Ultimate Hunter HP Rifle

[DanDeMan]

Ultimate Hunter HP Rifle

Given that we now have a 9 lb “Light Standard Rifle” for Hunter Class with only the requirements of:

2 lb or heavier trigger pull
26” long or less tapered barrel
Hunter style stock
Factory chambering

We now have at our disposal a fertile field within which to design an ultimate, legal Hunter HP rifle.  With that in mind let us first define “ultimate.”

Webster’s Dictionary defines “ultimate” as:

adjective;ultimate

furthest or highest in degree or order; utmost or extreme; "the ultimate achievement"; "the ultimate question"; "man's ultimate destiny"; "the ultimate insult"; "one's ultimate goal in life" ; how about a 40x40 with a Hunter HP rifle:-)

So with the definition well ensconced in our minds we need to define, for Hunter HP Silhouette, what that might mean as well as order the effects we need to review in order of their importance with respect to shooting the highest score possible.

The issues that must be discussed as far as the definition of “ultimate” is concerned for Hunter HP Silhouette are first without priority:

Accuracy
Recoil
Wind Deflection
Ram Knock-down

Of course we can only use legitimate cartridges.  Given what most of us know at this point in time the cartridge selection is a short list: 6mm BR, 6.5 Grendel, 6.5 Carcano, 6.5 Mannlicher Schonnaer, 260, 7mm BR, 7-08 and maybe a few more.  The reason this list is short is because we don’t need to list “over-bore” cartridges; those that have too much case capacity as they contribute to too much recoil for the exterior ballistics produced.  Most felt recoil is produced by the hot, high pressure gasses that exit the barrel as the bullet exits.  It is this gas that turns the barrel into a rocket aimed at our shoulder that produces most of the recoil.  If this was not true muzzle brakes would not work.  Over-bore cartridges burn more powder to achieve the same MV for a given bullet compared to  under-bore cartridges and thereby contribute to more recoil.  That is why we can get less recoil for the same bullet and MV out of an under-bore cartridge compared to an over-bore cartridge.  For instance the 6.5 TKS can push a moly-coated 139 Scenar to 2,775 fps with 35-grains of N150 while the 260 needs 43.0 grains of N160.  Both powders produce the same volume of high pressure gas per gain of powder.  Given that we see the 260 load produces about 23% more high pressure gas in the same length barrel that increases recoil.  These effects are not trivial.

Let’s next discuss accuracy.  All of the above listed cartridges are capable of 1/4-MOA accuracy as long as the smith is using a properly designed reamer and knows what he is doing, the rifle components are first rate and the reloader/shooter knows how to develop an accurate load for each animal for his or her rifle.  So, with that in mind we can cross accuracy off the list of parameters to optimize since that parameter should be a given.

Recoil is the mother of all issues for top performance in any shooting sport given that we are not messing up on other simple issues.  Some say they can handle recoil.  I’ve never heard that for a national or world class shooter, except from some of my Black Powder Cartridge Rifle shooting buddies.  I believe that David Tubb lists reduced recoil as his #1 focus for improving match performance.  So, reducing recoil without hurting wind deflection or ram knock-down is priority #1.  How that is accomplished is a function of bullet availability and experience with regard to what bullets at what MV will perform well on rams, 95% plus knock-down or 1 out of 20 rung minimum.

Low wind deflection is a function of high bullet BC and MV for HP rifles.  We don’t want to drive up MV too high or we have to deal with too much recoil, more important than wind deflection as long as we are dealing with high BC bullets.  Sure, a low BC bullet’s high wind deflection could be more important than recoil, but we are not going to extremes to disprove what I’ve written above.

Lastly we have ram knock-down to optimize.  The amount of delivered terminal momentum by the 6mm BR launching a 107 MK at 2,900 fps should have a high reliability on rams.  But, it does not.  The reason is “dwell time.”  Dwell time is the length of time the bullet exerts its toppling force on the ram.  With a light bullet, like the 107 MK, the dwell time is short due to the fact that the bullet “blows up” quickly so the terminal momentum does not act long enough to tip over the ram.  Bullet mass is important in this process.  From experience it seems that the 6.5mm 140-grain class VLD’s are minimum for high ram performance.  Optimally they should be shot between 2,750 and 2,800 fps for the best ram performance.  Faster than 2,800 fps seems to lower ram knock-down reliability as the dwell-time is reduced.  As a general rule, the tougher the bullet the higher the MV should be for optimum ram knock-down.  That is why a soft, high BC Berger 140 VLD is optimal at probably 2,600 fps and the tough 139 Scanar Lapua is optimum at 2,800 fps.  The Scanar ram performance is at a much higher level than the Berger.  The toughest bullets available should be used as they increase dwell-time, a very good thing.

