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

[SIDS01]

Has anyone though of necking down the 33xc to a 30 cal or a 30xc project build. Love to see how the heavy 230 smk or 240 smk would fair.

The overbore ratio would be between the 30/378 Weatherby and the 338 Snipetac, so similar barrel life, tolerance to shooting strings, etc..

QL suggests you'd be able to fill the case with H50bmg and just max out pressure, so it's still not so big you couldn't find slow enough powders.

I built a 7/338LI with a little more overbore than the 30/338xc would have. After a few hundred rounds, it would poof a bullet or two in a 10 shot string even after dropping the velocity 250 fps. It was all fun and games in the beginning though. The rpm a bullet will take isn't fixed, it depends on the bore condition, and what that level of overbore does to the bore isn't pretty. The higher BC bullets run at lower velocities, but they also need more twist, so there are hard limits on the high BC jacketed bullets at high velocity approach. Hunting rifles or entertaining toys can push things harder.

The 338 Snipetac would enjoy a larger selection of solid bullets than the 30 cal.

The 33xc has a level of overbore similar to the 416 Barret and improved 375CT cartridges. The 375xc is similar to the 338 lapua, 300WM, and a little more than the 408CT. I think the 33XC case capacity was well thought out.

 

[Dave62677]

anyone know any gunsmith can chamber 37xc in AXMC large shank?

spoke to milehigh, sales reps said his gunsmith is out of town
Emailed David Tooley, he said he don't have the barrel

 

[camotoe]

I would try Alex wheeler over on accurateshooter.com

Does excellent work

 

[White Mamba]

anyone know any gunsmith can chamber 37xc in AXMC large shank?

spoke to milehigh, sales reps said his gunsmith is out of town
Emailed David Tooley, he said he don't chamber that with AI

BGM rifles probably would, hes done a few AXMC barrels for me. You would probably have to have the reamer

 

[Catdaddy]

I am running a Schneider 31in 1-8 twist barrel shooting the 300 grain Berger and can only get 117.6 grains of BMG-50 before its starts to show pressure on the primmer. this gives me 3040 FPS. So far accuracy has been very good.

I am running the same barrel and am getting 3140 out of 300 grain BN coated SMK’s with 121 grains of RE 50. No pressure signs and would like to push it faster but with4.2/11 SD/ES I am happy with it as it is.

 

[DAVETOOLEY]

anyone know any gunsmith can chamber 37xc in AXMC large shank?

spoke to milehigh, sales reps said his gunsmith is out of town
Emailed David Tooley, he said he don't chamber that with AI

I think I said I didn't have a barrel. Not that I wouldn't do it. A 37 cal barrel for an AXMC is a rare bird.

 

[Dave62677]

I think I said I didn't have a barrel. Not that I wouldn't do it. A 37 cal barrel for an AXMC is a rare bird.

My bad, i edited my post. My apology.

 

[Yerman]

Any chance you guys running 33XC and/or 37XC can put some load data up? I'm looking to see how well you are able to keep your SD and ES down with the longer cases and long strings of fire.

 

[Catdaddy]

Yerman,
Here is a 10 shot string. 33XC 300gr. BN coated nose ringed SMK. 3138 FPS average with an SD of 4.2 and ES of 11.
I wish I could lay claim to this Load but it is Factory loaded ammo from David Tubb.
I will be reloading the Spent brass to the exact load he loaded for me. This wasnt load developed it was just the load he loaded for me according to the barrel and reamer spec he chambered for me. He loaded me 500 rounds and seated them too long to chamber. I played with the seating depth with a hand press and will just seat as many as I am shooting that day so I can continue to ride the lands as my chamber grows. I am about 400 rounds into this load and it has stayed the same so far.
33” Schneider 5P 1:8 barrel, 121 gr RE 50 and federal 210 primers, Peterson brass.

 

[MACHTECH]

Any chance you guys running 33XC and/or 37XC can put some load data up? I'm looking to see how well you are able to keep your SD and ES down with the longer cases and long strings of fire.

I just loaded 50 rounds for a friend of mine for fire forming his brass. I loaded 116 grains of Retumbo and seated the 300 grain Berger's right at the lands. His rifle is an AXMC with a 30" barrel. He called me from the range, super excited with the accuracy and velocity of just over 3100. That was just a starting point for us, I can get back to you when we finish load development.

 

[hypertex]

For use in Quickload, anyone have the H2O capacity for the 37XC? Found the 33XC in the lit @ 137.5gr

 

[odoylerules]

Anyone have the H2O capacity for the 37XC? Found the 33XC in the lit @ 137.5gr

I thought they were the same. The brass is identical, just necked up to become a 37xc

 

[jasent]

Yes both are 137.5 measured at bottom of the neck

 

[SIDS01]

Anyone have the H2O capacity for the 37XC? Found the 33XC in the lit @ 137.5gr

Measuring to the top of the case so QL can use it:

An unfired and sized piece of 33XC brass was 138.0 grains of water

The fired and unsized piece of 375xc brass shipped with the dies was 143.0 grains of water.
Sizing that piece of 375 brass brought it down to 140.7 grains of water.

