Min velocity for Rams w/ 168gr SMK in a 7-08

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Re: Min velocity for Rams w/ 168gr SMK in a 7-08

Post by cslcAl »

Snake,

When I started shooting silhouette back in '81, I was told a reliable ram load needed at least 1100 ft/lbs. of energy. I guess my answer to the topic's question would be 2560 fps. Using Sierra's V6 program 2560 fps. equates to 1103.8 ft/lbs of energy.

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Re: Min velocity for Rams w/ 168gr SMK in a 7-08

Post by DanDeMan »

cslcAl wrote:Snake,
When I started shooting silhouette back in '81, I was told a reliable ram load needed at least 1100 ft/lbs. of energy.......Al Foust
Al,

Terminal energy is a terrible metric with which to access ram knock-down performance because it goes by velocity squared, which skews the results in favor of light, high velocity bullets, which we know don't do well on rams. Momentum plus bullet toughness are way, way better at predicting ram knock-down performance. To get to the grist of my statement, here are two examples.

107 SMK, 6mm @ 3200 MV with terminal velocity at rams used for calculations: Energy=1.193, MO=1.065

177 Caut, 7mm @ 2,300 fp MV with terminal velocity at rams used for calculations: Energy=1.103, MO=1.317

As you can see, the 6mm load has a higher terminal energy, but the terminal momentum is in favor of the 7mm load by 23%. HOWSOMEEVER, the bullet toughness difference is off the Richter Scale, with the 177-gr Cauterucio being so far out in front of the soft-azz 6mm SMK that it's not even funny.
Last edited by DanDeMan on Fri May 04, 2012 12:32 am, edited 2 times in total.
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Re: Min velocity for Rams w/ 168gr SMK in a 7-08

Post by DanDeMan »

Al,

I just couldn't help myself :lol: :lol: :lol: , so here are the 6mm, 107 SMK vs the 7mm, 177 Cauterucio in a Smash-a-thon. The 6mm SMK load had a higher terminal energy, with the 7mm C getting the edge on terminal momentum. But, this picture shows the down and dirty truth with regards to what will work best at putting rams in the dirt more often than not.

107 SMK, 6mm @ 3200 fps: En=1,193, MO=1.065
177 Caut, 7mm @ 2,300 fps: En=1,103, MO=1.317

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Re: Min velocity for Rams w/ 168gr SMK in a 7-08

Post by cslcAl »

Dan,

Let me add to my previous post the 500 meter terminal momentum is 1.23 for a 168 SMK launched at 2560 fps. with 1103.8 ft/lbs. of energy.
Also I totally get the importance of momentum over energy. I have been playing with the Sierra V6 ballistics program plugging in different manufactures bullets at like velocities and the differences in momemtum is very interesting.

I think what would make this a lot clearer is if we had a minimum terminal momemtum figure instead of an energy figure. It is really not that hard to grasp, it's just changing 30 years of thought process that's tricky. The energy figures seem to be easier to understand because they are larger numbers. The momemtum figures are smaller and the increases are less, so it may not seem like a .19 increase is very much.

I asked the question before about how much is a significant increase in momentum. Could you explain this so we could understand better? This may not seem to some to be on topic, but right amount of velosity with the proper bullet will give the terminal momemtum needed to reliably knock down rams.

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Re: Min velocity for Rams w/ 168gr SMK in a 7-08

Post by DanDeMan »

cslcAl wrote:...Could you explain this so we could understand better? This may not seem to some to be on topic, but right amount of velosity with the proper bullet will give the terminal momemtum needed to reliably knock down rams.

Al Foust
Al,

We are back to bullet toughness, which has a substantial impact on a bullet's ram performance. And, I might add, also has a substantial impact on recoil because we can shoot tough bullets slower and thereby collect much less recoil and still knock rams silly. One of my old, 7mm, 8-twist rifles, with a min cartridge, only had a recoil of 8.5 ft-lbs but still cracked the rams like no other rifle on the line that typically had 50% more recoil. Say a 140 Berger and 139 Scenar are fired at rams, launched by the same MV. Both will have more or less the same terminal momentum upon impact with a ram. But, due to the Scenar's tougher composition, it will, in the long run, perform better at ram knock-down. And, I suspect, if we shoot the 6.5mm, 140 SST's at rams they'd do even better, even at the same terminal velocity due to their very robust bullet construction.

In the example previously stated that used the 107-gr, 6mm SMK vs 7mm, 177-gr Caut, even though the momentum difference is 0.25 lbs-sec, the bullet toughness difference is even more meaningful.

As to a meaningful difference in momentum between bullets, 10% is meaningful, but bullet toughness is even more important. If I was going to pull a number out of the proverbial hat (backside,) I'd say a terminal momentum of at least 1.20 lb-sec is advisable if one is shooting a "tough" bullet. Personally, I like 1.30 or higher just to be on the safe side at the ram line. But again, bullet toughness is king at the ram-line.
Last edited by DanDeMan on Fri May 04, 2012 2:25 am, edited 1 time in total.
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Re: Min velocity for Rams w/ 168gr SMK in a 7-08

Post by cslcAl »

Dan,

I am sure that back in the day someone shooting a .308 came up with the 1100 ft/lbs. figure based on shooting experience versus any hard scientific testing. If you feel comfortable with a momentum figure of at least 1.20, that's good enough for me.

