.375" on a CheyTac

#5
Re: .375" on a CheyTac

I have tested a longer version than the one Later has. They are being fired from a Lawton 8 twist screwed on an 8000 action.These bullets are 431 gr. and I have pushed them to 2965 fps with 150 gr US869. This is much faster than expected. There were slight ejector marks and the bolt was a little sticky however the primers showed no signs of excessive pressure. 145 gr US 869 pushed them to 2900 and the ES was in the single digits. I did all the testing with 3 pcs of the new brass marked 375 Chey Tac. I did this to see how many loads they would take before failure. I am at 32 loadings and they are still good, no split necks and the pockets are still OK. I had stability issues at the higher velocities and Noel is tweaking the design to resolve the problem. At lower velocities accuracy is very good. One three shot group at 600 yd went into 1.5 inches ( 1/4 moa ) several groups at 1020 yds were sub-half moa. I did have trouble with ES when shootig at lower velocities. ES on thes loads was around 20 fps and show the expected verticle stringing at distance. There is almost zero fowling in this barrel firing these bullets. After firing 10 rds I run a wet patch through 3 times then let it set all night. Prior to firing the next day I run a dry patch through. There is usually a trace of blue on the first pass. After that no blue can be detected. Another surprise is that they group well at 100 yds, they usually run in the .3 - .4 range. All in all I am of the opinion that this system is going to take ELR shooting to the next level. I expect the tweaked rds to be delivered in a couple of weeks.
 
#7
Re: .375" on a CheyTac

I am waiting on a BAT M action to have Kirby Allen build a 375 Allen Mag for me (improved 375 Chey Tac). Bullet wise, Sierra does (or did) a special run of 350 Match Kings for the 375. Kirby is getting around 3300-3400 in a 30" Lilja tube with this combo. Rumor is that a 385 version bullet is in the works if a guy can get a deal to go through to make the custom bullet to help with the BC. Should be a real hammer.
 
#10
Re: .375" on a CheyTac

Noel, the group at 600 was three shots and there was a crosswind from 10 to 6. The United States Flag flying over my Dads grave was used to time it. The wind was fairly predictable that day. As stated before I certianly dont expect to do this routinly. Quarter min. is hard enough to do at 100 with no external variences. The groups at 1020 was fired with a 2-3 mph wind with frequent lulls near zero. I feel like the 1/4 min three shot group at 600 in the wind was a result of some skill, an excellent rifle, good optics, high BC bullets, luck of drawing three rds in a row of identical velocities, and maybe the accuracy Gods smiling down and helping one factor off-set the shortcomings of another. Anyway it happened and it may not mean anything to any one else but me. From these test I came away with the belief that we are on the brink of seeing a system that is going to allow long range shooting to take a pretty long step foward. The success of this system is bigger than any one person, it will take many people spending the money to aquire the equipment to get in this game and deciding for themselvs if it is a big enough step foward to justify the cost. Again, one must ask the question ( Is the price of eggs worth the wear and tear on the hens ass? )
 
#11
Re: .375" on a CheyTac

I recieved some of Noels tweaked 375 gr solids, these were shooting .3 moa at 100 yds up to 2800ish. Groups began to open up after that and were tumbling at 2900. These are 421 gr copper and I pushed them past 3000 fps with US869. I did not test at distance. If you re-call the first bullets I tested a couple of weeks ago were becoming unstable at around 2600. The nose and tail was changed slightly and the stability improved significantly. I also shot some of the Vikings that Lutz sent over from Germany. I could not get them to stabilize out of my 8 twist barrel. They were tumbling at all velocities and some of them were missing a 4'x4' target backing at 100 yds.
 
#13
Re: .375" on a CheyTac

Yes,Noel is working on the problem, some of the problem has been fixed due to the change Noel did to the nose and tail. The second prototype was far more stable than the first. I think the rest of the problem is in the design of the first bands. I dont think they are strong enough to stand the initial shock as evidenced by recovered bullets. The next ones will have a small bearing surface on first contact. These will be made to eliminate the possibility of band failure. There may also be a problem with the 8 twist; however, I dont think this is the case. Noel may cut the new ones today so I should have them early next week. If the bearing surface allows the bullets to be pushed to the capacity of the case with stability, it will just be a matter of making the bearing surface as short as possible while retaining the desired effect.
 
#16
Re: .375" on a CheyTac

If they are stable at higher velocities we should neck down a .50 to .375/50 an see how fast it can go.

I can supply a .50 McM Fisher Action, and some brass
smile.gif
 
#17
Re: .375" on a CheyTac

Fredo, I have some of the 6.5 cal. bullets and have fired some of them out of the 8 twist. They are 400 gr and I pushed them to 3200. They also became unstable above 2800 fps. I believe their issues are not twist related because they become unstable at the same velocities as the 7 cals. I think the bands may be the culprit and the prototypes I get next weeks should tell the tale. Notaguru, Thanks Ill be looking for them.
 
#18
Re: .375" on a CheyTac

Also I want everyone to know I fired some of these without a brake to insure there was not a problem in that area. I would not recommend this practice unless you have a long eye relief scope and a fetish for self abuse.
 