I'm not sure what the capacity to the top of the shoulder is all about. Most of the information out there on other cartridges is to the case mouth. That's what QL uses. Water to the case mouth has enough accuracy problems, to the bottom of the neck is much harder to do repeatably.

The case lengths are the same, so the 375 capacity at the bottom of the neck will be lower than the 33 because the shoulder junction moves down with the larger neck diameter. The 375 capacity will be larger to the case mouth because of the larger diameter neck. Splitting hairs aside, that unfired 33XC brass will probably pick up a grain or two after it is fired and sized, bringing the capacities of the 2 cases closer together. These were single case measurements. Averaging a larger number of cases may give different results.

 

[hypertex]

Thanks

...
The fired and unsized piece of 375xc brass shipped with the dies was 143.0 grains of water.
Sizing that piece of 375 brass brought it down to 140.7 grains of water.
...

 

[hypertex]

Been wanting a switch barrel system ever since my friend GIXXER2000 got his PSR. Called up Superior Shooting Systems and had a very informative conversation with David Tubb. Bottom line is a new Tubb gun is in the works and it's going to be a 37XC Barrels are coming in and I'm on the list so I'm hoping that tracking number will be sent soon. All my rifles up to this point have been of traditional design, this is the first tube gun and it's a switch barrel to boot. Going to be nice!

Have been sizing and opening up some 33XC brass I received from GIXXER2000 and I'm looking forward to stretching some legs on the range. I'll start a new thread when I've got some real data.

 

[hypertex]

Got the rifle running; sending some rounds downrange just to get some pressure dope on the 37xc. Using 8133 on a 108 degree day here in AZ.

 

[hypertex]

Tubb ATR 37xc 33" 1:8 twist
Going to start a 37XC load thread since there isn't one...

 

[7mmShooter]

Looks great Hypertex

 

[SIDS01]

30" 1"9.3 Bartlein, once fired neck turned Tubb brass, 256 Warner at 4.440" oal (touching the lands), 215M, N570. 112, 113, 114, 115 grains. I used the solid bullet reamer spec with a few thou taken out of the neck diameter. 60 rounds down the barrel when these started. Air temperature was 88 degrees and these were out while I did another 25 shot ladder with barrel cool downs.

This was the first guess pressure ladder. It looks like it came out a few grains low. No pressure signs, no really. Extractor groove expansion was zero for 4 of the 5 shots in the heaviest charge. I'll do 3-4 more steps to see where it tops out and if the velocity spreads hold.

I'm not getting much joy from H50bmg and jacketed bullets yet. I've tried the 300 Hybrids and the 285 ELDm. The 285s did better. I also tried Retumbo with the jacketed bullets and the H50 did better.

 

[Jim Boatright]

30" 1"9.3 Bartlein, once fired neck turned Tubb brass, 256 Warner at 4.440" oal (touching the lands), 215M, N570. 112, 113, 114, 115 grains. I used the solid bullet reamer spec with a few thou taken out of the neck diameter. 60 rounds down the barrel when these started. Air temperature was 88 degrees and these were out while I did another 25 shot ladder with barrel cool downs.

This was the first guess pressure ladder. It looks like it came out a few grains low. No pressure signs, no really. Extractor groove expansion was zero for 4 of the 5 shots in the heaviest charge. I'll do 3-4 more steps to see where it tops out and if the velocity spreads hold.

I'm not getting much joy from H50bmg and jacketed bullets yet. I've tried the 300 Hybrids and the 285 ELDm. The 285s did better. I also tried Retumbo with the jacketed bullets and the H50 did better.

View attachment 7123393View attachment 7123394View attachment 7123395View attachment 7123396

These loads look very good for muzzle speed uniformity. "Gravity Drop" variation will run -2*(dV/Vmean)*total drop from bore axis at the target. You can use an "unbiased standard Deviation" for dV. For a 5-shot sample size, the "unbiased SD" is 1.118 times the SD computed in your chronograph.

I recommend using QuickLOAD(c) interior ballistics software to analyze your ladder firing data. Adjust the shot-start pressure for each bullet type for best muzzle speed matches. Their maximum average pressure estimates then indicate where you go next. Use the piezoelectric transducer (CIP) method for MAP data. I like loads in the 62 ksi MAP range for 338 LM. Look for one-time case head expansions of 0.0010 to 0.0015 inches.

The newest version of QL has VV-N565 powder characteristics, but does not include David's new 33XC/37XC cases. You can simply select the 338 LM cartridge and then lengthen the case length and enter your fired case water weight.

