Interesting BC test results: .17 cal

[Sam17H]

Hi all,

 

This may well be the first test of its kind, as I could find nothing online to suggest otherwise. As a quick intro, I decided to conduct a BC test using two different .17 calibre Hornady V-Max bullets fired from my rifle, as the published data was evidently quite a way off. Please read on for more info…

 

This all started when I decided to stretch the legs of my .17 hornet out to 600yds at Bisley one still morning recently. Rifle is a custom build based on the Anschutz Model 54 action mated to a 24” lothar-walther match grade barrel with a measured 1 in 9.25” twist. I had my well-developed hand loads with me; one using Hornady 20gr V-Max @3750fps, and the other 25gr V-Max @3550fps, again Hornady. Published BCs for the bullets are 0.185 for 20gr, and 0.230 for 25gr. These were entered into the app as I had no reason to doubt them.

 

Using the istrelok app to give me the drop data I thought I’d be good to go. Temperature and pressure were checked and input too. So, I went ahead, dialled in the required 12.5MOA elevation up from my 150yd zero, and fired a few warming shots into the sandbank to check whether I was somewhere near. First shot; nothing visible. “That was weird?” I thought, so I aimed a bit higher and saw the next shot land very low in the sights. The ballistics data was miles off!! In fact, I needed 22.5MOA elevation; of which 19.5MOA was the limit of vertical adjustment on the scope, so I used my vertical aimpoints to cover the remaining 4MOA. Scope is a Sightron SIII 10-50 x 60 with MOART reticule.

 

The next observation was when down in the butts patching the targets up and checking the group sizes the marker a couple of targets along was asking what I was shooting. I had a chat with him, at which point he explained my bullets were subsonic and all he could hear was the slap into the target and sandbank, but no crack. This intrigued me as the ballistics table suggests they would remain supersonic to around 700yds with the 25gr bullets, and somewhere transonic with the 20gr bullets at 600yds. An interesting observation for sure.

 

I checked at 100yds back home that day after my range visit, and indeed I was hitting 23” high at a measured 100yds, so the zero was pretty much bang on.

 

A week later I returned to Bisley at 500yds this time, along with a mate who was testing his new 7mm custom rifle. Having pondered what was happening with my ballistics back at 600, and assuming the ballistic data published by Hornady was well off, I adjusted the bullet BC down in the app to give me the 135” drop @ 600yds that I was experiencing, and used this data to give me a starting point on target for elevation adjustment. This was much better, and put me within 1/2MOA of where I was aiming. Disappointing though, as the BC for the 25gr bullets was down at 0.165* (*estimated at this point based on previous 600yd data) from the published 0.230… I wouldn’t expect perfection, but that really is a bus ride away from what Hornady reckon the BC should be! We both had our chronographs set up in front of us to capture data. In short, my 20gr loads were chronoing as expected at 3750fps, but were subsonic at 500yds (observed by me standing in the butts while my friend fired a few shots at the target), and the 25gr loads remained supersonic emitting a decent ‘crack’ as they passed overhead. Interestingly, those loads which chrono’d at lower velocities, i.e. 3520fps as opposed to 3550fps were noticeably quieter. This was enough evidence for me to suggest the 25gr bullets were ‘just about’ still supersonic at 500yds when spat out at 3550fps, so that further verified my drop chart from JBM ballistics which showed them entering the transonic region around 475yds (based on estimated data at this point)

 

In light of all this data I decided I would carry out my own BC test at home. Friday presented the perfect day – no wind, a mild 8c and I had a day off work. I borrowed my mate’s CED M2 chrono, and used my own Caldwell Ballistics Chrono linked to the ipad. We have a bit of land so I was able to set up a 269yd range with one chronograph at the muzzle and one down range. First up was to check for variance between the readouts of each chronograph by lining both up together, one in front of the other barely 6” apart, and sending some bullets over them. I switched each one around to eliminate the fact the rear-most chrono would inevitably read a tad lower as the bullet loses velocity over those 3 feet (oh the joys of small calibre firearms!). The average difference consistently showed my chrono reading higher by around 52fps, which I chose to divide in half and add 26fps to my friends’ chrono readouts, which would be at the muzzle and subtract 26fps from mine, down range. I set the chronos out so mine was downrange with a measured 267yds between chronos, and 3 feet between the muzzle and the first chrono. My friend believes his reads low anyway because his drop data using the chrono speeds from his chronograph puts him higher than it should do in terms of bullet impact on target at extended ranges.

