Been shooting 167gr SMK HPBT in my .308 bolt gun. Great at 300yards, but seem less stable in high wind at 500meters, so plan to shoot 175gr (also SMK HPBT) at 500m in two days, to hopefully handle the wind better. No time to zero before shooting - so my question is, if I was consistently in the black at 500 with 167gr (but blowing all over the black), will I need much or any elevation adjustment shooting 175gr?
Bumping .308 from 167gr to 175gr?
- Thread starter alamo_308
- Start date
Keith Glasscock
Gold $$ Contributor
That depends more on velocity than anything else. What are the velocities of the two bullets?
Ned Ludd
Silver $$ Contributor
I'm going to assume you meant the 168 gr SMK, not 167. Are these commercial ammunition or handloads? I'll also assume commercial ammo because if you were doing load development, you'd already have the pertinent velocity and zeroing data. If these are commercial ammunition, there can be (and most likely will be) a difference in point of impact at 500 yd.
The typical difference in velocity you'll see advertised for 168 and 175 SMK commercial loads is about 50 fps from a 24" test barrel (2650 fps vs 2600 fps for FGMM). Running these numbers through the JBM ballistics calculator with a generic set of atmospheric conditions (75 Degrees F, 70% hum, 29.98" Hg, 500 ft elev), it predicts a difference of only 0.1 MOA drop at 500 yd from a 100 yd zero for the two (168 = 11.5 MOA, 175 = 11.6 MOA). However, simple external ballistics are not the whole story because they assume you already have a solid 100 yd zero. Internal ballistics, notably barrel harmonics, can also play a big role in this process, i.e. where is the muzzle pointing when the bullet exits? The barrel moves (oscillates) as the bullet is moving through it. Whether the muzzle is at the upper or lower end (or in the middle) of its arc of travel when the bullet exits means the bullet could exit pointed slightly up, straight out, or slightly down, which will change its point of impact on the target. This is dependent on velocity and the oscillations of the barrel are extremely fast, so 50 fps difference in velocity can make a much bigger difference here than it might in the external ballistics. I've seen changes in 100 yd zero when switching between FGMM 168s and FGMM 175s in the same rifle of as much as 1" to 1.5", which would be multiplied by a factor of 5 at 500 yd. The other issue you might face is that there is no way to know whether the 175s will shoot with the same precision (grouping) in your rifle as did the 168 load. If your rifle doesn't group as well with the 175s, it means wider shot dispersion on the target, regardless of what the wind is doing. Unfortunately, you don't have time to see how well your rifle shoots with the 175s, so if you want the slight advantage they offer in wind resistance, you'll just have to go with them.
Bottom line is that there is really no way to tell from the information you provided. The stuff I calculated out above is likely way more than you will need to know for this match; it's just there for your edification. My guess is that the 175s would impact the target something like from 1"-2" to as much as 8"-10" below where the 168s impact at the same scope elevation setting. The good news is that it probably won't put you off the target. In your position, I'd look up the 500 yd target scoring ring measurements (diameters) in the NRA Highpower Rule book, and convert them to MOA (divide by 5). If you know those values, it will make it fairly easy to know how much elevation adjustment you need to dial in to the center, even if it turns out to be a large adjustment (i.e. dialing from a straight low impact directly on the 8-ring to the target center would require 2.0 MOA elevation on the conventional shooters' target and 1.5 MOA elevation on the F-Class target. Hope that helps and good luck in the match.
The typical difference in velocity you'll see advertised for 168 and 175 SMK commercial loads is about 50 fps from a 24" test barrel (2650 fps vs 2600 fps for FGMM). Running these numbers through the JBM ballistics calculator with a generic set of atmospheric conditions (75 Degrees F, 70% hum, 29.98" Hg, 500 ft elev), it predicts a difference of only 0.1 MOA drop at 500 yd from a 100 yd zero for the two (168 = 11.5 MOA, 175 = 11.6 MOA). However, simple external ballistics are not the whole story because they assume you already have a solid 100 yd zero. Internal ballistics, notably barrel harmonics, can also play a big role in this process, i.e. where is the muzzle pointing when the bullet exits? The barrel moves (oscillates) as the bullet is moving through it. Whether the muzzle is at the upper or lower end (or in the middle) of its arc of travel when the bullet exits means the bullet could exit pointed slightly up, straight out, or slightly down, which will change its point of impact on the target. This is dependent on velocity and the oscillations of the barrel are extremely fast, so 50 fps difference in velocity can make a much bigger difference here than it might in the external ballistics. I've seen changes in 100 yd zero when switching between FGMM 168s and FGMM 175s in the same rifle of as much as 1" to 1.5", which would be multiplied by a factor of 5 at 500 yd. The other issue you might face is that there is no way to know whether the 175s will shoot with the same precision (grouping) in your rifle as did the 168 load. If your rifle doesn't group as well with the 175s, it means wider shot dispersion on the target, regardless of what the wind is doing. Unfortunately, you don't have time to see how well your rifle shoots with the 175s, so if you want the slight advantage they offer in wind resistance, you'll just have to go with them.
