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Gain twist barrels for Palma: the next logical evolution in the sport of Palma.

The first Palma Trophy Match was held on September 1314, 1876 at Creedmoor Range, Long Island, New York with competing teams from Australia, Canada, Ireland, Scotland, and the United States. Since then, 27 official competitions have been held, along with three unofficial events, with the U.S Team winning 13, including that first one. Over the years, Teams from about two dozen countries have participated. The PALMA Council is the international ruling body and consists of one representative from each qualifying country. As written by this council, these events are dedicated "to sustain in its finest tradition the superb competition in long range rifle marksmanship, which since 1876 has engendered mutual understanding and friendship, warm goodwill, and above all good sportsmanship among marksmen."

Established in 1874, the Palma is a historic course of fire and has a certain rhythm with increasing difficulty as the event progresses with limited chances to make up for a poor shot. Where many Long Range competitions are held at a single distance, commonly 1,000 yards, a complete Palma match begins with unlimited sighters followed by 15 record rounds at 800 yards, then two sighters and 15 record rounds at 900, then again at 1,000 yards.

Within the United States, most Palma and other Long Range matches are held under the auspices of the National Rifle Association. American Palma shooters using NRA rules can effectively ignore the international Fullbore rules and shoot any .223 Remington/5.56 or .308 Winchester/7.62 iron-sighted rifles they choose with any bullet weight. International Target Rifle rules are more stringent, requiring a minimum trigger pull weight and .308/7.62mm cartridges using bullet weights of less than 156 grains or .223/5.56 with a maximum permitted bullet weight of less than 81 grains.

Palma shooting largely levels the playing field as everyone is forced to use less-than-optimum cartridges for the distances. This is an excellent way for people interested in precision long range shooting to develop wind reading skills. You will learn more about wind reading by shooting Palma matches, or a Palma rifle in long-range matches, than any other type of High Power or Fullbore match.

In some circles, 90 grain bullets in .223 Remington have been gaining popularity for Palma shooting where allowed. Hopefully this article will give you some ideas how to get more velocity and greater accuracy from your 90s, regardless if you choose boat tails or Very Low Drag profile. Gain twist barrels will work equally well when mounted on bolt guns or gas guns.

I suggest reading Robert Pitcairn's "A Mouse On Steroids" that appeared in the Summer/Autumn 2012 issue of Canadian Marksman, available free at DCRA.ca/marksman.php. Pitcairn's article approaches the use of 90s in bolt guns with uniform 1: 6.5" twists and contains valuable information on loads. My two-part article "Revisiting Gain Twist" in American Gunsmith November and December 2013 issues gets more into the history of gain twist, its use in rifles, pistols, blackpowder, as well as military applications. Decreased barrel heating, throat erosion, bore fouling, and other advantages are also covered in a greater depth. Though this goes into theories of why gain twist barrels seem to shoot so well, I did not cover gain twist for Palma.

Gain twist is not new. It has been around for at least a century and a quarter. I've been using gain twist barrels since the late 1980s and have about a quarter century of experience with them. It was an incident that happened in Australia that prompted my first interest. As a member of the U.S. Army Reserve Shooting Team, we were competing at Puckapunyal with other military shooting teams using our issue M16s. Our Australian hosts furnished their version of NATO SS109 62 grain 5.56mm ammo on that warm day, simply dumping a pallet of it on the ground uncovered. As the day grew hotter nearly all shooters, except the Ausies, started blowing primers. Contrary to intuition, our rifles were operating sluggishly, a U.S. National Guard shooter blew an extractor, and one of the South Africans actually blew up a rifle. The Australians seemed to be about the only ones that were immune and claimed our chambers were too tight, despite issue barrels having anything but "tight" chambers. The Thales F88, the Steyr AUG licensed and made in Australia for the Australian Defence Force, is a bullpup that operates with a piston and has 1:9 twist barrels instead of 1:7 more common in other NATO issue rifles.

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As this was well before 9/11, I was able to procure a small quantity of their ammo for the trip home. I made contact with the Lake City Army Ammunition Plant and they were actually anxious to analyze it. I shipped it to them and before long I had a report that said that the Australian ammo exceeded the chamber pressure recommended for the M16. The burn characteristics of whatever powder they used, however, caused the gas port pressures in our Ml6s to operate below specification, accounting for the sluggish operation of our rifles.