After years of experimentation, in my mind, the 7mm’s are the best for rams when we also consider recoil and wind deflection.  High BC 7mm’s like the A-Max, 168 JLK, 180 JLK, 175 MK are by far the ultimate ram bullets.  These bullets launched at about 2,400 fps will out perform any other bullet from a ram performance verses recoil perspective, bar none.  I did not list the 168 Bergers because they have very soft jackets and cores and do not perform well at tipping over 50-lb rams.  They are, however, very accurate for paper punching.

The downside of 7mm’s is how to reduce recoil on the short animals.  They constitute 75% of the score.  No major manufacturer makes a high BC light-weight 7mm bullet for our application that can compare to the 6.5mm 107 MK or 6.5mm 108 Lapua launched at 2,700 fps.  It is possible, because I still have about 500 Hall bullets that weigh 140 grains.  They have a BC in the 0.500 range, more than enough to shoot at c, p & t with light recoil and low wind deflection.  I also have a bullet design that has a 0.600 BC from a 140 grain bullet but the cost of dies, given that I’m not in the bullet business, is prohibitive so no efforts have been taken to put the bullet design into production.  But, there is another strategy and that strategy is launching the high BC commercial ram bullets at low MV.  It is possible to launch the 168 JLK at 2,000 fps and have lower wind deflection and less recoil than a 260 launching a 107 MK at 2,700 fps.  The plus side also includes the fact that you will not ring any pesky pigs with the 168 at 2,000 fps.

So, with the above in mind, my first pick for the ultimate HP Hunter rifle is the 7mm BR.  The rifle would have a #5 taper barrel that is 26” long with an 8.5-twist using a single shot XP-100 action or the Nesika Bay or other short action.  The reamer would be designed to properly seat the ram bullet of choice so that the brass shoulder/neck junction is in line with the bullet body/boattail junction.  The freebore would be 0.2840” in diameter, not the sloppy dimensions that some reamer manufacturers grind for their SAMMI specs.  Brass would be Lapua 6mm BR.

Writing about this just makes me want to build another HP Hunter rifle.

[tirador]

Hello Dan, everything you say regarding building the ultimate Hunter class rifle is very interesting and informative.  

There is a problem with trying to use single actions like the XP100 or the Nesika Bay if is a single shot action to build Hunter class rifles because the current rules in HP Hunter do not allow for their use.  

What does not make sense to me is that single shot actions are allowed in Smallbore Hunter class but not in HP Hunter class.  Is a rule like the one that lets us to pre load the magazines for SB Hunter but not for HP Hunter.  

It may not be a bad idea to ask the powers that be to change the rule to allow the use of single shot actions in Hunter rifle since at the moment they are allowing us to single load it as long as the ammo is run through the magazine first.

[nomad]

Tony,

I sent a letter to the committee before this year's meeting advising that the 'single-loading-through-the-magazine' interpretation had created a de-facto single shot hunter and suggesting that they might want to consider the change that you're suggesting.
They apparently wanted nothing to do with it...

[kahuna]

Dan
Give us a break this thing has been beat around so much no one wants to hear it anymore.
Larry

[ajj]

Dan: You left out the 6.5 Japanese. Just enough case capacity, good brass available from Norma and a weirdness factor right up there with the Carcano!  No, I'm serious.
If I sent you some 7 mm Finn rebated boattail bullets in 123gr and 145gr could you test them on the pendulum? Also, how do I test BC? Two chronographs? They LOOK like high BC bullets and the 123 at 2500 takes down pigs with real authority.
In 6.5 do you see any difference in the 139 and 144 Scenars? I'm hoarding my cache of the latter, rams only. I'm not sure we can still get the 144's.
Hey, it's wintertime. Can't shoot. Time for some bench racing.

[DanDeMan]

ajj,

Yup the 6.5 Japanese would work great.  The case capacity is about 69 gr of water.  The 6.5 Carcano holds about 70 gr and the 6.5 Mannlicher-Schoenauer holds about 72 gr.  A 260 holds about 78 gr of water.  The 7BR holds about 55 gr with the 6.5 Grendel at about 48 gr.