If we can reference that going forward and use some common sense with bullet selection our ram failures should decrease.

MOMENTUM RULES RAMS LOSE!!!!! That would look good on a tee shirt.

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Re: Min velocity for Rams w/ 168gr SMK in a 7-08

Post by cslcAl »

Hey Dan,

How's this sound; let's rename terminal momentum for rams "Ramentum".

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Re: Min velocity for Rams w/ 168gr SMK in a 7-08

Post by DanDeMan »

cslcAl wrote:Hey Dan,

How's this sound; let's rename terminal momentum for rams "Ramentum".

Al
Al,

Me likes. :P :P :P Ramentum it is. I just clicked on it to add it to my "Dictionary" on this site. After reviewing 6.5 and 7mm ram loads, that I know worked well over the past 17 years, I'm even more convinced that a Ramentum of 1.2 lb-sec coupled with a Known Tough Bullet (KTB) will give the shooter an extra level of ram knock-down performance. My best ram-killers had ramentums in the 1.30 to 1.35 lb-sec range shooting 180 JLK's or 177 Cauterucios. Those loads never, and I really mean never lost a ram; even at ranges with notoriously hard to knock-down rams. But, given crappy stands, bowed rams, heavy headwinds holding-up rams as well as mud on the feet and stands, one will ring rams no matter the round, short of a 30-06 launching a 220 SMK as fast as possible....major OUCH!!!...just thinking about it.

30-06 launching a 220 SMK to 2,500 fps: 1.752 lb-sec ramentum, recoil = 22 ft-lbs, wind deflection = 3.7 MOA. So, recoil is about 2.5 times the underdevelopment 7mm and wind deflect is a bit higher. Man, bullet efficiency in the wind as well as knocking-down the rams is where it's at. And, I'd be willing to wager that the 7mm under development will not lag the shoulder-destroying 30-06 load at ram performance by much.

We want a high "Ramfficiency;" that is a Ramentum divided by recoil.

The Best Coast R&D Ballistics Research Lab is currently developing a minimum recoil round for top ram performance. Current estimates are that just 29.0 grains of VarGet should propel the 177 Cauterucios to a ramentum of about 1.35 lb-sec. Recoil is estimated to be a paltry 9.1 ft-lbs out of a 10 lb rifle. For comparison sake, a 260 launching a 139 Scenar to 2,800 fps has a ramentum of 1.23 lb-sec and recoil of 11.1 ft-lbs. The wind deflection estimates for both rounds show that the 260's bullet will deflect, at the ram line, about 3.4 MOA in a 10 MPH crosswind while the 7mm-min-recoil round will deflect about 3.5 MOA.

So to summarize, the 7mm round under development will wind deflect about 1/2 of an inch more at the ram line, but have a ramentum that is (1.35 - 1.23) / 1.23 = 10 % higher and have a recoil that is about 22% lower. BUT, the 177 Caut is so much tougher than a 139 Scenar, that I'd be willing to bet that ram performance is much, much higher than the 10% increase in ramentum suggests. Here's a picture to get my point across.

-------------------139 Scenar-----------------------177 Cauterucio
Image
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Re: Min velocity for Rams w/ 168gr SMK in a 7-08

Post by bugabob »

Shot 36 and 38grs of Varget and 168 SMKs at 500m ram swinger today from a lead sled. Strong gusty wind at my back. Lighter load 5 shot group was roughly 6" and heavy load 8". Then shot several times from standing position and did fine with both. Will try the 36 gr load if I ever shoot in a match. This load dropped almost a foot more than the hotter load at 500m.
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Re: Min velocity for Rams w/ 168gr SMK in a 7-08

Post by EQ Guy »

DanDeMan wrote:
cslcAl wrote:Hey Dan,

How's this sound; let's rename terminal momentum for rams "Ramentum".

Al
Al,

Me likes. :P :P :P Ramentum it is. I just clicked on it to add it to my "Dictionary" on this site. After reviewing 6.5 and 7mm ram loads, that I know worked well over the past 17 years, I'm even more convinced that a Ramentum of 1.2 lb-sec coupled with a Known Tough Bullet (KTB) will give the shooter an extra level of ram knock-down performance. My best ram-killers had ramentums in the 1.30 to 1.35 lb-sec range shooting 180 JLK's or 177 Cauterucios. Those loads never, and I really mean never lost a ram; even at ranges with notoriously hard to knock-down rams. But, given crappy stands, bowed rams, heavy headwinds holding-up rams as well as mud on the feet and stands, one will ring rams no matter the round, short of a 30-06 launching a 220 SMK as fast as possible....major OUCH!!!...just thinking about it.

30-06 launching a 220 SMK to 2,500 fps: 1.752 lb-sec ramentum, recoil = 22 ft-lbs, wind deflection = 3.7 MOA. So, recoil is about 2.5 times the underdevelopment 7mm and wind deflect is a bit higher. Man, bullet efficiency in the wind as well as knocking-down the rams is where it's at. And, I'd be willing to wager that the 7mm under development will not lag the shoulder-destroying 30-06 load at ram performance by much.

