The new 33XC & 37XC cartridges designed by David Tubb

Nov 29, 2009
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#2
any links? haven't seen much other than David post on facebook that info is forthcoming. know its a rebated rim, will probably have to single load, etc.

think he said 20 more grains than lapua.. may be remembering something else at this age though.
 

Bradu

Full Member
Aug 24, 2011
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#3
Vestals gunsmithing posted some results with bullets and speeds that he got out of a couple rifles on his Facebook page
 
Nov 6, 2013
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#4
Per above, this is the info posted on Vestals.

https://www.facebook.com/plugins/post.php?href=https://www.facebook.com/permalink.php?story_fbid=1635492476559977&id=623885861053982&width=500

Introducing the new 33XC & 37XC cartridges designed by David Tubb - Superior Shooting Systems LLC!! Brass will be made by Peterson Cartridge Co which is among some of the best made today!! Here is the results:
Initial testing
33XC - 34 inch barrel. Warner 256 Flatline.
113 gr Retumbo 3375 FPS
118 gr Reloader 33 3400 FPS
37 XC 33 inch barrel. warner 364 Flatline
120 gr H1000. 3125 FPS
121 gr RETUMBO 3118
These charges will allow multiple reloadings with full use of the neck for bullet stability.
I loaded a single 37XC case over 20 times breaking in the Schneider 375 barrel.
Shot loads in that particular case that were to hot and the primer pocket became loose but never failed.
33xc brass is $2.21 per piece. Brass arrives end of August.
The 33XC (eXtra Capacity) has up to 130gr of useable powder capacity while leaving the .393” neck unfilled. Based off of a .580” bolt head, it extracts with ease when using a properly polished chamber & maximum powder charge. The 33XC has a 35-degree shoulder (.350” more body length with less body taper & additional .065” longer neck when compared to 338 Lapua case). Total case OAL is 3.087”. It favors 50BMG or Reloader33 burn rate powders with either 250 or 300gr bullets. 300gr jacketed/lead core bullets yield over 3150 fps & 250 gr jacketed/lead core yield over 3450 fps. Monolithic 250gr achieve the same velocities with approx. 3 grains less powder. (Test barrel: 28” Schneider 5 P/9 twist).
In 37XC, H1000 & Retumbo burn rate powders work well. Warner Flatline 361gr bullets fly at 3075fps with just over 120gr of either powder. (Used 33” Schneider 5P/7 twist) barrel.
If anyone is interested in either the 33XC and/or the 37XC, we will have the reamers, reloading dies and brass so give us a call so we can start your build.
Pic is a 338 lapua (empty)- 33XC Warner 256gr Flatline – 33XC head – 37XC Warner 361gr Flatline – 375 Cheytac (empty)
Note - the XC case length VS. the 375 Cheytac
XC.jpg

Dave and one other shooter both used a 37XC at the recent NRA Extreme Long Range Match, they ended up in 7th and 10th place.
http://bulletin.accurateshooter.com/tag/camp-atterbury/

Way too much everything for me (cost, barrel burner, recoil, etc), but if you are going to get serious about ELR, then it may be a good option.
 
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Lofty

Gunny Sergeant
Jun 14, 2008
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#5
I have a reamer for the .33 being cut by Dave Manson right now which will be throated for the 266 Flatlines. I pick up my Bartlein barrel this weekend to drop off to GAP. I am hoping brass is available by the time I get the reamer.

I'll post back in once its shooting.
 
Jan 26, 2014
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#7
Way too much everything for me (cost, barrel burner, recoil, etc), but if you are going to get serious about ELR, then it may be a good option.
Agreed, too much for me as well. I don't shoot competitive ELR, so this doesn't move the needle for me. Way too much expense for casual shooting. 338 Lapua AI more than scratches my itch for heavy artillery.

What are the arguments for choosing an 37XC over a 375 Cheytac? Performance seems to be comparable. Peterson makes brass for both. Cheytac already has a strong ELR following and lots of industry support. Just curious why someone would choose an XC over a Cheytac.
 
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W54/XM-388

Online Training Member
Oct 1, 2005
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#8
It seems also that things in the .4 range are getting popular again with various .416 setups.
Kind of funny how that goes around.. the rage was .408 then everybody went .375 now people are starting back into .416 etc.
 