#19
Re: .375" on a CheyTac

Haha...I still laugh that I forgot to replace the muzzle brake on my .408 Windrunner one day and got bonked pretty good.
 
#20
Re: .375" on a CheyTac

Anyone shot any of the TTI 300 grain Spritzer 408CT rounds and if so with what results? I had some but never got the opportunity to practice with them unfortunately. regards, Dale.
 
#21
Re: .375" on a CheyTac

I shot some 6.35 calibers this weekend and had to pack it up before i finished. But they were not tumbling and shot fairly nicely. I will be getting some more down next week i hope. Might even do some this weekend if i get some in time.

Oh and aug I am going to send some 119's with those RMB bullets for you to try.
 
#23
Re: .375" on a CheyTac

How is Cumberland Range? are there cover firing ports? how many slots? does it get crowed? I belong to Cherry Ridge it is only 30 mins. from me
 
#24
Re: .375" on a CheyTac

Update- I shot some of the latest 7 cal. 375 bullets from Noel today. These have a .125 bearing surface for first contact. The rest of the bands were not changed. To make a long story short, the results were identical to prior tests.
I also had the oppurtunity to shoot more of the 6.5 cal. versions, after firing a number of these a pattern began to emerge. These are staying stable at a little higher velocities than their 7 cal. cousins. It appears that they will stay stable about 75 fps longer than the 7 cal. As stated before the test barrel is an 8 constant twist. In light of the revelation that the 6.5s are indeed stable at higher velocities than the 7s I may have to revise my assessment to include that twist rate may be causing the problem. It does seem that if the twist is too slow, the projo should become more stable as the velocity increases. Obviously, in this case the reverse is true. Sooo, it looks like a seven twist is the next step. There are some 338 gain twist barrels about to be ready to test so I think I will wait to see what is learned before proceeding. In the meantime I intend to do testing at distance with the 6.5 400 gr and the 7 421 gr. at their stable velocities
 
#25
Re: .375" on a CheyTac

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Augustus</div><div class="ubbcode-body"> It does seem that if the twist is too slow, the projo should become more stable as the velocity increases. Obviously, in this case the reverse is true. Sooo, it looks like a seven twist is the next step. </div></div>

Not that I know anything, but this statement appears to contradict itself. Since the bullets are become less stable as the velocity increases, do you think the 8 twist might be too fast and a 9 twist might be the next thing to try?

I know we had a 10 twist out, and had the 400 and the 421 tumbling at 300 yards.

Dave
 
#26
Re: .375" on a CheyTac

No Dave, a longer twist will cause greater instability. It is a waste of time to go greater than 1: 8" with either the 7.0, or 6.5 caliber.

What Terry has proven is that the 6.5 is able to go ~75 fps faster than the 7.0 without the overturning moment over-riding gyroscopic stability imparted by the 8 twist at ~2,800 fps. If you look back in earlier posts, I was recomending a twenty caliber twist (1: 7.5") even for the 6.5. I knew the Lawton barrel was pushing the limit prior to this experiment.

The exercise was worthwhile however... now we know the exact point of instability.

 
#27
Re: .375" on a CheyTac

I will be watching curiously to see if faster will work, but as stated above, it seems to contradict what we already know.. if they are tumbling by more velocity it would seem to indicate that the twist is somewhat too fast, but again I am very new to this and have much to learn.

It also seems to contradict that the smaller weight bullet can be pushed faster and stay stabalized, so apparently I have no idea what is going on.
smile.gif


Why do you think they are becoming instable as the velocity is increased?

Dave
 
#29
Re: .375" on a CheyTac

Dave, I guess I tried to cover too much ground with too few words, conventional wisdom suggests that projectiles having stability problems caused by too slow twist should become more stable as velocity increases. This has been my experience when using conventional lead core bullets. These solids with relatively longer noses are marching to a different drummer. Theory, along with the limited testing that has been done is all we have to explain thier behavior. Now the only thing left to do is send some downrange in different twists to see what they like. Right now the testing suggests we need to go tighter. This is also backed up by the computer models Noel has been working with. Anyway it is a mystery that I have enjoyed working on and one that I believe is worthwhile. The gains made are going to be significant once the kinks have been worked out.
 
#30
Re: .375" on a CheyTac

I am watching very anxiously, we shot some of the 6.35 caliber (not sure what this even means) bullets out of the 10 twist, and they seemed to be stabalized just fine. I can't remember 100% what velocity we were pushing them, but since I have the 10 twist now, I will likely play with those more. I think down the road I will get a faster twist as well, just want to see what will work.


 
#33
Re: .375" on a CheyTac

Dave,

There are, basically, two opposing forces at work here, and they do not vary in direct proportion to each other.

You know about the stabilizing force. Gyroscopic stability increases as a function of RPM. The faster the twist, the greater the RPM at a given velocity, and therefore the higher stability imparted. An increase in velocity <span style="font-style: italic">also</span> raises RPM, but only by simultaneously increasing the other force... the overturning moment.