I believe that David mentioned using a case full of H1000 (118-gr?) with our 246-gr copper bullets. He fired our 246-gr monolithic copper bullets at 3394 fps mean muzzle speed optically measured with his Oehler System 88. ES was 32 fps and SD was 13 fps, though. Those bullets were made with an over-diameter 0.3386-inch rear driving band for gas obturation. I have since reduced that OD to 0.3384-inch, which should still seal the powder gasses effectively.

 

[SIDS01]

I recommend using QuickLOAD(c) interior ballistics software to analyze your ladder firing data.

QuickLoad dangerously over estimates the charge weight for N570 for the combination used in the pressure ladders documented above.

I'm not trying to be obtuse or confrontational, I just wanted to put that front and center before we have a conversation that's going to put half the internet to sleep.

I do use QL and find it very useful. Like any other modeling software, its a bit like a motorcycle. It'll launch you over a cliff if that's what you direct it to do.

I use a QL method similar to what you describe. I also adjust the scaling factor to reflect the overbore ratio. Starting with 0.45 for the 338 Lapua and lowering it to 0.35 for the 33XC. If this isn't done, the diminishing velocity returns effect with magnum cartridges is exaggerated. Unfortunately, in this case, it takes the model in the direction of higher charge weight estimates for N570. It does give better agreement with the Hodgdon Extreme powder line and jacketed bullets.

I moved to the extractor groove for my case head expansion measurements because it gave results less dependent on the case projection from the chamber. I take one measurement with a blade micrometer aligned on the first letter of the case manufacturers name before firing and a second after it's cooled. I'm not as interested in precisely estimating pressure as brass life. The assumptions there are if you can reload the brass multiple times, the load is safe in the gun, and that the primer pocket is going to limit case life. At this point, I'm not sure that's going to be true with this cartridge. The brass is very hard, which will keep those primer pockets tight. The case is also very long and the case taper very low, making sizing a pita with that hard brass. I think the sizing effort will encourage restraint on pressure.

That being said, the top load in that ladder is estimated at ~59 ksi using QL. At this point, I'm guessing that load will top out at 3350 fps. I won't really know until I load it in fresh brass, measure the extractor groove expansion, and then try sizing it.

There was some interest in N570 earlier in this thread. The purpose of the post was to provide some information on a safe starting point. It also confirmed that N570 gave both good velocities and great velocity spreads.

 

[SIDS01]

The reason I started with the 33xc is it was a cheap way to generate some experience with a variety of solid bullets. The 338 caliber allows a direct comparison between a variety of both jacketed and solid bullets. The idea was to start with a jacketed bullet load that was presumed to be straight forward to develop, and then compare the long range scoring of various solid bullets against it. Scoring, not raw ballistics, with an emphasis on BC variation induced vertical dispersion. We have a KO2M day 1 style course set up with permanent targets about 30 minutes away that we use for this type of testing. The targets run from 1200 - 2300 yards.

The approach is to start with pressure ladders to find primer/powder combinations that give low velocity spreads with this cartridge and the bullets we'd like to test, then move to the long range testing. It was assumed that the 215M/H50 combination was a done deal for the jacketed loads, but this hasn't proven to be the case. The problem is probably on my end. I was going to start with H1000 for the solids and keep the single/double based power comparisons for later, but opened with the N570 out of curiosity.

I started the testing with an off the shelf 1:9.3 Bartlein from Bugholes while waiting for a 1:7 from Bartlein. I'll do the bulk of the screening and jacketed bullet baseline with the off the shelf barrel, then test the solids again with the 1:7.

 

[Jim Boatright]

I find N570 to be perfect for our new 245.35-gr monolithic copper 338 bullets in 338 LM chambering. QL shows the Z1 and Pmax occurring exactly together. We are still using 10 year old Lapua-made cases with no neck turning. They have each been fired dozens of times in ladder and group tests with many different bullets. The first time each case was fully fire-formed with a load generating about 62 ksi MAP (Piezo CIP), the case heads expanded 0.0010 to 0.0015-inch and completed their work hardening to an "extra-hard" state for 70Cu/30Zn cartridge brass. No cases have been lost, and we do not do case-neck annealing. I use a Redding FL resizing die with a 0.366-inch TiN neck-sizing button with headspace controlled by bottoming-out against a custom-fitted Redding shell holder in my Redding UltraMag press. Keeps the brass straight and H/S within 0.5 thousandths. The ram and shell holders are lapped square with the press axis. We use Federal 215 or 215M primers exclusively, and are loading 100.0 to 103.5-gr of VV-N570.