We want a high "Ramfficiency;" that is a Ramentum divided by recoil.

The Best Coast R&D Ballistics Research Lab is currently developing a minimum recoil round for top ram performance. Current estimates are that just 29.0 grains of VarGet should propel the 177 Cauterucios to a ramentum of about 1.35 lb-sec. Recoil is estimated to be a paltry 9.1 ft-lbs out of a 10 lb rifle. For comparison sake, a 260 launching a 139 Scenar to 2,800 fps has a ramentum of 1.23 lb-sec and recoil of 11.1 ft-lbs. The wind deflection estimates for both rounds show that the 260's bullet will deflect, at the ram line, about 3.4 MOA in a 10 MPH crosswind while the 7mm-min-recoil round will deflect about 3.5 MOA.

So to summarize, the 7mm round under development will wind deflect about 1/2 of an inch more at the ram line, but have a ramentum that is (1.35 - 1.23) / 1.23 = 10 % higher and have a recoil that is about 22% lower. BUT, the 177 Caut is so much tougher than a 139 Scenar, that I'd be willing to bet that ram performance is much, much higher than the 10% increase in ramentum suggests. Here's a picture to get my point across.

-------------------139 Scenar-----------------------177 Cauterucio
Image
I ran into Dan at the local rifle range about the time he was posting this. He was working with two wildcat’s based on the 204 Ruger. One was a 6.5 mm and the other was a 7 mm. I assume this is the cartridge he was referencing above. This was the last time I saw Dan and I wish I had paid more attention to his wildcat’s.
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Re: Min velocity for Rams w/ 168gr SMK in a 7-08

Post by Snake »

For what its worth....I shot a 600 yard bench rest match with my silhouette rifle ( Pac-Nor 3 groove 8 twist .310 neck ....yes..the case necks are turned to .011) 168 gr MKs 39 grs XMR 4064 Federal primers and Winchester cases...That chamber was with a reamer made for Winchester cases ..it shot a 5 shot 2.8 in group (I placed 8th!)
So far the best ram load is the 175 GK on top of 37 grs XMR 4064 (about 2350+ fps). However a cursory test has shown great promise in the new 160 gr TMK over 38 grs Varget or XMR 4064....more on this later as OMalley and will be experimenting :-o
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Re: Min velocity for Rams w/ 168gr SMK in a 7-08

Post by Snake »

Today...OMalley and I conducted an informal test of the 7mm 160 TMK Sierra. With 38 grs of XMR 4064 in Lapua cases (fitted necks) and CCI Br primers .....the chrono said 2534 average FPS for 4 shots and 2 SD. We placed 3 fat legged rams on the center of the rail (not on the pads). We shot for that area 2 inches in front of the wheezer and 1 inch into the body. Ram #1 ...1 shot and down Ram#2 was a ringer and #3 1 shot and down. Allowing for the fact that the rail is wider than the feet....I'm pleased. Plus my elevation was a full minute lower :D
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Re: Min velocity for Rams w/ 168gr SMK in a 7-08

Post by cslcAl »

Snake<

Sierra Bullets, what else can I say.

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Re: Min velocity for Rams w/ 168gr SMK in a 7-08

Post by SteveD »

Snake wrote:Today...OMalley and I conducted an informal test of the 7mm 160 TMK Sierra. With 38 grs of XMR 4064 in Lapua cases (fitted necks) and CCI Br primers .....the chrono said 2534 average FPS for 4 shots and 2 SD. We placed 3 fat legged rams on the center of the rail (not on the pads). We shot for that area 2 inches in front of the wheezer and 1 inch into the body. Ram #1 ...1 shot and down Ram#2 was a ringer and #3 1 shot and down. Allowing for the fact that the rail is wider than the feet....I'm pleased. Plus my elevation was a full minute lower :D
Not sure why you would be happy with a 33.3% ring ratio.

Although the spot you picked is one of the worst, things are even tougher around the front leg. This is a map for a Smallbore Ram. I have taken a few measurements on a High Power Ram and the numbers seem to correlate.
Smallbore ram force map.jpg
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Re: Min velocity for Rams w/ 168gr SMK in a 7-08

Post by Snake »

As I pointed out the rams were set ON THE RAIL.....not the pads. The rail is 2" wider than the feet on the ram. Set on the center of the rail we should have had more ringers; we were trying to induce ringers. BTW as most will tell you hitting the front leg or the 'arm pit' area of the front leg and they go down...experience belies the assertion that the front leg is a 'bad' spot'
The 'ringer' was moved far enough on the rail that it probably would have gone had the target been set on the pad. A few targets have a curvature mid body from repeated hits....the more pronounced that bend the more problematic viscera hits....and if we have a north wind....well, then all bets are off
I'm happy with the results. The variables are very difficult to control or adjust for...especially bullet jackets and core bonding. But in comparison to the relative size of the 22 projectile to the rimfire target vs. the relative size of high power projectiles to high power targets...its understandable why there are no rimfire ringers
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