Bottom line is that there is really no way to tell from the information you provided. The stuff I calculated out above is likely way more than you will need to know for this match; it's just there for your edification. My guess is that the 175s would impact the target something like from 1"-2" to as much as 8"-10" below where the 168s impact at the same scope elevation setting. The good news is that it probably won't put you off the target. In your position, I'd look up the 500 yd target scoring ring measurements (diameters) in the NRA Highpower Rule book, and convert them to MOA (divide by 5). If you know those values, it will make it fairly easy to know how much elevation adjustment you need to dial in to the center, even if it turns out to be a large adjustment (i.e. dialing from a straight low impact directly on the 8-ring to the target center would require 2.0 MOA elevation on the conventional shooters' target and 1.5 MOA elevation on the F-Class target. Hope that helps and good luck in the match.
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My "F" class shooter friend in Nevada shot my 165 BT out to 1000 yds in his 308 Win and did not have a this problem. In fact this bullet bucked the wind very well for him. He was so impressed with it's performance, he asked me to make him 2000 identical bullets.
However, my 165 unlike the 168 MK has a much longer BT which keeps it sonic at long ranges. I believe closing the point on this bullet could make it even better at long range.
Bob Cauterucio
My "F" class shooter friend in Nevada shot my 165 BT out to 1000 yds in his 308 Win and did not have a this problem. In fact this bullet bucked the wind very well for him. He was so impressed with it's performance, he asked me to make him 2000 identical bullets.
However, my 165 unlike the 168 MK has a much longer BT which keeps it sonic at long ranges. I believe closing the point on this bullet could make it even better at long range.
Bob Cauterucio
Ned Ludd
Silver $$ Contributor
.Learning to accurately dope the conditions will help as much if not more than bullet weight.
I'm sure it won't be you.
My bullets only reflect the user's marksmanship capabilities.
A shooter in 2009 has already proven the accuracy of my bullets, by winning a World Individual "F" Class Open Championship with them.
Mid & Nancy Tompkins, using my bullets, broke two 1000 yd. records in 1995 at Camp Perry. Mid called me after the matches and said," Bob every shot that went down range
was on call."
My bullets will not break or set any National Records until used by shooters capable of setting and or breaking records.
Even 16" artillery pieces require doping the conditions.
The shooter I talked about on this thread, did not want to spend extra money to build an "F" class rig. He thought it would be wiser and less costly to use his existing 308 Match Rifle to shoot a few "F" class matches just to see if he would like to go down that path.
FYI the last 3 matches he shot he did not shoot any nines. However, I do not or never did recommend a 308 Win for "F" class. But its a darn good over the coarse NRA High Power cartridge.
For anyone's information I've never had the pleasure of meeting Bob Cauterucio but I know of his reputation as a bullet builder and he is no 'Johnny come lately'! Years ago I made Delta Precision Bullets which did better than good in NRA HP comp for Service Rifle Shooters as I made a 173 gr. rebated BT bullet designed specifically for the M1A and M1 Garand shooters. I got the design from a recommendation by name of Robert McCoy who at the time was Chief Ballistician for Aberdeen Proving Ground Facility. I wore both shoulders out making the damn things and finally quit; Bob kept on making bullets and is still at it! I've read about and seen the results of Bob's quality work in building bullets and if Mid and Nancy Tompkins shoot them one can damn well believe that his bullets are TOP QUALITY!!
