Any consensus on 5R rifling, gain twist for cast bullets ?

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  • Last Post 26 September 2015
mtngun posted this 16 September 2015

Perhaps this has already been discussed but a search did not turn up much other than a single pro-5R comment by Ed Harris.    

I'm planning to build a halfway serious benchrest gun for high velocity cast, with a name brand cut-rifle barrel.   The most common offerings are either 4-groove or 5R.    Is 5R good, bad, or indifferent for cast bullets?   I'll be shooting Loverins or Ardito-sized Loverins, so support for a bore riding nose is not a consideration.

Some of the makers offer gain twist.  Of course Harry Pope advocated gain twist, but that was for relatively sedate velocities and soft bullets.   Is there any proven advantage at modern velocities with hard alloys?   Anyone winning CBA matches with them?   I'm trying to wrap my head around how the gas seal is maintained as the bullet is continually being engraved by an ever-changing twist?

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grouch posted this 17 September 2015

Wish I could tell you. I have a Ron Smith gain twist(18 to 12 in 24") in 30 30 on a P14 Enfield action, and so far haven't set the world afire. That's not to say the barrel won't shoot, it sometimes does. It's best 5 shot 100yd group was .257", it's best 4 group aggregate was just a shade over 1/2” and it' best 200yd 5 shot group was very close to 3/4". It shows signs of doing better, but is probably limited by my shooting ability(bench rest is fairly new to me), the home made stock, bedding, and maybe the old Lyman scope on the rifle. I can say with certainty that it shoots better with this barrel than it ever shot with the fixed twist heavy 35 cal. barrel it started out with. It's shot its best at moderate velocities(1500-1600fps) with 20:1 alloy and does reasonably well with a variety of bullets from 150 to 220gr. For what it's worth, the plain base bullet crowd do well with these barrels, Smith's barrels have quite a following there. So - I've replied at some length and not told you much - only that I'm not sure I could do any better with any of the better known barrels. Maybe someone will reply that truly knows the answer. Grouch

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mtngun posted this 17 September 2015

Thanks for the info on your gain twist barrel, Grouch. Quarter inch groups are not too shabby.

I haven't made up my mind yet but am leaning toward “playing it safe” on this particular project and going with conventional 4-groove rifling and conventional constant twist. Possibly a Brux 30 cal, 298x308, 15” twist, for use with 135 - 150 gr. bullets.

I do like to experiment but there is a time to experiment and a time to “play it safe.” Spending money on an expensive barrel with a long lead time seems like a time to play it safe. :D

I have nothing against button rifling, it's just that I've never tried cut rifling before and want to try it at least once.

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Tom Acheson posted this 17 September 2015

One of our local CBA shooters uses a Broughton 5C barrel. It is chambered in 30 BR and it is accurate. This is on a CBA Heavy category rifle and using cast bullets of course. The twist is 1:12, bullet weighs 216-grains from an Accurate mould and a mv of about 1900 fps. Not sure about the cut or button detail.

Tom

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mtngun posted this 17 September 2015

Thanks for the info on the 5C rifling, Tom. So at least one CBA competitor is getting good results with 5R/5C !

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OU812 posted this 17 September 2015

You can learn a lot by watching others shoot. A heavy rifle with good target stock that is supported and rides the bags well is really important. Probably more important than rifling type.

Watch this video. You may have to copy and paste to watch.

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?v=WeD8MfeSVoE

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OU812 posted this 17 September 2015

I also hear that 5r rifling works good with taper cast bullet designs. Bore riding bullets work good using six groove rifling with wide lands...wide lands help support the bore riding section.

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mtngun posted this 17 September 2015

Yes, OU812, agree with all that. I've been shooting for about 55 years, but am new to benchrest guns and still have a lot to learn about benchrest technique. :D

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OU812 posted this 17 September 2015

The waiting list is about 1 year for a Bat B action (left port, left bolt, right eject). Notice in video his right arm hardly moves using left bolt, left port feed. Stock is a Shaheen BR stock with flat 3” wide forearm. His rifle and method of shooting takes away lots of shooter error.

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mtngun posted this 17 September 2015

I'm afraid my build will be with a slightly tweaked M700, a Richard's Microfit “basement bin” benchrest stock with 3” forearm, and prolly a Sightron 36x scope. I'm going to set it up as a switch barrel so that I can use the same gun for testing several calibers and twists, limited only by my budget (which is a significant limitation :D ).

