I'm working on enhancing accuracy of my Ruger RPR 6.5 CM using 140 gr Hornady ELD Match bullets. Published cartridge OAL from both Hornady and Lyman is 2.800". Using Hornady's OAL gauge, I have determined the maximum overall cartridge length for my RPR to be 2.850. Backing off 0.030" for bullet jump gives me 2.820", which exceeds the published OAL by 0.020". Anyone see any issues with this?
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6.5 Creedmoor Bullet Jump
- Thread starter Warthogge
- Start date
Your "published" COAL is the SAAMI standard so that cartridges will (should) fit in any 6.5 Creedmoor & function reliably.
Notably, what will fit in magazines.
If YOUR bullet choice fits in YOUR magazine, and gives YOU best accuracy at a longer COAL, then go for it!
I tend to use Savage rifles without detachable magazines. Which have fairly generous magazine lengths. Or if absolute best accuracy is desired, i single load.
SAAMI COAL is thrown out the window.
Notably, what will fit in magazines.
If YOUR bullet choice fits in YOUR magazine, and gives YOU best accuracy at a longer COAL, then go for it!
I tend to use Savage rifles without detachable magazines. Which have fairly generous magazine lengths. Or if absolute best accuracy is desired, i single load.
SAAMI COAL is thrown out the window.
No, other than both manuals need to be more careful with stating recommendations for
the modern .264 bullets which have very high ballistic coefficients.
Most bolt action magazines have much more available OAL than these recommendations.
ARs are an exception, and many manuals simply use an AR magazine length limit for their recommended length.
The recommended seating depth in the Sierra manual is 2.810 for their 130 TMK, 140 SMK, and 142 SMK bullets.
130 TMK has 1.375 bullet length and bullet base to ogive (BTO) of 0.763
140 SMK has 1.300 bullet length and BTO of 0.785
142 SMK has 1.367 bullet length and BTO of 0.762
There is no logical reason for the recommended OAL to be the same for all three bullets, but the manual has the same OAL recommendation for each.
140 ELD-M has 1.372 bullet length and BTO of 0.745
174 ELD-M has 1.442 bullet length and BTO of 0.792
Is it even reasonable that the OAL for these bullets should be the same with a manual recommendation 0.010 shorter than the Sierras?
If you go with the Hornady manual recommendation you will be seating these long bullets far back into the neck and increasing chamber pressure.
I would suspect that 2.800 was chosen for older bullets that were designed for the original 6.5mm European calibers rather than for the more modern high ballistic coefficient ELD-M bullets. Perhaps, the manual writers were just too lazy to measure the new bullets.
Comments on bullet jump:
I normally consider 0.020 as jump to start with, but your rifle will tell you what works best, but you need to experiment with your particular.
My original 6.5mm CM bolt action initially preferred 0.011 to 0.019 jump by a slight margin and that was out past 2.840 when the barrel was new.
I now have three 6.5 CM bolt actions, and each barrel had slightly different camber depths, and different jump preferences but they are all distributed around 0.020
But all three rifles shot best with OAL lengths much longer than the OALs recommended by the manuals.
As my original rifle's lands begin to erode with use, after 2,500 rounds the measured cartridge base to ogive grew 0.036 due to erosion.
I just kept increasing the seating depth to keep the preferred jump.
From my experience, how close to Pmax you load your rounds will determine the rate of
erosion. But, be advised, nothing stays the same with wear from use.
Your magazine will give you some idea of what max OAL limits are for your mag, if you want to use your mag, but that is not normally the limit of the chamber since with modern high BC bullets, there is lot of bullet tip that extends past the start of the lands.
I single load with single round follower if the OAL resulting from my preferred jump setting causes the OAL to exceed the mag length.
the modern .264 bullets which have very high ballistic coefficients.
Most bolt action magazines have much more available OAL than these recommendations.
ARs are an exception, and many manuals simply use an AR magazine length limit for their recommended length.
The recommended seating depth in the Sierra manual is 2.810 for their 130 TMK, 140 SMK, and 142 SMK bullets.
130 TMK has 1.375 bullet length and bullet base to ogive (BTO) of 0.763
140 SMK has 1.300 bullet length and BTO of 0.785
142 SMK has 1.367 bullet length and BTO of 0.762
There is no logical reason for the recommended OAL to be the same for all three bullets, but the manual has the same OAL recommendation for each.
140 ELD-M has 1.372 bullet length and BTO of 0.745
174 ELD-M has 1.442 bullet length and BTO of 0.792
Is it even reasonable that the OAL for these bullets should be the same with a manual recommendation 0.010 shorter than the Sierras?
If you go with the Hornady manual recommendation you will be seating these long bullets far back into the neck and increasing chamber pressure.
I would suspect that 2.800 was chosen for older bullets that were designed for the original 6.5mm European calibers rather than for the more modern high ballistic coefficient ELD-M bullets. Perhaps, the manual writers were just too lazy to measure the new bullets.
Comments on bullet jump:
I normally consider 0.020 as jump to start with, but your rifle will tell you what works best, but you need to experiment with your particular.
