North Fork Bullets Design Philosophy

North Fork Bullets Design Philosophy
One Man’s Opinion
Mike Brady

North Fork Bullets

Design Philosophyby Mike Brady

This article goes into the design philosophy behind North Fork products. A philosophy is just like an opinion and opinions are just like that other thing – everybody has one. So here is mine.

I am of the old school that appreciates the terminal performance reliability of a lead cored bullet. But I also like the indestructible nature of a solid sectioned bullet. When you marry the two concepts, the result is a bullet with a bonded lead core in the front and a solid rear section.

The design itself is surely nothing new. I have seen examples from as early as the 1930s, and I bet that someone somewhere had a similar notion and experimented with it even earlier.

As far as I know, the earliest commercially available bulletwith a lead core in front and solid rear section was offered byP. O. Ackley in the late 1940s and early ‘50s. It was called theAckley Controlled Expansion Bullet. Prior to bringing it tomarket, Ackley spent 10 years experimenting and refining hisidea to come up with an internal design that would retain thestructural integrity of the bullet on impact. Roughly ten yearslater, Jack Ashurst, better known for manufacturing reloadingdies under the name of Jax Dies, made a bullet of similardesign. The most reliable sources say that they were commerciallyavailable from 1958 through 1960.

A brief history of the bonded core bullets starting with P.O.

Ackley’s original design and ending with North Fork’s HG

(Heavy Game) version. (1) P.O. Ackley .308 caliber 180 gr.

circa 1949-51; (2) Jack Ashurst (Jax Dies) .308 caliber 220 gr.

1958-60; (3) Bill Steigers (Bitterroot Bonded Core Bullets)

.375 caliber 300 gr.; (4) North Fork .308 caliber 180 gr. and

(5) 200 gr. HG.

That next step in evolution was left to none other thanthe designer of the daddy of all bonded bullets, Bill Steigers ofBitterroot Bonded Core Bullets. In the late ‘60s, Steigers solda product based on the Ackley design but improved with hisown core bonding process. He had Ackley’s permission to callit the Ackley Style Solid Base Expanding Bullet.

However, since this was before we had reliable and(relatively) cheap CNC equipment, this bullet was so laborintensive that Steigers eventually dropped the Ackley designand went back to his own homegrown and already perfecteddesign, which, by the way, will always be known as the bulletthat started the bonded era and to which all other bondedbullets are (or should be) compared.

As with everything else in this industry, there is rarelysomething completely new. You just find different peopledoing it. The Ackley design has been copied by many (myselfincluded) over the past 50 years.

In addition to tweaking the internal design to improvethe range of usable terminal impact velocities, my primarycontribution to the evolution of the type was to put reliefgrooves in the solid section of the bullet.

Solid sections, especially of soft copper, have always hadtwo inherent problems as a result of forcing an essentiallysolid object down a rifled barrel – increased fouling and possible pressure spikes. In a solid sectionedbullet, there is nowhere for the materialdisplaced by the rifling to go. In a fulllengthlead cored bullet, the deformationof the lead core actually makesroom for the displaced jacket material.

Not so in the case of a solid sectionedbullet. But by adding groovesin the solid section you give the materialdisplaced by the rifling lands aneasy (lower stress) escape route. If thestresses between the bullet and the barrelare kept below the sheer strength ofthe jacket material, that material is notgoing to be ripped from the jacket anddeposited within the barrel.

Terminal Performance

I wanted North Fork bullets to performover the widest impact velocity rangepossible. The useable impact velocityrange of a bullet is the velocity at whichthe bullet first opens to the size of a useful,lethal mushroom, subtracted fromthe max impact velocity that the bulletcan withstand and still remain intact(i.e., one piece).

In other words, I wanted the bulletto open at low impact velocities ANDremain intact at the maximum impactvelocity that could be expected from anyspecific caliber. There are many bulletson the market that will perform well ina narrow velocity range of as little as 300to 400 f.p.s.

There are bullets in the North Forkproduct line that have a useful impactvelocity range of 2000 f.p.s. Most willoperate in the over 1500 f.p.s. range.None will operate in less than a 1000f.p.s. range, but that is mostly becauseguns or cartridges that can drive themfast enough to find out if they’ll domore simply don’t exist.

North Fork .416 caliber, 370 gr bullets recovered at progressively higher impact velocities.

1735 f.p.s. / 99.5% retention; 2000 f.p.s ./ 99.4%; 2200 f.p.s. / 99.3%; 2400 f.p.s.

/ 97.8%; 2600 f.p.s. / 95.0%. The core bonding process achieves 95% weight retention

even at 2600 f.p.s. impact velocity.

When we talk about terminalperformance, we also have to considerthe balance between penetration andtrauma inflicted. Now, the controversyover this one will start more barroombrawls than “tastes great/less filling.”I’m not trying to fan any flames becausethe true believers on both sides of thefence will never be swayed. Luckily foreveryone, there are products out thereto satisfy both camps.

My observation, based on severalthousand impact tests, is that penetrationand trauma inflicted are polaropposites. If you want more of eitherone, you have to give up some of theother. Bullets that make small holespenetrate deep. Bullets that make bigholes penetrate shallow.