Not wishing to experience such frustrations and safety dangers again, I analyzed my firearms options for future years. I felt certain that the faster 1:7 twist of our M16 was a major contributor to our pressure issues. I considered 1:9 barrels and instead opted for two gain twist barrels. One began at a 1:11 twist in front of the NATO chamber and ended at 1:9 at the muzzle, and the other was a more aggressive 1:20 in front of the chamber to 1:10 at the muzzle. In other words, it effectively doubled twist rate in the span of a 14.5" M4 carbine barrel.

When the barrels were installed and I was ready to zero at distance, I used issue M855 62 grain, the closest I had to Australian issue, at 600 yards. U.S. green tip ammo has rightfully earned a reputation for being inaccurate. Despite this, my pit puller radioed back after my first group asking if I had substituted a match rifle with match ammo! The improved accuracy was an unexpected bonus, but how did the gain twist deal with the pressure of Australian issue ammo? I never got to find out. Shortly after, the Reserve Shooting Team fell on hard financial times and hasn't been back to Australia since. I kept those two uppers in the gun safe for years hoping the team would get better funding. As it never happened, I sold one for a fraction of the amount I had in it. I still have the other one. Make me an offer I can't refuse ...

Gain twist, also known as progressive rifling, hints at how it works. We choose rifling twist rates based on what bullets we intend to " shoot. Long bullets have to be spun faster to stabilize than shorter bullets. When Stoner first designed the AR-15 he used a very practical twist rate of one bullet revolution in every 14 inches of barrel to stabilize the short 55 grain bullets of the Viet Nam era, written 1:14 and resulting in roughly 160,000 RPMs. Now we are shooting much longer 90 grain bullets requiring a much faster 1:6.5 twist with RPMs exceeding 300,000. As far as the bullet stability in flight is concerned, the only twist rate that matters is that right at the muzzle. There is no need to start rotating a heavier, longer bullet at 300,000 RPM's way back near the chamber. In fact, there are very good reasons not to do that. Gain twist barrels start rotating the bullet slower at the chamber and pick up the twist rate uniformly as the bullet approaches the critical twist rate at the muzzle.

I have already given examples of a gain twist rates I've used in M4 barrels. In 20" Service Rifle barrels I typically use 1:13 at the Wylde chamber and terminate at 1:6.5 at the muzzle. In 26" Match Rifle barrels I use 1:14 to 1:6.8. This allows about 2,600 fps of muzzle velocity with the 20" barrels and about 2,700 fps with the 26" barrels using Berger 90 grain Boat Tail Match bullets and easily hold a supersonic velocity to 1,000 yards. Both gain twist barrels also shoot magazine-length 77 grain bullets just fine as well.

It is one thing to acknowledge intellectually how the twist rate changes along the length of the barrel but I needed to physically see it. I had a 20" AR-15 Service Rifle length barrel split in half length wise to show my customers. Visit me at Camp Perry on Commercial Row, Building 910-A in July during the Service Rifle National Matches. I have a big banner with the Bartlein Barrel logo outside. Unfortunately, I am only there during CMP week and I leave before the Long Range matches begin.

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I start my 32" Palma barrels at 1:23 in front of a dedicated Palma chamber which is about 1/10" longer than a standard Wylde dimension. For 30" barrels my beginning twist rate is 1:21". Both have a final twist of 1:6.8 at the muzzle. There are two good sources of gain twist barrel blanks for Palma. Bartlein Barrels (262/649-1574, BartleinBarrels. com) offers single point cut rifling in both 5R and 4 groove. I prefer the 5R but it is a little more susceptible to cleaning rod damage and for those shooting gas guns, a land will always be cut or severed when the gas port is drilled. I don't know that cutting a land with the port necessarily causes any permanent accuracy harm to the barrel but it does make the break in process very difficult. Usually you'll see a heavy streak of copper fouling just forward of the port and about the same width, with the streak going from the port forward about two inches. It is very difficult to get all that copper out between break-in shots but is absolutely critical that every bit of it be removed between shots in order to get a good break in. If you fail to do it right the barrel may copper there for the rest of its life and that can contribute to poor accuracy. I covered this in my October 2014 article, "Gas Gun Barrel Break In".

The groove width of the 4 groove Bartlein gain twist is wide enough to contain a gas port without cutting a land provided the gunsmith knows how to locate the port to center it in a groove. Drilling haphazardly unlikely will. Compass Lake Engineering (850/579-1208, CompassLake.com) turns and chambers my blanks for me. Having built a fixture for this, they are pretty good at centering gas ports. Bartlein barrels are available in both chrome-moly and stainless. I recommend the former.

