.20 cal BC's

[Big Al]

Im currently spending a lot of time deliberating over the caliber for a new build, so much so my head aches!

 

The 20 cal's are right up there in my considerations but every now and again I come across questions over the BC's of the 39gr SBK's and 40gr VMax, suggestions that the true BC's are nearer 0.240-0.250 but I can't find anything that confirms or denies this and no info from Litz that I can find. Im also looking at 55gr .204 Bergers in this which Im hoping have a true BC considering the involvement of Litz.

 

To compare calibers all I can use are published figures but if these are wrong then all the number crunching could be futile and real world experience of these calibers is something I don't have.

 

I really want to avoid paying for a good rebarrel to suck it and see so any help would be most appreciated.

[pork chop]

I used to get hung up on bc's ,these days i dont see the point,as you have come to realise quoted bc's you can take with a pinch of salt so have what you fancy .when you have found a bullet your rifle likes stick with it and learn how to use it

[Sherlock]

Sierra claim a BC of the 39 gr SBK of 0.287 - at velocities only above 3600 fps.

If your initial muzzle velocity was 3700 fps - the bullets would be below that figure with 25 yrds..

 

Some shooters often use the 0.289 BC as the true BC of the bullet... We know this isn't correct and Sierra themselves actually produce a sliding scale based of velocities.

 

Here is data from Sierra for the regarding the BC from the 39 grn SBK.

 

.287 at 3600 fps and above
.270 between 3600 and 3400 fps
.255 between 3400 and 2800 fps
.236 between 2800 and 2300 fps
.210 between 2300 and 1900 fps

 

The average of that is a BC of 0.250. Which I believe is closest to the truth.

 

 

ATB

S

[gbal]

+1 on the detail about BCs-some don't seem to be aware that BC varies with velocity,though the losses are much the same between similar BCs,so COMPARATIVELY published BCs are helpful-unless the manufacturer's are deliberately making it hard to compare fairly-unlikely,most will publish the best highest velocity BC.....but care is needed....

 

A further important point is that out to 3/400y ,Velocity matters and BC differences are less important,but after that BC takes over (bearing in mind we are comparing close contenders-at close velocities) eg drop /drift for these: (10 mph):

 

40g SBK BC .287 @ 3750 300 y 4.7/7.8 400y 14.1/14.7

 

40 Vmax BC .275 @ 3900 300y 4.3/7.8 400 13.2/14.7

 

Pretty much identical

 

Small velocity advantage cancels small BC advantage or vice versa,if you prefer. Also compare:

 

40g Accutip BC .257 @ 3900 300 4.3/8.6 400 13.2/16.2 where the slightly lower BC starts to increase wind drift-

 

though you might well think ,not a lot given that substantial correction is needed whatever is used.

 

I would not ignore these rather small velocity/BC details,but I would not rate either above a small accuracy difference either!

 

Given the human error in wind reading,these differences are no big deal,though of course "it all helps"-but not much!

 

gbal

[Big Al]

I used to get hung up on bc's ,these days i dont see the point,as you have come to realise quoted bc's you can take with a pinch of salt so have what you fancy .when you have found a bullet your rifle likes stick with it and learn how to use it

 

Thanks for that, the in depth technical answers are always the most useful.

 

Of course I won't really know what I fancy until I can appraise its ballistic performance and have a decent idea what exactly I will be getting for my hard earned.

[pork chop]

technical no practical yes,been there and done it.just cant help some folk

[Andrew]

 

Thanks for that, the in depth technical answers are always the most useful.

 

Of course I won't really know what I fancy until I can appraise its ballistic performance and have a decent idea what exactly I will be getting for my hard earned.