Bradu

Full Member
Aug 24, 2011
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#9
Agreed, too much for me as well. I don't shoot competitive ELR, so this doesn't move the needle for me. Way too much expense for casual shooting. 338 Lapua AI more than scratches my itch for heavy artillery.

What are the arguments for choosing an 37XC over a 375 Cheytac? Performance seems to be comparable. Peterson makes brass for both. Cheytac already has a strong ELR following and lots of industry support. Just curious why someone would choose an XC over a Cheytac.
It's a great option for someone to get into elr without getting a cheytac or bmg sized action. Rebarrel a 338 action and you can at least get your feel wet to see if it's for you. That's my take on it and want to try it in my Desert tech. That is an affordable way for me to get into elr vs spending 4500-5k on a dedicated system plus optics.
 
Likes: LastShot300
Apr 6, 2014
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#10
U can get Cheytac cases with rebated rims for the Lapua .585 bolt face...I believe Peterson. The reason Dave developed his new case is the Cheytac case was designed for the .408 and at .375 it is way overbore and u end up with a cartridge that has a low fill ratio with higher peak pressures. So, overbore, poor fill ratio, and high chamber pressure all lend themselves to less chance of broad stable nodes which equate to high ES and SD equalling poor accuracy at range. His goal was to design a cartridge with perfect fill ratio for .375 that's optimized for modern powders like H1000 that are less temp sensitive trying to get the best ES/SD
 

Rust

Sergeant
Apr 18, 2001
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#12
Let's see, intial development for the .338 Lapua was done in the US using a shortened .416 Rigby case. The principles abandoned development due to personal conflicts and it was subsequently picked up and finished by Lapua. The case was made stouter to enable higher pressures. So it looks like the new case is essentially a lengthened Rigby with (if I read it right, haven't seen a drawing) a case length of 3.139" vs the 2.90 of the parent Rigby case.

Probably fifty year back my old man knew a couple of guys playing with necking down the Rigby case. The only problem is the old Rigby cases were balloon heads (like original .220 Russian cases)and couldn't be loaded especially hot. Nor were the slow powders of today available.

Still, gotta give "El Reye" (David) credit for bringing it to market. It takes a sizable investment and big brass ones to bring a propriety cartridge to market as an individual. Fair amount of risk is assumed with any new venture but if anyone can pull it off. As it turns out I have a suitable action laying about and had been thinking of wildcatting a Rigby anyhow as some of the new brass wasn't old style balloon head. Hmmm.
 
Nov 6, 2013
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#13
. . . The reason Dave developed his new case is the Cheytac case was designed for the .408 and at .375 it is way overbore and u end up with a cartridge that has a low fill ratio with higher peak pressures. So, overbore, poor fill ratio, and high chamber pressure all lend themselves to less chance of broad stable nodes which equate to high ES and SD equalling poor accuracy at range. His goal was to design a cartridge with perfect fill ratio for .375 that's optimized for modern powders like H1000 that are less temp sensitive trying to get the best ES/SD
If you have ever seen him shoot ELR, you will appreciate this concept very quickly!


TubbELR.jpg

He shoots with a Magneto Speed on his rifle so he can constantly measure his Muzzle Velocity. At ELR ranges muzzle velocity is a total make or break issue.

Everyone is chasing the pot of gold at the end of the rainbow! Interestingly David is going about it in a different manner. Rifle design, cartridge design, and techniques.

It is very cool to see the birth and evolution of a new shooting capability. Give it a couple of years, and shooting at 2,000 yards will start to look a lot more like shooting at 1,000 yards.
 
Dec 30, 2017
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#15
Let's see, intial development for the .338 Lapua was done in the US using a shortened .416 Rigby case. The principles abandoned development due to personal conflicts and it was subsequently picked up and finished by Lapua. The case was made stouter to enable higher pressures. So it looks like the new case is essentially a lengthened Rigby with (if I read it right, haven't seen a drawing) a case length of 3.139" vs the 2.90 of the parent Rigby case.

