Small 7mm's

[RamSlammer]

At tthe recent Early Australia Day Match here in OZ two of the competitors where using 7mm TCU's one built with a 19 inch barrel and the other with a 25 inch one. These rifles seem to have more than enough power on rams completely out of proportion with their size. How do others find the smaller cases including the tcu's and br's as they have to give a recoil advantage?

[drags]

I shoot a 7br and I use the 130gr smk at 2500fps for c,p,t and the 168 gr smk at 2400fps for rams, and the 168gr works well for rams. My 7br is long throated and I could probaly get 2450 out of the 168smk without loading it hot. With the new 175smk it should be even better on rams, but Sierra states in there ad to use 8.5 twist barrels for the 175smk. My gun is a 9" twist and the 175smk shot about 1/2 inch at one hundred yards but I haven't tested them a 500 meters yet, as soon as the weather breaks I will test them at 500 meters. Also I use Varget powders in all loads, the first lot of Varget powder I had I could get 2434fps with the 168smk using 30.5 gr of Varget with the second Lot I had to go to 31.5 gr of varget to get 2400 fps. All said I like the 7br good accuracy low recoil and does well on all the animals.
Drags

[RamSlammer]

Thanks drags Fortunately varget is made here in Australia it's called AR2208. It is sold to hodgen and sold by them as varget. I am c gratefull for the info. thanks
                             ramslammer

[while99]

I have a Ruger 77 in .280 Remington with a heavy barrel.  I believe Ruger made a few of these about 20 years ago.  It seems to be very accurate with factory ammo.  I haven't shot any handloads in it yet.  My question is, does anybody use a .280 for silhouette shooting any more or is it a dead issue?

[drover]

There is certainly nothing wrong with the 280 for silhouette except for the fact that it has substantially more recoil that most shooters want to put up with.  The more recoil one has to contend with the more difficult it is to shoot competitive scores.  That is why most people are using the minimum cartridge that gets the job done.

Also not to start a flame but as a rule Rugers have never been serious contenders in competition, the lock time is too slow, the triggers are difficult to tune to a consistent level and they are generally just so-so for accuracy.  Remington is the most popular on the line, not necessarily because they are the best but because they are easy to work on and there are lots of aftermarket parts, at a reasonable price, available for them.

[while99]

Thanks for you input.  This rifle has a long action so the lock time would not be as quick as a Remington 700 short action.  The trigger is not bad but probably not good enough for the real world of competitive shooting.  What caught my eye is that it shot 3/4" groups with out-of-the-box Hornady factory ammo and a 30+ year-old K6 steel-tube Weaver.  My thoughts are that with a little trigger work, some good match-grade handloads, and a competition-quality Leupold scope, this rifle should shoot down around the 1/2 minute mark.  I guess that is something to try this summer.

[Troy G]

I am not meaning to hi-jack this thread but . . .

What is the minimum velocity that would be required to reliably take down rams with a heavy 7mm bullet like the Cauteruccio 176, JLK 180, Berger 180, Sierra 175gr MatchKing.  Hell might as well throw in the 168 gr range 7mm bullets.

What bullet then would be suitable/recomended for the CPT lines, at what velocities?

Assuming that you are shooting a 180gr 7mm at 2400fps and a 6.5mm at 2700fps which is going to give you more felt recoil assuming a Standard gun where everything is identical?  

Mr. Theodore care to comment on these questions?  :grin:

[dave imas]

while99,
not to discourage your effort with your .280...  i'm sure it is as accurate as you suggest.  But back to Drover's point, regardless of the intrinsic accuracy of the rifle, off the rest if you will, because of the recoil of your particular caliber, your functional accuracy will not be as high as you might like.  bluntly...  which i am far more comfortable with...  your .280 is going to kick the crap out of  you when you stand there and shoot 60 rounds between sight-in, practice, and the match.  your ability to hold and follow-thru will be diminished at a far faster rate than if you were using a lower recoiling caliber.  all calibers do it, we all feel the effects of recoil from our rifles, just some much faster than others...  again, this is why we choose to shoot the smallest, least recoiling caliber that will get the job done reliably.  with that in mind most of us make a conscious choice to give up the odd ram to allow us to hit everything else.  i'm pretty certain your .280 or a 30.06 can be loaded to get an extremely high knock down percentage on rams but you have to hit them first.  those calibers tend not to allow you to hit them.  which is why you rarely see them on the firing line.  
did i repeat myself enough?  :)  sorry.
dave imas

[ajj]

On the other hand: I think all would agree that a person interested in trying HP Silhouette and who just happened to have an accurate .280 should, by all means, bring it to a match and jump in the water. The "problem" with the cartridge is that it has too much powder capacity to be ideal for this sport. Even mild handloads burn more powder, thereby producing more recoil and muzzle blast than, say, a 7-08 in order to produce equal ballistics with a given bullet. That's no reason to hesitate about giving the sport a try, with factory ammo if necessary. Most people shoot their first matches with real hunting rifles in popular calibers. It's a heck of a lot of fun!

