M.L. (Mic) McPherson
What it Takes to Launch Bullets Faster Than 5000 fps
From a useful gun:
With useful varminting accuracy and performance:
Winchester introduced the 220 Swift in 1935; an era when most shooters remembered being awestruck by loads reaching 3000 fps and when older shooters remembered when 2000 fps was essentially unobtainable. Hence, original advertised Swift velocity, 4130 fps, was sensational, to put it mildly.
Eventually, incremental improvements in barrels and propellants, and technological advances in bullet and cartridge design, allowed handloaders to significantly surpass performance of the original Swift. The culmination of those improvements is what this article is all about.
What Wanninger and I did
About 1995, my late partner, By Smalley, began to scientifically analyze case design. We figured out that case design matters. Then we figured out how to design the ideal case. This culminated with parametric SMc patents. Design features include modest body taper (ala P.O. Ackley), a specific (relatively large) body diameter, an elliptical shoulder, and a relatively long neck. As proven in the Norma Ballistics lab, for any given capacity, these features maximize velocity, while minimizing barrel heating and bore damage.
The Chief Ballistician at Norma, Christer Larsson, tested the 6.5-284 and the 6.5/60 SMc using 140-grain Hornady SP bullets and the correct charge of Norma MRP (ideal for the 6.5-284) to generate 62,300-psi. He fired ten 6.5-284 rounds, testing pressure and velocity for each shot.
The Master Machinist then rechambered that barrel to use the shorter, fatter 6.5/60 case. He left everything forward of the original shoulder-to-neck junction unchanged. Larsson then fired ten 6.5/60 rounds, again, testing pressure and velocity for each shot.
With the tested load, the 6.5/60 had 4% less usable capacity than the 6.5-284; nevertheless, it gave 60-fps higher velocity. Shot-to-shot velocity variation in the 6.5/60 was less than one-third what it was in the 6.5-284. And, the 6.5/60 pressure curves were, by far, the most consistent Larsson had ever seen in his decade of experience as Chief Ballistician at Norma, where he had tested tens of thousands of loads in hundreds of barrels and dozens of chamberings.
The SMc design gives higher velocity for several reasons. We explain why in the U.S. patent documentation. That information is too technical to cover here. The same advantages result in less barrel damage and less barrel heating.
In separate experiments, covered in another article on this site, we compared barrel heating in otherwise identical rifles chambered in 5mm/35 and 204 Ruger. We tested loads in each gun using the same bullet and propellant. Barrel heating was essentially indistinguishable. But, the 5/35 load gave 300-fps higher velocity.
My 28-inch barreled 5/35 launches the 32-grain BT at 4600 fps. This bullet has a higher BC than the original 48-grain SP Swift bullet. With a more efficient bullet launched much faster, this 5/35 load vastly outperforms the original Swift. And, it generates only half the recoil.
Barnes introduced the 26-grain Varmint Grenade about 2005. Summer of 2006, Smalley and I tried to safely launch that bullet at 5000 fps. Limited by the 28-inch barrel, longest we could then get, we failed. We only reached 4960-fps.
Since then, three things have happened:
For the following tests, we insulated the plastic tip of the NTX bullet, to prevent frictional heating from melting it during flight. At these velocities, this is almost certainly a necessity. The molybdenum-disulfide layer insulates, radiates heat, and sublimates (evaporates). This keeps the tip cool enough, long enough, for the bullet to slow enough so that tip melting is no longer a problem.
While talking with Brad Schwartz, who then owned Custom Reloading Tools, LLC, I happened to mention the 5/35. I explained that if only we could get a 32-inch barrel, 5280 fps should be possible with the 24-grain NTX. Schwartz suggested a new barrel company he had heard of.
I mentioned this company to my friend, Martin Wanninger. He immediately telephoned the owner. We bought the necessary special tooling and that company got busy. Soon it had made us four, 20-caliber barrels 33-inches long (maximum their machines would handle). So, thanks to a chance discussion with Schwartz, this project finally came to fruition.
It then later reneged on its promises. It stole the tooling that Martin had bought and paid for, and it refused to make more barrels. I mention this here as a warning to others. I cannot possibly express how badly I want to expose this cretin and his company by names, and warn others about his dishonesty, I will not do so. I will note his company makes barrels, or at least they did make barrels when we did this project, in Montana. In any case, before you deal with any new barrel company, carefully check out its reputation, please.
After that experience, we then approached Pac-Nor, as we should have done in the first place. After paying for another set of tooling, we were able to obtain superior barrels from that reputable company that has long been known for making match-winning barrels (refer to my article on the egg shoot).
I do not have room here to begin to explain how invaluable Wanninger was to this project. I can say with certainly that without his efforts, and considerable investment, it would never have happened. Equally, Savage Arms was most helpful, it went out of its way to get us a supply of Long Range Precision Varminter actions to work with.
