Sabots and Crowns

[Ga.Smokey]

So I built a couple sabot hunting rifles out of CVA scout rifles in 45/70.
One for my son and one for myself.
My goal is to build a walkabout/ tree stand gun with an effective range of 200 yards.

So off to the store and we both came back with blued cva scouts.
I went with a modified savage ml2 breach plug and prb variflame ignition.
Our target load for both builds is 57 grains of imr 4198 with a furry 225 in a HLB.
I'll have to start another build thread on the guns. Although I'll post a picture of each here.
Plain plastic stock for my son

Boyds stock on mine.
Here is where it gets to the point of the post.
At our first range season we both had issues loading sabots. The rifling was sharp at the crown cutting the sabots upon entry.
I wish I had a picture but I don't.
The loading was inconsistent at best.
The groups left some accuracy on the table.
Tge first two started farely straight and shaved a little.
The 3d shot on right shaved alot. And dispersed accordingly.
Cosistencey wasnt there.


So off to the work shop to address the issue
The stock crown is a recessed flat crown.

I used my target 11 degree cutter to angle and deepen the crown.

Then used the 90 degree cutter to heavily champher the crown. I had to run a pilot on the lathe to that bore to keep the crown concentric to the bore.
Tge finished machine work.

After blue touch up

Sabot pushed down after new crown

Off to the range.
I noticed that the sabot was much tighter to load but more importantly very even down the bore and no more plastic shaving.
Now if I pay attention when I start the round I get much better results.

5 shot group the first 2 I noticed tge petals weren't square but I'd already started them so I shot them. They are high in the group.
The next 3 in the lower right area were started with much more care and precision
Making sure they were squared up before starting them.
Going to shoot it more and get used to it more.
I think with care in loading I will have a nice walk about rifle.
John

 

[Mnt monkey]

Great post, and a good result ,look forward to more groups.

 

[Ga.Smokey]

Found out some interesting things today with the remington 16 twist 45 caliber rifle.
There is another post detailing this rifle build and its journey to accuracy and power.
More on this subject over there.

So as you guys know I've been experimenting with crowns and there effect on sabots. I have some hard data to now share out of this particular barrel. Sample of one more data to come.have another 16 twist barrel to try out.
I've detailed the process I've used to recut the crown and here is one of the results.
I feel that now I'm not shaving plastic from thr sabot I'm getting much better seal and efficiency out of the powder I'm expending.
The imperial data from many 45 caliber shooters shows a 57 grain charge of imr 4198 pushing a furry 402 in a harvester light blue to 2350ish velocity.
I would agree with that give or take 50 on any given day.
That is where I started with my quest for accuracy.
And had good results at first.
When I saw tge glaring problem of in essence full forming tgr sabot by shaving I knew I wanted to correct that couldn't be very consistent
I was able to solve that problem and that created another problem the gun went squirely in a bad way.
I had sealed up the barrel so good that I was blowing out the sabots.
So I scratched my head for a couple days and retrieved sabots looked at them asked advise to others in private and we all agree that I was pushing them to hard.
So I broke out the chrono and shot a course ladder from 53 to 57 grains in 1 grain step increments.
I didn't get the 53 shot and I'm bummed out because the recoil Impulse felt right.
I forgot to press tge reset button when I turned on the chrono.
I suspect that 53 is the load but will verify I suspect 2375 area.
54 shot 2418
55 shot 2591
56 shot 2534
57 shot 2546
It was interesting to see tge velocity increase from 54 to 55 as a percentage was a larger step.
My target velocity is 2375 average.
Tomorrow's test is 53 grain grouping and chrono testing.
In conclusion I believe that the crown is as important to entry of the sabot as to exit maybe even more important.
Properly aligning sabot is very important.
Running your load over a chrono is absolutely necessary.
I think with any gun proper tune is the key to accuracy and precision.
I see huge versatility in sabot loads
I won't settle for mediocre accuracy.
I will get pin point accuracy
Then calculate the external balistics to place precision shots
The difference in 2375 and 2600 is minimal on game at practical / ethical distance.
It's just a different place on my reticle

the economic impact is less powder by around 10 percent
I'm hoping I'm in that range where a cci200 shoots well
I have 5000 so i need something to work with them.
54 grains

57/56/55 grain all imr 4198

John

 

[Mnt monkey]

Excellent post ,,I really appreciate it a lot, and I think a lot of us never ever consider the effect of having a really square nice crown the difference is pretty phenomenal I'll be watching closely for more results,,!! good stuff

 

[Ga.Smokey]

Something I just noticed the SD of the 3 charge ladder was 28.
Just 5 years ago I would get excited about that in a center fire
That's a 3 grain difference.
Can't wait to see a 3 or 5 shot string of tge same load.
Might be on to something.....

 

[bronko220002]

Those Scouts really shoot. great guns for the price. Because I don't have all that fancy machining, I use a capnut on an appropriate bolt chucked in a drill and with a bit of valve grinding compound get a very nice smooth crown. Works like a charm.
BTW I love the stock on your Scout. I just checked Boyds and I don't see a listing for the fore end for the takedown model.

 

[Ga.Smokey]

Those Scouts really shoot. great guns for the price. Because I don't have all that fancy machining, I use a capnut on an appropriate bolt chucked in a drill and with a bit of valve grinding compound get a very nice smooth crown. Works like a charm.
BTW I love the stock on your Scout. I just checked Boyds and I don't see a listing for the fore end for the takedown model.

They have a forend for the takedown.
I have a stainless v2 I'm going to build real soon.

So I'm curious how you keep the crown face perpendicular to the centerline of the bore axis
some sort of pilot?

Eyeball it ? Measure crown offsets 4 side?
A pic would help me understand

I assume a deep clean is inorder after exposing your bore to valve lapping compound.
It's a great idea for guys that don't have access to a machine shop. Or like me sometimes the machines have jobs set up for extended periods and I don't have access.
However our situation dictates we get there I think it's important we do get there.
I'm learning so much from this it's humbling to see the knowledge this group has as a collective.
The atmosphere of sharing is a special brotherhood....

 

[Ga.Smokey]

Those Scouts really shoot. great guns for the price. Because I don't have all that fancy machining, I use a capnut on an appropriate bolt chucked in a drill and with a bit of valve grinding compound get a very nice smooth crown. Works like a charm.
BTW I love the stock on your Scout. I just checked Boyds and I don't see a listing for the fore end for the takedown model.

There standard stock for arm is for the take down
The non take down is for the blued model non takedown.
Cheers
John

 

[bronko220002]

They have a forend for the takedown.
I have a stainless v2 I'm going to build real soon.

So I'm curious how you keep the crown face perpendicular to the centerline of the bore axis
some sort of pilot?

Eyeball it ? Measure crown offsets 4 side?
A pic would help me understand

I assume a deep clean is inorder after exposing your bore to valve lapping compound.
It's a great idea for guys that don't have access to a machine shop. Or like me sometimes the machines have jobs set up for extended periods and I don't have access.
However our situation dictates we get there I think it's important we do get there.
I'm learning so much from this it's humbling to see the knowledge this group has as a collective.
The atmosphere of sharing is a special brotherhood....

You have to have the appropriate size cap nut so that its big enough that only the round tip fits over the muzzle. Then its just a matter of keeping everything parallel. It works just like a chamfering tool only slower. I wish I had a pic of the finished crown but I deleted it after selling my Encore pistol.