You are probably aware that all bullets travel at a slightly nose-up attitude relative to the axis of travel. This generates lift ahead of the center of gravity, and left unchecked by the gyroscopically generated resistance to movement, the bullet would flip the nose up, and over.

In this case, that point is reached at ~2,800 fps, and 252,000 RPM (12/8*2,800*60). Any RPM lower than this is now empirically demonstrated to result in instablity at 2,800 fps, it is no longer theoretical.
 
#36
Re: .375" on a CheyTac

Dave,

In theory, overspinning a bullet causes it to maintain static stability at the expense of dynamic stability.

In other words, the projectile retains the same axis of spin throughout it's trajectory, and flies belly forward in the terminal phase of travel. A bullet which actually enters this state will roll rapidly in the direction of spin, and soon thereafter loose all dynamic stability.

As a practical proposition, you will never have to worry about that in the twist rates we are using.
 
#38
Re: .375" on a CheyTac

Jamison International is making a solid copper bullet for the 375 Cheytac. It's a copy of the Lost River projectiles. I bought some last month. .95 BC 350 grains. They are a little costly at 2.55 each. They are comming out with a Sierra match king for the 408 if anybody is interested.
 
#40
Re: .375" on a CheyTac

Hi,
Interesting thread.
I am having a 375 Snipe-Tac build, it will be ready about June or July.
The rifle will have a 32" barrel with a 1.10.5 twist and heavy contour with heavy/large flutes.
I will shoot GS Custom Bullets a 291 grn solid copper bullet, a bit light I know.
I am a GS Custom distrubutor and will try to get Gerard from GS to make a Heavy bullet to fit the twist, I am thinking 330 grn or more.
I want a special bullet but NOT a rifle with a twist that can not shoot the "classic" 350 SMK. It is always a compromise
grin.gif


I am having custom .375 Snipe-Tac brass made by Dieter Horneber from Germany, they should be done in about a month or so.

Here is a picture and data on the 291 grn SP bullet by GS Custom.

Cheers,

Master Diver

http://www.gsgroup.co.za/375291SP174.html


375291SP2.jpg


 
#44
Re: .375" on a CheyTac

I am getting heavy contour with heavy flutes, the rifle will be build by Dave Viers (Black Diamond Rifles) Manners MST-4A stock with all the works, on a Lawton 8000 action.
I think the rifle will be around 20-22 lbs (9,5kg).

Something like the one belov.

Cheers,

Master Diver

AW2.jpg




 
#46
Re: .375" on a CheyTac

It iis a Lawton beschmark barrel with a standard 1:10.5 twist.
I will be shooting drive bands solids and SMK 350 grn.
Hope it will work??????
shocked.gif

What do you think? Those Lost River bullets have a large surface touching the rifeling!
I am thinking a 330 gr high BC bullet from GS Custom would be just what the doctor ordered. Your thoughts?

Cheers,

Master Diver
 
#48
Re: .375" on a CheyTac

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Master Diver</div><div class="ubbcode-body">It iis a Lawton beschmark barrel with a standard 1:10.5 twist.
I will be shooting drive bands solids and SMK 350 grn.
Hope it will work??????
shocked.gif

What do you think? Those Lost River bullets have a large surface touching the rifeling!
I am thinking a 330 gr high BC bullet from GS Custom would be just what the doctor ordered. Your thoughts?

Cheers,

Master Diver </div></div>


Ok sir I rifled that barrel. You will not be able to use the lost river style bullets in that at least they prob wont shoot well. You will have to go with the predators, Noels bullets, Barnes (when they come out), and Rocky Mountain Bullets (again when they come out).


As far as a ligher bullets are concerned for 2k+ yards they will not work. You need a weight vs bc vs muzzle velocity combo to strech the bullets that far.


Oh and hey ross did you hear the transonic boom when you were spotting down range just after it struck the plate or before?
 
#50
Re: .375" on a CheyTac

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: NotAGuru</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Master Diver</div><div class="ubbcode-body">It iis a Lawton beschmark barrel with a standard 1:10.5 twist.
I will be shooting drive bands solids and SMK 350 grn.
Hope it will work??????
shocked.gif

What do you think? Those Lost River bullets have a large surface touching the rifeling!
I am thinking a 330 gr high BC bullet from GS Custom would be just what the doctor ordered. Your thoughts?

Cheers,

Master Diver </div></div>


Ok sir I rifled that barrel. You will not be able to use the lost river style bullets in that at least they prob wont shoot well. You will have to go with the predators, Noels bullets, Barnes (when they come out), and Rocky Mountain Bullets (again when they come out).


As far as a ligher bullets are concerned for 2k+ yards they will not work. You need a weight vs bc vs muzzle velocity combo to strech the bullets that far.


Oh and hey ross did you hear the transonic boom when you were spotting down range just after it struck the plate or before? </div></div>

Ok great, hope it turned out well
grin.gif

I am the GS Custom Bullet distrubutor of Scandinavia and will hopefully use this rifle as a platform for showing potential customers how great these bullets are. The driveband bullets should work well in a standard rifling, if not I will rebarrel the dang thing
grin.gif


Cheers,

Master Diver
 
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