Send the Finn bullets, I'll measure the BC and test them for toughness.

The pre-discontinuation 6.5mm 144 Lapuas were tougher than the new production bullets.  Last year I tested the latest production 139 Scenar and 144's for a friend.  The Scenar 139's were tougher.  I believe Lapua changed their jackets and cores when they ran the special runs for silhouette shooters a few years back.  I still have some old 144’s for comparison testing against the new batches.

To test in-flight BC using two chronographs is quite simple and straight forward.  First you need to calibrate the two chronographs by over-lapping them in parallel (not in sequence) and shooting about 30 rounds of 22LR ammo over them.  Record the velocities for both.  Next, add all 30 velocities from each of the overlapping, parallel chronographs and find their respective average.  Take the difference in averages and use it to off-set the test data.  If chrono1 had a 30-shot average of 1,111 fps and chrono2 had a 30-shot average of 1,099 fps then the off-set for calibration purposes would be 12 fps.  Say we put chrono2 down range and chrono1 at the muzzle.  We record both velocities during the testing for the number of shots for each load.  I’d suggest at least 10 rounds be shot during the test.  When the data is analyzed crono2’s data will have 12-fps added to the average.  Next find the average of the near and far velocities.  These two numbers with the off-set added to chrono2’s average plus the temperature, humidity, altitude and barometric pressure are needed to determine the in-flight BC as well as distance between the centers of the two chronographs.  Air density has a substantial effect of BC as well as bullet stability.  The higher the density the lower the BC as well as stability.  We want to “standardize” the results so they can be compared to other bullets tested under different atmospheric conditions.  For instance, if the tests were conducted at Raton (6,700 ft) on a hot, dry day the calculated BC’s would be too high if atmospheric conditions were not taken into account.  The same loads tested at sea level on a cold day would have substancially lower bullet BC’s.  The place to input you data is:

http://www.eskimo.com/~jbm/calculations/bcv/bcv.html

As to how to setup the chronographs, set the near one up just as you would for load-testing.  Set the far one up in front of a target.  It is also wise to have another sight-in target just off to one side that can be shot at from the bench setup you will use to reduce the risk of nailing the down range chrono.  Having two Oehler P35’s with printers is the way to go.  If only one P35 is available use it for the far chrono as you can go down range and retrieve the printout after each string of fire.

[DanDeMan]

Now that some of you are interested in what was written in the first post, some numbers to drive the point home should do the trick to explain what is possible concerning how to design the ultimate HP Hunter rifle.

For this exercise it would seem that four cartridges for the short animals and ram load will do.  Since the 260 is probably the most common HP Hunter out there it should be included as well as the 7-08.  For the smaller case capacity cartridges let’s pick the 6.5 Grindel and the 7BR.

For the 6.5mm’s the 139 Scenar and 108 Scenar are two very good choices.  For the 7mm’s let’s just use the 168 JLK.  Also, we should assume that all barrels are 26” long with the 6.5’s using an 8-twist and 7’s using an 8.5-twist.  All rifles weight 9 lbs.

The issue of recoil is a sticky wicket.  The current equations that are implemented in programs used to calculate recoil are lacking as the inputs are rifle weight, bullet weight, powder charge weight and MV.  Those 4 parameters are necessary but not sufficient to really compare “felt” recoil between calibers or even within a caliber using different cartridges.  The reason I believe this to be true is that for a given caliber and load the “felt” recoil diminishes as the barrel lengthens.  The reason that is so is because the exit gas pressure goes down as the length of the barrel increases and lower exit gas pressure means lower felt recoil.  This has been shown through experimentation by gradually cutting back barrel length from 27” down to 20” using a 6.5TKS.  My good buddy the MetalHead, AKA Mr. Marvin did the smithing.  A standard was used for comparison, a 24” barrel 6.5TKS chambered with the same reamer as the experimental rifle.  The 27” long barrel produced noticeably less recoil for both the ram and short animal loads than the 24” barrel.  Both rifles chambered the same ammo.  When the experimental rifle barrel was cut back to 24” both rifles delivered the same felt recoil.  When the experimental rifle’s barrel was cut back to 20” both loads produced more “felt” recoil than the 24” barrel used for comparison.  Not only that but the 20” barrel launched the 107 MK about 100 fps slower than the 24” barrel and the ram load was about 135 fps slower.  So with the short 20” barrel there was more recoil and lower MV.  Both rifles were stocked with identical McMillan silhouette stocks and were weighted to have the same balance point.  Balancing was done after every bobbing of the barrel on the experimental rifle.  XP-100 actions were used for both rifles as well as 24X BR Leupold scopes mounted with the same bases and rings.  Two shooters shot both rifles for each of the 3 tests and reached the same conclusions.