The second source of rifle gain twist blanks is RKS Enterprises (Box 635, Wimborne, Alberta, TOM2GO (Canada), 403/631-2405). Like Bartlein, they use a single point cut rifling process and their barrels shoot every bit as accurately. RKS barrels are all 6 groove, so gas ports will cut a land. Ron Smith, the owner, says a finished length of 30" is as long as he can go. Both steel types are available but their stainless seems to shoot better. The price difference between the two companies is nearly break even. RKS can give you the same twist rate gains that I have recommended.

When you purchase a blank from either company, specify what twist you want in front of the chamber and the final twist at the muzzle. Bartlein normally makes their blanks about an inch over the desired finished length, with a half inch taken off either end during machining. Most .223 Remington match chambers occupy about two inches before the rifling begins, so it's important to call the manufacturer and discuss your project with a technical representative so you end up getting the twists you want where you need them. You also need to have a conversation with the machinist that will be turning and chambering your blank. Most will want to make a final shallow lathe cut to true the outside dimension of the blank, so the blank must be slightly fatter than the final diameter and you need to convey that to them.

Regardless of which source you choose to purchase your barrel blank from, there are two internal dimensions you need to specify. The first has to do with the land height. The standard .22 caliber centerfire land height is 0.219" with a taller 0.218" available from both barrel makers. Every bullet I've ever shot out of an AR-15 performed better with the 0.218" land and the 90 grain is no exception. Though this causes additional constriction resulting in increased pressure, the slow gain twist at the front of the chamber compensates. The accuracy improvement is key to getting the tightest groups possible.

Groove depth is the other critical dimension to specify. The standard groove depth for a .22 centerfire is 0.2240". Through years of extensive research I have found that a slightly deeper groove depth of 0.2245" improves accuracy and reduces fliers when using 90 grain bullets. Cutting the groove that half-thousandth deeper has the added benefit of lowering pressures. With taller lands and a deeper grooves, pressure ends up being almost identical to standard 0.219" x 0.2240" dimensions but there is no comparison with regard to accuracy!

Concerning reduced pressures, when powder begins to burn and build up gas pressure to eventually force the bullet forward, the inertia of the resting bullet also has to be overcome and rotated several hundred thousand revolutions per minute. Because we don't have to do that immediately, starting with a slow twist just in front of the chamber can get that bullet to begin rotation easier and with less pressure. I am able to load about 0.3-0.5 grains more powder, yielding 30-50 fps more muzzle velocity. Cartridges with more powder capacity than the wimpy .223 can benefit even more. I have been told that the .338 Lapua can get up to three grains more powder with gain twist. As with all load recommendations, work up gradually while watching for signs of pressure.

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Receivers for Palma AR-15s

Most Palma shooters use barrel lengths around 30". AR match barrels of that length normally have diameters of an inch for the majority of their length. Original AR-15s had a 20" barrel (1/3 less than a Palma tube) and the 1960s barrels were skinny. A Palma gun today has to support a far greater weight than the skinny receiver was designed to accommodate. A2 barrels weigh about 2.5 pounds whereas a 30" Palma AR barrel will tip the scales at nearly 5.75, more than double the weight.

What can be done? The threaded portion of the front of the receiver has to remain as Stoner designed it. Otherwise, the barrel nut would never fit. Fortunately, nearly 2/3 of the barrel extension lives aft of the threaded section. It is possible to thicken that area. Two companies make thick-walled flat tops. DPMS (DPMSinc.com, 800/578-3767) makes the Lo-Pro, thought it lacks a forward assist and ejection port cover, and SunDevil Manufacturing (SunDevilmfg.com, 480/833-9876) offers heavy-wall lowers and uppers, with either or both the assist and cover. Compared to conventional flat top receivers, the thicker receivers are roughly double.

In order to harvest the potential accuracy of any AR barrel/receiver combo, the gunsmith needs to properly stabilize the barrel extension fit to the receiver. Oversize BAT Machine match barrel extensions will help. To learn how to do this right, read my two part article "The Relationship Between Barrel Extension Diameter And Accuracy In The AR-15" in the March and April 2013 issues. If built right, an AR-15 Palma rifle can be built with all the expensive match sights, adjustable stocks, etc. as a bolt rifle and rival them in accuracy.

