7.65 X 53 mm Mauser will give you similar ballistics at pressure levels the M-93 can handle. Same case head as the .308 and you can resize 7mm or 8mm Mauser brass if the 7.65 is hard to find in your area.

Good shooting!

RT

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mtn_runner posted this 23 June 2011

All,

Thanks much for the suggestions and recommendations.  My hesitation as setting up a M93 action in a .308 has been re-enforced.  As long as I am shooting slow-poop heavy cast bullets at subsonic speeds, there should be no problem.  But as you know, these rifles get passed on.  As you also know, when trying to make something 'fool proof' you also have to recognize that the 'fool' generally has much more influence than the 'proof'.

So the recommendation for .35 remington is good, I like even more Mr. Harris's suggestion for a 7.62x39.  So these would be pretty short in a long magazine, and I don't know what needs to happen on the bolt for a smaller diameter cartridge

Again - appreciate any recommendations.

For Tom - I've got a big german shepard, 3 years old, that keeps deer out of my garden.  I also have a few bee hives, and he lets me know (usually at 2 or 3 in the morning) when a bear is looking for an opportunity.  Bears around here are proliferating because of wacky Colorado game laws.

So as you say, SSS prevails, usually with my Ruger #1 in 30-06, and abundant acreage the I have access to.  None the less, I am aiming to do this without so much disturbance to the neighbors.

Regards ...

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TomG posted this 23 June 2011

I've used 7.62X 39mm brass in cast bullet bench guns blown out to 7.62 X 39 Kern and it worked pretty well in a std. 308 size boltface and extractor. This was in a Kelbly Stolle Panda single shot action.    But, I think it would be kind of iffy in a Mauser as it is smaller than a 308 ctg. head. It has to drag the empty ctg. all the way back to hit the ejector to kick it out of the receiver.  It will most likely fall off the bolt face before that happens.  To modify the bolt properly will take a new custom extractor fitted to the case head and a lump on the opposite side of the extractor on the bolt face  to keep the case from falling away from the extractor on extraction

Mauser magazines can be blocked off in the rear to accommodate a shorter cartridge with some amount of work.  Whenever you take an old Mauser and change to a different cartridge, you get into a lot of custom gunsmithing. Information on how to do it yourself is available from several sources. 

Ed's suggestion of the 7.62 is probably the best for a sub sonic but, I'd have to see if it will extract and eject first..  That's why I suggested the 35 rem. 

The 35 Rem. can be a very good cast bullet ctg. with no modifications. I made one up on a Rem 788 for a customer and he chose a slow twist for the bullet he wanted to use.  He had to drive it over 2300 fps to get good accuracy and was complaining of the recoil.  It can be quite powerful with cast bullets. He shot a lot of CBA br matches here in MI. with a 98 mouser in 35 Rem. and did pretty well with it. 

Tom Gray 

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raytear posted this 24 June 2011

mtn_runner,

If you decide on a .35, I'll be glad to send you some NEI .358-282 CBs to try. Cast of wheelweight metal they come out around 295 grains in a similar profile to the old Lyman 3589. The slug is about 1.25” long and works best in my .35 Whelen with a gas check.

Good shooting! RT

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mtn_runner posted this 24 June 2011

RT,

Thanks very much for the offer.  On Monday, I plan to consult with my local smith about modifications to the bolt and magazine for a 7.62x39.  If this turns out to be more of a project than I want, then I see midway has A&B barrels for small ring mausers already chambered in 35 Rem for about $80 bucks.

Not sure how good these barrels are, but man, the price is hard to ignore.

Going this route will require buying new dies, brass etc, but at least I can use my collection of .38/357 molds for starters.

I'll let you know how the decisions go and whether I can take you up on your most generous offer.

Regards ... 

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mtn_runner posted this 24 June 2011

Hi Tom,

I've just spent the better part of an hour on the JBM Ballistics website that you recommended.

All I can say is WOW!!! what a great resource.

After fiddling around with the drag and twist calculator for a while, I went to the bibliography and printed off an article by Don Miller on estimating rifling twist.

Since I'm just a geologist (which a lot of people don't think is even a real job, and I can't argue too much with them), I'll need to get my son who is finishing up a degree in physics with a minor in mathematics to go through the article with me.

Regards ...

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TomG posted this 24 June 2011

mtn_runner wrote: Hi Tom,

I've just spent the better part of an hour on the JBM Ballistics website that you recommended.

