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Tundra Class

(New Photos of Tundra Magnum 6-13-01.... ctr. of page)

(mini-article ... "Balancing your PCP rifle" ... btm. of page)

page 3

The Tundra Class prototype (with optional barrel shroud)

Back to the Range

Field Testing Continues 3-12-01

Wanted to try various slugs and power ranges. Also - test differences between internal reservoir groups and regulated feed groups.

That's a 50 Yard 3 shot group - 140 grain cast slug @ low power (approx. 185 ft. lbs.)

Here's a slightly different Regulator hook up I wanted to try. This is the typical 3,000 psi braided stainless hose we often use for fill lines. A gentle crescent loop like this seems to be tolerated with the Bi-Pod set up @ 50 yards. I was shooting the groups with the line attached. Reg. refills for each shot in this set-up.


Tundra ... one sweet Magnum

The Tundra Magnum

I've had to wait my turn ... this one's mine.

 

It's a very heavy, long range bench rifle. Accurate target shooting is the game.

Careful... color laminated stocks have been known to cause "whiplash" double-takes upon opening of rifle case ...

 

A real treat to shoot. I like that big Tasco Custom Shop Side Wheeler too ... that adds another ten pounds or so ... ha ha

I had a number of slug designs with me for a range session today. The Tundra Magnum liked several of them. This was a three shot group of "Raptors" @ 50 yards.

I enjoy shooting with the tank regulator at the bench. BUT ... I wanted to show you that the internal valve regulates just fine as well. (This was the end of a long session - excuse the plugged target. I just shot at a previously repaired clean target face).

What we have here are shots #2,3,and 4 @ 50 yards from a fill. You can clearly see that relative velocity was nearly identical for shots 1-4. Power was set around 350-400 ft. lbs. I'd used shot #1 for another purpose ... below

 

I've been challanged to a good natured contest @ Standing Stone.

Shooting cans off-hand @ 50 yards. The fella is a great off-hand shot and I'm not. But ... thought I'd try it. Now ... remember, this is a very heavy bench rifle ... As I swayed in the breeze, right before my back gave out ... the can went by the scope one more time and I squeezed. Pure luck but don't tell ... This was shot #1 of the string above.

 

These exact Legacy Tundra Models are not currently available for order - however; a new version of the Tundra Class will soon be available for order - check the catalog pages please


Mini-Article: Balancing Your PCP

For "Internal Reservoir Groups" (those shot off of the rifle's reservoir - no line hook up), you must establish the "plateau" of your reservoir fill and power range balance.

To do this by shooting groups: You shoot all of your shots, at one point of aim, at a distance relative to the power of your rifle. I like to use 50 yards. Having shot off ten shots, several of them will cluster together (because of the relative velocity consistency of those shots - we're assuming you've done enough range work to be confident that you are shooting well and have a proper slug which matches your rifle). If you shoot ten shots and numbers 4 thru 8 are all clustered together - while shots 1 thru 3, and 9 and 10 are scattered somewhat; you can pretty well determine that numbers 4-8 were on your "plateau" for this power range and slug balance. On the other hand, if you get a random clustering such as 1-4-7-10 clustering - you either have inconsistent bullets where some fly well and others don't, or else just dumb luck placed some holes close together. A clustering must be of consecutive shots to be of any use.

To do this with the chronograph: Fill the rifle and shoot a long string of shots across the chronograph. Record each shot's velocity. If it's possible to balance your rifle at all, you will find a peak cluster of velocity figures which hover tightly together. The quality of the engineering in your rifle will determine the balance possible. An unbalanced rifle will just start out at high velocity and fade and fade in a descending curve. If all of the shots are at a vastly different velocity, you will not be able to compensate for this and groups will dramatically suffer.

As you know, one of the concepts behind my design of the Tundra Class, was to offer a variable power range pcp rifle. If you are not a PCP designer, you have no idea how difficult this is. (More on that later - that's a whole story in itself). Let's just say that I'm pleased that the Tundra can provide world record PCP power levels AND ALSO balance out to shoot mildly at more sedate levels.

For the purposes of testing, I've set minimum levels where I feel a 45 caliber pcp rifle is appropriate. For the sake of reasonable trajectory, I've set an approx. velocity minimum of 671 fps. (I like this magic figure where the power output in foot lbs. equals the projectile weight in grains - Examples: 22 grains @ 671 fps. is 22 ft. lbs., and 200 grains @ 671 fps. is 200 ft. lbs.) The velocity of 671 fps. is also fast enough to offer good trajectory. This is very important for shooting at variable distances. As well; it's pointless to balance out a 45 caliber pcp rifle at such a low range that it's of little use. I could keep going down and down in power, and get more and more shots per fill. I could show you longer and longer strings of relative velocity figures. But; what's the point of doing so at power levels which can easily be duplicated by smaller caliber pcp rifles? I can produce over 200 ft. lbs. in 32 caliber. Therefore; with these items in mind, I set out to examine the balance characteristics of my own Tundra Class design.

From my limited testing of the Tundra Class to date (about three weeks when this article was written), I've quickly been able to balance the prototype rifle for a 200 grain slug at minimum levels. That gives me a 200 grain SWC slug with an average of 679 fps in a string of 5 shots that does not vary more than 36 fps. Five relatively level shots @ 204.8 ft. lbs. is quite usable.

In addition, a 156 grain custom slug will fly @ an average of 741 fps. The Tundra will balance for them and provide 5 shots within 39 fps @ 190.2 ft. lbs.

I've saved one of the Best Features - The quoted balance figures begin with a fill pressure of only 2,350 psi.! How would you like to have your tanks useful down that far? As you know, when you have a rifle which requires 3,000 psi for a fill (especially a big bore), you only get just a few full fills out of your tank before it fades and requires you to "short fill" your rifle to keep shooting.

As you think about it, you'll note that this section is talking about setting the Tundra down to it's lowest practical range and STILL producing strings of 200 ft. lb. shots WHILE only filling to a relatively low 2,300 psi.

Then, don't forget; within a couple of minutes, you can reset the Tundra to blast out over 400 ft. lbs. if you wish! This is the impossible rifle everyone has asked about for years.

Much of the above process should remind you of charting out a FT rifle or Sporter. You record the velocity figures for your entire reservoir's number of shots. Determine which few are the closest in velocity. You fill to the psi level which starts you off on that plateau and you then shoot the number of shots on the plateau. With a FT rifle (which is only porting perhaps 1/60th of it's total reservoir for each shot) you might have 30+ shots up on that plateau, that are level enough in velocity to work with.

It's a much larger job for a Big Bore. You may only have 10 shots to begin with (when your rifle is producing significant energy of 200+ ft. lbs.). You can see that, if you are porting 1/10th of your total stored reservoir with each shot, compensating for that vast volume loss with each shot is difficult. That's why it's a far simpler task to achieve single digit shot to shot velocity figures for small bore, then it is to get the above posted figures with Big Bore.

The above figures are only the results of early testing and tuning. Even so, it's clear that my design goals have been achieved. Tundra Class is the Beast who can also attend the Ball.

Direct e-mail link: Tundra3@glbarnes.com