 

The results:

I tested both the 20gr v-max and 25gr v-max during the testing process by firing across the first chronograph 3feet in front of the muzzle, and over the second one a further 267yds away. Positioning a 12” shoot n see target directly behind the target chronograph helped visually inspect where the bullets were landing, as well as a further two zero targets either side away from the chrono to check initial zero when switching bullet weights. I videod the target end with a gopro camera to capture each bullet hit and also to watch the screen on the ipad so I could verify each individual shot as it passed over the chrono and attribute it to a reading from the muzzle end. Each shot was recorded at the firing point to state whether it was a ‘test’ shot or aimed over the chronograph. The chrono was protected by a thick concrete paving slab to prevent a stray bullet damaging it (one bullet would have hit it, incidentally had I not done this!) At one point I achieved an 8 shot group with the 20gr v-max bullets measuring a fraction under 2”, but annoyingly my chronograph didn’t save the shot string and I was unable to pick up the readings on the camera! Learning point for future nonetheless.

 

I wasn’t intending on publishing all the data as I had lots of readings, so instead I’ll explain how I worked out the figures:

 

The near reading (muzzle) was via my borrowed chronograph, which from my earlier test I know reads low compared to mine, so I added 26fps to each reading from this one, and subtracted 26fps from the downrange chrono (mine) to split the error. This then gave me a difference in velocity between each across the known 267yd distance. For each bullet I averaged out the velocities from each chronograph to give me the figures I wanted to work with. I read the temperature via the istrelok app which gave me 8c and 30.02Hg. Then, I experimented with the BC by entering my initial velocity plus 5fps to bring it to true muzzle velocity, and played with the BC figure in the app until I was achieving the average downrange velocity for that bullet weight. Turns out I was extremely close with my previous ‘estimated’ BC figure having used the 600yd drop data and again adjusted the BC to correspond correctly to that amount of drop. Final figures are as follows:

 

Hornady 20gr V-Max: BC (published) = 0.185 / BC (tested) = 0.155

 

Hornady 25gr V-Max: BC (published) = 0.230 / BC (tested) = 0.164

 

As you can see, the tested figures are a long way out from what is published; a shocking amount in my eyes, and quite a shame really as I had high hopes for the 25gr bullets carrying a considerable amount more energy out to longer ranges. Of course, they still do carry more energy as they start with 700ft/lb vs 610ft/lb, but they drop more than the 20gr’ers and in reality the BC isn’t that much better. 20gr bullets seem to expand a lot more violently too; no doubt because they’re spinning quicker and going faster generally, plus I feel more comfortable that they self-destruct better over flatter ground better than the 25gr bullets (where I shoot this is much more beneficial to me).

 

All-in-all a very surprising test, although I set out on this mission realising I wouldn’t be achieving the published data given my experiences so far at long range.

 

Hopefully that’s been a good read for a few people?!

 

Sam

 

 

 

[treetop]

Very interesting !

[gbal]

What is the velocity of a 25g 17 Hornady bullet?

 

Well,you say-very reasonably-it depends on what it is fired from-it's velocity varies.

 

Absolutely correct-it's very considerably faster fired from a 17rem than from a 17 Hornet.

 

So what......well,G1 BCs vary with velocity too,so -just as a 17 25g bullet has no fixed velocity,nor does it have a fixed BC,especially a G1 BC.And as it slows down,after firing,the bullet's BC reduces.

 

Let's see what Sierra offers-more detail-thus: for their 204 32g bullet:

 

velocity 3950+ BC .221

3625+ .218

3300+ .204

2225+ .189

1750 .179

 

In reality,of course,the BC and velocity are continuously co-variable-but at least Sierra are honest and give values for the BC at several velocities,as above.

