Test results from 338 ST *pics and chronograph data*

[Black Diamond 408]

338 SnipeTac rifle

Viersco custom repeater action(3 shot), stainless steel
Barney Lawton stainless barrel, 33" 1x11.25 twist
Holland style brake
Lone Wolf carbon fiber stock
6x24 IOR 35mm tube scope
Tuned rem 700 trigger
Total weight 16.75# with magazine
Cases formed from 408 CheyTac necked to 338cal
Neck length .350
H2O capacity 165grns
Overal length w/ 300MK bullet 4.150 (touching lands)

Today i did some testing with US869 powder, 300MK bullets.
The cases were blank fire formed before starting.

The first test was 147 grns of US869 Hodgdon. Bullet was seated to just touch lands. Group was .750 at 100yds, no pressure signs. The chronograph was set at 10 feet from muzzle. Three shots were, (3426 clean bbl), 3454, 3464.

Next three shots i bumped up the load to 150grns of US869.
I did not clean. 3505, 3525, 3520. The first two shots cut an oblong hole, third shot was just off a bit, could of been me? As you can see in the pics, my bench is very poor. The group size was .533 Extraction was easy, shows some signs of the primer starting to flatten. Maybe able to bump up the load to 152. Temp outside was 65deg. Light wind from the left. Recoil was moderate, i could shoot this all day. I feel 3500fps is plenty fast and i am going to call this my top load. I'm sure i could get 3550-3600fps, if you wanted to push it to the limit, you may also cut the barrel life down and loose some cases. Remember this is a carry rifle for hunting. 3500fps with the 300MK bullet is very impressive out of a 33" tube.

I'm hoping to test some 350grn WC bullets tomorrow.

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Pic of 100yd target, 150grns of Hodgdons US869 powder, 300MK
3520 fps

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Pic of rifle on my portable bench

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Dave

 

[daveosok]

Dave thats some good info.

What would you expect from a 40 inch barrel?

 

[mindcrime]

That's some SWEET equiptment!!! /ubbthreads/images/graemlins/cool.gif

 

[lerch]

that is one **** impressive rig!!!! I cannot believe a 300gr bullet at 3500fps!!!!! I almost feel sorry for whatever is centered in your cross hairs. I am excited to see what you get out of the 350gr uld , then i wanna see what Kirby can get out of it with his longer bbl.

is your gun a repeater???? Some time over the next year or two I am gonna get some kinda big 338 in a repeater for elk and bear hunting. I really like the Kahn but I i like to keep my options open. I cannot imagine the power of a 325gr flatbase bonded bullet slamming into a brown bear at 3350fps, OUCH!!!!!

Dont feel bad about the bench, the one me and BJ shoot off of is a ***!!!! Most of the time we just lay on the ground, except during summer in Oklahoma, you catch a sandbur in the nipple it hurts!!! /ubbthreads/images/graemlins/blush.gif /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/grin.gif

Looks like one hell of a gun

take it easy
steve

 

[Fiftydriver]

BD408,

Congrats on an obvious successful test session. Seems US869 will offer a bit more then H-50BMG will get us in the big 408 based 338s!!!

How are primer tightness at 3500 fps. Curious how long the primer pockets last over repeated firings at this level. Yet to get mine tuned up and on the range. Will hopefully fireform some cases tomorrow and get her out to the range is possible. Will try some US869 and see what happens.

One tech question for you, what is the diameter of your firing pin?

Congrats again!!! Good building, good loading, good shooting!!! /ubbthreads/images/graemlins/grin.gif

Kirby Allen(50)

 

[Black Diamond 408]

Kirby:

So far the primer pockets are still tight. I measured the expansion on the web area, its right at .004 so i think the 150grn load is about tops without ruining the brass, at least in this gun.

I turned this firing pin to .069 there is very little crater on the primer. Im using a 25# spring also, i have a 27# but dont think i need it.

In the process of cutting a FL size die, my reamer is a bit small so i have to hone the body out so i dont over size the brass. I figure about .001 undersize is plenty. We will see. As soon as this is done i can load up some 350's. I'm hoping for 3400 with them.