Given the above results, a 26” barrel, the maximum allowed, should be used for HP Hunter if reducing recoil to a minimum is your objective.

For “felt” recoil comparisons between calibers, in this case 6.5mm and 7mm, we also have the issue of a larger volume in the 7mm bore for the same barrel lengths and therefore lower felt recoil that results from the lower gas pressure on bullet exit of the 7mm.   The currently used equations and software do not capture this phenomenon.  The larger volume means that if we have 140 grain 6.5’s and 7’s launched from BR cases with the same powder charge of say N140 for the 6.5mm and N135 for the 7mm and both produce the same MV, the “felt” recoil of the 7mm would be about 10% lower than the 6.5mm due to reduced gas pressure pushing the rifle backwards upon bullet exit from the barrel.  With that in mind the recoil for the 7mm’s listed below will be reduced by 10% from the calculated values to take into account this phenomenon.

We need an improved recoil equation that uses caliber, barrel length and cartridge volume to better estimate “felt” recoil.

For comparisons of the short animal loads between cartridges and calibers, recoil and wind deflection from a 10 MPH cross wind at the turkey line are used.  For the rams the recoil and 10 MPH crosswind wind deflection will be used.  Terminal momentum, a good indicator of ram knockdown performance, will be listed for the ram loads.

260 loads:
108 Scenar, 34.5 g N135 @ 2,700 fps, recoil 7.3 ft-lbs, turkey-line wind deflection 9.2”
139 Scenar, 42.0 g N160 @ 2,800 fps, recoil 12.3 ft-lbs, ram-line wind deflection 12.7”
Ram line terminal momentum = 1.22 ft-lbs

6.5mm Grendel loads:
108 Scenar, 28.0 g N133 @ 2,700 fps, recoil 6.5 ft-lbs, turkey-line wind deflection 9.2”
139 Scenar, 32.0 g N140 @ 2650 fps, recoil 9.5 ft-lbs, ram-line wind deflection 13.9”
Ram line terminal momentum = 1.14 ft-lbs

7-08 loads:
168 JLK, 31.0 N133 @ 2000 fps, recoil 6.9 ft-lbs, turkey-line wind deflection 9.1”
168 JLK, 36.0 N135 @ 2,450 fps, recoil 10.3 ft-lbs, ram-line wind deflection 13.8”
Ram line terminal momentum = 1.28 ft-lbs

7BR loads:
168 JLK, 26.0 N133 @ 2000 fps, recoil 6.6 ft-lbs, turkey-line wind deflection 9.1”
168 JLK, 31.0 N135 @ 2,450 fps, recoil 9.8 ft-lbs, ram-line wind deflection 13.8”
Ram line terminal momentum = 1.28 ft-lbs

As you can see the wind deflections are about the same for the bullets used and MV’s listed.  The issue that tips the scale in my mind for the 7mm’s is the ram knockdown improvement.  Terminal Momentum is about the best measure to compare ram performance, but that does not tell the whole story.  Bullet toughness, which increases impact dwell time, also contributes to ram knockdown performance.  Another issue that is in favor of the 7mm’s is that a 168-grain bullet will have a longer dwell time than a 139-grain 6.5mm bullet for two reasons.  Those reasons are, first, there is more mass to blow up on the ram so the dwell time is longer and second, the 7mm bullet is moving slower at impact which also increases dwell time.  So, the calculated terminal momentums do not tell the whole story.

One last issue, the 7mm short animal loads are not likely to ring pigs.  The light 6.5mm bullets have a nasty reputation of leaving those pesky porcine erect and laughing at us.  That is why a number of top shooters have gone to 120-grain bullets for pigs.