You do not mention varying the Shot-Start (SS) pressure in QL. That, along with "usable combustion chamber volume" are the primary QL rifle/chamber variables affecting calculated peak MAP chamber pressure versus chronograph measured muzzle speeds. I use SS = 12,250 psi for my non-coated, over-diameter (0.3386-inch), half-hard copper prototype bullets to agree with Magneto-Speed measurements. This SS pressure does not include the 2 or 3 ksi chamber pressure required to release the bullets from the case necks, but that should be included in SS pressure when "jam seating" any bullet into the throat or when bullets are seated "contacting" the lands. I am using a 4-degree throat half-angle as a "worst-case" test for SS pressure requirements. Our Rear-Driving-Band dual-diameter bullets cannot be seated into contact, but they do sometimes momentarily pause before engraving the rifling---requiring them to overcome static friction during that engraving process.

 

[Jim Boatright]

SID, you mentioned having difficulty in FL-resizing your 33XC brass. If you are already using Imperial Sizing Die wax ("sparingly"), and your chamber and die are properly polished internally, that sounds like a minor disagreement between their dimension specifications. In my custom 338LM reamer, I reduced the taper of the chamber case walls from the CIP-spec 0.2154-inch per 20-inches to 0.1983-inch/20-inches by reducing the 0.200-inch chamber ID reamer dimension from 0.5917-inch to 0.5880-inch. I retained the CIP-spec 0.5452-inch shoulder ID for compatibility with standard dies. This works very well with my Lapua-made brass. I recommend a 0.3690-inch neck and a 0.3388-inch ball seat ("freebore"). No neck turning should be required with any bullet OD. By tightening the rear ID of the chamber, the cases never bulge asymmetrically just ahead of the case web. I experience no difficulty in FL-resizing in my Redding UltraMag press as described above. I am only setting back the case shoulders about 0.5 thou in each reloading. I set the TiN neck-sizing button to resize only about the front half of the case neck.

I use a "minimum brass movement" philosophy for FL-resizing, and never use a "neck expander" ball or any type of "neck-size-only" or "shoulder-bump" die. Excessively headspacing the brass is probably the single biggest problem in attempts at precision reloading. I use the same "GO" chamber headspace gauge both in chambering each barrel and in setting my FL-resizing die. Tolerances are +/-0.0005-inch. I de-prime fired cases using a Neil Jones custom "plier-type" tool followed by case cleaning and hand washing to avoid abrasive primer dust contamination. I run in a carbide primer pocket uniformer tool for cleaning, but mainly to check for brass bulging down into the primer pockets. I do occasionally run the case necks over a carbide end-cutting reamer to eliminate the internal "dreaded donut" which bottlenecked cases are prone to developing in repeated firing. Those reamer/mandrels are made as mandrels for K&M neck turning tools. I do not turn neck OD's, though, with good brass.

 

[SIDS01]

I find N570 to be perfect for our new 245.35-gr monolithic copper 338 bullets in 338 LM chambering. QL shows the Z1 and Pmax occurring exactly together.

You do not mention varying the Shot-Start (SS) pressure in QL. That, along with "usable combustion chamber volume" are the primary QL rifle/chamber variables affecting calculated peak MAP chamber pressure versus chronograph measured muzzle speeds.

My first experience with N570 was bad. I was testing the benefits of using temperature sensitive powders on cold days in a 300wm. I started with best practices for my standard H1000 load, which included the use of a standard large rifle primer. It was about 35 degrees. I'd taken several grains out of the max load suggested by QL and it was still hotter than expected. It also hang fired. I stayed away from it for quite awhile after that.

The most positive experience with it before these 33xc ladders was with a 30/338 Lapua Improved load with a 198 Flatline. The average velocity is 3560 fps, SD 7, ES 20 using development brass. I have a fresh batch of brass loaded up that I hope will drop the velocity spreads some.

I'm not familiar with the Z1 / Pmax timing criteria, perhaps you could explain that?

What follows is my working mental model of QL. I"m not suggesting it's correct or that anybody else needs to subscribe to it. It serves my purposes, which are varied, but the most critical is identifying powders and starting charge weights that let me get through the first pressure ladder with both eyes and all my fingers.

I do use an effective case volume concept rather than just the measured case capacity in some models. Its easy to accept that the freebore contributes to the effective case volume, but I have trouble rationalizing using less than the measured volume. I think you mentioned higher than typical bullet pull requirements being one explanation. I'm OK with the notion that different powders will require different modifications to the measured case volume.

I also vary start pressures to get the models to line up with chrono data and my guess on what the peak pressures are. I keep in mind that I don't really know what the pressures are because I don't have any way of measuring them. The next observation is the model might match one load pretty well, but it doesn't actually track the full pressure ladder. Or the next powder. I think a big problem with the start pressure adjustment is it's an incomplete description of whats going on. There is an engraving force, and its duration varies with bearing surface length. The length or duration of the engraving is different for each bullet but we have no way to describe that. It also affects different powders differently. I also think there is a timing aspect from the combined effects of jump, ogive shape, and throat angle.

I use the weighting factor to alter the peak pressure / velocity relationship. Lower values lower pressure estimates and increase the velocity estimate. Again, different powders can require slightly different weighting factors, but the largest driver is overbore ratio.