 

Ther was once a suggestion that the published BC's from Hornady were exaggerated when the poster unwisely compared them to a Berger bullet. He stated that he 'trusted' Berger's data but not Hornadys. It was nonsense: He cmpared two entirely different bullets and ignored the added length of the Hornady VM, using only weight and diameter to make his comparison. Makers publish BC's so that people can plug them into ballistic programs and if they are exaggerating, the shooter quickly debunks them. BC's change with atmospheric conditions and altitude, but these published values are pretty good. FWIW ! used Hornady's published BC for the 204 x 40 grain VM and in field use it was spot on out to 400 yards. I am at 3000 ft altitude and it was 100F outside.~Andrew

[Big Al]

technical no practical yes,been there and done it.just cant help some folk

 

You certainly can't help a technically minded guy who is looking in great detail into the performance of various calibers with answers like "buy whatever you fancy and learn to use it" thats for sure.

[pork chop]

Shooting is meant to be fun.if i like something i buy it and learn to use it .why get hung up on numbers that don't add up.why ask a question then take offense to a simple answer .i'll not bother in future .really don't understand people with attitudes like yours

[triggersqueezer]

 

You certainly can't help a technically minded guy who is looking in great detail into the performance of various calibers with answers like "buy whatever you fancy and learn to use it" thats for sure.

wow reading this i thought pc was just chipping in to some friendly conversation,that is what were here for?still if your not interested in a chat with a chap with a proven shooting record at least you made it clear.

[silpig]

Well, I can't add much to the topic of the accuracy of claimed bc's, but I can recommend the Nosler 40gn BT! I'm surprised more 20 cal' shooters don't use them. I know there are cheaper alternatives but IMO they are better made than the likes of Hornady. Definitely worth a try it you do go for a .20!

[Big Al]

Shooting is meant to be fun.if i like something i buy it and learn to use it .why get hung up on numbers that don't add up.why ask a question then take offense to a simple answer .i'll not bother in future .really don't understand people with attitudes like yours

 

I was not offended by your answer Pork Chop and Im sorry if my direct replies have upset you, that was not my intention.

 

I asked a serious question with the hope of some serious answers, unfortunately you didn't give one, that wasn't my fault. Its not accurate for you to say the numbers don't add up, that could suggest the fairies made them rather than ballisticians. The numbers may not be perfect but they are functional and will help someone like me (and Im sure many others) make up their minds when looking to spend good money on a new caliber.

 

I have to have a reason to fancy something before I can pick it and practise using it. Im sure you didn't just walk into the local RFD and say "giz a gun, any gun will do and I'll learn to shoot it"?

[pork chop]

Simple fact is i have found bc's to be out,yes they will get you on paper but for vermin on paper isn't good enough.when i said learn to use it i should have said learn your drops end of the day thats the best way to do it i think .as for fairies making up bc's who do who think make up?

I'd say the manufacturers and why do you think one would try and out do the other.because bc's sell bullets

[Big Al]

Simple fact is i have found bc's to be out,yes they will get you on paper but for vermin on paper isn't good enough.when i said learn to use it i should have said learn your drops end of the day thats the best way to do it i think .as for fairies making up bc's who do who think make up?

I'd say the manufacturers and why do you think one would try and out do the other.because bc's sell bullets

 

Are you specialising in pointless answers at the minute PC? now Im really starting to struggle with your contributions in this thread????

 

Go back and read my original post, its not about learning my drops, its about comparing the performance of different calibers using a widely recognised method of comparison, namely velocities, BC's and predicted drop/drift. Yes they may not be perfect but generally they are good enough to decide on a caliber which is what Im trying to do! I started this thread to ask about suspect BC's not to be told how to shoot, I can do that quite well already.

 

Learning the drops happens when I own the rifle, not when Im trying to decide which one to buy.

[pork chop]

your really not worth spending time on seems you know it all already.try to be friendly,going to leave it at that now

[Andrew]

If you wonder how accurate a maker's BC can be, plug it into a program using your intended velocity then change temps, humidity, barometric pressure and altitude. Watch what happens.