If only one-and it's always the best G1 that is given - is fed into modest ballistic programs,then the output drop correction figures are going to be correspondingly out as distance increases,velocity and therefore real BC decrease from this entered maximum published value....

 

This is true for all bullets-Sierra just don't do a 17.But you can see the change is in the ball park of your data....

Bryan Litz has made the point,and the motivation for 'his' G7 values is largely to get a BC figure (G7) that is relatively constant across likely bullet velocities,so that program output more closely matches reality.

 

(there are,of course,other variables that start to take their toll as distance increases-transonic is one,as you say-but try entering the G7 and check against actual shooting clicks. G7 are very approx half of G1 if you want an easy run at it. That suggested, for flat base bullets, G1 might be adequate-it gets complex! Not quite the same,but try to compare tangent and secant and hybrid ogives,and note their differences at 1000y-and yes,there are a whole raft of G s.

 

Holes on paper are the best guide to reality.

 

gbal

[Sam17H]

What is the velocity of a 25g 17 Hornady bullet?

 

Well,you say-very reasonably-it depends on what it is fired from-it's velocity varies.

 

Absolutely correct-it's very considerably faster fired from a 17rem than from a 17 Hornet.

 

So what......well,G1 BCs vary with velocity too,so -just as a 17 25g bullet has no fixed velocity,nor does it have a fixed BC,especially a G1 BC.

 

Let's see what Sierra offers-more detail-thus: for their 204 32g bullet:

 

velocity 3950+ BC .221

3625+ .218

3300+ .204

2225+ .189

1750 .179

 

In reality,of course,the BC and velocity are continuously co-variable-but at least Sierra are honest and give values for the BC at several velocities,as above.

If only one-and it's always the best G1 that is given - is fed into modest ballistic programs,then the output drop correction figures are going to be correspondingly out as distance increases,velocity and therefore real BC decrease from this entered maximum published value....

 

This is true for all bullets-Sierra just don't do a 17.But you can see the change is in the ball park of your data....

Bryan Litz has made the point,and the motivation for 'his' G7 values is largely to get a BC figure (G7) that is relatively constant across likely bullet velocities,so that program output more closely matches reality.

 

(there are,of course,other variables that start to take their toll as distance increases-transonic is one,as you say-but try entering the G7 and check against actual shooting clicks. G7 are very approx half of G1 if you want an easy run at it. That suggested, for flat base bullets, G1 might be adequate-it gets complex! Not quite the same,but try to compare tangent and secant and hybrid ogives,and note their differences at 1000y-and yes,there are a whole raft of G s.

 

Holes on paper are the best guide to reality.

 

gbal

Good reply gbal.

 

It's interesting to see Sierra's offering of different G1 BCs for different velocity bands. I must say, that even looking at the variation across their published data, the .17cal difference is still a fair bit larger. I would expect the BC to be slightly different when fired from a .17rem, but even then they're only travelling around 500fps faster. Yes, its a fair bit, but I still believe there's more going on than just a matter of the velocity being slightly lower in comparison. I wonder how much different the BC would be in warm weather?

 

My main aim for doing this was to create a true drop chart table; which inevitably I'd managed to achieve very closely to reality using my 600yd test data, but I wanted a tested BC to enter into the software; more as a check really. I also planned the test to be carried out at what I'd reasonably expect to be normal maximum range shooting - as much as i'd love to pick off vermin out beyond 250yds, the land I shoot on just doesn't offer those opportunities. The rifle is certainly capable though. I managed a 5 shot group just over MOA at 600yds with the 20gr bullets!

 

Sam

[247sniper]

What is the velocity of a 25g 17 Hornady bullet?

 

Well,you say-very reasonably-it depends on what it is fired from-it's velocity varies.

 

Absolutely correct-it's very considerably faster fired from a 17rem than from a 17 Hornet.