I don't change powder characteristics. Those were tested and at this point we're at least 2 layers deep in a heavily compromised model. The idea of adjusting actual data to make the model match doesn't work for me. It's also not required for the way I use the model.

I think QL is a great tool for wildcat loading, but it's limitations need to be respected. Even with standard cartridges, virtually every long range load is a wildcat.

 

[SIDS01]

SID, you mentioned having difficulty in FL-resizing your 33XC brass. If you are already using Imperial Sizing Die wax ("sparingly"), and your chamber and die are properly polished internally, that sounds like a minor disagreement between their dimension specifications. In my custom 338LM reamer, I reduced the taper of the chamber case walls from the CIP-spec 0.2154-inch per 20-inches to 0.1983-inch/20-inches by reducing the 0.200-inch chamber ID reamer dimension from 0.5917-inch to 0.5880-inch. I retained the CIP-spec 0.5452-inch shoulder ID for compatibility with standard dies. This works very well with my Lapua-made brass. I recommend a 0.3690-inch neck and a 0.3388-inch ball seat ("freebore"). No neck turning should be required with any bullet OD. By tightening the rear ID of the chamber, the cases never bulge asymmetrically just ahead of the case web. I experience no difficulty in FL-resizing in my Redding UltraMag press as described above. I am only setting back the case shoulders about 0.5 thou in each reloading. I set the TiN neck-sizing button to resize only about the front half of the case neck.

I use a "minimum brass movement" philosophy for FL-resizing, and never use a "neck expander" ball or any type of "neck-size-only" or "shoulder-bump" die. Excessively headspacing the brass is probably the single biggest problem in attempts at precision reloading. I use the same "GO" chamber headspace gauge both in chambering each barrel and in setting my FL-resizing die. Tolerances are +/-0.0005-inch. I de-prime fired cases using a Neil Jones custom "plier-type" tool followed by case cleaning and hand washing to avoid abrasive primer dust contamination. I run in a carbide primer pocket uniformer tool for cleaning, but mainly to check for brass bulging down into the primer pockets. I do occasionally run the case necks over a carbide end-cutting reamer to eliminate the internal "dreaded donut" which bottlenecked cases are prone to developing in repeated firing. Those reamer/mandrels are made as mandrels for K&M neck turning tools. I do not turn neck OD's, though, with good brass.

I also use Imperial Sizing wax. The 338 Lapua chamber has a .0215"/" case taper. The 33XC only has .009"/", so it's a different animal. The reloading area was nearly 100 degrees when I sized the cases. The sizing wax was pretty runny, which may have contributed to the problem.

I agree that tightening the base of the chamber reamer would help, but am reluctant to do that in general. I don't have any control over what the next lot of brass will look like, so I stick with the standard dimensions for the case body portion of the reamer. For this project, I went with Tubb's dimensions on the body, but did take some out of the neck. With neck turning, I have more dimensional control over that end of the case and am less at the mercy of lot variations. It's also proven to be worth the time when I've tested it in other cartridges. 338 lapua, maybe not. I've been experimenting with necked down and improved 338 Lapua cases. It's been a requirement with those and it's just not that big a deal at this point. I used 0.012"/" for the case taper on those.

For the ladder above, the brass was once fired in pressure ladders with Retumbo and H50bmg. It was turned to 0.0145" neck thickness before firing with the K&M tool that also cleans out the inside. There wasn't even the start of a tight spot at the shoulder/neck junction. It was decapped with a Lee universal decapper that had been bored to clear 338 improved cases, cleaned in SS pins, chamfered inside and out before sizing. Lubed with Imperial including inside the neck, sized with the Tubb die and a 0.363" bushing, expanded with a Lyman M die. The inside of the neck was honed with a 338 caliber bore brush in a drill. The lube was removed in a vibratory cleaner filled with walnut shells that don't have any polishng agents and are only used for removing case lube. The idea is to leave a very light coat of lube on the case. Powder was dumped with a Hornady trickler and trickled to weight with Adams trickler on a FX120. N570 chokes the original Autotricklers powder drop. V3 should be here any day now, we'll see how it does. Hand prime with the Frankford Arsonal tool. I put a light coat of Imperial on the FlatLine boat tail transition and bearing surface, then seat with Tubb's die.

I have to figure out a trimming scheme next.

I understand that another 100 fps isn't going to change anything, but I also bought a magnum and don't need brass to last forever either. If I find that the 33xc is going to be a keeper, I might do more testing to define best practices for the components available for this cartridge. That test will start with 2 sets of 10 cartridges. One will be the baseline, the other will have changes to the process evaluated. If the velocity spreads stay in the range of those above, I won't bother. I will section a case or two in this first batch every few firings.