 

The best way (the only accurate way) to determine BC is to calculate it yourself with a pair of chronographs, using your rifle, at your speeds, at your altitude, etc. Otherwise, you're unlikely to get the results you expect... and a 'faulty' BC from the manufacturer won't necessarily be the problem.~Andrew

[247sniper]

I can speak from experience here as I have carried out some extensive research on this subject to find out the truth and to also get the best from my kit.

 

Tested with a chrono out to 500 yards,

 

The 39 grain SBK out of my custom rifle (3750 ftps) has a TRUE BC of 0.251 and not the Sierra advertised value of 0.287! So they ARE over stated !

 

The 40 grain Vmax out of my custom rifle (3750 ftps) has a TRUE BC of 0.242 and not the Hornady advertised value of 0.275! So they ARE over stated !

 

Funnily enough the 40 grain Vmax has an identical BC to the advertised 40 grain Nossler, I bet if I was to test the nossler BC it would come out like advertised at around .240!

 

The .204 is still with out doubt my go to sub 350 yards vermin destructer! the true |BC's combined with high muzzle velocities result in very very good down range win beating results.

 

Hope this helps you put Al?

 

 

Steve

[Big Al]

If you wonder how accurate a maker's BC can be, plug it into a program using your intended velocity then change temps, humidity, barometric pressure and altitude. Watch what happens.

 

The best way (the only accurate way) to determine BC is to calculate it yourself with a pair of chronographs, using your rifle, at your speeds, at your altitude, etc. Otherwise, you're unlikely to get the results you expect... and a 'faulty' BC from the manufacturer won't necessarily be the problem.~Andrew

 

I should maybe qualify my reasons for the original post.

 

Im currently looking to build a new rifle that will shoot out to around 500yds. It will be for varminting at whatever distance I feel confident in but that confidence will only come from shooting accurate groups on paper first. I don't want to go above 6mm/.243 and more likely it will be either a .20 or .22 cal.

 

Plugging BC's and predicted velocities for different bullet weights and calibers is all I have available to me to settle on my final choice. Its only by doing this that I have gained some valuable insights into calibers and this has allowed me to dismiss some and focus more closely on others. The problem now is as the list has narrowed down Im trying to establish as good a comparison as I can.

[Big Al]

I can speak from experience here as I have carried out some extensive research on this subject to find out the truth and to also get the best from my kit.

 

Tested with a chrono out to 500 yards,

 

The 39 grain SBK out of my custom rifle (3750 ftps) has a TRUE BC of 0.251 and not the Sierra advertised value of 0.287! So they ARE over stated !

 

The 40 grain Vmax out of my custom rifle (3750 ftps) has a TRUE BC of 0.242 and not the Hornady advertised value of 0.275! So they ARE over stated !

 

Funnily enough the 40 grain Vmax has an identical BC to the advertised 40 grain Nossler, I bet if I was to test the nossler BC it would come out like advertised at around .240!

 

The .204 is still with out doubt my go to sub 350 yards vermin destructer! the true |BC's combined with high muzzle velocities result in very very good down range win beating results.

 

Hope this helps you put Al?

 

 

Steve

 

Yes this does help Steve, exactly the kind of info Im looking for. Now if I could get the same for 75gr Amax and .20 Berger 55's and a few other calibers then I would be able to complete my research.

 

Ive read that Todd Kindler feels that the 55gr Bergers with a quoted BC or 0.381 seem to perform in the field nearer .400, now shoving them out at ever 3200 from a 20BR which will be very easy gives a round capable of mixing it with 22BR and 75gr Amax, I know where there is over 1000 of these so enough to take the caliber seriously. All of this needs to be chewed over before I push the button on the build.

[gbal]

Steve,

That is helpful (cf Andrew's post-not sure two chronos are needed,but readings at Diffferent distances are)

Is that not rather like Sherlock's excellent post,with data?

 

So,Steve,just to clarify:is your real world calculated BC of .251 an average for the bullet/velocities used (Sierra 39 BK,with 204 type velocities?)