 

So what......well,G1 BCs vary with velocity too,so -just as a 17 25g bullet has no fixed velocity,nor does it have a fixed BC,especially a G1 BC.

 

Let's see what Sierra offers-more detail-thus: for their 204 32g bullet:

 

velocity 3950+ BC .221

3625+ .218

3300+ .204

2225+ .189

1750 .179

 

In reality,of course,the BC and velocity are continuously co-variable-but at least Sierra are honest and give values for the BC at several velocities,as above.

If only one-and it's always the best G1 that is given - is fed into modest ballistic programs,then the output drop correction figures are going to be correspondingly out as distance increases,velocity and therefore real BC decrease from this entered maximum published value....

 

This is true for all bullets-Sierra just don't do a 17.But you can see the change is in the ball park of your data....

Bryan Litz has made the point,and the motivation for 'his' G7 values is largely to get a BC figure (G7) that is relatively constant across likely bullet velocities,so that program output more closely matches reality.

 

(there are,of course,other variables that start to take their toll as distance increases-transonic is one,as you say-but try entering the G7 and check against actual shooting clicks. G7 are very approx half of G1 if you want an easy run at it. That suggested, for flat base bullets, G1 might be adequate-it gets complex! Not quite the same,but try to compare tangent and secant and hybrid ogives,and note their differences at 1000y-and yes,there are a whole raft of G s.

 

Holes on paper are the best guide to reality.

 

gbal

 

 

 

Well said Gbal, spot on mate.

 

Steve

[The_Dogge]

 

It's interesting to see Sierra's offering of different G1 BCs for different velocity bands. I must say, that even looking at the variation across their published data, the .17cal difference is still a fair bit larger. I would expect the BC to be slightly different when fired from a .17rem, but even then they're only travelling around 500fps faster. Yes, its a fair bit, but I still believe there's more going on than just a matter of the velocity being slightly lower in comparison. I wonder how much different the BC would be in warm weather?

 

I don't think the BC will be any different in warm weather, your method of calculating it has already taken into account the atmospherics, BC has to be relative to a standard atmosphere. If you did it again on a warmer day, you'd get higher retained velocity, but the app would give you the same BC because you put in the higher temp.

 

Thanks for the write up, very interesting, I think the main effect you are seeing is, as gbal says, the variation on G1 BC with speed due to the poor match of the shape to the reference projectile. This is coupled with the fact that the little .17 bullets have the widest possible range of speeds, starting at 4200+ ft/s and falling all the way to subsonic. Hornady will want to publish the highest BC possible, so they are not necessarily lying when they say 0.23, it's just that that is only true at something over 4000ft/s.

 

What was your average speed in your tests? (I mean average all the way to the far chrono)

 

In his book "Modern Practical Ballistics" Arthur Pejsa has a formula for estimating the BC of a bullet based on it's weight, diameter, and just a "shape class" of 1,2,3 or 4, depending on whether it is pointy, has a boat tail, etc. Most of his stuff is uncannily accurate, the formula predicts a BC for the 25gn bullet of 0.168. :-)

[Sam17H]

 

I don't think the BC will be any different in warm weather, your method of calculating it has already taken into account the atmospherics, BC has to be relative to a standard atmosphere. If you did it again on a warmer day, you'd get higher retained velocity, but the app would give you the same BC because you put in the higher temp.

 

Thanks for the write up, very interesting, I think the main effect you are seeing is, as gbal says, the variation on G1 BC with speed due to the poor match of the shape to the reference projectile. This is coupled with the fact that the little .17 bullets have the widest possible range of speeds, starting at 4200+ ft/s and falling all the way to subsonic. Hornady will want to publish the highest BC possible, so they are not necessarily lying when they say 0.23, it's just that that is only true at something over 4000ft/s.

 

What was your average speed in your tests? (I mean average all the way to the far chrono)

 

In his book "Modern Practical Ballistics" Arthur Pejsa has a formula for estimating the BC of a bullet based on it's weight, diameter, and just a "shape class" of 1,2,3 or 4, depending on whether it is pointy, has a boat tail, etc. Most of his stuff is uncannily accurate, the formula predicts a BC for the 25gn bullet of 0.168. :-)

I was achieving from memory around 3500 at the muzzle and around 2000fps downrange, so a loss of 1500fps over the 267yds, so I make that 2750fps average.