[dave imas]

yes.  AJJ is absolutely correct.  bring what you got.  just attempting to give some insight for future endeavors.

[9inarow]

Have to agree with the general thread of the discussion.  Shot my first HP event last year using my .30-06 hunting rifle.  About half way through the match, developed an incredible case of the "flinches", hit nothing after that, and had a sore shoulder.  Took me a month of air rifle shooting to un-learn the flinch.    Bottom line, it was a lot of fun, I am hooked and I just finished building a HP rifle in .260 Remington.....

[drags]

Troy, I checked  my ballistic program for the 7mm 175gr smk and 168gr smk. The 175 has a bc of .608 and the 168 has a bc of .496, the  168 at 2400fps has 918 ft-lbs of energy at 550yds the 175 at 2400fps has 1123ft-lbs of energy 550yds, at 2300fps the 175smk still has 1024ft-lbs of
energy at 550yds. I shoot the 168smk at 2400fps for the rams and it does well so the 175smk should do much better, only question for me is that sierra recomends a 8.5 twist and my barrel is a 9 twist. I tried the 175smk at 100yds and it shot about 1/2 inch but I haven't tested them at 500 meters yet. With the introduction of the 175smk the small 7mms may become popular again.
Drags

[Troy G]

Drags when I started comparing the bullets I took the highest BC of the 6.5mm bullet and a 7mm bullets I knew of.  I used the 140 gr JLK with a BC of .630 and the 180gr JLK with a reported BC of .728.  I ran the 140s at 2700 and the 180s at 2400.  I really have no idea what would be attainable in a 7mm version of a TKS or 7mm BR but thought that 2400 might be done.

For energy I got 1399 for the 7mm and 1308 ft/lbs of energy for the 6.5mm bullet.  How can you mathematically/scientifically measure bullet dwell time on the target?

Wind drift for the 7mm was 8" and the 6.5 was 7.91" with a 5 mile an hour crosswind at either 9:00 or 3:00.

What factors would a person have to consider when trying to calculate felt recoil?

What advantage would a 7mm have over a 6.5mm besides shooting slightly less powder?  Unless there is something to a slower bullet with the same amount of energy I cannot see why one would bother making a 7mm.  I need to be enlightened.  :grin:

[CB]

Never tried the 180's in a 7BR but I'd have to say based on experience with 162's and 168's that 2400 would be a mite hard on brass, as for "enlightenment" a few seasons spotting for a top level shooter should do the trick. Wind drift tables and BC numbers don't always add up as planned in a real world, 'sectional density' is another term seldom mentioned but would do well to ponder on, Help me out here Dan!!:-D

[DanDeMan]

Troy,

I have an 8-twist 7mm PPC Improved with a 26" barrel that I had built about 9 years ago.  It has never rung a ram in a match even at ranges with very nasty rams.  My ram load is 30 grains of VarGet that drives the 180 JLK to 2,300 fps.  Even when the hot loaded 308's launching 180 grain MK bullets to 2,500 fps are ringing rams that little cartridge is knocking them down.  More than a few guys have been left scratching their heads after watching that little cartridge go to work on rams after laughing at me before the rams starting hitting the dirt.  The reason is the very high BC and a tougher, longer 7mm JLK bullet.  The 180 JLK is going faster at the ram line than the 308 180-MK's.  Recoil with that load is very mild and is probably the most efficient ram load out there.  I'm defining ram knockdown efficiency as shoulder pounding divided by ram knockdown performance.  It should be noted that the reamer was specially designed by yours truly for the long 180-grain JLK.  A standard design will not work.  The 7mm PPC Improved has a case capacity about half way between the 7mm TCU and 7mm BR.

But, if the barrel twist is not sufficient for the bullet and there is much over 1 to 2 degrees of bullet yaw (wobble) the BC plummets and the advantage is lost.  One can check for yaw by shooting through heavy corrugated cardboard at say 100 yards and checking to make sure the holes are round.  If they are they will be round all the way to the ram line.

If I was going to build a new HP Standard rifle I'd be very interested in building an 8 or 8.5 twist 7mm BR with a properly designed reamer for the long, heavy, high BC bullets.  SAMI spec reamers are OK sometimes, sometimes not.  If the freebore length and diameter as well as the leade angle are not optimized for the long bullets these small cartridges do not work up to their potential in the HP Silhouette game.