That does tie in with great similarity (exact?) to Sherlock's .251,which is explicitly the average( so of course,not very accurate at either extreme!)

 

If only people could get their heads around the fact that BC is a variable,just like velocity (and indeed correlated with velocity-it decreases as velocity decreases...then one of the main complaints ('figures don't add up' sort of thing?) would be much reduced.

And of course it's a continuous variable not just 'velocity bands' as used to summarise the changes.Maybe some ballistics calculators incorporate this,and maybe some don't....

 

Manufacturers of course tend to quote the best BC (muzzle velocity) quite legitimately,but if they all do (or at least the ones you are comparing do) then ' misinformation ' is reduced for comparative purposes (your rifle etc will not necessarily be a ballistic clone of the test data anyhow-even if all your relevant data is accurately entered- which seldom happens,and coincides with the manufacturer's test data).If the issue-as here-is a comparison of contenders,then good comparative data will do-ultimately real shooting tests are needed-maybe that is what has been alluded to as 'fun'/'practice'....it is essential,agreed.But for the seriously interested it does not eliminate researching the options...the findings from that being the basis for 'fancying something' more objectively.If you have already bought (on some other basis),then clearly the field test will be more of an adventure.Different mind sets,there is choice.

 

gbal

[Laurie]

If only people could get their heads around the fact that BC is a variable,just like velocity (and indeed correlated with velocity-it decreases as velocity decreases...then one of the main complaints ('figures don't add up' sort of thing?) would be much reduced.

And of course it's a continuous variable not just 'velocity bands' as used to summarise the changes.Maybe some ballistics calculators incorporate this,and maybe some don't....

 

 

 

 

Hmmmm .... I'm always a little leery when people quote 'real BCs'. As Gbal says, the only reliable way is to measure both muzzle and terminal velocities and back-calculate the BC from the combination of distance and speed reduction. That's not the end of the job either as the test venue (ASL etc) and ambient conditions on the day (temperature, humidity, atmospheric pressure) are often significant enough to affect results. All of Bryan Litz's G7 BCs for longer range bullets have the raw results corrected to a single ballistic norm in post test processing, so the published results are as they would be if they'd been fired on a sea level venue on a day with 29.92 inches mercury pressure at 0% humidity and 59-deg F air temperature.

 

Most 'real BCs' seen in articles and forum posts are based on scope elevation settings comparing actual on-the-gun elevations needed v what the ballistic program says should apply. That's not as accurate as using real speeds even at it's best, but at the very least they must have the scope elevation adjustments calibrated to have any accuracy. The myth still exists that just because you've spent a grand (or three these days!) on a quality scope, a 20-MOA (say) change on the turrets = exactly 20 x 1.047" x distance in numbers of 100 yards at the range being shot over. (Not to mention that not all firing ranges are that accurately measured, the '1,000yd' firing point at Blair Atholl's Glen Tilt range being an actual 984 yards, and while people might think that being 16 yards adrift at this distance doesn't make much if any difference, it is noticeable on the elevation setting especially when it's allied to the venue's altitude). On field firing tests, do people measure the precise range from shooting position to target set up in a field or hillside every time they go out, or is it a plus or minus x yards actual situation?

 

That's not to say there are no benefits in using scope settings for comparative purposes. Using the same rifle and scope at 800 yards at Diggle two weeks apart with pretty similar weather conditions, I found needed I needed an extra 2-MOA elevation for Lapua's new 180gn 7mm Scenar L compared to the 180gn Sierra MK, despite the latter having their meplats left as the factory made them and the Scenars being trimmed and pointed to correct the extremely large meplat diameters they come with. The Scenars also had a 40 fps higher MV. Since Lapua quotes a G7 BC that's barely discernably different from that of the very efficient 180gn Berger VLD and the SMK, that suggests that there is something not quite right about the value. (Interesting as Lapua BCs are allegedly based on full trajectory Doppler radar testing.)

