Monolithic solid projectiles in polygonal rifling

[bill alexander]

Every now and again work has me delve into a subject where the data is limited. In this instance to look at barrel life and the influence of rifling form when firing what is essentially a solid projectile. As expected muzzle velocities are required to be quite high and the working pressures are right up there. Hence the post is in the ELR section where it is a regular occurrence to drive solids along quickly with healthy pressure levels

What I am looking for is experience using polygonal profile rifling forms in this discipline. How do they tolerate variations in projectile weights/lengths? How sensitive are they to projectile alignment? (neck turn, bullet jump) and any other incidental observations.

Thank you in advance.

Bill Alexander

 

[THEIS]

Hi,

Polys and monos are a good combination for the most part.

My personal experience has shown no signs of any measurable barrel life since the barrels' burnout at throat happens long before shooting the rifling out of the barrel, whether Poly, Gain, Normal, Micro, Ratchet, etc etc of rifling profiles.

To me they are no different in their characteristics of how they "act" then normal rifling profiles.....proper chamber and they are good to go.
But I am gain twist biased for monos, so hopefully some other members with more poly experience will be around shortly to assist you.

David Tubb pretty much uses Schneider Poly barrels for all his stuff IIRC.
@DTubb

Sincerely,
Theis

 

[Alan Warner]

What Theis said.
Talk to David. He has a lot of experience with poly barrels. IIRC, he told me he saw higher velocities with Polys @ same charge amount than
4 groove or 5rs.

 

[Ledzep]

How does land cross-sectional area compare with poly vs. 4/5 groove?

More velocity at the same charge almost always means more pressure (nothing is free) and the onset of the pressure build happens in the throat.

 

[jbailey]

More velocity at the same charge almost always means more pressure (nothing is free) and the onset of the pressure build happens in the throat.

Not if the in-bore friction is reduced. That is how Flatlines result in improved MV at the same charges/pressures.

 

[Alan Warner]

Not if the in-bore friction is reduced. That is how Flatlines result in improved MV at the same charges/pressures.

Actually, Flat Lines need more powder to get to velocity with the same weight pill because os reduced bearing surface. Similar to using moly.

 

[Ledzep]

Bearing surface and bore surface finish being the same, powder charge being the same, and "only" rifling differing, I'd expect an increase in MV to be from an increase in pressure from an increase in engraving forces, which is why I pose the question. I've been wrong before, though.

 

[GIXXER2000]

I have had 2 Schneider Poly barrels 1 for a 33xc in my AI-PSR and the other for my AIAE in 308. The 308 seems to be no different speed wise then the AI factory barrel. It shoots very well and I have not had any issues The 33xc barrel had issues i have very high pressure that i was never able to overcome. When I had Dave Tooley look at at it he said said there was a lot of wear down the barrel for less the 250 rounds so I just scraped the barrel. It sounds like just a bad piece of steel and could happen to any barrel maker.

 

[bill alexander]

How accurately does the major bore diameter have to match up with the projectile diameter to realize decent accuracy. We are stuck with a predetermined projectile whose tolerances are awful. Any opinion as to is polygonal is more or less forgiving

Other reason to ask is that the basis of the question is to try and offset bore erosion in the throat and barrel mid section. Pressure is well up into the 90k psi area and we are using heat treated barrels with heavy chrome. Also looking at some CVD coatings. Removing the edges from the lands experimentally shows increased barrel life vs conventional types but I note that this has never been implemented in cannon applications where it was tested.

If the design is more forgiving it also provides the option of relieving the bore at the rear to drop the force applied to the bore and hence reduce some of the mechanical damage to the chrome then choke the muzzle.

 

[THEIS]

Hi,

@bill alexander
Can you PM me a number to reach you at? I would like to discuss a few things regarding your latest reply on this matter

Sincerely,
Theis

 

[JB.IC]

Hi,

@bill alexander
Can you PM me a number to reach you at? I would like to discuss a few things regarding your latest reply on this matter

Sincerely,
Theis

no fair. I want to see this conversation and use my public education to try to understand the discussion.

 

[DAVETOOLEY]

I have had 2 Schneider Poly barrels 1 for a 33xc in my AI-PSR and the other for my AIAE in 308. The 308 seems to be no different speed wise then the AI factory barrel. It shoots very well and I have not had any issues The 33xc barrel had issues i have very high pressure that i was never able to overcome. When I had Dave Tooley look at at it he said said there was a lot of wear down the barrel for less the 250 rounds so I just scraped the barrel. It sounds like just a bad piece of steel and could happen to any barrel maker.

The 33XC barrel had heat checking on the outside edges of the lands for about 8-10". I would expect to see that after many many hundreds of rounds at which point the throat would have been long gone.