At North Fork, we wanted maximuminflicted trauma with ENOUGHpenetration. “Enough” is anotherloaded word that can have as manymeanings as there are people to defineit. To me, “enough” means that the bulletalways penetrates through the vitalsof the animal and on to the hide on thefar side. Once it has reached the offsidehide, it doesn’t matter to me whetherit exits or not. The maximum amountof destruction to the vital organs hasalready been done. For the record, Ibelieve that it is a penetration failure ifa bullet does not reach the offside hide,even from a 45-degree shot angle.

The large calibers are more likely tobe found under the offside hide than thesmaller calibers. There are two reasonswhy – the physical construction of theanimals they are used on and the impactvelocities of those bullets. Where I havesamples or photos of 15 or more largecaliberbullets recovered from largerAfrican animals, the number of smallercalibers (284, 308, and 338) retrievedfrom animals (mostly raking shots onelk and moose) is so small the whole lotof them could fit in the watch pocket ofyour Levis.

How to control penetration andtrauma? By limiting the size of themushroom. This is where the oftenover-worked marketing term “controlledexpansion” comes in. That termhas been so overused, misused and otherwiseabused that the customer usuallyplaces no credence in it whatsoever.That puts it in the same category as theeven more abused marketing term “premium.”

As I see it, controlled expansionmeans the expansion is STOPPED, notjust in a narrow impact velocity rangebut over the entire range of impactvelocity. This requires a physical barrierto further expansion. If there is nophysical barrier, there is no “controlledexpansion,” at least by my definition ofthe term.

In a conventionally constructedbullet with a core that extends the fulllength (or nearly so) of the bullet, thereis no way to limit the formation of themushroom and consequently no way tocontrol penetration over a wide impactvelocity range.

L-R North Fork bullets .416 370 gr.; .423

380 gr., and .458 450 gr.

All bullets have a penetration profile.Picture a graph with the x (horizontal)axis representing impact velocityand the y (vertical) axis representinginches of penetration. At low-impactvelocities below the velocity that initiatesexpansion, ALL bullets will penetrateto a great depth, as long as theyremain stable.

The .423 caliber 400-gr Woodleigh

expanding bullet is an excellent conventional

design that demonstrates the

decrease in penetration as impact velocity

increases.

In contrast, the North fork .423 caliber

380-gr bullet actually continues to penetrate

with increase in impact velocity.

But this is irrelevant tooutcome.An even slightly pointed expanding bulletthat does not expand inflicts aboutas much trauma as stabbing the animalwith a hypodermic needle. The classicexample of this is the animal that is shotat such a great distance that the bulletdoes not open and therefore inflicts noimmediately lethal trauma. The result,more often than not, is a wounded animalthat is lost.

Back to the graph – once the conventionalbullet begins to mushroom,the penetration is reduced by the dragof the mushroom. In a conventionalbullet (bonded or not) penetration continuesto decline as the impact velocityincreases.

Penetration of a North Fork bulletis also going to slow once expansion isinitiated due to drag. The difference isthat once the North Fork bullet reachesa velocity of approximately 2100 f.p.s.,there is no more lead to feed the mushroomand it stops expanding.

How does that affect penetration?On our graph, the North Fork’s penetration,like other bullets, starts veryhigh at impact velocities that do notcause mushrooming. As the impactvelocities increase and the bullet beginsto mushroom, penetration decreasesuntil the size of the mushroom stabilizes.From that point on, as impactvelocities increase, so does penetration.

So the graph shows a line thatdecreases until approximately 2100f.p.s. and then the line reverses andcontinues to go up along with theimpact velocity. Somewhat counter intuitively when compared to conventionalbullets, with North Fork bulletshigher impact velocities result inincreased penetration.

I often tell customers not to intentionallyreduce the velocity of NorthFork bullets if they are expectingincreased penetration. If you are lookingfor more penetration, reducing thevelocity will not get you there.

Folks often ask why North Forkbullets, especially the larger calibers, areoffered in unusual weights and sectionaldensities that are less than “traditional.”

Two reasons:

First, the limited amount of core,which allows us to control the size ofthe mushroom, means that the remainingweight of the bullet by necessity ismade up of the jacket material. Sincejacket materials are approximately 80percent as dense as lead, a bullet of “traditional”weight would be too long.

That in itself is problematic. Twistrate of a rifle doesn’t care about theweight of the projectile; it only caresabout the length. A too-long projectilecan be unstable from a standard ratetwist. That instability can show up inthe air (accuracy) and/or in the animal(penetration). Either way, it renders thebullet useless.

An overly long bullet also robsavailable powder space from the cartridge.In some cartridges (the .416Rigby, for example), this isn’t really aconcern. But in cartridges like the .416Taylor and Remington, it is a problem.

The second reason North Fork bulletscome in “non-traditional weights”goes back to velocity. An increase inweight would reduce velocity. In aNorth Fork bullet, less velocity equalsless penetration.

Our extensive testing over the yearshas shown us that a maximum sectionaldensity of ~.305 gives the best balanceof weight, powder room, velocity andpenetration FOR THE DESIGN OFTHIS PARTICULAR BULLET.

When it comes to expanding bullets,speed kills and more speed killsbetter IF the bullet is up to the taskstructurally and there is no reductionin penetration. The people who wantto argue that point are basing theirassumptions on conventionally constructedbullets (bonded or not) thathave been the norm for 100 years. Forthe newer generation of bullets – NorthForks included – those assumptions nolonger apply.

North Fork Technologies

P.O. Box 850

Philomath, OR 97370

Phone 541-929-4016

CopyrightNorth Fork Technologies. P.O. Box 850, Philomath, OR 97370