90 Grain Bullets

At one time there were as many as four different 90 grain bullet choices. The JLK was the first. It was a VLD, which required chasing the throat, and seemed to like the 5R rifling pattern in barrels with deeper 0.2245" groove. While the JLK line is still manufactured by Swampworks (SwampWorks.com), their web site currently lists the 90 grain .224 bullet as out of production due to problems getting the jackets. If you are addicted to this bullet, send me an email (NCC1701@penn.com) and I'll supply contact information for a stocking dealer where you can still purchase them.

Next came the Berger VLD, which is still available. It has a high ballistic coefficient (0.551) and, like all VLDs, requires chasing the throat. I could get a wider variety of 1:6.5 twist barrels to shoot accurately with the Berger VLD as compared to the JLK.

Not all shooters want to go to the extra work of chasing the throat and constantly lengthening their ammo to keep up with throat erosion. A maintenance-free boat tail 90 grain bullet arrived from Sierra in 2005.1 was still Armorer for the Army Reserve Team at the time and started doing load work ups. Sierra recommended a muzzle velocity of 2,650 fps for 1,000 yard shooting, however, the second day on the range I started experiencing midair bullet blow ups. I called Sierra and they still cite me as being the first creditable source of the problem. As more shooters tried the bullet word soon got around. It appears that the jacket is just too thin. Sierra felt that rough obturation to the back of the bullet was a contributing factor. This led me to gain twist as a potential solution. I checked first with the two companies I had purchased gain twist blanks from back in the late 1980s, but one had gone out of business and the other had dropped the gain twist option. I checked all over and couldn't locate a single source of gain twist barrels. This was before Bartlein was offering them. I continued to work with Sierra and their 90 for about two more years, trying every barrel option I could think of, including 5R, polygonal rifling, even and odd numbers of lands and grooves, different heights of lands and depths of grooves, varying land-to-groove ratios, cut rifling, and button rifling. I never was able to come up with any configuration that was "Sierra proof", though I have used other Sierra bullets with great success. The 90 Sierra Match Kings were accurate but shooters just couldn't rely on them holding together to make it to the target.

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I threw in the towel and approached Berger. Obviously, like most everybody by then, they had heard the talk in the pits about Sierra's jacket failures but could see a potential demand for a reliable and accurate .224 90 grain boat tail. I also suspect knowing a major military shooting team would be trying the bullet may have also encouraged them. In talking to Berger we easily agreed upon the need for a thick jacket. It wasn't long until the first pallet of Berger 90s arrived. The bullet boxes even had the word "THICK" boldly printed on them.

The first thing I did was torture test them. I couldn't get those bullets to blow up no matter what and they were as accurate as any Berger product. Just as Mr. Pitcairn mentioned in his article, I found the Berger BT to pressure more, especially compared to VLDs, as boat tails have a bit more bearing surface. The Berger bullet had a slightly higher B.C. (0.512) than the Sierra and Berger recommended a muzzle velocity of 2,600 fps for reliable 1,000 yard shooting. I had more pressure issues trying to get the Bergers to 2,600 out of 20" AR-15 Service Rifle barrels than I had getting Sierra bullets to shoot 2,650, likely due to the thicker jacket.

By this time, Bartlein was in the gain twist barrel business. I worked with them on rates of gain and the various internal dimensions and after some trial and error I arrived at the specs mentioned previously. Not only did the gain twist barrels solve the pressure problems, the accuracy was stellar! Comparing the performance of hundreds of barrels, the new combination of the Berger 90s fired from gain twist barrels to more common 80 grain loads, the 90s tightened groups by 7.7% while shooting about half as many fliers. Fliers with the 90s were out 50% less and the 90s fight wind drift about 17% more efficiently than the 80.

So life with the Berger 90 was good, but the new offering had its work cut out for it in perception as there remains much confusion among shooters regarding 90 grain bullet blow ups. In the tens of thousands of rounds I've fired, I have never blown up any 90 grain bullet other than

Sierras. Unfortunately, not all shooters got the word and some think all 90s are prone to blow up. Berger tried to counter this, including that "THICK" label on the boxes.

As word of the heavy jacket and stellar accuracy of the new Berger 90 got around, more shooters made the transition. Most of them I have talked to are happy. I believe that had the bullet been given a couple more years to prove itself in the face of High Power competition it would be more commonly used. However, as events and politics caused a demand for guns, ammo, and components to skyrocket, Berger was running a year behind in production. Something had to give and Berger decided to furlough production of a number of their bullets for the most popular. Sadly, the 90 grain boat tail was among those. Berger still has the dies and production equipment to resume production. If you are a fan of theses, make your wants known to the factory. For now, email me if you are having difficulty finding a source or check on Gun Broker.