I have some VV 24N21 on the way to try with the jacketed bullets. I'm going to try a couple more steps in the 256 FlatLine ladder. I'll use that information to set up ladders for the 277 MTAC and 285 flatline. Then I'll be able to move to the long course. I don't really like all this 100 yard testing.

 

[Jim Boatright]

In the lower left-hand quadrant of the QL display screen, I usually select a display of chamber pressure and bullet speed versus bullet position in the barrel. The bullet position at maximum chamber pressure (Pmax) is annotated as a black vertical line going through that pressure. There is a break-point (Z1) in the mathematical function defining the burning rate of each type of powder. It is annotated as another black vertical line. It just turns out that the best burning-rate propellant for most loads is found when Z1 coincides very closely with Pmax.

Weigh the water contained within a topped-up fired case carefully and several times. Enter the average water weight into QL and DO NOT DORK WITH IT. Over-ride any default value with actual measurements as well for case length, bullet length, and (especially) cartridge over-all length (COAL). Select and enter accurate data for boat-tail base treatment as appropriate. Let QL calculate the usable combustion chamber volume. Enter the powder type and amount, noting the fill ratio displayed. QL overestimates case fill by up to 5-percent for the way we "swirl in" our powder charges. Dump the powder slowly from a weighing pan into a caliber-specific funnel on the case mouth. Pour the powder in near the lip of the funnel and directed tangentially so that it always swirls down toward the discharge hole. This more dense powder packing is important for burn consistency and really cannot be obtained by any other method. I never use compressed loads of smokeless propellants and prefer a 90 to 99.5-percent case fill. Approaching 90-percent fill ratio, powder positioning at firing time becomes an increasingly significant variable which must be controlled.

Fire the lightest loads of you ladder and, while the barrel cools, enter one of those loads into QL. Adjust the Shot-Start (SS) pressure so that QL calculates that measured muzzle speed. Inspect the chamber pressure function displayed, checking where Z1 falls relative to Pmax. Z1 will be to the left of Pmax for powders which are too fast-burning in these conditions. Try some of the heavier charges of your ladder in QL and see if you really want to fire them. Any Pmax less than 70 ksi should be safe enough in stout, well fitted, custom target rifles, but might damage your brass. As always, switch to a slower-burning propellant to obtain faster muzzle speeds with lower peak pressures.

There is very little wrong with QL if it is properly used. It is "frighteningly accurate."

My earlier discussion of neck release pressure and dynamic versus static friction concerned the TIMING of these SS pressure components. If the bullet releases from the neck (earlier) and accelerates into the throat, minimum SS pressures will be needed to match measured muzzle speeds. [I standardized on Magneto-Speed measurements to eliminate the variables of downrange positioning and span of optically sensing chronograph screens.] If the bullet is seated into "contact" with the lands, the SS pressure used in QL must be increased due to the bullet having to be simultaneously releasing from the neck, overcoming static friction, and engraving the rifling.

 

[John Glidewell]

enter one of those loads into QL. Adjust the Shot-Start (SS) pressure so that QL calculates that measured muzzle speed.

why not adjust the Ba burn rate of the powder to match? If everything else is correct?

 

[Jim Boatright]

That's fine Gwain, as long as you just vary one parameter at a time and have a reason for doing it, such as powder lot variation.

Shot-Start Pressure covers a multitude of variables in QL, which is one of it weaknesses. QL also does not consider variability of primer characteristics. I also do not really like the way QL handles friction modifying coatings. But these are just quibbles. It is a really great product for serious riflemen.

 

[John Glidewell]

Thanks. Still learning. Sometimes it is dead nuts, and other times it is not. (multiple rifles and bullet/powder combos) When it is on I can norm see pressure where I would think according to QL. Other times it well before or after, even if the rest of it is right. It seems very sensitive to input data so maybe I am screwing up data in the other profiles.

 

[Jim Boatright]

Yes, Pmax is very sensitive to combustion chamber volume and SS pressure in Ql which is true in real life, as well. That is why I warn tyros about playing with bullet seating depth (or "bullet jump") near a max load.

Making mistakes and sometimes learning from them is called "experience." I have almost 60 years of that kind of experience.

 

[biffj]

Having no primer information makes it really tough. I found that the standard match large rifle primers worked best in my 33XC as I was seeing pressure signs at much lower charge weights and resulting in lower velocity and accuracy with the Magnum match primers. Unfortunately there is no way to determine in QL which primer is best so a lot of powder is wasted trying to determine that one thing.

Frank

 

[John Glidewell]

I will run the same load with different primers and save them with the primer name. Helps to show which ones are hotter etc. Yes, not having specifics makes it tough some times, I just build a profile and create my own data to use.

 

[SIDS01]

2x fired 33xc brass, 215M, VV 24N41, 285 ELDm @ 4.180" and 285 Flatline @ 4.505", both bullets just touching the lands.

