GS Moly Coated Bullets

[MontanaRifleman]

Gerad,

Thanks very much for the reply. If I understand you correctly, the HV bullet is essentially an SP bullet made to open and expand? If that is the case, if we took the SP 308/197 with a current BC advertized @ .942, and modified to an HV type bullet, do you have an idea what the BC would be for that bullet? Same question for the 338/295 with a current advertized BC of 1.132?

Thanks,

Mark

 

[Gerard Schultz]

Steve,
The drag profile is G1.

Much of the work done, to establish what drag profile best suits a particular shape or profile of bullet, is based on data developed through range experiments with a variety of standard models. These tests took place at a variety of locations over many decades and usually by military authorities with very deep pockets. We have the problem that there does not really exist a model for a full drive band shank, hollow point, rounded boat tail projectile.

There is no way we can go down that road, the expense would kill a company 100 times bigger than us.

So we use a standard G1 drag profile, use the calculation method developed by McCoy and ask that our BC numbers be regarded as a guideline/factor to work with. It is a uniform method across all bullets so, if you find that under your specific conditions a difference is apparent, it will be a constant across our entire range.

 

[Gerard Schultz]

Mark,
The meplat size and ogive curve and length play the major roles in determining the BC of a bullet. The 197gr SP has a meplat diameter of 0.03". To assure full expansion at 1600fps and to be stone cold reliable as a hunting bullet, the meplat needs to be much larger than 0.03". This is what the 177gr HV has and it drops the BC to .638/.603/.589.

Fitting a tip to the hollow point would raise the BC but compromise reliability and accuracy. This is not acceptable to us. Contrary to popular opinion, a tip on a hollow point bullet does not increase expansion, it hampers it. It is a simple experiment to prove this. Work up some mild loads with a tipped bullet and load two or three with the tips in place and load some with the tips removed. Fire them into water (or any aqueous medium you care to use) and observe the result.

As a matter of interest, the 295gr .338" SP needs a 1:7" to 7.5" twist rate to work.

 

[RockyMtnMT]

Gerrard,

Does the 177g HV need more twist than the 173g HV, both in .308? If so how much more? I am generally shooting @ 3000ft above sea level or more.

Thank you,

Steve

 

[MontanaRifleman]

Gerhard,

Is the 308/177 the HV version of the SP 308/197 minus 20 gr of tip and cavity? If the 177gr bullet actually does have a BC in the .638 - .589 range, then that combined with a possible 200 fps increase in velocity would make it equal to or better than any other LR bullet of it's cal and size that I know of.

And yes, I have no doubt that an un-tipped hollow point would open and expand more readily than a tipped point of similar construction. That is basic physics. And yes again, I noticed that these longer bullets required tighter twists.

If you could humor with another question - Is it possible to compromise between the meplat/cavity of the HV and the meplat of the SP and sacrifice lower expanding velocity for higher BC? In other words, design a bullet (or have one custom made) to expand at 1800 fps vs 1600 fps? My thinking is that a higher BC bullet would retain more velocity down range, at let's say 1200 yds, arriving at 1200 yds with a vel of 1800 fps vs the lower BC bullet arriving at 1200 yds with 1600 fps of velocity. The advantages would be greater momentum, less TOF, less winddrift and less drop at long range.

Thanks for your participation and experience.

Mark

 

[Gerard Schultz]

Steve,
The twist requirement for the two bullets are virtually identical. If you go to the HV Bullets page (or SP or FN) on our site and follow the links to Technical Data, there is a link to each individual bullet for detailed tech data on that particular bullet. We are still building the pages for most of the SPs and FNs but some are completed. The HVs are all but done.

The twist/stability factor chart assumes sea level so elevation will increase the s/f slightly. As with all the data we have available, it is an approximation and some leeway must be given for individual conditions. Only actual testing and drop chart development will be precise.

Mark,
They are two individually designed bullets so there are differences in the shaft length as well as the boat tail length and shape. The center of gravity requirement and terminal behaviour of a hollow point differs from that of a spitser and asks for a design from scratch rather than a modification of design. In rare instances it can be done but mostly not.

Assume a speed increase of 80 to 100fps over similar weight non-driveband bullets.

We have seen in practise that a mono that is designed to expand at a certain speed will have a window of erratic behaviour that spans a speed range. As the speed required for expansion increases, the window for erratic behaviour increases. In practise it means that our HVs will expand completely from 1300fps to 1600fps. We say 1600 because we know that is safe.

Others might say 1600 because sometimes it happens with their product, but what they really mean is 1800. It depends on the medium encountered the angles of incidence and attack and so on. A bullet designed for expansion at 1800fps is sometimes erratic in behaviour up to 200fps either side of 1800.

Once again there is an element of unpredictability that we find unacceptable. We need to do some more work in this area as there is clearly a demand for it.

Remember that all this is just my opinion, I may be wrong.

There is a refreshing attitude on this forum. By now most forums would have had someone saying that speed and BC means nothing and that all hunters must learn to stalk to spitting distance.

 

[RockyMtnMT]

Gerard,

Is there a good reason to choose the 173g HV over the 177g HV, or visa-verse?

According to my calculations, I can't find another bullet that will run with the 177g HV out to any yardage. The 240 smk doesn't catch it for windage until 3000yrds. This is well beyond effective velocity.

You won't get anyone hear telling you that you have to get closer. The only criticism here will be for too low a bc making a bullet not effective far enough out.

Do you have plans to produce HV bullets in other calibers in the the higher bc's. Specifically, around here people will be interested in .270, 7mm, and probably most of all .338.