 

The other factor here is G1 v G7. As Gbal says, BCs are continuously variable throughout a bullet's flight as they are speed dependent, but G1 is far more badly affected than G7 with up to 15% variations in real values over a full flight pattern compared to ~4% for G7. The problem of course that in comparing 20s to 22s only G1s have been available for the former until now, whilst we've had fully field tested G7 values for the heavier 22s including the 75gn A-Max for some time. I really have trouble in my head using G1 BCs for anything that's more aerodynamically efficient than the .22 LR's 40gn LRN bullet and/or making comparisons over short ranges. Once one gets onto 500/600 yards performance comparisons - especially with small calibre bullets that start out fast but lose a much higher percentage of their initial velocity than a 7mm or .30 cal bullet - the opportunity for major error increases dramatically.

[Andrew]

Agreed. BC's are highly variable. The best you are hoping for is an average of sorts. Unless you shoot under the exact same conditions, ballistically, as the maker you may not get close. A radical example, but I tested the 33 grain VM used in Remington 22WMR. At WMR speeds of 2150 fps the BC was around .138. At 3200 fps from my Hornet the BC was .087. Same bullet, same day.~Andrew

[Finman]

when I got my .204, I didn't have in mind a 'BC' nor did I get it because I wanted to hit things at 400+ yds....I got the rifle because I liked the spirit of the cartridge (high speed, quirky 5mm calibre, inherent dislike of the .223). Getting hung up on 'which bullet shall I use on a rifle I haven't even got', is IMHO, the wrong end of the stick as is the attitude that has been displayed by the OP in some of the messages.

 

BCs are highly variable and indeed not that great in the smaller calibres. Using a 50-55gn bullet in a .204, as far as I'm concerned defeats the purpose. Let alone the fact that they don't behave that well on vermin: I have shot side by side with a very good friend and member here who was, at the time, shooting a 1:8 20TAC and 50gn Bergers. Better BC and all that palaver, we were both hitting the same things at the same distances and they wre not going far. Apart from foxes, where the 50gn occasionally did not behave as well as the 39gn SBK and we had long tracking jobs in the middle of the night.

 

Bottom line: want to hit stuff at 400yds? get a 6mmBR and up. Want to enjoy low recoil, cheap reloads, great speeds and explosive vermin impacts? get a .204Ruger, use a 39gn SBK, learn its behaviour at various distances by shooting the damn thing (use other bullets if you like and do the same) and don't expect all the answers through the keyboard and other folks' experience. Nobody hit anything from a keyboard (unless they worked for NORAD or some such place flying drones!) and nobody got a better shooter because they chose the right BC: they all did it with time behind the butt...

 

 

my 2p

 

Finman

[gbal]

I have had a good look at my FAC-it doesn't prohibit me having a keyboard as well.

 

There is a pretty good case to make that some shooters do better with better BC bullets. Many are competitors in the target sports.

 

It may matter much,much less if you shoot barn doors at sub 100yards.

 

Effective practice is a good idea.

 

gbal

[Finman]

Fair point gbal, but I have very frequently (as I'm sure have others) found that my rifle goes an inch above the drop at distance x than the ballistic chart predicts. Some times it goes 2 inches below as well...(not same rifle, same bullet or same conditions I hasten to add). What allowed me to hit the deer/target/vermin/barn door at each time though was learning why I missed the last time, and, trust me, the last thing to blame was the BC of the bullet I was using.

 

A hair can be split infinite times, but, so far, from the opening message, one does not get any 'real life' experience, just theoretical analysis. Pork Chop said it first and I, for one, am with him... and for reasons of clarity, I refer to the messages that spurred mine....

 

all the best

 

Finman

 

 

technical no practical yes,been there and done it.just cant help some folk

 

 

Thanks for that, the in depth technical answers are always the most useful.

 

Of course I won't really know what I fancy until I can appraise its ballistic performance and have a decent idea what exactly I will be getting for my hard earned.