Probably fifty year back my old man knew a couple of guys playing with necking down the Rigby case. The only problem is the old Rigby cases were balloon heads (like original .220 Russian cases)and couldn't be loaded especially hot. Nor were the slow powders of today available.

Still, gotta give "El Reye" (David) credit for bringing it to market. It takes a sizable investment and big brass ones to bring a propriety cartridge to market as an individual. Fair amount of risk is assumed with any new venture but if anyone can pull it off. As it turns out I have a suitable action laying about and had been thinking of wildcatting a Rigby anyhow as some of the new brass wasn't old style balloon head. Hmmm.
Actually, I believe the XC case is a bit wider than the Rigby. Somewhere around .6" width at the base and using a rebated rim, I suspect the the base width is closer to the .378 Wby width measured at the belt.

Although this is designed for ELR, I think this would make for a great bear, elk or safari gun if we could only could get a longer mag action.

Maybe we could coax Peterson or ADG to make a higher pressure capable version of the Rigby case available.....?
 

Rust

Sergeant
Apr 18, 2001
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#16
Actually, I believe the XC case is a bit wider than the Rigby. Somewhere around .6" width at the base and using a rebated rim, I suspect the the base width is closer to the .378 Wby width measured at the belt.

Rigby - .589 rim, .590 base so if the Rigby wasn't the parent, I believe it at least provided a template

Although this is designed for ELR, I think this would make for a great bear, elk or safari gun if we could only could get a longer mag action.

Probably. The big CZ Safari action will handle a full length Rigby which would be suitable using conventional hunting bullets. Seems to me there used to be a European more or less standardized .375/.416 many years ago. Pre WWII?

Maybe we could coax Peterson or ADG to make a higher pressure capable version of the Rigby case available.....?
I doubt they would consider it practical to produce a limited production slightly less capable version of Davids design competing with it just on cost benefit analysis.
 

DAVETOOLEY

Gunny Sergeant
Jun 14, 2009
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#24
So Dave,

Please correct me if I'm wrong but looking at the chamber print it appears that the cartridge is no longer a rebated design but basically a longer version of a 338 Lapua?

Great design! Seems like it would be a perfect fit for the Surgeon XL single feed action....
I'm relieved that David didn't go with a larger case diameter and rebated rim. There are people/smiths that will build this on Rem 700 size actions. That would have long term problems. It's just a stretched version of the Lapua/416 Rigby/ 30-378 Wby with no belt. Back in the early 90's I did a 30-378 Wby with no belt because of extraction issues caused by inadequate sizing in front of the belt and few custom actions that were designed correctly. We quickly moved on to the 404 Jeffery case. pre RUM days.
 

Jim Boatright

New Hide Member
Feb 21, 2018
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#27
When David tested my prototype 338 copper bullets over 1000 yards, he mentioned using about 109 grains of H1000, so I knew he was not using even a 338 AI case. With the 225-gr base-drilled bullets at 3378 fps (5-shot ES=13; SD=3) his Oehler 88 measured BC(G1) of 0.794 (ES=.037; SD=.014) the initial gyroscopic stability was 2.75 from his 7.5-inch twist Schneider barrel (30+ inches in length). He said he could fire them much faster still. The first thing I noticed was his time-of-flight of 1.068 seconds to 995.7 yards.

I like his new 33XC/37XC case design. The 35-degree shoulder angle is great in a bolt-action, and it appears to have a nice long neck to help minimize throat erosion with the slow powders used. I will eventually rechamber my 338LM Surgeon XL rifle's Schneider 7.0-inch twist barrel for his Peterson 33XC brass. I also have in hand a Bartlein 5R 338 barrel with 6.6-inch twist (20 calibers per turn). The 33XC should be better than Lapua all the way around.
 

Lofty

Gunny Sergeant
Jun 14, 2008
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#28
I will eventually rechamber my 338LM Surgeon XL rifle's Schneider 7.0-inch twist barrel for his Peterson 33XC brass. I also have in hand a Bartlein 5R 338 barrel with 6.6-inch twist (20 calibers per turn). The 33XC should be better than Lapua all the way around.
Jim, are such fast twist rates a result of using solids? Which bullet are you planning on using in yours. I have a 1-8 twist barrel I was planning on using and wondering if its fast enough.
 