Most of the barrels that I will use will prolly be standard grade Shilen chrome-moly because they fit my budget and I've been impressed with the two that I have tried so far. But I want to try at least one name brand cut-rifled barrel just to see if I am giving up anything with my econo-barrels.

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Ken Campbell Iowa posted this 17 September 2015

i believe cm barrels are as good as stainless .... at the top level of mj benchrest . don't feel you got 2nd best .

glad to see a serious attempt at those 1 hole groups with cast ... i will be following with great interest .

ken

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mtngun posted this 17 September 2015

Well Ken I'm not holding my breath waiting for one hole groups with cast.  But if I could consistently get 10 shot groups of 1.0 - 1.5 MOA at 2700 fps I would consider that a major accomplishment.

The econo-CM Shilen barrels are not lapped or air-gaged at the factory, whereas Shilen's “Select” barrels are lapped and air-gaged and guaranteed to closer tolerances.   However, I have found that the econo-Shilens are decent as they come from the factory and that 5 - 10 firelapping rounds compensate for the lack of factory lapping.    For the price they are a bargain.  

I'm tentatively planning to begin this project with a 14” twist 6mm econo-Shilen, and a 15” twist 30 cal cut-rifled barrel from someone else.

So far Brux has not responded to my email about lead time so I may have to try Krieger or Bartlein or Obermeyer even though I've heard nothing but good about Brux and their prices are a few bucks less than the others.     Last I heard Brux had a one year waiting list ???   :(

Some of the cut-rifled companies offer deeper than normal grooves, i.e. .298” x .308” 30 cal.    I dunno if that makes any difference but it sounds good in theory for cast, so I want to try it.

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Ken Campbell Iowa posted this 18 September 2015

i prefer not to do firelapping on a match barrel .... instead do hand lapping AFTER chambering ... it gives you more confidence that the barrel is smooth ... no draggy spots ... also that there are no oversized sections ... it only takes an hour or so, i use only ~300 grit ; 8 or 10 passes are all it takes ... unless there is a tight or loose spot ... in which case you can improve it there .... at least you will know about it ( heh ) .

if budget is a biggie, i have one of the good blackstar varmint blanks in 6mm 14 twist . i also have a blank 308 lilja, but i can't remember the wt. or twist ... dang old age . pm me if interested, i will dig them out .

good luck

ken

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mtngun posted this 19 September 2015

Ken, thanks for the offer on the barrels but they were not what I had in mind, not that I have anything against either Blackstar or Lilja. . Update on my switch barrel benchrest gun project:    the comments here seem to suggest that the 5R / 5C rifling is “ok” for cast bullets (though no one has claimed that it is superior for cast)    So I went ahead and mailed an order for an Obermeyer .298” x .308” 1:15 twist.     Like most of the cut rifling makers Boots has a long lead time so no telling when I'll receive the barrel -- I didn't even bother to ask.   As I sometimes tell my customers, if you have to ask about the lead time, maybe you're at the wrong place.   :D   :D   :D

So it may be a year or so until I am able to report back on how the 5R barrel worked out for me.

It turns out that Shilen does not make a 1:14 6mm in chrome moly, only in stainless which I didn't want to pay for, so instead I bought a “bargain basement” Pac-Nor 3 groove for less than a Ben Franklin.    I've never had a Pac-Nor before let alone a bargain basement Pac-Nor so it's a bit of a gamble.   But I am not a competitor, merely an experimenter, so as long as the barrel is “decent” it should serve my purposes.   I'll probably be getting a bargain basement 7mm 1:14 Pac-Nor, too.

As mentioned previously, the plan is to set up the gun as a switch barrel so I can use it for testing cast bullets in different calibers.   The donor action is M700 long with a .30-06 size bolt.    To avoid the cost of a buying a new bolt or modifying the existing bolt I'm leaning toward using the 6mm BR cartridges (and 7mm BR and 30 BR) even though the BR's case capacity may be a bit large for 6mm cast.     

A “bargain basement” benchrest stock was ordered from Richard's Microfit.     Richard's reputation is not the best but the price fit my budget.   They tell me that his 99% inletted stocks actually require quite a bit of fitting and sanding, but that's OK considering my budget.

