I'll see what I can come up with. As for the crown, doesn't look spiffy to me, but then again I've read barrel length/velocity studies where they sequentially shot the barrel after cutting off an inch with hack saw... so no crown at all. Wait, I can't remember if it affected the groupings, but for sure it did not affect the MV's. Anyway, regardless your barrel deserves a return visit to the criterion guys, let them look at it and your results.
But I'll plug this all into my spreadsheets, let you know what pops out.
It does look to me as though there should be loads for each powder that would group well with an optimized coal... AR Comp's advantage is it is less temp sensitive than the CFE... if you're in WI that could be a benny for you.
NFL, Green Bay, hey? or Minnesota...?
"Down the floor, out the door, Go Brandon Go!!!!!"
grayfox Wrote:I'll see what I can come up with. As for the crown, doesn't look spiffy to me, but then again I've read barrel length/velocity studies where they sequentially shot the barrel after cutting off an inch with hack saw... so no crown at all. Wait, I can't remember if it affected the groupings, but for sure it did not affect the MV's. Anyway, regardless your barrel deserves a return visit to the criterion guys, let them look at it and your results.
But I'll plug this all into my spreadsheets, let you know what pops out.
It does look to me as though there should be loads for each powder that would group well with an optimized coal... AR Comp's advantage is it is less temp sensitive than the CFE... if you're in WI that could be a benny for you.
07-12-2018, 01:43 PM (This post was last modified: 07-12-2018, 01:46 PM by grayfox.)
I do a couple of things when looking for good loads, MV with SD<10 and ES in the teens, and a linear portion of load grs vs MV. Ideally powder, for typical ranges in a typical case, should behave pretty much in a linear fashion unless you get into real low or really compressed loads (but I avoid those types of loads), plus the SD/ES requirement usually shows you are in an OBT node, meaning the barrel muzzle tip is "far away" from the longitudinal pressure wave in the barrel steel... all of which are good things.
I'd estimate your 22" barrel has a node in the range 2480-2520 ("node #7" in the xls below). There are definitely other nodes as well but this one works for the 2 combos you show. Note the 2477 for CFE and 2509 for ARC (I'd also say you probably would find low SD/ES at 27.4 of AR comp, around 2490 ft/s, I interpolated that value on the graph). So for either or both of those loads play with coal in 0.010's of difference to see which coal will group the best. 2.250, 2.260, 2.270... or maybe 2.255, 2.265, 2.275 etc, something like that. My bet is that one of those will group tightly. What does the Coal variation do? It doesn't appreciably change the MV but it does change the timing of the bullet's arrival at the muzzle tip... and since these scenarios deal in microseconds of time, a 0.010 delta will allow for slight bullet tip length deltas but show timing changes by tighter or looser groupings.
[ATTACH=CONFIG]12222[/ATTACH]
[ATTACH=CONFIG]12225[/ATTACH]
"Down the floor, out the door, Go Brandon Go!!!!!"
grayfox Wrote:I do a couple of things when looking for good loads, MV with SD<10 and ES in the teens, and a linear portion of load grs vs MV. Ideally powder, for typical ranges in a typical case, should behave pretty much in a linear fashion unless you get into real low or really compressed loads (but I avoid those types of loads), plus the SD/ES requirement usually shows you are in an OBT node, meaning the barrel muzzle tip is "far away" from the longitudinal pressure wave in the barrel steel... all of which are good things.
I'd estimate your 22" barrel has a node in the range 2480-2520 ("node #7" in the xls below). There are definitely other nodes as well but this one works for the 2 combos you show. Note the 2477 for CFE and 2509 for ARC (I'd also say you probably would find low SD/ES at 27.4 of AR comp, around 2490 ft/s, I interpolated that value on the graph). So for either or both of those loads play with coal in 0.010's of difference to see which coal will group the best. 2.250, 2.260, 2.270... or maybe 2.255, 2.265, 2.275 etc, something like that. My bet is that one of those will group tightly. What does the Coal variation do? It doesn't appreciably change the MV but it does change the timing of the bullet's arrival at the muzzle tip... and since these scenarios deal in microseconds of time, a 0.010 delta will allow for slight bullet tip length deltas but show timing changes by tighter or looser groupings.
[ATTACH=CONFIG]12222[/ATTACH]
[ATTACH=CONFIG]12225[/ATTACH]
Thanks for this post sir.