THEIS

Hi, Sincerely
Nov 27, 2017
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#29
Hi,

@Lofty
Check the hyper-stabilization paper from Jim that is in the resource section here on the hide. It explains the fast twist rates better than any post can :)
Jim has his own projectile design also.

Sincerely,
Theis
 
Mar 26, 2005
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#34
Based on the 33XC velocities printed above with the 256 Flatline, it looks to be about 100-150fps faster than a Lapua Improved.
I would of thought it be more than 100-150fps when considering that the 338-378 weatherby imp 40 deg. (338 Kubla Khan) has that on the 338 Lapua
shooting the 300 gr bullet
 

Jim Boatright

New Hide Member
Feb 21, 2018
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#35
I think David could have fired my 225-gr and 242-gr copper ULD bullets about 200+ fps faster than the 3378 fps and 3335 fps which he used for 1000-yd tests. We are well into the realm of "diminishing returns" here for MV versus case capacity.
Any 40-degree shoulders are difficult for Peterson to form with dies. The 35-degree shoulders are just as good IMO. This should be a great ELR case in this caliber range. You can fire-form them to P. O. Ackley's 40 degrees easily if you prefer. If you are specifying a custom reamer, I recommend reducing the specified radius at the neck/shoulder junction. That would help control "brass flow" into the neck (case lengthening) with repeated firing/resizing cycles. You should ream the "dreaded donut" from the base of the neck frequently with any cases having shoulder angles over about 20 degrees. I use custom carbide end-cutting reamers from Sinclair made for K&M neck turning equipment. That small annular ring of brass does interfere with gas flow behind the moving bullet.
 
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Apr 8, 2009
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#36
I shot Mr. Tubb's ( Purely out of respect for what David has accomplished ) 33 XC rifle on Sunday afternoon at the Precision Rifle Expo.
Lowlight's video interview gave me more insight into what was going on and some of the technology David is utilizing. I wish I had seen it before going to GA. so that I would have paid a bit more attention while I was up close and personal with him, the rifle and the ammo.
The rifle was impressive to shoot, in terms of recoil management with the brake and weight and accuracy. I did manage a sub MOA group at 1000 yards my first time firing the rifle.
 
Mar 26, 2005
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#37
I shot Mr. Tubb's ( Purely out of respect for what David has accomplished ) 33 XC rifle on Sunday afternoon at the Precision Rifle Expo.
Lowlight's video interview gave me more insight into what was going on and some of the technology David is utilizing. I wish I had seen it before going to GA. so that I would have paid a bit more attention while I was up close and personal with him, the rifle and the ammo.
The rifle was impressive to shoot, in terms of recoil management with the brake and weight and accuracy. I did manage a sub MOA group at 1000 yards my first time firing the rifle.
I used to own a T2k back when they first came out,and that design and platform was ahead of it's time .it was a very accurate rifle at the time,well built and thought out system.i've been researching all the different switch barre/caliber platforms available to settle on one rifle and have the versatility to switch barrels and calibers.been looking at the new Tubb Rifle (ATR) ,spoke to them on the phone and i'm kinda leaning in that direction,however it just looks like a bigger version of the original T2K system,only larger frame and the weight seems kinda light for a big bore set up.

You had a chance to get behind the rifle,what are your thoughts? recoil management for a 20-22 pound rifle.
I have fired numerous big bore magnums in the 20-22 lbs range in the past and they beat the crap out you.
pros and cons...
 
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Likes: scottwwv
Apr 8, 2009
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#38
I only put 4 rounds thru the rifle, so it wasn’t a comprehensive shooting session by any means. Recoil was manageable from the prone position but there was no doubt when the round was touched off.
 
Aug 23, 2017
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#39
The 33XC is the logical choice for anyone wanting a bit more performance over the 338LM. All that is necessary is to punch out the chamber and get a set of reloading dies. Given the cartridge length increase the 33XC will be a single load proposition in Lapua sized rifles. At the Precision Rifle Expo David and me ran several tests for bullet BC uniformity with ringed vs. non ringed bullets. The 33XC loads we shot were 300gr bullets at 3175fps. This setup shoots pretty flat, about 10 mils at 1500 yards in dense South GA air.
 
