7mm BR/TPP Preliminary Report

[DanDeMan]

The optimum caliber, bullet(s) and cartridge for HP silhouette have been topics of hot debate since the sport first sprouted wings in this country back in the 60’s

In the beginning there was the venerable 30-06 launching bullets that dealt heavy recoil to the trigger puller.  Wiser men and women prevailed and voila, the 308 came into its own as the cartridge of choice.  Then, some iconoclast wondered why not the 7-08 and thereby ushered in the 7mm era.

The desire to reduce recoil even more drove some at the top of the game to consider the 243 and 244.  Lack-a-lass, ringing rams is not conducive to shooting top scores so off to 6.5mm-land those chasing the holy grail of HP silhouette went.  For the past 8 or so years the 6.5-08 or 260 Remington has pretty much dominated the game.

Most top competitors are launching 107 to 123 grain VLD bullets at the chickens, pigs and turkeys.  The rams demand more oomph, so 140-grain VLD’s are launched at rams.  The downside to the current crop of 6.5mm HP Silhouette rifles is that if 6.5mm, 107 grain bullets are shot at pigs, every once in a while the petulant porcine will remain standing from a low-center hit.  This writer has bore the brunt of that particular porcine predicament on a few too many occasions that resulted in the dreaded LOSS OF MATCH.  Not a trivial issue and often prone to simulate the gray matter between one’s wing-nuts.  And, the 140-grain class, 6.5mm VLD’s will on occasion leave a rambunctious ram remaining on the rail from a low-center hit.  What to do, what to do?  Being put on suicide watch as a result of ringing rams or pigs is not the only option after dinging, ringing & losing.

With the current crop of high ballistic coefficient bullets in 7mm, the new 175-grain Sierra MK’s in particular, a new look at the 7mm’s is certainly in order.

After receiving some samples of the 175 Sierra MK and the 139 Hornady SST some good old fashion computer simulation was the order of the day to see what MV’s these bullets should be launched at and what the terminal momentum, wind deflection and recoil would be compared to a typically loaded 260 Remington, the dominant caliber in the HP Silhouette game for both Hunter and Standard Classes.

Recoil was set to about the same force for both the 7mm BR/TPP (Theodore, Pearson, Perry) and 260 Remington so we can compare and contrast the efficiency of both cartridges from the perspective of terminal momentum and wind deflection.  Mr. Marvin Pearson (MetalHead) built the first 7mm BR/TPP Hunter HP rifle for Mr. Jared Perry.  This writer will be putting it though its paces in short order.  Below are the simulated results.  Testing to measure actual live-fire average 500-meter ballistic coefficient for the ram loads as well as actual live-fire recoil acceleration for all loads will be executed over the next few months.  The 8-twist barrel has been broken-in, cases fire-formed with load-testing to commence shortly.

So, here are the preliminary results from using state-of-the-art exterior ballistics software:

7mm BR/TPP:

175 Sierra MK
MV = 2,400 fps
500 m Velocity = 1,712 fps
10 mph wind deflection at 500 m = 3.7 MOA
500 m Momentum (ram line) = 1.34 ft-lbs
9 lb rifle recoil estimate: 11.5 ft-lbs

139 Hornady SST
MV = 2,400 fps
385 m Velocity = 1,679 fps
10 mph wind deflection at 385 m (turkey line) = 3.6 MOA
300 m Momentum (pig line) = 1.15
9 lb rifle recoil estimate: 7.2 ft-lbs


260 Remington:

142 Sierra MK
MV = 2,700 fps
500 m Velocity = 1,886 fps
10 mph wind deflection at 500 m = 3.6 MOA
500 m Momentum (ram line) = 1.20 ft-lbs
9 lb rifle recoil estimate: 11.5 ft-lbs


107 Sierra MK
MV = 2,700 fps
385 m Velocity = 1,844 fps
10 mph wind deflection at 385 m (turkey line) = 3.7 MOA
300 m Momentum (pig line) = 1.01 ft-lbs
9 lb rifle recoil estimate: 7.1 ft-lbs

From years of testing and experimentation the relevant parameter to predict animal knock-down is momentum.  And, even that is not quite enough.  Bullet dwell-time on target (how long the bullet pushes on the target before splattering completely) also contributes to efficacy of animal knock-down.  So, even though the 7mm BR/TPP loads have a higher momentum compared to typical 260 Remington loads, which do not tell the total tale of animal knock-down efficacy, the 7mm bullets above described and their terminal momentum are much more capable of tumbling steel critters than even their terminal momentum suggests.