Being new to loading in general this puts the effects of changing seating depths in a format my poor old Cajun brain can understand for effect on groups.
I adapted the studies by Chris Long, the long family, on OBT methods and his empirical formula for barrel nodes.
Put it into an Excel format. My approach is that, for a shooter whose barrel length is obviously fixed, the variables available for timing the bullet exit are MV (through bullet, powder and load grains selection) and COAL. A shooter doesn't really care what the node's particular number is for his barrel (ie, #3, #4, #6, etc), only that the bullet is exiting on or near the node.
I use this approach mainly because it relies on strictly objective data, the physical properties of steel, and the physics of accelerating an object to a terminal velocity. My personal shooting abilities are not perfect enough for me to judge nodes via shot placement on paper, there are too many variables (probably in the 0.001's of an inch even) in shooting technique and little pushes/pulls/flinches/cheek welds, etc during the shot. A true competitive or marksman shooter can probably do that, but I haven't been able to do so. Hence, the search for objective data instead.
grayfox Wrote:I adapted the studies by Chris Long, the long family, on OBT methods and his empirical formula for barrel nodes.
Put it into an Excel format. My approach is that, for a shooter whose barrel length is obviously fixed, the variables available for timing the bullet exit are MV (through bullet, powder and load grains selection) and COAL. A shooter doesn't really care what the node's particular number is for his barrel (ie, #3, #4, #6, etc), only that the bullet is exiting on or near the node.
I use this approach mainly because it relies on strictly objective data, the physical properties of steel, and the physics of accelerating an object to a terminal velocity. My personal shooting abilities are not perfect enough for me to judge nodes via shot placement on paper, there are too many variables (probably in the 0.001's of an inch even) in shooting technique and little pushes/pulls/flinches/cheek welds, etc during the shot. A true competitive or marksman shooter can probably do that, but I haven't been able to do so. Hence, the search for objective data instead.
Very impressive; much respect! Have you found other variables, like bullet type or weight, have any effect on these nodes?
I like your approach to load development. I’m going to follow your steps on my next super long range 7mm/Berger load. Ladder test combinations of powders/primers to find ultra low SD’s in the middle of large nodes with little POI shifting. Finalize load by adjusting seating and possibly neck tension.
Couple other things you can test for is use of a
a) different primer. Couple of studies online show primers can affect MV for a particular load-grain (not as importnat as you can usually add or subtract a 0.1 or 2...) and can tighten or loosen the SD spread. I've also done this a couple of times to pick one primer over another. In Grrr some of my loads use cci 450, some use Fed 205M's.
b) Of course brass mfr, and case uniformity. In my 308 Hornady and Remmy brass are thicker (smaller free volume) so a given grs of powder gives up to 150 ft/s more MV than the same load in a Win case. Almost went TOOOOOOOOOOOOOO hot in one ladder!! but caught it in time.
In my tests, bullet type or weight can affect ultimate MV that is possible for a given powder and barrel, but don't appreciably affect node per se... actual MV may move a bit, ie, if one 123 gr you can get a good node/accuracy at 2500 ft/s, another 123 may do slightly diff powder charge and shoot for you at 2485... but in reality it's the same node.
I have some 65 Creed loads for 129 SST, one powder is a node at 2706, sd-5, another powder 2691, sd-4. A different 129-er (Ablr) 2691 and 2743, again 2 diff powders... [granted mild loads but I like 'em] but basically the same node even though 2743 seems at the top end of that node. All of these are ~0.5 moa when I'm steady at the bench, and pretty much same POI. Now this is not exhaustive but it fits in with this being an empirical approach... I'm sure there are variables in the barrel and the bullet that we don't know or can't model but his OBT formula seems to work well anyway... his constants probably include those unknowns as a sort of "lumped estimate".
And, to top it off, your barrel may shoot these with slightly diff powder charges and wind up at say 2715 or 2685, or 2700, but that's what your barrel does. You have to let your barrel talk to you about what works and what doesn't.
"Down the floor, out the door, Go Brandon Go!!!!!"