Likes: wildcats
Mar 26, 2005
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Honolulu,HI
#40
The 33XC is the logical choice for anyone wanting a bit more performance over the 338LM. All that is necessary is to punch out the chamber and get a set of reloading dies. Given the cartridge length increase the 33XC will be a single load proposition in Lapua sized rifles. At the Precision Rifle Expo David and me ran several tests for bullet BC uniformity with ringed vs. non ringed bullets. The 33XC loads we shot were 300gr bullets at 3175fps. This setup shoots pretty flat, about 10 mils at 1500 yards in dense South GA air.
That's what ive been thinking ,build 300 norma mag switch barrel and then chamber the other barrel in 33xc and have the best of both worlds..a big 30 and the 33xc.
 

THEIS

Hi, Sincerely
Nov 27, 2017
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#41
Hi,

@Esoteric Junkie
In regards to the ringed vs non-ringed projectiles....
Was there any variations between the two in regards to elevation requirements to reach 1500yds?
Was there any variations between the two in regards to windage requirements (Given same wind conditions) to reach 1500yds?
What make 300gr projectiles were yall using?

Sincerely,
Theis
 
Aug 23, 2017
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#42
Theis,
We did not shoot 1500 yards while at Blakely. All the shooting we did was at 1000 yards. I was only using 1500 yards as a reference point for 10 mils of elevation with the 33XC combination. We were testing some 300gr bergers and some solids. We also did a good bit of testing with the Sierra DTAC 115gr bullet running 3200fps.
EJ
 

Jim Boatright

New Hide Member
Feb 21, 2018
90
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#43
Theis,
We did not shoot 1500 yards while at Blakely. All the shooting we did was at 1000 yards. I was only using 1500 yards as a reference point for 10 mils of elevation with the 33XC combination. We were testing some 300gr bergers and some solids. We also did a good bit of testing with the Sierra DTAC 115gr bullet running 3200fps.
EJ
David Tubb's idea of ringing the noses of long-range rifle bullets is great for any bullets designed with tangent ogives, any multi-ogive bullets, and any secant-ogive bullets having RT/R ratios greater than about 0.5. This "turbulator" ring serves aerodynamically to "trip" the initially laminar flow boundary layer into turbulent flow at that ring location. The reason secant ogives with RT/R=0.5 fly so well is that they have a 4.75 to 5.0-degree "break angle" in the surface of the bullet where the base of the ogive joins the cylindrical shank of the bullet which reliably trips the boundary layer flow-fields at that location, at least for "small caliber" bullets. Thus, the lower skin-friction (drag) of laminar boundary layer flow pertains over the entire length of the secant ogive nose, but higher-drag turbulent flow reliably pertains over the afterbody of the bullet. This is how VLD rifle bullets fly.

Tangent ogive bullets meet the bullet shank with zero-degree break angles. Except for really small-caliber (<22 caliber), very short length, tangent ogive rifle bullets, Reynolds Number constraints inevitably cause fairly random axial-location tripping of the laminar flow into turbulent flow due to microscopic surface irregularities. This then causes small random variations in air drag from one shot to the next and destabilizes individual bullets in flight. The effect is similar to the attached versus detached flow aerodynamic effects which disrupt the trajectories of low-speed baseballs, etc. A conical ogive (RT/R=0) has the largest possible break angle for any given nose length without considering concave nose shapes. The 4.75-degree break angle of VLD bullets is large enough to guarantee tripping of the boundary layer at the typical nose lengths used for bullets up to about 20 mm in caliber. Doubling that angle with a conical nose design would have no additional benefit. All of the multi-ogive designs which I can imagine would produce several smaller break angles in the surface which might not cause reliable tripping of the boundary layer.

So, ring the noses of tangent-ogive Sierra MK's and Berger multi-ogive bullets, but not those of true VLD bullets nor of my prototype ULD bullets. I would suggest, however, based on Reynolds Numbers, ringing tangent-ogive rifle bullets at about 1-inch behind their noses for reliable boundary layer tripping with slightly less air-drag penalty.