Much more to be published as testing proceeds.

[RamSlammer]

G'Day Dan
              My daughters 7TCU should be ready for the Australian Nationals on the 30th Sept, I used my mates last month at a club shoot and was impressed. I'll let you know how it goes with the 168mk's ambling along. I am confident that if she hits the Rams they will topple, it's her first HP match so I don't know how many she'll hit. Will be in touch.
Juddy

[Arizona Jake]

Dan, the ideal 6.5 and 7mm cartridges were designed over 25 years ago.

They are the 6.5 and 7mm IHMSA cartridges.

They give superior performance over the 6.5mm/7mm BR-based cartridges with less powder and recoil than the 260 and 7-08.  They both have a proven track record and data was available from Hornady for a good number of years. Dies are readily available from RCBS, Redding, et al, and Hodgdon Bechmark, Varget and IMR/H 4350 are the powders nto use.

[Tony Tello]

Dan, thank you for the good information.

One thing to consider though, as the 7mm BR barrel wears out the velocities will drop and the rams would be harder to knock down.

It happened to my friend Ralph Corral who shot a 7mm BR for a couple of seasons and was forced to re-chamber the barrel to 7mm-08 after he started having trouble knocking down rams.

With other calibers that have more case capacity we can add more powder to regain the lost velocity due to barrel wear but we can’t really do much in regards to BR or TCU size cases.

[Bulletman]

Dan,

Can ya tell us what your "live-fire recoil acceleration" test is??? Is it simply physical hand-held firing or do you measure it?

Bulletman

[DanDeMan]

Jake,

I've shot both the 6.5mm and 7mm IHMSA cartridges in pistols and rifles.  They are certainly fine cartridges.  But, IMHO, they have much more case capacity than is needed in a 15" barreled pistol.  They also have more case capacity than is needed for HP Rifle Silhouette IF the correct barrel twist and bullets are used.

I shoot a 7mm PPC Improved that launches the 180 JLK to just a bit over 2,300 fps with 31 grains of VarGet.  The recoil is very mild for a ram load.  It will knock over rams better than any hot 260 launching a 139 Lapua at 2,800 fps with about 1/2 to 2/3 the felt recoil.  It's all in the BC, bullet toughness and mass of the bullet.

[DanDeMan]

Tony,

I've not seen any problems with reduced MV from bullet wear that a little more powder can't correct.  I shot a rechambered 9-twist 7BR for a while that had over 10,000 rounds through it.  It was originally DaveI's 7TCU built by Wally.  There was plenty of case capacity in the 7BR to add a grain or so more powder to keep the MV of the 168 JLK's over 2,450 fps.  That load was death to rams.

The key to making these underbore case capacity cartridges work is proper barrel twist and ram bullet.  With the 175 MK we have a ready source of 7mm bullets that will work great on rams.  The 139 SST's by Hornady have the highest BC for the 140-grain class bullets for out to turkeys.

[DanDeMan]

Dan,

Can ya tell us what your "live-fire recoil acceleration" test is??? Is it simply physical hand-held firing or do you measure it?

Bulletman

Bulletman,

The recoil will be measured using an accelerometer taped to the rifle stock and plugged into a laptop computer.  The readout will give impulse in G's over time.  The device to be used is based on the technology used in airbag actuators used in automobiles.

[Arizona Jake]

Dan,

Thank you for the all the continuous investigative work you do to squeeze every last ounce of minimal cartridges to reliably get the job done and sharing the information with the rest of us.

I always learn something from your efforts.

[DanDeMan]

Guys,

Here is some "eye candy" for you.

Sorry guys the link is not working.

How have some of you posted pictures on this site??