I stopped by the Criterion shop last Friday and dropped the upper off. The Criterion guys have unbelievable customer service....better than I deserve anyways. Here is their finding:
On Jul 19, 2018, at 10:11 AM, CBI Customer Service <contact@criterionbarrels.com> wrote:
Eric,
Yes, I had a chance to take an in-depth look at your upper and I found several areas that are effecting accuracy. Starting from the muzzle and working our way back down the upper:
I found that the clamp on gas block was slightly off center. This is not so much a problem in regards to gas flow as the port hole was still inside of the gas block gas hole, however, when the gas block is out of alignment, it cants the gas tube. When the gas tube is not properly aligned it is not truly “free floated” as torque is applied to the tube when it enters both the upper receiver and every time the bolt carrier moves forwards and backwards and the gas tube slides in and out of the gas key (contact is made). This movement/contact applies torque to the barrel because the gas tube is affixed to the barrel via the gas block and negatively effects barrel harmonics (accuracy).
Barrels are like giant tuning fork and in order for them to perform consistently from shot to shot, all aspects of the rifle, ammunition, and shooter need to be exactly repeatable. When inconsistent tensions are applied to a barrel impacts will shift. Additionally, it appears that you ground down the gas block screws so that they wouldn’t make contact with your handguard (showing that you know about the benefits of a free floated barrel), however, there is now no way to remove the screws as there is no depth to the screw head to unscrew and realign the gas block properly. I do have replacement gas blocks on hand and would recommend using a more low-profile version that both avoids contact with the handguard and uses the set screw design in conjunction with our barrel dimple. This ensures a more solid attachment to the barrel and guarantees perfect alignment when the screw is aligned with the dimple recess. Clamp on designs do work very well but I prefer set screw gas blocks as they are more rugged. Clamp on versions can come out of alignment with the gas port hole if the gas block takes a hard enough blow and can render the gas gun into a bolt gun rather quickly.
I would be happy to remove the old gas block and replace it with a more serviceable gas block. I can also ensure that the gas key makes minimal contact with the gas tube and “free float” the tube. I generally true up the upper receive (both the raceway and the face of the receiver) to ensure that the barrel is not canted as it enters the upper (I have never found any upper from any manufacturer that is perfectly true from the factory). I would also recommend bedding the barrel into the upper using a slip fit compound to take up any slop in the fitment between the upper and the barrel extension. Lastly (and this is minimal), I found that you had trimmed the ejection port door rod. This is a good thing to avoid contact with the handguard, but it appears that a little too much material was removed as it can be pushed all the way to the handguard and come out of the rearward alignment hole. Surprisingly, I find that the port door rod also effects harmonics with the rifle if it makes contact with the barrel nut/handguard area which yours is currently doing.
Let me know how you would like to proceed and I will happily get to work on your upper truing it up and accurizing it for optimal performance (both accuracy and function). I do have several pictures and short video clips of your upper demonstrating the issues I addressed in this email. Unfortunately, I cannot send them from work as I do not receive very good reception out here. If you’d like to see them I can send them out to you as soon as I have service to forward them on. If you have any questions please let me know and I will get back to you as quickly as I am able.
Criterion response to my reply and direction to proceed:
Eric,
Sorry for the delay in my response. I completely went over your Grendel build, trued up your upper receiver (both the raceway and the face), bedded your barrel (again, as I saw that you had done that already), and replaced your adjustable gas block which was not serviceable with an SLR Rifleworks (adjustable) gas block at your request. I also replaced your port door rod with one that properly fit with your upper and handguard. I ensured that the gas tube was properly aligned and free floated. After building up your upper, I took it out to the range and shot several sub MOA groups (many were in the ½ MOA range and a few were sub ½ minute). I used a couple of different factory match loads. Of the factory ammunition I tested, your barrel seemed to like Hornady “Black” 123 grain ELD Match ammo the best.
-As far as Remington pre-fit barrels are concerned, we do produce barrels in a wide variety of chambering offering. Here is a link to the Remington pre-fit barrels:
Feel free to stop by the shop tomorrow evening and I will have your upper waiting for you. If you have any questions please don’t hesitate to contact me directly.
I thought I would close this thread on a positive note! Criterion has amazing customer service and I would highly recommend! Below is a load I have just finished with Hornady 123 SST’s for deer hunting. I’m very satisfied with the accuracy especially considering that these are hunting bullets.
I plan on working up a 130 Nosler RDF for 1000 yards next
VikingCruze Wrote:I thought I would close this thread on a positive note! Criterion has amazing customer service and I would highly recommend! Below is a load I have just finished with Hornady 123 SST’s for deer hunting. I’m very satisfied with the accuracy especially considering that these are hunting bullets.
I plan on working up a 130 Nosler RDF for 1000 yards next