No Pointing

I discourage "pointing" Berger's thick jacketed 90 grain bullets. This practice was one of those "flavors of the week" about the time the 90 grain boat tails were coming out. One of the members of our team purchased a pointing kits and used it on the new 90s. They looked fine and I understand the lure of the improved ballistic coefficient that the manufacturer of the pointer claims. We loaded some of the pointed bullets and sent them out for field testing. Reports were not good. A number of folks noticed decreased accuracy and there were reports of pressure issues on hot days when regular non-pointed bullets were doing fine. I saw the same two problems on my machine rest tests. I asked one of the shooters whose gun was blowing primers with the pointed bullets to measure the diameters of ten of them and average the readings, then to repeat with non-pointed bullets. Although I had already performed this same test I didn't hint what my findings were. Working independently, we both arrived at an increase in bullet diameter of 0.0003" for the pointed bullets. My theory was that because the pointing is basically a swaging operation, the thick jacket is resisting the process and resulting in bullets bulging ever so slightly in the bearing surface. I also admit that perhaps our swaging tool operator wasn't sufficiently polished in its operation at that early stage. Whatever the cause of the problem, nobody ever asked for any more pointed 90 grain Berger boat tails.

Which 90 grain bullet is best for you? Service Rifle shooters going out to only 600 yards mostly choose the Berger boat tail because it is so easy to get shooting accurately and equally easy to keep shooting well. Folks with a casual interest in Palma might also want to try the boat tail. Palma shooters knowing how to chase the throat should at least try the Berger VLD because of its superior ballistic coefficient. I would also do a load work up for the boat tail and pick the one that shoots the tighter groups. In a two mph full value wind pick up at 600 yards, the VLD will drift about a half-inch less than the boat tail. At 1,000 yards that difference in wind drift will be about 1.5". As a shooter you will have to evaluate for yourself how important such differences are.

As mentioned, my first idea for fixing the Sierra 90 grain blow ups was to go with a gain twist barrel that wasn't available at the time. With these available, I've since conducted torture testing with one or two Sierra 90s in each gain twist barrel I test fire. So far, I have not been able to blow one up! It may be that the more gentle obturation caused by slower burning powders used in 30 and 32 inch Palma barrels coupled with gain twist and seating the bullet out further in the neck will conspire to keep 90 grain SMK jackets in place. If you choose to try the Sierras remember the old saying, "Let the buyer beware!"

Palma Chambers

I use Wylde chambers in all my Service Rifle and Match Rifle guns. Both of those disciplines use magazine-length 77 grain bullets at the 200 and 300 yard lines and then 90s at 600, and for occasional Long Range event for shooters that are interested. There are things I like about the Wylde chamber, especially the gradual one degree 15 minute leade angle. For sure, if you are even remotely considering ever trying the 90 grain SMK bullet that gradual leade angle is going to be a must!

Although I am using the Palma reamer for what are technically gas operated AR-15s, since they are never fed from a magazine they are essentially single shot rifles and I'm able to tighten certain dimensions to a similar degree as a bolt gun. The neck dimensions in gas guns are typically quite fat for reliability of feeding. I was able to tighten that up considerably. That in itself helps to better align the bullet to the center axis of the bore. I recommend a neck of 0.2526" for heavy wall casings like Lapua and 0.251" for thinner walled casings like Lake City. If you outside neck turn your brass, those recommended dimensions can be tightened up. Consult your reamer maker.

Free bore was the next consideration. I had tried Vihtavuori N150 powder before in my match rifles. Accuracy was stellar and velocities were very consistent. With my Wylde chambers, however, I just couldn't pack enough of the very coarse powder into the casing to get the kinds of velocities I wanted for 1,000 yards. I wanted to be able to get 25 grains in my Palma loads with the entire neck to have contact with the bearing surface of the bullet, that is, the area above the junction with the top of the boat tail. I simply loaded up some dummy rounds until I was able to get 25 grains with the VLD bullet and 24.5 grains with the boat tail of N150 to fit. A 90 grain Berger boat tail loaded in a conventional Wylde chamber will give an overall cartridge length of about 2.50". My Palma chamber increases that length to about 2.60" with the Berger or about 1/10" longer than the Wylde. To get that, specify a free bore of about 0.1640". That places the top shoulder of the boat tail just slightly below the casing neck/shoulder junction. This provides good support for the bullet and allows the shooter to straighten any rounds that are not seated concentric with the casing without loosening the grip of the neck on the bullet. This chamber also has enough room to lengthen the bullet seating length to compensate for erosion for those shooting VLD bullets.