Notice that both 7mm BR/TPP rounds have plenty of bullet shank in the cartridge neck.  Each of the rounds is about 5 to 10 thou into the lands for top accuracy also.  The Ram bullet is the 175 Sierra MK.  The CTP bullet is the 139 Hornady SST.  Target MV is 2,400 fps for both bullets using H4198 or N133 for the 139-grain SST and VarGet, RL15 or N140 for the 175 MK.

[Troy G]

Dan, I tried opening your link and it asks for a sign in name and a password.

Here come the questions as per usual:

I assume you are using a 26" barrel?  

Are the bullets naked or coated?

Primer being used?

Do you believe that this is typical acheivable velocity for this reamer design?  How many barrels have been chambered in 7BR/TPP?  Are the results all similar?

[DanDeMan]

Troy,

The rifle was built as a HP Hunter rifle.  It has a 26" barrel.

The bullets are not coated.

F205M primer used

Since the load testing hasn't been done yet what I have to say now is only an estimate.  Since my 7mm PPC Imp is capable of launching a 180-grain JLK to 2,325 fps I don't see why a 7mm BR is not capable of 2,400 fps with the 175 MK.  Of course barrel bore/groove will affect pressure as well as MV.

This is the first rifle built with the 7mm BR/TPP reamer.  A second is under construction as I type.

[Troy G]

Thanks Dan.  I always enjoy your evaluations and experimenting.  I look forward to your future reports on how things are going with the 7mm.  I managed to stock pile 4200 JLK 180gr bullets before Jimmy retired so all of this is good news.

[DanDeMan]

Greetings Gents and Gals,

Today I managed to do some preliminary load development using the 7mmBR/TPP Hunter HP rifle.  First the caveats: the carbon fiber stock is to die for offhand, but is less than optimum off the bench.  The drop in the butt stock is great for offhand, but a real challenge for bench work as just a little recoil produces substantial vertical in the groups.  Not only that, but the stock flexes a bit too much for top notch bench work.  But, this is not a bench stock.  It is marvelous off-hand.  That being said, the rifle still produced ¼ MOA groups with loads that should perform most excellently for silhouette.

These test loads were focused on determining proper powder charge for each of the bullets.  For the 175 Sierra MK the obvious choice from years of experience was VarGet or VVO N140.  I was not let down on that call.  VarGet did indeed produce some fine accuracy and appropriate MV’s for the Hunter HP Silhouette game.

For the out-to-turkey loads, Hornady 139-grain SST’s and Hodgdens H4198 Extreme performed very well.  VVO N133 should also do the trick with the 139 SST’s.

More load development will be undertake with the VVO powders, but at this point the initial choices look very good.

A range of powder charges with the same cartridge OAL for each bullet, was tested with both bullets today.  The “match loads” from today’s testing look very good.  Both loads listed below produced ¼ MOA groups at 100 yards and sub 30 fps extreme spreads over the Oehler chronograph.

Out-to-turkey load:
139 SST Hornady bullet
26.0 grains of H4198
F205M primer
MV: 2,347 fps
Extreme Spread: 20 fps
Groups Size C-to-C: Horizontal 0.249”, Vertical 0.245”

Ram Load:
175 MK
32.5 grains of VarGet
F205 Primer
MV: 2,375 fps
Extreme Spread: 26 fps
Groups Size C-to-C: Horizontal 0.249”, Vertical 0.108”

Both of the above 5-shot groups had one shot that opened up the group substantially.  Both times the shot was on call.  Without those “flyers” the groups would have been around 0.150.

More testing to come and results reported.  Moly coated bullets will be tested next as well as naked bullets with higher powder charges with Hodgdens and VVO powders.

[Metalhead]

Geeze Dan...1/4 MOA groups with a cutting edge Mark Pharr Out stock ?.....I need to try harder to improve on the metalhead work....Marv

[DanDeMan]

Good Evening,

Today was another interesting day at the range engaged in load-testing the 7mmBR / TPP HP Hunter rifle built by the MetalHead, AKA, Marvin Pearson.  The rifle was benched a bit differently during this load-testing session to diminish the challenging way this very fine off-hand rifle stock rides the bags, NOT!!!  Anyway, as was reported in the first load-testing post, the stock is to die for off-hand but off the bags it is difficult to shoot consistently due to several design parameters.  In the past when benching a flexible stock or one with a lot of drop in the toe that causes the rifle to recoil in a manner which induces considerable vertical due to the butt dropping under recoil as it slides back in the rear bag a harder hold is required.  But, a harder hold is death to groups if the stock is flexible, what to do, what to do.