The purpose of this test was to generate information on the use of VV 24N41 as a H50bmg substitute and to compare the start pressures of the solid and jacketed bullets. The stars aligned and the Usable Case Capacity under the seated bullets is nearly the same when the bullets have the same jump to the lands.

The steps are wide because I didn't have a lot of confidence in where I was starting and wanted to make sure the ladder started low enough to get something useful from the trip. I thought I'd be pulling the bullets on the top loads rather than shooting them. I don't have a lot of confidence in the consistency of the neck prep for this set. This was the first time the cases were trimmed, and my first time using the new Lyman trimmer. The cuts were clean and consistent, but in some cases the cutter put a pretty good thump on the cases and I trimmed after I set the neck tension to avoid expanding the necks through a mixture of case lube and trimming swarf. This may have affected the SDs.

Compressed loads started at 121 grains.

At 68 F.

For the 285 ELDm:
115 grains, 2981 fps, 6.5 SD
117 grains, 3049 fps, 13.4 SD
119 grains, 3100 fps, 8.2 SD
121 grains, 3168 fps, 7.1 SD
123 grains, 3231 fps, 7.7 SD

No ejector marks, bolt lift effort went up at 123 grains with the ELDm, but not the Flatline and it wasn't heavy. I'm going to use 121 grains as max for now.

For the 285 Flatline:
117 grains, 3026 fps, 12.2 SD
119 grains, 3069 fps, 10.5 SD
121 grains, 3137 fps, 7.6 SD
123 grains, 3202 fps, 10.1 SD

From the velocities, it looks like the start pressure for the Flatline is lower. That results in ~30 fps lower velocity at the same charge weight. QL suggests it takes ~1 grain more to match the velocity, and ~2 more grains to match pressure which gives another ~25ish fps over the jacketed bullets. That's on top of the ~16% higher advertised BC.

These are the most promising single base powder jacketed bullet results I've had so far. I think the next step is using this powder to try to work the velocity spreads down with neck tension and jump for charges between 119 and 121 grains with the 285 ELDm. What I'm trying to set up is a relatively inexpensive all temperature go to load to evaluate the solid bullet and double base powder performances against.

YMMV

 

[jasent]

37XC shooters
Are you necking up your self or having superior Shooting Systems do it when you order brass. I have a .375 expander

 

[MACHTECH]

I've not read completely thru this entire thread, so forgive me if this has been covered already....

Is anyone else experiencing extremely tight resizing with your Tubb resize die? After fireforming to the Manson .250 FB chamber, the body of the case has expanded to a point that the cases are getting stuck in the die and tearing the cases out of the shell holder. I have two other friends experiencing the same thing. I'm curious if anyone has talked to David about this issue? I have to contact him this week or just ID grind the die to fit my case.

 

[biffj]

I used the Dave Manson reamer with the .1 freebore and have had no issues at all with the dies or chamber. I bought the throater for the jacketed bullets too in case anyone wanted to shoot them but so far no takers. Everyone has wanted to run solids. I don't know of anyone else having problems with cases sticking in the die. I've been using the Hornady paste lube for sizing.....not sure if that makes any difference. I did find that the rcbs water soluble lube wasn't worth a crap for my 338 lapua but the hornady stuff did great.

Frank

 

[SIDS01]

Is anyone else experiencing extremely tight resizing with your Tubb resize die? After fireforming to the Manson .250 FB chamber, the body of the case has expanded to a point that the cases are getting stuck in the die and tearing the cases out of the shell holder. I have two other friends experiencing the same thing.

I've had tight resizing with higher pressure loads. Backing off the load took care of it. The loads in post #235 had difficult sizing with both bullets at 123 grains and with the jacketed bullet at 121 grains.

The die was scraping the lube off creating a dry ring on the case. Stopping the sizing before it became too difficult and spreading the lube back around before finishing the reszing salvaged the cases. I'm using Imperial Sizing Wax. The problem is worse when the die is new or after cleaning it.

The sized cases are 0.002" under the reamer drawing at the shoulder and lower datum, so the die looks right. I think the combination of low body taper and hard brass make difficult sizing set the pressure limit, and it's way up there.

 

[hypertex]

I use the Sinclair expander mandrel die to

37XC shooters
Are you necking up your self or having superior Shooting Systems do it when you order brass. I have a .375 expander

I use the Sinclair expander mandrel die to neck up. Hope Petersen offers a direct solution soon.

 

[Catdaddy]

33XC David Tubb recommended load for 33 inch barrel chambered by Tubb shooting BN coated 300 grain SMK. RE50 Fed 215 primers.

 

[Dan Warner]

2x fired 33xc brass, 215M, VV 24N41, 285 ELDm @ 4.180" and 285 Flatline @ 4.505", both bullets just touching the lands.