All I can say is WOW!!! what a great resource.

After fiddling around with the drag and twist calculator for a while, I went to the bibliography and printed off an article by Don Miller on estimating rifling twist.

Since I'm just a geologist (which a lot of people don't think is even a real job, and I can't argue too much with them), I'll need to get my son who is finishing up a degree in physics with a minor in mathematics to go through the article with me.

Regards ..

Yes,  it is a really neat program.  Drag and Twist is the one I would go by.  You'll need to input the density of the bullet.  I just took a quick look at the program the other day and Brad didn't list the lead alloy densities.  Many years ago, I purchased his program when he sold it on a disk.  It has the densities in it but I don't know if I could find the old disk again.  I'm running windows 7, 64 bit and a lot of my old programs won't run any longer.  He has since made it free to use on his website.  I'm sure that if you asked him, he could provide the density for WW's. and Lino. or whatever alloy you plan to use.  If you want to stay subsonic, WW's with 2% tin should be fine.  

As I stated earlier, I would take the stability info from this program to the bank as my experience has shown that  when I had a bullet that calculated out to be marginally stable, it was indeed marginally stable when I shot it. 

You'll also find that if you do a little modelling with the programs, it becomes clear right away that increasing velocity a few hundred fps. only increases stability a small amount.  Whereas, with a small increase in twist, you get a large increase in stability. 

Other experimenters have tried long heavy cast bullets and haven't always had good success. One of the problems is that it requires a fast twist to stabilize a long bullet and you can reach a point where the rifling cannot start it turning with only .003” of land height engaging the skin of the bullet.  I don't know if anyone ever tried taller lands to get more purchase on the bullet.

Pat Iffland went in this direction several years ago and he would be a great resource if you decide to do this. He was making his own moulds and designing his own bullets. He used to be active on this forum as a co monitor with me. 

Tom

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delmarskid1 posted this 24 June 2011

A nice thing about the .35 Rem is that you would be able to use pistol bullets. Lots of gang molds around for them.

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delmarskid1 posted this 25 June 2011

One other thing that I have remembered, Green Mountain Barrels has 20” 9mm blanks for around 33 bucks. They are air gauged and button rifled. The .355” would be tight for jacketed bullets but I'm thinking cast bullets might like it.

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kendog posted this 27 June 2011

Ed Harris wrote: The recipe which has worked well for me is a boltgun chambered for the Lapua version of the 7.62x39 cartridge, which has a gradual forcing cone of about 1 degree with no cylindrical ball seat, and a .3114 diameter forcing cone entrance. I use a pull-off .30-'06 match barrel of normal .30 cal. .300 bore x .308 groove dimensions and ten inch twist, which came off somebody's heavy barrel match rifle, cutting off the '06 chamber, setting it back to 22 inches and rechambered. This will adequately stabilize #311299 or #314299 subsonic with very good accuracy, and the bullet can be seated out with the GC located at the base of the neck.

What action are you using? I have one of those reamers and havent settled on an action yet.

To the OP, I use a 311284 with 16+- grains of 2400 in two different rifles.

In 30-06 out of a Rock Island '03 w/a 10” twist, I can give the jacketed 168 matchking boys a run for their money on the SR target  at 200 yards in vintage military bolt gun matches.

The same load in a Rem PSS 308 with a 12” twist shoots a pattern rather than a group. Maybe 9” at 200 if I am lucky. Really bad key holing at 300.

 I think at the velocities I am running, the long bullet likes the 10 twist much better.

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huffmanite posted this 31 August 2011

Hmmmmm, 93 chile 7x57, Sure its not a 95 Chile? Anyway, noticed your list of barrels to use.....might as well add the Midway A&B barrel to it. Yea, it is an inexpensive barrel, but have a number of small ring type mauser action rifles barreled with them and I'm satisfied with them when it comes to accuracy and etc. Heck, even have an A&B on a Ruger 77 tang Safety and it is one of my more accurate rifles....in 7x57 by the way. Sorry, but you do not exactly have a primo type action to build on...why install a much more costly barrel in it when an A&B F34 contour barrel will be more than adequate for your hunting needs. For what its worth, nothing wrong with throwing large grain 7x57 bullets down the bore....don't think a 30 cal bullet is necessary. Sorry, do not mean to offend in anyway, just my opinion.

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