 

That's really interesting what you mention about Arthur Pejsa's formula, and it really is damn close to what I calculated! I'll be doing some research into that - nice find

 

Sam

[Wiltshire Boy]

I thought there was an absolute MV limit at bisley of 3280FPS ? although I may be wrong.

 

Beware what you post.

 

Cheers

Rich

[The_Dogge]

I was achieving from memory around 3500 at the muzzle and around 2000fps downrange, so a loss of 1500fps over the 267yds, so I make that 2750fps average.

 

That's really interesting what you mention about Arthur Pejsa's formula, and it really is damn close to what I calculated! I'll be doing some research into that - nice find

 

Sam

 

He knows his stuff, but I seriously wouldn't buy the book, it's not very well written and unless you already have a reasonable grasp of aeroballistics I just don't think it would make much sense. It's very much an engineers approach, which can skip the theory and jump straight to approximations introduced without proper explanation.

 

Just googling around I can't find either a claimed G7 BC, or a reference velocity for the published G1 BC, which would allow me to calculate the G7 BC, for this bullet. Anybody have a reference for either? I don't suppose Litz has tested this bullet?

[gbal]

Some more/varied interesting points raised....as accepted elsewhere,it really gets pretty complex...

 

For field use,velocity tends to be king out to 350y (hot cf )maybe 250 for Hornet class...then BC really matters (not that 100 fps make much difference in the 350y,it just isn't dropping so rapidly til then).

Pejsa's work in 1980 was important,though his 4 categories of bullet are very unlikely to me more sophisticated than the G1 to G8 from other work.His results were best for supersonic speeds(as most are-instability is a disruptive extra factor-one reason many 168 30 cal bullets rather fall off a cliff before 1000y).

Serious Ballistic programs like Prodas tend to be "6 degrees of freedom' ones (probably a simplification-there are fifty shades of grey,after all)-but need very detailed and elaborate input,and take way too much computing power for the 'iphone' based programs-professional military research only.

 

And then there is accurate Doppler measurement-not a 'guestimated' 1/2 inch from a 'group' of three shots (technically indistinguishable from random)...here are some such BCs for a 50 Browning:

 

BC at 500y 1.040 ,rising to a stable 1.67 from 1000 to 1350y then dropping back to 1.042 by 1900y

 

Go figure...take a week...!

 

Of course,'we' can get close much easier,but the underlying point is that this business is complex indeed,and you need to input some very detailed and accurate data indeed to get an approximation back out-and it won't be too well tuned to your rifle,which is generally better than most.

 

g

 

PS not sure if Bryan Litz has G7 for the 17 cal bullets,but the corrections that can be applied to G1 will help,as will field testing,as done here.

No way 17H is a 500y varmint cartridge-any varmint that has a 6 inch kill zone needs more energy than is left at that range,and crows are less than 3 inches wide at any distance....rabbits usually 3 inch max in elevation......

Read B Litz on the guaranteed max hit range on a 6 inch target,with a 100y 1/2moa 80g 6mm-no shooting wobbles- it's 248y.

That assumes wind reading better than most shooters can manage,and at any greater range there will be some shots outside the 6 inch circle-laws of physics-and a lot more if we factor in human errors,and more wind.

g

[scranx]

I thought there was an absolute MV limit at bisley of 3280FPS ? although I may be wrong.

 

Beware what you post.

 

Cheers

 

Rich

I would recommend strongly you read the range regs.Rich is correct.