The return to battery post was removed from the front rest so the forend could be pushed forward to allow the recoil lug to line up with the back of the front pedestal.  This technique allows for a more rigid and shorter section of the stock to be supported by the front and rear bags.  The results certainly showed up on paper.

Please be advised that the below reported loads are only safe in my rifle.  Your rifle may not tolerate the listed loads so you must workup your loads with lighter chargers of powder taking such things as chamber dimensions, barrel bore/groove diameters, bullet seating depth and a host of other variables that can conspire to create dangerous pressures that can cause injury.

There was also a serendipitous aah-haaa today, but that will be the subject of a separate thread about moly-coated bullets.

Remington 71/2 primers and VVO N150 powder were tested along with heavier charges of the VarGet and H4198 Extreme.  These last two powders were tested during the first testing session.  For moly-coated bullets in the 168 to 180 grain range in the 7mmBR, VarGet has shown to be the powder that delivers high MV’s and great accuracy.  However, with naked bullets, N150 is looking mighty good.  If you think the 7mmBR does not have the stuff to whack rams, the N150 produced MV’s above 2,500 fps with no pressure problems.  As a matter of fact, the heaviest charge tested, 35.0 grains of N150 produced an average MV of 2,521 fps.  Probably the case will accommodate 36.0 grains of powder, but I don’t know if pressure problems will make loads heavier than 35.0 grains of N150 unsafe in my rifle.  From extensive experience it has been shown that a bullet like the 175 Sierra MK only needs to be launched to 2,300 fps to be more effective on rams than the hottest 260 Remington out there, and I do mean that in spades.

Group sizes were very consistent in the ¼ MOA range with the 175 Sierra MK and charges of N150 from 32.5 all the way to 35.0 grains.  This is the kind of result that I like very much as it shows that temperature variation will not affect groups size if the middle of the charge range is used for match loads.

During the first testing session, 26.0 grains of H4198 was the heaviest charge used with the 139 Hornady SST’s.  That charge produced a ¼ MOA group.  Today 26.5, 27.0 and 27.5 grains were also tested.  26.5 grains also produced a 1/4 MOA group.  27.0 was a bit larger in the 1/3 MOA range and 27.5 grains opened up to a bit over 1/2 MOA.  From this series of tests with H4198 and the 139 SST’s the sweet spot for this rifle is between 25.5 and 27.0 grains.  My preference would be for loading somewhere between 26.0 and 26.5 for the match load, probably 26.5 grains.

Remington 7 ½ primers were used with VarGet and the 175MK’s.  Three heavier charges were tested above the first testing session.  The reason the Rem primers were used is because the F205’s were cratering with 32.5 grains of VarGet.  This session 32.5, 33.0 and 33.5 grains were tested.  The 33.5 grain load showed cratering similar the 32.5-grain F205 load.  Average MV was 27 fps higher than when F205M primers were used with the 32.5 grain load of VarGet.  Accuracy was in the 1/3 to 1/2 MOA range for all three loads.

At this point, N150 looks to be the powder of choice for the 175 Sierra MK’s.  Some more testing will be done with N133 and the 139 SST’s as well as some N150 and 177 Cauterucios.

[Troy G]

Very interesting results Dan.  What barrel manufacturer are you using with this new toy?  

Any testing of the 500 series powder in the future, not that it would be really necessary anyway but . . . ?  I never would have imagined that you could get that much velocity out of a standard BR case.  :shock:

Thanks for keeping us posted on the results.

[DanDeMan]

Troy,

The 7mmBR/TPP is barreled with a 26", #5 taper, Shilen Match, 8-twist barrel.

After considerable testing with the N500 series powders I will not be testing them.  They are too temperature sensitive as are all double base powders.