For cpt's I'd shoot the cheap 162 AMax with about 26 to 28 grains of N133 or similar powder.  This load will produce less wind deflection than the 6.5mm, 107 MK's at 2,700 fps with milder felt recoil.

[DanDeMan]

Troy,

I forgot to address your last question.

"Assuming that you are shooting a 180gr 7mm at 2400fps and a 6.5mm at 2700fps which is going to give you more felt recoil assuming a Standard gun where everything is identical?"

If we take a typical 260 ram load composed of the 139 Lapua under 42 grains of N160 that produces a MV of about 2,800 fps, a high performing ram load and compare it to a 7mmBR launching a 176 Cauterucio to 2,300 fps we find some interesting and counter intuitive results.

First, the recoil from the 260 Ram load will be much higher than the 7mm BR ram load.  Second, the milder recoiling 7mm BR ram load will knock more rams down.  It's a two-fer; less recoil and more ram knockdown power.  Life it good:-)  And, the 7mm BR barrel will last longer.

[DanDeMan]

Troy,

The equations for recoil are not accurate as they do not take into account some very important variables.  That is a long discussion for some other time.  The missing variables from the current recoil equations are caliber and barrel length.

Next, don't believe any manufacturer's BC listing as BC is a marketing and sales tool.  There are ways to properly compare BC's.  I use one that works well.  It entails measuring the bullets and plugging those dimensions into a computer program which kicks out the BC over the defined velocity range every 10 fps.  The BC of the 6.5mm heavy bullets are all about 0.580 to 0.590; 142 MK, 139 Lapua, 140 JLK.  The highest BC 6.5mm heavy bullets are the ones Cauterucio is making with the closed meplats.  They are expensive but the BC's are in the 0.650 range.

Another issue to bring up is that "energy" is not a good way to compare ram knockdown performance as the terminal velocity is squared.  Ram knockdown is better compared by calculating terminal momentum.  A 6mm bullet can have a high terminal energy and not knock down a single ram.

Here’s an example of why terminal energy will give a result that will lead one to make a wrong decision when it come to comparing ram knockdown.  First let’s start with a 45-70 Black Powder Cartridge Rifle used in BPCR Silhouette.  A typical load that launches a 550-grain cast slug to about 1,100 fps will produce a terminal velocity at the ram line of about 850 fps.  That load will not ring a ram in your life time.  The rams don’t tip over they are slammed off the rail like you have never seen by a HP Silhouette rifle.  The terminal momentum is 2.09 and the terminal energy is 887 ft-lbs.  Now consider a 243 launching a 107 MK to 3,300 fps.  It will hit the ram line at about 2,289 fps.  The terminal momentum is only 1.09 but the terminal energy is 1,251 ft-lbs.

The terminal energy of the heavy, slow cast bullet is only 887 ft-lbs while the 243 produces a terminal energy of 1,251 ft-lbs.  That 243 will ring rams regularly, but the 45-70 will not.  When the 243 hits a ram, if it goes down, it will go over in slow motion.  The 45-70 will knock the crap out of the ram.  Now compare the terminal momentums of both loads.  The 243 has a terminal momentum of only 1.09 while the 45-90 has a terminal momentum of 2.09.  This is why terminal energy is less than useless in comparing ram knockdown and why terminal momentum should be the only metric used.  Even it is not sufficient as bullet toughness and dwell time also contribute to ram knockdown effectiveness.

[Troy G]

Many thanks Dan for taking the time answer my posts.  The reason for all my questions is that I cannot get more than 2675 fps out of my 6.5 TKS.  I had talked to you off the forum about this problem and tried a 6.5 Lilja 3 groove barrel at 28" in length with the same results.  I could not get above 2700 fps without destroying Lapua brass.

I went back and read your posts on another thread called the Ultimate Hunter where many of the same questions have been addressed.

My new questions:

What is your opinion of a 7mm TKS with 1/8 or 1/8.5 twist 24"-26" barrel with the reamer set-up for a 180gr JLK or Bob's 176gr bullet?

Have you been able to shoot both the JLK and Bob's bullet with success in the same gun.  The only reason I ask is that I have measured Bob's 7mm bullets at .2855 and have talked to people that have had trouble chambering them with reamers speced for other 7mm bullets.