Some might say this analysis is an exercise in chasing mice nuts, but what the heck, it is fun to do and is due.  The 260 is an excellent cartridge and the 6.5 Grendel sure looks interesting, but will require a serious shooter to ring all the potential performance available from its under-bore case capacity.  I believe it is possible to compete at the highest levels with the 6.5 Grendel, but not by a casual riflemen.  For my money if I had to start from scratch and build a new HP Hunter rifle it would be a 7mmBR: 26” long, #5 taper, 8.5-twist barrel with a Pharr or Nesika Hunter Stock and a Nesika repeater action or the Ti Remington Short Action.  I’ve already got a very nice 260 Hunter HP so building a new one is not a current option.  Maybe when the barrel is shot out there could be a 7BR in the works.

[lucho]

Dan

Good post.  I saw all the data and your explanation was clear.  If I ever shoot out my one of my high power barrels I would give the 7 BR a try.

I guess I just have to shoot more.

Lucho

[Steel killer]

Hi Dan
What a great discussion. Dan you have been shooting a lot longer than I have. I have to disagree with sending the 7MM down range in the 2200-2400fps range. I have tried it with the 7-08 and my 7 TNT. You are loosing too much of the BC at that speed,and have much more drift to deal with than you are suggesting. At the ram line those loads are shedding FPS so fast and are coming in at such a steep angle, you are not getting any dwell time, the bullets want to deflect downward instead of pushing back. I have seen it in my spotting scope when conditions are just right.

   The best way to deal with recoil at these levels is to exercise, and shoot. If you  weight train you will better handle the trauma of recoil. You should harden you body just as a fighter would.

I shot my first match the month after my daughter married 6 yrs ago.
I spent the summer in the health club with the goal of shedding 30 lbs,
I not only lost the weight but got hard again. I went to the match 3 days early and shoot 400 rounds of 308-(168-175) gr match kings @ 2700 fps.
in prep for the match.  I shot as well on Sunday as I did on Thursday
To date that is still my best match. I have fallen off the wagon and gained
back 20 and got soft. At my last two matchs I shot real well on friday, Sat soso,and on Sunday I was not worth a dam.  I know this may not be well received but I am sure of what I am suggesting. I have been shooting my 375 H&H to get ready for a spring time hunt next year, my 6.5 & 7MM
doest scare me anymore , my follow through is much better and my groups on paper are smaller.

Good shooting
Steel Killer

[drover]

Dan,

I have to agree with your analysis of the 7 BR.  It is the nearest thing that I have shot that is a "magic cartridge".  I shot one in my heavy rifle, with a 26" barrel, for 5 years and according to my records I only lost 8 rams the entire time.  This was when I was competing quite heavily and shooting at least 2 high-power matches per month and on ranges that were notorious for having rams that were hard to knock over.  

I came to the basically the same conclusion as you in that it is the "dwell time" that seems to do the trick.  While watching other people using 7 BR the animals, rams in particular , seem to be pushed over rather than knocked over.  Sometimes they go so slow that you begin to wonder if they will ever fall at all but they end up on the ground in the end.

 I have been shooting the 260 for the last 3 years and honestly have never been quite satisfied with it, now that the magazine loading issue is somewhat settled  I am currently in the process of putting together a "hunter rifle" in 7 BR and am looking forward to getting re-acquainted with an old friend.

[DanDeMan]

Steel Killer,

For the 7mmBR to work up to its potential very low drag (VLD) bullets MUST be used for all animals.  If one is contemplating using the 168 Sierra MK they are missing the point.  As I’ve said for 25 years, “Ya gotta shoot the highest BC’s.”  For rams a MV of between 2,400 and 2,500 fps with a 168 JLK or the new 175 Sierra MK will do the trick.  You will have the same wind deflection at the ram line with substantially more ram knockdown than compared to a 260 load.

If one is contemplating using the 7mm 130 Sierra MK for the short animals, they are also missing the point.  These bullets do not allow the 7mmBR to out perform the 260 from a wind deflection point of view even if we drive them to the same MV as the 260 launching the 107 MK.  The BC of the 130 MK is lower than the 6.5mm 107 MK.  At 2,700 fps the 6.5mm 107 MK has a 0.418 BC while at the same MV the 7mm 130 MK has a 0.389 BC.  So for a wind deflection at the turkey line given a 10 MPH 9 O’clock wind we would have about 10.4” compared to the 6.5mm 107 MK with a wind deflection of 9.2”.  But, that is not the whole story.  The recoil from our 9 lb HP Hunter rifle is only 7.2 ft-lbs for the 260 load but a whopping 9.9 ft-lbs of recoil from a 708.  To put that into perspective, since we decided to shoot the 7mm 130 MK at the short animals instead of the 168 JLK at 2,000 fps we would generate about 38% more recoil and have about 13% more wind deflection than the 260 load.  As was said earlier, high BC bullets are what make the under bore cartridges like the 7mmBR work so well.