As an aside, I had many conversations with Bob McCoy over a period of five years and upon occasions discussion of the Sierra 168 gr. HPBT came up! It was designed for 300 meter competition and it has set world records at that distance. Many Service Rifle shooters attempted shooting them for 1000 yard matches out of the M1A but due to pressure requirements for the M1A the velocity obtained (safely) was not sufficient and the projectile would enter the subsonic region at about the 800 yard distance and we could always tell which targets in the pits had Service Rifle competitors shooting on them because the bullets would keyhole into the target frames. Bob stated that the Sierra 168 bullet had a 13 degree tapered BT and that any bullet of it's design, due to the degree of BT had/has the same drag function as a flat-based bullet! Bob also stated, when I asked him about making my bullets with the rebated BT as to why he was making that rec to me? His reply was that every projectile that he had fired through his sparkgraph range for the US Military showed a distinctive 5% increase performance due to less drag! Five percent doesn't sound like much.....but when matches are decided many times by X count....it could mean THE WINNER!!
FWIW!!
As an aside, I had many conversations with Bob McCoy over a period of five years and upon occasions discussion of the Sierra 168 gr. HPBT came up! It was designed for 300 meter competition and it has set world records at that distance. Many Service Rifle shooters attempted shooting them for 1000 yard matches out of the M1A but due to pressure requirements for the M1A the velocity obtained (safely) was not sufficient and the projectile would enter the subsonic region at about the 800 yard distance and we could always tell which targets in the pits had Service Rifle competitors shooting on them because the bullets would keyhole into the target frames. Bob stated that the Sierra 168 bullet had a 13 degree tapered BT and that any bullet of it's design, due to the degree of BT had/has the same drag function as a flat-based bullet! Bob also stated, when I asked him about making my bullets with the rebated BT as to why he was making that rec to me? His reply was that every projectile that he had fired through his sparkgraph range for the US Military showed a distinctive 5% increase performance due to less drag! Five percent doesn't sound like much.....but when matches are decided many times by X count....it could mean THE WINNER!!
FWIW!!
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So good to hear from a brother National Match Course shooter from the past. I've improved on the BT of the 168 Intl. I make a 165 with a 9 degree BT just under .250"
long. The bullet stays sonic all the way to 1000 yds and stabilizes in a 12 twist. Wish I would have had this when I shot High Power.
Stay well and good shooting
Bob Cauterucio
Next week I'll order some and see how they perform on some of these pesky coyotes around these parts! Haven't seen any past three months as the corns kept them hidden but they're in for a hard time now!!
Enjoy the coming holiday! Got a buddy north of you up in Mill Vally; Mike Dunia! Great Palma/Course shooter! We shot together on the Army team!!
Rick, I remember Mike very well. One real nice guy and awesome shooter. The only way
to beat Mike was to take a hammer to his rear sight knobs when he wasn't looking.
PM me when you want some of these bullets to try. I make them in 165 & 154 gr. The only way to differentiate between the two is with a scale. Both are made on the same jacket and in the same die.
Praying that the devastating bad weather gave you and the community a wide birth.
Sincerely,
Bob Cauterucio
We're 200 miles north of Baton Rouge so we missed all that thank the Good Lord! Have brother down there but he just built a new house on some elevated ground....such as it is. I'm up in Redneck Country aka North Louisiana sixty miles west of Vicksburg, Miss 4 miles south of I-20. Our flood up here was back in March. Probably had 7000 homes wrecked but I'm on higher ground and had no problem! Had 26-30" rain in 48 hours! I'll call you next week! Mike and I email each other quite regularly!
I'll just PM you soon...give you the address and you can let me know what to send $$$$wise! I know the phone drove me nuts when I was working!!
Getting back to the original post that started this now-meandering thread: Suggested elevation change at 500m when switching from the lighter projectile I had been shooting, to 175gr, with no time available to get to the range for practice session with changed ammo?
Posed the question to a long-time veteran fellow shooter here, the evening before the match. His answer: "Just take your first sighter, and you'll be in the black about 7 inches low. Adjust from there as needed."
In keeping with the principle of K.I.S.S., he of course was right on with the most concise, practical, and perfect advice. Result: ...Success.
Posed the question to a long-time veteran fellow shooter here, the evening before the match. His answer: "Just take your first sighter, and you'll be in the black about 7 inches low. Adjust from there as needed."