The purpose of this test was to generate information on the use of VV 24N41 as a H50bmg substitute and to compare the start pressures of the solid and jacketed bullets. The stars aligned and the Usable Case Capacity under the seated bullets is nearly the same when the bullets have the same jump to the lands.

The steps are wide because I didn't have a lot of confidence in where I was starting and wanted to make sure the ladder started low enough to get something useful from the trip. I thought I'd be pulling the bullets on the top loads rather than shooting them. I don't have a lot of confidence in the consistency of the neck prep for this set. This was the first time the cases were trimmed, and my first time using the new Lyman trimmer. The cuts were clean and consistent, but in some cases the cutter put a pretty good thump on the cases and I trimmed after I set the neck tension to avoid expanding the necks through a mixture of case lube and trimming swarf. This may have affected the SDs.

Compressed loads started at 121 grains.

At 68 F.

For the 285 ELDm:
115 grains, 2981 fps, 6.5 SD
117 grains, 3049 fps, 13.4 SD
119 grains, 3100 fps, 8.2 SD
121 grains, 3168 fps, 7.1 SD
123 grains, 3231 fps, 7.7 SD

No ejector marks, bolt lift effort went up at 123 grains with the ELDm, but not the Flatline and it wasn't heavy. I'm going to use 121 grains as max for now.

For the 285 Flatline:
117 grains, 3026 fps, 12.2 SD
119 grains, 3069 fps, 10.5 SD
121 grains, 3137 fps, 7.6 SD
123 grains, 3202 fps, 10.1 SD

From the velocities, it looks like the start pressure for the Flatline is lower. That results in ~30 fps lower velocity at the same charge weight. QL suggests it takes ~1 grain more to match the velocity, and ~2 more grains to match pressure which gives another ~25ish fps over the jacketed bullets. That's on top of the ~16% higher advertised BC.

These are the most promising single base powder jacketed bullet results I've had so far. I think the next step is using this powder to try to work the velocity spreads down with neck tension and jump for charges between 119 and 121 grains with the 285 ELDm. What I'm trying to set up is a relatively inexpensive all temperature go to load to evaluate the solid bullet and double base powder performances against.

YMMV

Interesting results there. I am rather surprised at how close the velocities compare between the two bullets with the same charge behind them. While they are slower as you report, I would have expected something closer to 100fps difference between them. In most cases, one needs more of, or even the next faster powder behind the Flatline to achieve the same speeds. For those that don't know, this is because the bearing surface is so much shorter, so the coefficient of friction is a fraction of that of the jacketed pill.

 

[SIDS01]

Interesting results there.

I think it's unusual to have the bullet weight, remaining case capacity, and bullet jump to line up like this.

At the end of the day though, it's only a comparison between just one of the Flatlines and one jacketed bullet with a single powder that probably favors the jacketed bullet. A faster powder might be a better way to exploit the lower start pressure, even at the same bullet weight. If the same powder wasn't used for both bullets, the results would be more subjective.

The 285 ELDm also appears to have a lower start pressure than the 300 Hybrid, which probably would be a more typical comparison with the Flatline.

If a 30 fps and 16% BC advantage is what we're down to, it's not so bad.

I agree the Flatlines can be used to create combinations that stack and compound their advantages over jacketed bullets. The 256 Flatline / N570 loads in post 220 are an example. In that case, I think N570 is too fast for the 285s and will wind up running the 256s until N575 or N580 comes out. It's just a guess though, I haven't tested the 285/N570 combination yet.

 

[Arvindthube]

I had my 338 LM barrel converged to 33XC with a Manson reamer. It shot lights out with 112 gr Retumbo and 300gr Berger. Shot furthest at a mile with it. SD was single digit.
I am shooting AI AXMC. Got 2 new barrels now .... Schneider 1:9 twist with Manson reamer per David’s specs. Going to run 50 TMS bullets from David this weekend before trying the load that worked before for me. I was getting 3030 for 300gr Berger. So far I am pretty happy with the cartridge.

 

[Arvindthube]

BGM rifles probably would, hes done a few AXMC barrels for me. You would probably have to have the reamer

Robert Dunett at Rubicon Precision

 

[Arvindthube]

I think I said I didn't have a barrel. Not that I wouldn't do it. A 37 cal barrel for an AXMC is a rare bird.

Schneider makes one for my AXMC. Measure the shank of your current barrel and call Gary. Schneider. He will help you out.

 

[DAVETOOLEY]

I've done Scheinder's for AXMC. I can get other manufactures barrels.

 

[odoylerules]

Any load data out there for a 33xc with a Berger 300gr and N570? I’m building this combo for a hunting rifle. Thanks

 

[47chevycoe]

Anybody know where I can pick up some 33xc dies? Tubb’s are out of stock and was told they have no idea when they will be back in stock. Really itching to put some rounds through this barrel.

 

[Matthew488]

Whidden should be able to make you some but I don't know what the lead time would be. They made my 375 BAS dies and are really nice.