The angle at the ram line for a 7mm 168 JLK launched at 2,450 fps out of a 7mm BR is about 0.65 degrees.  That is less than 1 degree of trajectory angle at the ram line.  We need to put that old canard about steep trajectory angles to bed once and for all.  Even a black powder cartridge rifle launching a big heavy lead slug at 1,300 fps out to 1,000 yards only has a trajectory angle of about 4 to 5 degrees at the 1,000-yard target.

When I first started shooting HP Silhouette rifle matches the 6mm’s launching VLD’s at over 3,000 fps were all the rage.  “Common” wisdom was that the super flat trajectory was a big advantage.  Compared to what, a 0.65 degree trajectory angle at the ram line out of a 7mmBR loaded with a 168 JLK?  I don’t think so.  The drop you are seeing in the scope happens over about the last 200 meters before the ram line.  It is an optical illusion.  The bullet is traveling down range so fast compared to the drop from gravity the human eye can not perceive what is really going on.  From our perspective while looking through a spotting scope it looks like the bullet is dropping quickly just in front of the ram line when in fact it is not.  Over the last foot to the ram the bullet only drops about 0.137”.  The maximum height above the line-of-sight for the 7mm 168 JLK launched at 2,450 fps is about 2 feet.  So the bullet drops 2 feet over the last 200 meters as the high point of the trajectory is about 60% of the trajectory range.  That works out to an angle of about 0.17 degrees.  The bullet travels the last 200 meters in about 0.355 seconds so we “see” the bullet drop 2 feet in that time but it drops that amount over 200 meters or about 656 feet.  The bullet “dropping out of the sky” statement I’ve heard from many a spotter who has seen the glint of the bullet as it travels down range is an optical illusion.  The calculation that showed the real angle is closer to 0.65 degrees was done using the drop between 500 meters and 501 meters as the bullet’s trajectory angle increases with range.

As to recoil, recoil is enemy number one right before wind deflection when shooting at a high level in HP Silhouette matches given our rifle was built by a MetalHead type smith and we know how to load for accuracy and ram performance.  I’ve heard for years from the BPCR Silhouette crowd that recoil does not bother some of them.  Recoil reduces EVERYBODY’s ability to break the shot properly and follow through.  Just because you had a career high score shooting a hot 308 proves nothing concerning the effects of recoil.  Sure, I know a few guys that recoil does not bother as much as most others, but they are the exception, not the rule.  Ask any national level HP Silhouette shooter if they would like a lighter recoiling rifle that would have low wind deflection and great ram performance and I’d wager none of them would say, “Naaaa, give me more recoil.”  I’ve seen way too many guys that say recoil does not bother them only to see them flinch with the best of us when a round does not go off.

As to the 168 JLK shedding BC at the ram line that is not of any consequence as all bullets launched supersonic and remain at supersonic speeds during their entire trajectory have reduced BC’s that is a function of the bullet slowing down.  Here is the BC as a function of MV from 2,450 fps MV down to ram impact at 1715 fps for the 168 JLK.

2,450 fps = 0.610 BC
1,715 fps = 0.570 BC

For comparison purposes here is what happens to a 6.5mm 142MK when launched at 2,800 fps.  The bullet will hit the ram line at about 1,971 fps.

2,800 fps = 0.576
1,970 fps = 0.538

Notice that the 168 JLK only loses about 735 fps on its trip to the ram line while the 142MK loses 830 fps.  One of the metrics I used years ago to compare “efficiency” of proposed cartridges and loads was to compare terminal momentum delivered by the bullet at the ram line to recoil at the shoulder.  When that ratio is applied to the 7BR launching the 168 JLK at 2,450 fps verses the 260 launching the 142MK at 2,800 fps we find an interesting result.

Bullet Efficiency (BE): Terminal Momentum at Ram Line / Recoil

7BR BE = 1.28 / 9.8 = 0.1306
260 BE = 1.22 / 12.7 = 0.0961

So the Bullet Efficiency of the so loaded 7mmBR is about 36% higher than the 260 load as described above.  For your 308 load the difference would be much, much greater.