A Basix ERV3 trigger is en route to replace the factory trigger.

For the time being I'll probably borrow a 36x Weaver scope from another gun. 

In general the theme of this project is “a halfway serious benchrest gun.”   “Halfway” because it is budget constrained so other than the one cut rifled barrel it will be economy class all the way.   :cool:  

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Larry Gibson posted this 20 September 2015

mtngun wrote: Well Ken I'm not holding my breath waiting for one hole groups with cast.  But if I could consistently get 10 shot groups of 1.0 - 1.5 MOA at 2700 fps I would consider that a major accomplishment.   That level of accuracy at that velocity with a 12” twist will prove very allusive.  You can come close with a long (26” +) 14” twist.  In my own 14” twist Palma barrel I shoot that kind of accuracy with the XCB and 311466U using the .308W cartridge.  The Barrel is a 4 groove standard rifling Shultz & Larson barrel 27.6” long on a M98 action.    In my Match .308W M70 with 26” barrel with 12” twist barrel with 4 standard grooves I can hold that accuracy with the XCB and 311466U bullets at  2400 - 2500 fps.    Above 2600 fps for 1 - 1.5 moa accuracy to 300 yards I use a Broughton 31" heavy Palma contour barrel with 3 grooves and a 16” twist.  It holds 1.5 moa accuracy to 300 yards with 10 shot groups to 2850 fps.  It will hold 10 shots inside 2 moa upwards of 2950+ fps,  The Broughton barrel is chambered in the 30x60 XCB cartridge and is also on a BRNO M98 action in a B&C Premier stock.    LMG

Concealment is not cover.........

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mtngun posted this 20 September 2015

Appreciate you input, Larry. :)  I didn't realize you had worked your way up to a 1:16” twist.   Any particular reason you went with the 3 groove Broughton rather than their standard 5C rifling ?

As I mentioned I ordered a 1:15 twist 30 cal barrel.  

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Larry Gibson posted this 21 September 2015

Not many barrel makers make a 16” twist which is what I wanted. Broughton 3 groove barrels have an excellent accuracy reputation and could make what I wanted. My actual request was for equal 4 L&Gs. When they explained their 3 grooves were very close to that L to G area so I decided to try it. Absolutely no regrets!

LMG

Concealment is not cover.........

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mtngun posted this 22 September 2015

Minor Update: the bargain basement 3-groove Pac-Nor 6mm, 1:14 twist showed up. I assume it is some sort of factory 2nd, but don't know for sure. At any rate the inside looks nice and the only possible problem I have found is that the rifling seems a bit shallow. As best I can measure the bore is .2380” and the groove is 0.242” - 0.2425", though it was tough to get consistent measurements. Perhaps the shallow rifling will be a problem for cast bullets but in any event it'll be interesting data point in the education of a cast bullet shooter.

A 6-groove 1:14 7mm Pac-Nor is on its way, also a bargain basement barrel from the same seller.

Eventually I'd like to accumulate a 22 caliber 1:12 or 1:14, and a 35 caliber 1:20.

I'm wondering if I could use a PPC bolt head to shoot 357 magnum in the switch barrel bolt gun?

I still have to buy brass, and buy or make dies, make reamers, etc., so it'll be quite a while before this project is up and running.

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Ken Campbell Iowa posted this 23 September 2015

shooting 357 brass in remmy 700 ::

the rimmed and straight 357 brass should be seated contacting the barrel breech ... so the garter-belt extractor of the rem 700 will be problematic . it might be worth installing an m16 extractor which would be more universal . about $40 in parts and you can install it yourself if you have a lathe and bridgeport .

back in 1998 pac-nor were great barrels ... not sure about now, no recent experience .

ken

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Ken Campbell Iowa posted this 23 September 2015

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bandmiller2 posted this 24 September 2015

Mtngun, I'am not into benchrest but have two cut rifled barrels I machined chambered and fitted. They were both left over culls from a small unknown barrel maker. One is chambered for 358 Win on a savage 99 action the other 25-20 fitted to a ruger #1 action. Boath are very accurate smooth inside and a joy to use, cleanup can be done with a tite dry patch. What I'am trying to say is you don't know a barrel unless you fire it, it may be a pedigree or a mutt but the only proof is at the target. Frank C.

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