At this point charge between 32.5 and 35 grains of N150 under the 175 Sierra MK's would be my choice for a Ram load.  The CTP load will be played with a bit more as I want to see what N133 does in the 28 to 30 grain range.

[Gringo Grizzly]

Dan,
I've enjoyed following the progress of your testing with the new 175 SMK.

I used the 7BR when this cartridge became popular back in the mid-80's.

Even with 168's, my ram dropping % was pretty good.  In fact, as good as the .260 I've been using of late.
This % could be due to the targets that I shoot - as our most recent family of rams (purchased about 4 years ago) are notoriously tough to knock down vs the targets we were shooting at way back when.

My only problem with the BR was that although accuracy was great at short range, I had quite a bit of vertical dispersion out at 500, something I then attributed to low velocity.

I wasn't running these nearly as fast as you are though.
My load of 28.5 H335/168 was doing well to get 2250 fps from the muzzle.
Neither Varget or N150 even EXISTED at that time.
I'm hoping you'll do some testing at long range with the 175 smk to see how accuracy holds up.

A side benefit of using this cartridge would be increased barrel life.
Moly or no.

Gringo

[DanDeMan]

Gringo Grizzly,

You said:

"My only problem with the BR was that although accuracy was great at short range, I had quite a bit of vertical dispersion out at 500, something I then attributed to low velocity."

My current thinking on the vertical dispersion you talked about above is that the probable cause is low bullet stability.  What barrel twist were you using to launch the 168MK at 2,250 fps?  Marginally stable bullets are greatly affected by atmospheric conditions tipping them into instability at times.  Low bullet stability also means that the bullets are greatly affected by the wind, not a good thing.  I've been working on the bullet stability issue for longrange BPCR match shooting and have developed a deep appreciation for how important that is.  Using a 6PPC benchrest mentality for longrange shooting concerning bullet stability is not a good idea given what I've seen from extensive testing in both HP and BPCR.

I even think a 7TCU, properly throated, would be a real winner for the recoil shy.  I'm thinking that one could launch the 175 Sierra MK's to about 2,250 to 2,300 fps with the right tinkering.  Lapua brass would need to be used as the Rem and Win brass would not hold up to that high of a pressure.  The primer pockets would be toast after just a few firings.

I plan on shooting groups at 500 meters this week so we shall see how the 100 yard accuracy predicts 500 meter accuracy.

[eroyd]

Why not stick with the 175gr's for everything with lighter loadings for CPT's as discussed in your "ultimate hunting rifle" thread?

[Gringo Grizzly]

Dan,
I think that barrel was a 1-9" twist/ W Leek taper 7BR, chambered at Hart's facility.
It was certainly accurate out to the turkeys using 150 SMK's.
The 168's could indeed have been on the "fringe" with the 1/9.

If my aging memory serves me correctly, I was using Remington BR brass with small rifle primers, and my choice at the time was CCI BR.

Since a slower bullet is also prone to drift more in the wind, even if the twist rate WAS ok,  my problems could have been a combo of the two factors.

In the early days of silhouette shooting in Tx, some of my friends used the 175 grain Sierra HUNTING bullet on rams from their then-new 7/08's - with good results.

The new bullet should be even better and akin to hitting a ram with a telephone pole!
At least one good shooter here in Pa is using it from his hunter with good results.

Gringo

[DanDeMan]

Why not stick with the 175gr's for everything with lighter loadings for CPT's as discussed in your "ultimate hunting rifle" thread?

Eroyd,

This is not my rifle so I'm load-testing as was agreed to by the rifle owner.  Shooting the 175 MK's at say, 1,800 fps would be a neat way to go.

[DanDeMan]

Guys and Gals,

It seems that a few have misunderstood what I was trying to say about the very fine, high performance Hunter stock that Mark Pharr designed and has manufactured.  When I said it was flexible, the stock was being compared, in my mind, to a heavy, stiff type of stock designed for bench work of which I shot quite a few.