So you see the issue of a bullet losing BC as it slows down (the drag increases as the bullet slows down) is of no real consequence.  I’d have done the same for you 308 168MK but I don’t have one to measure for the BC profile.

[mkrall]

Dan, and...

   There is a recoil and velocity calculator on [url]www.handloads.com[/url] (near top on right of home page under "calculators". The inputs don't include bore size. The outputs are: "recoil impulse, velocity of recoiling firearm, free recoil energy".
   I ran the 260 and 7 BR ram loads from Dan's post and the output numbers are a little different. Why? Does it mean anything?

Dan,

   Have you toughness data for 6mm bullets -- 105 Lapua, 105 Hornady, 107 Sierra, 90 Sierra FMJ, 100 Clinch River? If you do, I'd love to hear it.

Mike Krall

[DanDeMan]

Mike,

I checked the site you listed in your post.  There is an error in their recoil calculation.

The 105 Lapua Scenar is the toughest 6mm bullet I've tested.

[mkrall]

Dan,

   Would you be willing to post the recoil formula you use or point me to the calculator used, if that is the case? Also, is there a momentum formula you could could pass on or do you use the pendulum for that number?

Thank you, Dan...

Mike Krall

[DanDeMan]

Mike,

I believe that the differences one finds in recoil calculation results is a function of different values for gas velocity.  The pistol site you used probably used a value close to 4,000 fps.  I'm guessing the value used by the software I use is closer to 5,200 fps.

Hatcher's Notebook has the equation if I'm not mistaken.  I don't have the book.  I use the software developed by Brad Millard that uses equations developed by the US Army at the Aberdeen Proving Grounds Ballistics Research Lab.

Momentum = Mass x Velocity

Bullet Mass = (Bullet Weight in grains) / (7000 x 32.17)
Velocity is in fps

For example for the 168 JLK ram load that hits the ram at 1,715 fps we have:

Mo = (168 / (7000 x 32.17)) x 1,715 = 1.2795 ft-lbs

[eroyd]

Just a tiny question,  :oops: Whats a JLK?

I'm thinking about building something and was pretty much decided on the 260 rem. but the 7 BR has a certain cool factor. After reviewing a few catalogs I see that Lapua appears to be lacking in the 7mm area, which seems odd, however there are a few choices in 6.5. Being in Canada, ordering bullets from the US can now be a P.I.A. so I would rather stick to something readily available. (Lapua, Sierra, Hornady etc.)

Hows the 7BR for feeding from a Remington short action magazines?

[Troy G]

That one I can answer for you.  JLK are bullets made by Jimmy and Carlene Knox.  They are excellent quality bullets.  I am shooting the 6.5 140 in my 1000yard bench gun and his 52 gr LD in my varmint guns.  

Jimmy makes bullets in .224, 6mm, 6.5, 7mm and .30.  He also makes a 7mm 180 with a BC of .738.  I would have thought these bullets to be too soft for silhouette but maybe with the lower velocities of a 7mm BR this is not really an issue.

John Hoover at and Otto Weber at www.okweber.com sell his bullets.  I have John's email and phone number at home, as well as Jimmy's number.  I can post later if Dan or another member does not.

I would have thought that Bob Cauterrucio's bullets would be better for silhouette since he makes them with Sierra jackets.  Bob's 7mm bullets have a higher uncomfirmed/reported BC.

How are you or will you guys get the 7mm BR to feed properly from the magazine or are you just single feeding based on the poorly written rule?

[ajj]

JLK Bullets: 414 Turner Rd., Dover, AR 72837 (501) 331-4194.

[mkrall]

Dan,

   Thank you for the input.
   I've come on to another calcuator (through a friend) at BearTooth that doesn't exactly agree with either your or Handloads' results. Through the same friend, there is a recoil area on the Remington site. I was told it doesn't agree with anyone else's calculations by a long ways... ah, well...

   If the gas pressures used are all different and there are effecting variables not in the formulas, a person about has to pick one and use it on a relative basis.

   I didn't ask you a question I intended to. You said the 6mm 105 Lapua was the toughest you had tested. Would you be willing to post the other 6mm bullets tested? I would appreciate it.

Mike Krall

[DanDeMan]

Mike,

The other 6mm VLD's tested for toughness along with the toughest, 105 Lapua Scenar were:

107 Sierra MK
105 Berger
106 JLK
115 Berger

[mkrall]

Dan,

   Thank you... that is a lot of help!

Mike Krall