Jim Boatright
 
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steve123

Lt. Colonel
Mar 16, 2008
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Flagstaff, AZ
#45
David Tubb's idea of ringing the noses of long-range rifle bullets is great for any bullets designed with tangent ogives, any multi-ogive bullets, and any secant-ogive bullets having RT/R ratios greater than about 0.5. This "turbulator" ring serves aerodynamically to "trip" the initially laminar flow boundary layer into turbulent flow at that ring location. The reason secant ogives with RT/R=0.5 fly so well is that they have a 4.75 to 5.0-degree "break angle" in the surface of the bullet where the base of the ogive joins the cylindrical shank of the bullet which reliably trips the boundary layer flow-fields at that location, at least for "small caliber" bullets. Thus, the lower skin-friction (drag) of laminar boundary layer flow pertains over the entire length of the secant ogive nose, but higher-drag turbulent flow reliably pertains over the afterbody of the bullet. This is how VLD rifle bullets fly.

Tangent ogive bullets meet the bullet shank with zero-degree break angles. Except for really small-caliber (<22 caliber), very short length, tangent ogive rifle bullets, Reynolds Number constraints inevitably cause fairly random axial-location tripping of the laminar flow into turbulent flow due to microscopic surface irregularities. This then causes small random variations in air drag from one shot to the next and destabilizes individual bullets in flight. The effect is similar to the attached versus detached flow aerodynamic effects which disrupt the trajectories of low-speed baseballs, etc. A conical ogive (RT/R=0) has the largest possible break angle for any given nose length without considering concave nose shapes. The 4.75-degree break angle of VLD bullets is large enough to guarantee tripping of the boundary layer at the typical nose lengths used for bullets up to about 20 mm in caliber. Doubling that angle with a conical nose design would have no additional benefit. All of the multi-ogive designs which I can imagine would produce several smaller break angles in the surface which might not cause reliable tripping of the boundary layer.

So, ring the noses of tangent-ogive Sierra MK's and Berger multi-ogive bullets, but not those of true VLD bullets nor of my prototype ULD bullets. I would suggest, however, based on Reynolds Numbers, ringing tangent-ogive rifle bullets at about 1-inch behind their noses for reliable boundary layer tripping with slightly less air-drag penalty.

Jim Boatright
Did you mean 1/10th inch behind their noses???
 

Jim Boatright

New Hide Member
Feb 21, 2018
90
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#47
No, I meant to recommend placing the ring about 1 inch from the tip of the bullet. The maximum distance over which the boundary layer flow can remain laminar is about 1.25 to 1.50 inches, depending upon what value the "critical Reynolds Number" turns out to have. McCoy says one can safely assume laminar flow over the ogive (nose) and turbulent flow over the afterbody (or L/T flow transition skin friction drag) for rifle bullets up to about 20 mm in diameter.
 
Likes: LastShot300
Apr 6, 2014
179
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#48
David Tubb's idea of ringing the noses of long-range rifle bullets is great for any bullets designed with tangent ogives, any multi-ogive bullets, and any secant-ogive bullets having RT/R ratios greater than about 0.5. This "turbulator" ring serves aerodynamically to "trip" the initially laminar flow boundary layer into turbulent flow at that ring location. The reason secant ogives with RT/R=0.5 fly so well is that they have a 4.75 to 5.0-degree "break angle" in the surface of the bullet where the base of the ogive joins the cylindrical shank of the bullet which reliably trips the boundary layer flow-fields at that location, at least for "small caliber" bullets. Thus, the lower skin-friction (drag) of laminar boundary layer flow pertains over the entire length of the secant ogive nose, but higher-drag turbulent flow reliably pertains over the afterbody of the bullet. This is how VLD rifle bullets fly.