 

d Limits as to Calibre, Muzzle Velocity and Muzzle Energy No firearm and ammunition combination which develops a muzzle energy exceeding 7000 J (5160 ft lb) may be used on any of the Bisley ranges without the specific permission of the CE which must be sought in writing well in advance of the planned use. The following limits apply: i ii for Rifle ranges, no specific calibre limitation but: a maximum muzzle velocity of 1000 m/s (3280 ft/s) and a maximum muzzle energy of 4500 J (3319 ft lb); for Gallery Rifle and Pistol ranges, no specific calibre limitation but: a maximum muzzle velocity of 655 m/s (2150 ft/s) and a maximum muzzle energy of 2030 J (1496 ft lb). iii for High Muzzle Energy (HME) firearms (see sub-para g below) the limits are: a maximum muzzle velocity of 1000 m/s (3280 ft/s) and a maximum muzzle energy of 7000 J (5160 ft lb);

 

The only variation to the limit would be

3. Vermin calibre cartridges with an MV up to but not exceeding 1350 m/s (4429 ft/s), may be used providing the ME does not exceed 2600 Joules (1918 ftlbs). (taken from bsrc range regs and only valid for bsrc static targets, 100yrd)

 

Range regs can be hard going as a "light read" but I would encourage everyone who shoots on any range MOD or not to make themselves familiar with the regs for that range fore warned is fore armed and all that.

 

Paul

[Murph]

He knows his stuff, but I seriously wouldn't buy the book, it's not very well written and unless you already have a reasonable grasp of aeroballistics I just don't think it would make much sense. It's very much an engineers approach, which can skip the theory and jump straight to approximations introduced without proper explanation.

 

Just googling around I can't find either a claimed G7 BC, or a reference velocity for the published G1 BC, which would allow me to calculate the G7 BC, for this bullet. Anybody have a reference for either? I don't suppose Litz has tested this bullet?

Use your real g1 bc you've calculated and multiply it by .512. This should convert it to a g7 value for you. Hope this helps.

[The_Dogge]

Use your real g1 bc you've calculated and multiply it by .512. This should convert it to a g7 value for you. Hope this helps.

What is the velocity that conversion factor is referenced to? I can calculate a precise conversion factor, if I know what speed they are quoted for!

 

This came up when I was mulling over buying a 17Rem, I thought the BC quoted for the 25gn V-Max bullet was suspiciously high, so I calculated the "form factor" for the small calibre V-Max bullets and .204 blitzkings. they were all pretty similar, except the 17gn bullet used in the HMR, which being a boat tail should if anything be better, but was in fact much worse. This must be due to it being referenced to a much lower velocity, 2550ft/s as advertised for HMR.

[Murph]

What is the velocity that conversion factor is referenced to? I can calculate a precise conversion factor, if I know what speed they are quoted for!

 

This came up when I was mulling over buying a 17Rem, I thought the BC quoted for the 25gn V-Max bullet was suspiciously high, so I calculated the "form factor" for the small calibre V-Max bullets and .204 blitzkings. they were all pretty similar, except the 17gn bullet used in the HMR, which being a boat tail should if anything be better, but was in fact much worse. This must be due to it being referenced to a much lower velocity, 2550ft/s as advertised for HMR.

What velocity were you getting through your chrono?

[gunner]

Sam thanks for putting in the time and effort for this test , very interesting read.

[Alycidon]

good read, I am just working up a 25gr load for my 17AH.

 

If you do any more work on the 25gr Hornady HP please post it, well done to date.

 

Thanks

 

A

[treetop]

Hi,

Can I ask ..

What load data have you got for you 20gr and 25 grn

 

What powder ect ?

 

Thanks

Al.

[247sniper]

I thought the BC quoted for the 25gn V-Max bullet was suspiciously high, so I calculated the "form factor" for the small calibre V-Max bullets and .204 blitzkings. they were all pretty similar,

 

A misconception also with .20 cal bullets and their magnificiantly highly bullet BC's referenced to velocity banded G1 standards!

 

Velocity banded, G1 standard bullet BC's are all well and good calculated and the muzzle at hyper velocities but don't give an accurate real life performance and resemblance down range in the field where it matters, an average G1 standard bullet BC can be used across the intended range expectancy if measured correctly but is also not a true resemblance of a G7 Standard modern long range bullet BC.

 

Steve

[Guesty]

Great info, thanks for posting Sam.