In keeping with the principle of K.I.S.S., he of course was right on with the most concise, practical, and perfect advice. Result: ...Success.
He shoots....he scores! And the crowd goes wild!
I'm glad you set the record strait Bob.
Robin
Turbulent Turtle
F-TR competitor
I think you guys are being needlessly harsh on Dean. This thread was started by someone asking for information on bullet trajectory comparing two differennt bullets.
Bob jumped in to talk about his bullets. Not everyone knows Bob or of Bob, and in F-class, I don't know that his bullets are used much. It's not a judgement, it's an observation. Also, when Bob refers to the discipline as "F" class, and then states he does not recommend the .308 for it, I tend to believe that while he knows a great deal about high power and so on, F-class is not his forte. Dean is a good man, an awesome shooter and a fierce F-TR competitor and he definitely knows what's what in F-TR. His comment about 200gr+ was right on the mark but the current kerfuffle is due to a difference in outlook on competitions. Dean was looking at this thread from the F-TR angle and Bob was looking at it from the high power point of view.
That said, in F-TR, we are always looking for "the better bullet," and currently the 200+ grainers are the ones that are favored by many top competitors. BOBC, if you have .308 offerings for long range, that have a G7 BC north of say .350, I think a lot of people would like to at least hear about them. Is there a website we can visit for some info?
Thank you.
Bob jumped in to talk about his bullets. Not everyone knows Bob or of Bob, and in F-class, I don't know that his bullets are used much. It's not a judgement, it's an observation. Also, when Bob refers to the discipline as "F" class, and then states he does not recommend the .308 for it, I tend to believe that while he knows a great deal about high power and so on, F-class is not his forte. Dean is a good man, an awesome shooter and a fierce F-TR competitor and he definitely knows what's what in F-TR. His comment about 200gr+ was right on the mark but the current kerfuffle is due to a difference in outlook on competitions. Dean was looking at this thread from the F-TR angle and Bob was looking at it from the high power point of view.
That said, in F-TR, we are always looking for "the better bullet," and currently the 200+ grainers are the ones that are favored by many top competitors. BOBC, if you have .308 offerings for long range, that have a G7 BC north of say .350, I think a lot of people would like to at least hear about them. Is there a website we can visit for some info?
Thank you.
Medic505
Gold $$ Contributor
Many thanks for the kind words Denys. You put my wise crack into a better perspective.
Bob, Congratulations on making the bullet that won the 2009 worlds. Quite an honor, no doubt about it. But that was 2009. Compare those scores with scores from the 2013 worlds and I'm sure you'll see a huge difference. That said, I'd nearly bet that scores from 2013 probably won't win you much in 2017. F-Class is a fierce sport and if a shooter expects to shoot well, he or she has to be on the leading edge of technology. Your comment that I won't be shooting your bullets was spot on. I'll be shooting the highest BC bullet that I can get to shoot accurately. The last 2 records that we set in F-TR @1000 yards were shot with bullets of 200 grains or more. Like Denys said, if you can build a bullet that shoots with a 200 Berger hybrid or a 212 JLK BC wise, the F-TR world would beat a path to your door.
An interesting comment from Danny Biggs, who has won about everything there is to win in US F-Class. A couple of times.
P.S. BTW, my next F-Open build will adopt the .308 cartridge using 215's.
Bob, Congratulations on making the bullet that won the 2009 worlds. Quite an honor, no doubt about it. But that was 2009. Compare those scores with scores from the 2013 worlds and I'm sure you'll see a huge difference. That said, I'd nearly bet that scores from 2013 probably won't win you much in 2017. F-Class is a fierce sport and if a shooter expects to shoot well, he or she has to be on the leading edge of technology. Your comment that I won't be shooting your bullets was spot on. I'll be shooting the highest BC bullet that I can get to shoot accurately. The last 2 records that we set in F-TR @1000 yards were shot with bullets of 200 grains or more. Like Denys said, if you can build a bullet that shoots with a 200 Berger hybrid or a 212 JLK BC wise, the F-TR world would beat a path to your door.
An interesting comment from Danny Biggs, who has won about everything there is to win in US F-Class. A couple of times.
P.S. BTW, my next F-Open build will adopt the .308 cartridge using 215's.
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