Tangent ogive bullets meet the bullet shank with zero-degree break angles. Except for really small-caliber (<22 caliber), very short length, tangent ogive rifle bullets, Reynolds Number constraints inevitably cause fairly random axial-location tripping of the laminar flow into turbulent flow due to microscopic surface irregularities. This then causes small random variations in air drag from one shot to the next and destabilizes individual bullets in flight. The effect is similar to the attached versus detached flow aerodynamic effects which disrupt the trajectories of low-speed baseballs, etc. A conical ogive (RT/R=0) has the largest possible break angle for any given nose length without considering concave nose shapes. The 4.75-degree break angle of VLD bullets is large enough to guarantee tripping of the boundary layer at the typical nose lengths used for bullets up to about 20 mm in caliber. Doubling that angle with a conical nose design would have no additional benefit. All of the multi-ogive designs which I can imagine would produce several smaller break angles in the surface which might not cause reliable tripping of the boundary layer.

So, ring the noses of tangent-ogive Sierra MK's and Berger multi-ogive bullets, but not those of true VLD bullets nor of my prototype ULD bullets. I would suggest, however, based on Reynolds Numbers, ringing tangent-ogive rifle bullets at about 1-inch behind their noses for reliable boundary layer tripping with slightly less air-drag penalty.

Jim Boatright

Jim,

Would you be willing to explain laminar flow vs. turbulent flow? I am picturing laminar as layered like an onion and turbulent as erratic and multi-directional. Are the results being seen with the "turbulator" ring specifically less vertical dispersion or less generalized dispersion? The reason I ask, ....are the results being seen from tripping the laminar flow into turbulent simply creating less friction/drag, through low pressure, over the area of the bullet with the most surface area--i.e creating more consistent MV's down range at target? Or is their possible effects of less aerodynamic jump--i.e. less weather vaning?
If my memory serves me right, when I talked to Dave, he was specifically seeing less vertical dispersion with the ring.
 

Jim Boatright

New Hide Member
Feb 21, 2018
90
81
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#49
Jim,

Would you be willing to explain laminar flow vs. turbulent flow? I am picturing laminar as layered like an onion and turbulent as erratic and multi-directional. Are the results being seen with the "turbulator" ring specifically less vertical dispersion or less generalized dispersion? The reason I ask, ....are the results being seen from tripping the laminar flow into turbulent simply creating less friction/drag, through low pressure, over the area of the bullet with the most surface area--i.e creating more consistent MV's down range at target? Or is their possible effects of less aerodynamic jump--i.e. less weather vaning?
If my memory serves me right, when I talked to Dave, he was specifically seeing less vertical dispersion with the ring.

Yes, you have the right ideas about laminar versus turbulent flow in the boundary layer. You can sometimes just make out the thin boundary layer in high-resolution shockwave photographs of supersonic bullets. The laminar (layered) flow-fields are smooth in cross-section, while the turbulent flow looks lumpy. Turbulent flow involves tiny vortices rolling along the surface. I believe that higher-energy turbulent flow is actually preferred over the surface of the boat-tail, and helps increase aerodynamic base-pressure to reduce drag. The boundary layer is thick enough to completely submerge the rifling marks, but not too much thicker.

Also, I would expect the added trip-rings to regularize the overall drag for most types of rifle bullets flying to great ranges. As discussed above, I believe this effect should produce a measurable decrease in vertical-direction dispersion in group shooting at long distances.

Measuring the shot-to-shot muzzle speed variations with a Magneto-Speed system would also help in the management of this vertical dispersion. If I recall correctly, the variation in impact vertical (dZ) from the mean is equal to -g*(tof*tof)*dV/V = -2*Drop*dV/V where dV is shot-to-mean velocity deviation, Drop is the mean drop from the bore, V is the mean group muzzle speed, and tof is mean time-of-flight to the target distance. The MS unit allows "calling" how much of the observed vertical error dZ of one shot is due to muzzle speed variance dV measured for that shot.
 
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Skookum

Entropy Personified
May 6, 2017
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Your mom's
#50
No, I meant to recommend placing the ring about 1 inch from the tip of the bullet. The maximum distance over which the boundary layer flow can remain laminar is about 1.25 to 1.50 inches, depending upon what value the "critical Reynolds Number" turns out to have. McCoy says one can safely assume laminar flow over the ogive (nose) and turbulent flow over the afterbody (or L/T flow transition skin friction drag) for rifle bullets up to about 20 mm in diameter.
So this would place the ring right in front of the ogive/body junction? What is the effect of having the ring break up the laminar air flow so close to the ogive/body junction vs placing the ring further forward on the ogive?