Thanks again for your input,

Steve

 

[Gerard Schultz]

The 173 is a harder bullet that will open more slowly than the softer 177. At extreme ranges the 173 may open too slowly where the 177 will still be ok. At close range the 177 will be pretty explosive especially of bone is hit going in. Also, the more slender ogive of the 177 increases BC making it more suitable for distance. The 173 was done as a 500m hunting bullet and the 177 came later, to fill the need for going out farther than that. The 173 can be fed from a magazine without worries about deformation of the meplat. If the rifle is rough on the bullet/cartridge feeding from the magazine, or the magazine is very short, the 177 is best fed one at a time.

We will be getting illustrations of the bullets on the bullet profile pages I mentioned above. This will show the differences in bullet profile very well.

 

[MSU Marksman]

Gerard-

Is the SP bullet intended for hunting?

 

[Gerard Schultz]

Officially, no. (But yes)

No, because not many reloaders understand the principles involved in creating a sufficient wound channel to kill as effectively as possible. Remember that reloaders are made up from those who have just started to those who have great experience and those who know it all.

With an expanding bullet, understanding how it works is not required. The reloader does not really have to worry himself over the mechanism by which the bullet will work terminally. As long as he uses a bullet within the recommendation of the manufacturer, it will usually do the job. The SP does not expand and the terminal ballistics mechanism is different. It requires a better understanding of what happens with a bullet that does not expand.

So we play safe and say that the SP is a tactical/target bullet.

Yes, as long as the following is understood and taken into account. For hunting it is accepted that the formation of a large secondary (temporary) wound channel will ad to the demise of the animal. Without expansion, and the resultant forwards shift of the CG of the bullet, an ogived bullet will start rotating on impact if the stability factor is sufficiently low. Too high, and the bullet axis tries to remain aligned with the flight path and rotation becomes a hit and miss affair. So, for hunting, an SP must be chosen that can launch with a stability factor somewhere between 1.2 and 1.4. On impact it will then start rotating and do either a 180 or a 360 degree rotation. The lower the s/f can be at launch and still give accurate and stable flight, the better it will work terminally.

If this is clear as mud, please ask clarification.

 

[MSU Marksman]

I can understand the stability factor taking into account for determining if a non-expanding bullet could be used for hunting. But this raises a few other questions.

Is the stability chart shown on your website used to choose barrel twist based on stability at the muzzle, or down range?

Isn't stability a factor of bullet RPM? In other words, could a bullet with a higher muzzle velocity actually stabilize in a slower twist barrel as long as the RPM's were the same at the muzzle?

 

[MontanaRifleman]

We need to do some more work in this area as there is clearly a demand for it.

Yes, there is a demand for high BC LR bullets. As Steve pointed out the most popular calibers would be 338, 308, 284 (7mm), and 270, probably in that order. BC's in the .6-.9 range are generally wha folks are looking for. Which brings me to another question. While browsing through your FAQs, I noticed you (or a company rep) mentined that you have provided custom orders for 275 gr, 284 cal bullets. I was wondering what the estimated BC was on these bullets as well as twist and are they a hunting bullet? The 284/140 HV that you show with a BC of .489 would be a little lite for elk out 1000 yds.

 

[Gerard Schultz]

MSU Marksman,

The charts on our website are for stability factor at the muzzle.

As the bullet goes down range, stability factor increases because forward speed decays faster than rotational speed. So, although rpm is decreasing in real time, rotation relative to forward motion is increasing and that increases the s/f. RPM does not determine stability factor for projectiles in flight. It does for a spinning object where the rotational axis has no linear motion, such as a spinning top.

Muzzle velocity does affect stability factor but it is easier to pick the right length bullet for the twist rate because speed has only a small effect. Bullet length / twist mismatches cannot be fixed with adjustment to speed.

Some examples:
243 83gr SP - Twist = 1:8" -- MV 2100fps - s/f = 1.10
243 83gr SP - Twist = 1:8" -- MV 2300fps - s/f = 1.13
243 83gr SP - Twist = 1:8" -- MV 2500fps - s/f = 1.15
243 83gr SP - Twist = 1:8" -- MV 2700fps - s/f = 1.17
243 83gr SP - Twist = 1:8" -- MV 2900fps - s/f = 1.18
243 83gr SP - Twist = 1:8" -- MV 3100fps - s/f = 1.20
243 83gr SP - Twist = 1:8" -- MV 3300fps - s/f = 1.21

243 83gr SP - Twist = 1:8.5" - MV 3000fps - s/f = 1.05
243 83gr SP - Twist = 1:8.5" - MV 3200fps - s/f = 1.06
243 83gr SP - Twist = 1:8.5" - MV 3400fps - s/f = 1.07
243 83gr SP - Twist = 1:8.5" - MV 3600fps - s/f = 1.08
243 83gr SP - Twist = 1:8.5" - MV 3800fps - s/f = 1.09
243 83gr SP - Twist = 1:8.5" - MV 4000fps - s/f = 1.10

Mark,
I am trying to find the reference to the 275gr .284 bullet on our site. It must be a typo because we have not made even a 175gr bullet in .284. Can you point me to where you saw it please?

We will extend the number of bullets available for long range hunting. There are projects that are under way that must be completed before we get to that but it will be done.

 

[MontanaRifleman]

Gerard,

My error, after going back and reading the reference, it says that you have been asked for them, but the reply was that they would not work in the hollow point and it was 175 not 275 (a typo).

GS CUSTOM BULLETS - Twist Rates and Bullet Length

What do you think is the heaviest mono hollowpoint bullet that can be made in the 284 cal?