Back to the Barrel
Yes, 34-inches is an unusually long barrel. But, it causes no problems when shooting over a portable bench, which is how we usually hunt varmints. And, besides the velocity advantage this offers, it reduces noise to the shooter and to the vermin.
Usefulness of such a load is entirely limited to smaller species. But, in that application, it has significant benefits, including:
A flatter trajectory helps, even when we can use a laser rangefinder to measure target distance. First, it reduces the need to range targets. Second, it reduces the number of high and low misses when one does not range the target. And it limits misses when one gets a bad rangefinder reading. Often when varminting I have gotten a rangefinder reading from terrain or vegetation closer-to or farther-from the intended target.
Few shooters, even dedicated varmint hunters, realize just how detrimental recoil is. The 17/23 SMc is the little brother to the 5/35 SMc. My custom 17/23 weighs 7½ pounds. It launches the 25-grain V-Max at 4230 fps. With the unusually effective LAW muzzle brake, recoil is similar to a typical 22 Long Rifle gun firing standard 22 Long Rifle ammunition.
Those who have shot at vermin with my 17/23 are uniformly awestruck. They hardly feel the gun move and always see the impact. A 5/35 of typical varmint-rifle weight launching the lighter 20-caliber bullets and fitted with the LAW muzzle brake generates similar recoil.
LAW: Lightweight Air Working. This brake incorporates Rocket Science and my best ideas to provide maximum recoil reduction without adding noticeably to perceptible muzzle blast for the shooter or others on the shooting line. It works. As an added bonus, it dramatically reduces down-range noise, so vermin are far less apt to be alerted. Pacific Tool is working to produce these brakes for us, only the current (circa 2020) and recent catastrophic business circumstances have prevented this already having happened. Perhaps by the time you read this we’ll have LAW brakes available.
Having an effective long-range gun that generates so little recoil changes everything about varmint hunting. You can see your hits and misses. Seeing the hits is part of the game. Seeing the misses helps you make corrections so you can see more hits.
If the question is, “How much recoil is too-little recoil?” The answer is: “There is no such thing as too-little recoil.”
The first day we fired only enough shots with each load to get baseline data. The second day we fired twelve shots of each promising load from the first day. And we tested two more propellants, VN540 and LEVERevolution.
As luck would have it, we tested LEVERevolution last, when our hope of reaching 5280 fps had stretched to the breaking point. Then, Wanninger fired the first LEVERevolution shot. I looked at the chronograph reading and had to stifle a grin. Wanninger asked, “What did that one do?” I replied, “Just keep shooting, we only have eleven more shots to finish this testing.” So, he stoically proceeded. When he finished, I told him he needed to look at the chronograph. Wish I had gotten a picture of his face when he did!
Accuracy of the best-tested loads suggests that by adjusting bullet-to-rifling jump we should find several excellent varmint loads. Accuracy of at least seven of the ten loads was already good enough for most varminting.
Soon, we will test CFE-223 and AR-COMP. That will cover all readily available propellants that are apt to top 5000 fps.
Wanninger built his excellent custom rifle using the Savage F-class action and stock. With the revolutionary AccuTrigger, this extremely rigid single-shot action is a superior platform for any accurate rifle. I am prejudiced: I provided input toward designs of both the action and the stock, and I skeletonized that particular stock, removing more than 40% of the weight, without noticeably reducing rigidity — that’s another story for another time.
What about barrel life
Surprisingly: Of itself, muzzle velocity has nothing to do with barrel life.
Hot, corrosive propellant gasses damage the bore. If each shot uses a similar charge of a chemically similar propellant; and, if peak pressure (temperature) is similar, bore damage will be similar. Bullet weight and, therefore, muzzle velocity, does matter. But, the correlation is exactly opposite of intuition. Shooting heavier bullets results in greater bore damage. Why so? Because shooting a heavier bullet subjects the bore to equally hot and corrosive gasses for more time.
Smalley got 5000 rounds of useful barrel life out of his original 5/35. His standard load launched the 35-grain Berger HP at 4450 fps, using about 33.5 grains of propellant. While that barrel showed significant corrosive damage, it still shot fine and velocity was close to what it got when new, the problem was, it finally got to the point where cleaning took enough time and effort that By decided it was no longer worth it. He bought and installed a new barrel — good idea!
With the LEVERevolution load, because of the heavier charge, we would expect less barrel life — perhaps 3500 rounds. But, the shorter barrel time could improve that to over 4000 rounds.
A promising alternative is IMR-8208, which generates less fouling and is less sensitive to temperature. Therefore, it might be more useful during long days of varminting (less need to clean the bore), when the temperature might change by 30º Fahrenheit (less need to reduce the load to prevent excessive pressure at hither temperatures). With the lighter charge, 5000 rounds of useful barrel life is entirely feasible.