Bullet Seating Depth

Equally important as the actual chamber dimensions is tailoring the bullet seating depth to that chamber to arrive at the gun's accuracy sweet spot. With boat tails, I start with the bullet seated about 0.004" deeper than where it would contact the throat, jumping them. I fire a ten round machine rest group at these initial settings, then seat the next batch 0.002" longer. The micrometer dial on quality competition seating dies, such as from Redding or Bonanza, helps. If my second groups are better I'm going in the right direction and I continue to lengthen my cartridge overall lengths until my group size increases, indicating I've gone too far. If that second group with the longer seating depth shoots worse, I go in the opposite direction by seating bullets deeper. Normally my boat tails end up with between 0.000 and 0.010" of initial jump. With VLDs, I start with the cartridge loaded length about 0.006" longer than contacting the throat, jamming the bullet into the throat, and adjust from there. My VLD's usually end up jamming between .000 and .010". Each gun will demand its own individual jump or jam and nobody can tell you in advance what that specific amount will be. With boat tails, once you have established the right amount of initial jump you can load up a full case and shoot at that setting for the entire season. With VLD bullets, however, you have to take nightly chamber readings and constantly increase the seating length to compensate for throat erosion. In other words, whatever amount of jam your initial test results arrive at must be maintained through the entire shooting season. This process is called "chasing the throat." It is not difficult but does require attention to detail and takes a little bit of time on the seating step.

With a good rifle machine rest it takes me about a half day to accomplish what I have described. It can be done on a bench rest with sand bag support but I would suspect it would take longer. No matter how long it ends up taking, it is time well spent performance wise.

Concentricity

According to the GunTec Dictionary, bullet run out is, "The measurement (usually in thousandths of an inch) that a bullet and/or case are misaligned in relation to the centerline or axis of the entire case." Cartridge concentricity is a matter of protracted discussion that we don't have time to cover in this article. What we can say is that no barrel, whether of conventional uniform rifling or gain twist, can accurately shoot "crooked" ammo. I strongly recommend using a cartridge straightening tool. My article, "Better Ammunition" in the April 2016 issue has more information.

.30 Caliber Gain Twist

Ballistically, a 90 grain Berger boat tail bullet fired out of a .223 at 2,800 fps will equal any boat tail bullet fired in a .308. Likewise, a 90 grain VLD from a .223 at 2,850 fps will equal any VLD fired in a .308. And the .223 can do so at a fraction of the cost and recoil.

Gain twist works in pistols, muzzleloaders, and modern rifles. If you choose to shoot Palma with a .308, gain twist should work just fine for either bolt guns or gas guns. Everybody worries about how much gain to use. From what I have seen there is no magic formula. Smith & Wesson uses a gain twist barrel in one of their heavy hunting revolvers. Their rate of twist doubles from 1:20 at the back of the barrel to 1:10 at the muzzle. Colerain Barrels (ColerainBarrel.com, 814/632-7513) specializes in gain twist for muzzle loaders. Their 42" barrels begin at a twist rate of 1:96 and speed up to a final twist of 1:48.

Doubling the twist rate has worked very well for me in 20" Service Rifle and 26" Match Rifle lengths. While not cast in stone, doubling is a good start. If the shooter determines he needs a final twist rate of 1:12 to stabilize a .30 caliber bullet, a good start twist in front of the chamber is likely 1:24, though a start twist of 1:23 or 1:25 would probably shoot as accurately. A few years ago when gain twist started to become popular again, some bench rest and long range shooters tried using very modest gains, such as starting at 1:12.25 and finishing at 1:12; only a quarter inch gain in twist in barrels as long as 26 or 30 inches. While such barrels shot as well as conventional, uniform twist barrels, I don't think the accuracy improvements and reduced pressures of the more aggressive gain twists were ever realized and I don't hear much about anyone using such modest gain twists these days.

Readers with experience about all these topics are encouraged to write to me at NCC1701@penn.com and share their experiences.
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Title Annotation:TECH TOPICS
Author:Carlos, Joe
Publication:American Gunsmith
Geographic Code:1CANA
Date:Dec 1, 2016
Words:5545
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