Later

Dave

 

[ewallace]

Where are you getting US869 Hodgdon?
Crow Mag

 

[Black Diamond 408]

Lerch:

This gun started as a single shot, then i milled the bottom out for my detachable magazine system. It uses a 3 shot clip, similar to a 788 rem. Feeds very well, single stack mag. I can build them to hold more rounds but they get too long for my taste.

I made lots of the 338-378wby wildcats in the past, the only thing i dont like is the Belted case. I would go with the 338-416 rigby imp. The brass is better and the same results.

Dave

 

[Black Diamond 408]

Crow Mag:

I got my US869 from Graf & Sons. www.grafs.com

 

[Black Diamond 408]

I tested the 350grn Wildcat bullets this morning. The results were not good. My barrel twist will not stabilize the long heavy bullets. I feel you will need a 10 or under for this. All my new SnipeTac rifles have a 9.25 twist, this barrel was a prototype i had made several years ago for testing this new round. With any new wildcat it takes time and lots of testing to find the proper twist rates. This is a whole new area when you contiplate running 300gr bullets over 3400fps, spin rate becomes an issue, just how much can the bullet take? Therefore you are experimenting with twist rates, can get expensive, or get lucky on the first try! This twist will work ok for 300 and smaller bullets. I have shot 200grn Noslers in this barrel, they all go into the same hole at 100yds, 3900fps. Not an ideal choice for hunting or barrel life, was just for fireforming and test loads at the time.

I shot several of the 147grn loads with the 300MK for sighters. It was 55deg out today and light winds. The same load yesterday at 65deg produced 3420 on ave. Today with 10 deg cooler temp it was 3375fps ave.

I loaded up 3 test loads with the 350grn bullets, 142, 143, 144 with US869. All loads opened easy, little resistance on the last load. Velocity was from 3140, 3160, to 3205fps highest being the last load. I was mostly looking for what speed the 350grn will be capable of running. The recoil was no different from the 300MK.

More testing will be needed with the new 9 twist barrels when i get one done.

Dave

 

[Fiftydriver]

BD408,

I was curious to see what would happen with the 350 gr ULD RBBTs in your 1-11.25 twist. I have tested them in my 1-10 twist 338 Kahn at 2800 fps and accuracy was VERY good at ranges under 300 yards but seemed to open up at longer ranges and would not hold as tight as the 300 gr ULD RBBT at 3050 fps.

I figured you may get about the same results with your slower twist barrel but as you correctly mentioned, with these wildcats we are playing in uncharted waters. No one knows what will happen until bullets get in the air and that can be a spendy situation which I know very well as I know you also know very well.

Your velocities are about exactly where I was expecting them to be. I suspect you will top out in the 3200 to 3250 fps range but again, thats just a guess on my part.

You will not have a problem overstressing these bullets with your 1-9 twist I am sure. They have a pretty stout jacket on them. With this much bullet weight and length combined with this huge powder charge you may see a measureable increase in pressure for a given load comparing the 1-11 twist to the 1-9 twist.

I know you will start lower but just want to be your conscience a bit here!!! /ubbthreads/images/graemlins/grin.gif

Still, a 350 gr ULD RBBT at 3200 fps.... ****, right at 8000 ft/lbs of energy ain;t to bad in a .9 BC bullet!!!

Keep us posted. I hope to get some cases formed today and load up some test loads here soon as well. Will let you know how my bullets fly in the 1-10.

Kirby Allen(50)

 

[ewallace]

Do you have a pic of a 350g WC bullet next to a 300g SMK?
What are you using to fire forming?
Crow Mag

 

[Brent-AR-30-338]

BD 408,
How do you like that prochrono, are they any good?
Oh, and by the way....freakin awesome rifle, looks like you could use a new bench /ubbthreads/images/graemlins/grin.gif
How much did that lighten your checkbook? /ubbthreads/images/graemlins/cool.gif

 

[traks44]

HOLY ************* /ubbthreads/images/graemlins/shocked.gif

I just ran some numbers on the 300 SMK at 3500!!!

only 15 inches drop at 1000, WITH A 100 YARD ZERO!!!!!

I am speechless.............. /ubbthreads/images/graemlins/shocked.gif /ubbthreads/images/graemlins/shocked.gif