I personally have a kevlar Brown Precision Hunter HP stock that is way more flexible than the Pharr stock.  It was that stock and the old Remington plastic stocks we used to use in HP Hunter that motivated me to remove the stop post on my front rest so the stock could be moved forward so that the recoil lug was at the back of the front pedestal.  With the Brown stock I couldn't hardly shoot a MOA group with the front of the forend aginst the stop post on the front rest due to forend flex.

The Pharr Hunter stock is the stiffest, lightweight, high performance stock I've ever used, no if's and's or but's.

[Troy G]

Dan, not to mention the fact that Mark is one helluva nice guy to all his customers whether you are Troy Lawton or Troy Nobody.  

[DanDeMan]

Good Evening,

One more go at load-testing with the 7mm BR/TPP was undertaken today.  The first two testing sessions certainly showed the top-flight accuracy of the rifle built by the one and only Marvelous Marvin, AKA, The MetalHead.

About 80 rounds have been fire-formed with a load of 24.0 grains of H4198 Extreme and the 168 grain Sierra MK.  Only about 15 were shot off the bench to break the barrel in with the shoot-clean sequence.  The Shilen Match barrel did not require much work to get it shooting.  The rest of the fire-form rounds were shot off-hand.  Man, this stock and The MetalHead’s trigger setup is to die for.  Dang, why have a Standard Class when you can shoot a rifle like this.  Mr. MetalHead milled the bottom of the titanium Remington action to accommodate an Anschutz 2-stage trigger.  Dudes and dudettes, this trigger will pickup my 2 lb, 2 oz weight and I still have to jerk the rifle to get the trigger to go off AND the second stage feels like it is 4 to 6 oz, way no fair by a long shot, sorry about the bad pun.  The MetalHead’s setup for the Anschutz trigger has no mickey mouse bracket or other junk.  This is the real deal with a specially designed cocking piece and state-of-the-art milling that includes a great Nesika Bay bolt release.  Not cheap, but if you want the best and you’ve tried the rest, this is your deal.

Today’s testing was all about determining what N133 would do accuracy-wise with the 139 SST’s by Hornady.  I was not disappointed to say the least.  Loads from 28.0 grains up to 30.0 grains in 1/2 grain increments were shot at 100 yards over the chronograph.  I’ve got to say that N133 sure showed its stuff.  Accuracy was excellent for all charges with 28.5 grains, producing a MV of 2,407 fps, came in at just over 0.20” with a velocity extreme spread of 8 fps for a 5-shot group.  I could ask for more!  At the other end of the powder charge range super accuracy was yet again attained.  This load produced a round 1/4 MOA group with an average MV of 2,528 fps and extreme spread of 10 fps.  I’m partial to the 28.5 grain load for reduced recoil

This exercise in load development was a kick, reduced that is, and the metal work and stock show what is possible if one goes with one of the top silhouette gunsmiths.  There are many top gunsmiths, but after years of having match rifles built I strongly suggest always going with a specialist that shoots the game.  I must say in the past I had a top smith from one shooting discipline build an Across-the-course match rifle and totally screw the pooch and I mean BIG time.  It was a painful experience for both my shooting pard and I as we both got the screw.

The recoil acceleration testing as well as 500-meter accuracy testing still remain.  But right now, match loads are a done deal.  For CPT the 139 SST by Hornady ignited by the F205M primer powered by 28.5 grains of VVO N133 and the 175 Sierra MK’s ignited by the same primer and powered by 33.0 grains of VVO N150 are my choice.

[Troy G]

After all this testing do you think it would be possible to post some pictures of the rifle and the metalwork?

[DanDeMan]

Troy,

Marvin and I will be writing an article about the build, break-in, load-testing and ballistic analysis to be published in the near future.  Marvin just sent a CD with pictures of his part of the deal, The Build.

[Troy G]

Dan,

Where is the article going to published?

Was hoping to see the trigger mod Marv is doing so that one does not have to use the Briley adapter for the Anschutz trigger.

Would also be nice to have a bolt release when using the Annie trigger.

Troy

[DanDeMan]

Troy,

I was thinking of submitting the 7mmBR / TPP article to Precision Shooting.

I'm sure Marvin took some pictures of the bottom of the action with the Anschutz trigger.  I'll send a copy to you when the CD with the pictures arrives.