[DanDeMan]

Troy,

I’m surprised your 6.5mm TKS is not delivering more than 2,675 fps without destroying your Lapua brass.  There are a number of guys shooting that cartridge and they don’t have any problem getting over 2,700 fps with no brass problems.  My current ram load produces 2,775 fps with the moly-coated 141 Cauterucio VLD.

There are several issues that might cause your brass/pressure problems.  First, you might have a very soft batch of brass.  I’ve got brass I’ve been shooting for years with no failure.  The cpt brass is kept separate from the ram brass.  The ram brass has way over 20 firings without, to the best of my memory, a single case failure.

Second, there might not be enough clearance between the neck of a loaded round and the chamber neck.  My ram loads are 0.282” in diameter at the neck and the chamber is 0.284” at the neck.  If there is less than 0.001” per side clearance excess pressure problems can occur.

Third, the bullets are mol-coated.  One thing moly does do is allow the small case capacity cartridges to perform at higher velocities with lower pressures.

Fourth, the barrel bore/groove diameters might be too small.  That will drive up pressures quickly.  When a button or broach is at the end of its life, it produces a barrel with inside diameters that are a bit too tight.

The 6.5mm TKS was originally to be a 7mm TKS, but Kurreck was set on shooting a 6.5mm so I designed the reamer for the 108 and 139 Lapua Scenars.  The 7mm TKS would be a most excellent cartridge for HP Silhouette.

There should be no problem shooting Cauterucio’s bullets or the JLK’s or the Amax because I’ve shot all 3 in the same 8-twist and 9-twist 7mm’s.  The 8-twist was the 7mm PPC Improved and the 9-twist was a 7mm BR.  In the BR the 168 JLK’s or 156 Cauterucio’s were death to rams.  I’ve just tested Cauterucio’s newest version of his 7mm 156-grain closed point bullet and can report it is mind bogglingly accurate and smacks the rams silly.  Even though it is stable in a 9-twist and only weighs 156-grains, because of the new design it has a 2,400 fps BC of 0.588!  The new 7mm Sierra MK has the same BC at 2,400 fps but it weighs 175 grains.

If I was to design a reamer and spec a barrel for HP Silhouette right now, it would be a 7mm TKS with an 8 or 8.5 twist barrel between 27” and 29” in length.  The taper would be like a Palma taper with about 20” fluted in the middle.  Stock would be one of the new hot stocks by your Canadian compatriot or one of the Pharr models.  Lapua 6mm BR brass would be used.  The brass would be opened to 7mm, ram bullets of choice seated optimally, neck measured and then 0.002” would be added to spec the reamer neck.  Freebore would be long enough to allow the long bullets to seat so the base of the boattail is at the case shoulder/neck junction or at most a bit lower.  Freebore would be at 0.2840” and leade angle would be 1 degree per side, 2 degrees included.

[Troy G]

All I have to do now is shoot out all my 6.5 barrels and find a barrel maker that is willing to export a barrel to Canada.  This will entail filling out paperwork, juggling chainsaws, swimming in a pool of sharks, sacrificing a rooster, and then maybe I will be able to get a barrel from the States.

Dan have you done any stabilization tests with the heavy 7mm bullets and a 1/9 twists?  I would have no trouble getting a 1/9 twist 7mm barrel but getting a 1/8 or 1/8.5 twist 7mm barrel into Canada from the States is not as easy as calling the barrel maker and having them ship one out when it has been completed.

Troy

[DanDeMan]

Troy,

For a 9-twist you can shoot the 168 JLK as well as the 156 Cauterucio and the 162 AMax.  All three are excellent choices for a 7mm BR and 9-twist barrel.  My 7BR was a 9-twist.  It shot all three bullets very well and punched round holes at 100 yards.  I've not tested the new 175 MK, but it might be a bit unstable from a 9-twist barrel.  The 176 Cauterucio, 180 JLK and 180 Berger (not a good choice for rams as the bullets are very soft) will not shoot in a 9-twist.

My choice for a 9-twist 7mm BR for rams would be the Cauterucio 156 at 2,400 fps and the 162 AMax at about 1,900 to 2,000 fps for the rest of the animals.  Another option for the cpt is the new 139 Hornady SST.  I've shot that bullet recently in a 9-twist.  It shot well and has a much better BC than the 130MK.

[RamSlammer]

Dan One of the rifles I mentioned in this post I loaded for and used 162gr sst's. These worked a treat one hit was comparitive to a earlier 308 hit that stood but the 7tcu took the ram down no problems. The other bloke was using 168mk and only had 1 out of 9 rams stand. The 162sst load is doing 2191fps and when we where sighting in performed better in the wind than 155 palma's out of the 308 (18" less drift at 500). As I said earlier they perform way beyond what you would expect!