My original 6.5mm CM bolt action initially preferred 0.011 to 0.019 jump by a slight margin and that was out past 2.840 when the barrel was new.
I now have three 6.5 CM bolt actions, and each barrel had slightly different camber depths, and different jump preferences but they are all distributed around 0.020
But all three rifles shot best with OAL lengths much longer than the OALs recommended by the manuals.
As my original rifle's lands begin to erode with use, after 2,500 rounds the measured cartridge base to ogive grew 0.036 due to erosion.
I just kept increasing the seating depth to keep the preferred jump.
From my experience, how close to Pmax you load your rounds will determine the rate of
erosion. But, be advised, nothing stays the same with wear from use.
Your magazine will give you some idea of what max OAL limits are for your mag, if you want to use your mag, but that is not normally the limit of the chamber since with modern high BC bullets, there is lot of bullet tip that extends past the start of the lands.
I single load with single round follower if the OAL resulting from my preferred jump setting causes the OAL to exceed the mag length.
As long as it fits in the magazine or you dont mind single feeding it should be fine.
I have given up measuring off the lands. They erode and move over time, giving you a moving point of measure. Also i have not found a specific distance that correlate to accuracy.
I currently use eric cortinas method. I seat at factory col. Then i seat in 0.003 increments deeper to tune to the barrels harmonics. Usually 5-7 groups total 1 at each seating depth will tell me what i need to know. This has given me the best accuracy.
Heres his video, stop chasing the lands.
https://youtu.be/oRXlCG9YZbQ
I have given up measuring off the lands. They erode and move over time, giving you a moving point of measure. Also i have not found a specific distance that correlate to accuracy.
I currently use eric cortinas method. I seat at factory col. Then i seat in 0.003 increments deeper to tune to the barrels harmonics. Usually 5-7 groups total 1 at each seating depth will tell me what i need to know. This has given me the best accuracy.
Heres his video, stop chasing the lands.
https://youtu.be/oRXlCG9YZbQ
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My first thought or suggestion for this, would be for you to study up on COL, which is cartridge overall length, base to tip, and CBTO, which is cartridge base to ogive.
Be aware that COL (COAL) cartridge over all length (base to bullet tip) is an industry standard term and an industry standard (max) length for every commercial cartridge.
CBTO (cartridge base to bullet ogive) is a fairly new term, made up by some reloaders and refers to a spot they pick on the bullet ogive. This spot is usually where the bullet ogive contacts the rifling, and as such, will be different for every different bullet design and every different rifle.
The definitions in the standard ammunition glossaries (such as found in reloading manuals) are pretty uniform in their definitions, and the ogive of a bullet is the ENTIRE curved or sloping portion of the bullet between the full bore diameter body of the bullet and the tip. Ogive is not a single point, but the people using CBTO treat it as such, which I feel, is incorrect.
Those people aren't wrong, using a point they choose ON the ogive as THEIR reference point, they just seem to do a very poor job of explaining the fact that is it their personal choice, and that the point on the ogive that provides that reference will be different (in a different spot, measured from the case base) with every different bullet design and every different rifle, due to both intentional design specs and manufacturing tolerances.
jetinteriorguy
New member
I use the term Cartridge Base To Datum, CBTD. Datum referring to the datum point on the ogive that will contact the lands. Just my preference.
Datum referring to the datum point on the ogive that will contact the lands. Just my preference.
Which works for you with what you are using. But doesn't mean much to anyone else using a different rifle and/or bullet.
Talking with guys that make custom bullets specifically for match use, forming the ogive is the hardest part (and hardest to do consistantly) of making a bullet.
They also note that due to this, there can be a fairly big difference from one single bullet to the next.
While they are usually able to keep the length of the bullet fairly consistant.
Weight can vary a couple tenths of a grain.
Hence why i don't do CBTO.
They also note that due to this, there can be a fairly big difference from one single bullet to the next.
While they are usually able to keep the length of the bullet fairly consistant.
Weight can vary a couple tenths of a grain.
Hence why i don't do CBTO.
In a classic definition…
CBTD - Case Base to Datum - This is defined as putting a case base on a flat plane. Then measuring to a parallel planer circular touch point on the case shoulder. This is called out on the case dwg.
CBTD - Case Base to Ogive - This is defined as putting a case base on a flat plane. Then measuring to a parallel planer circular touch point on the bullet.
The throat is a complex shape, so the toolmakers are not cutting tools to a set std. Hornady cuts a circle just below groove diameter….maybe related to land diameter. Sinclair cuts a throat snap in their tool to replicate how different ogive shapes touch off at different points.
The same is true for the CBTD measurement. They are not comparable across brands because there is no set std for how to cut the tools. It would be nice if SAAMI created a std for how to measure this and publish it.
CBTD - Case Base to Datum - This is defined as putting a case base on a flat plane. Then measuring to a parallel planer circular touch point on the case shoulder. This is called out on the case dwg.
CBTD - Case Base to Ogive - This is defined as putting a case base on a flat plane. Then measuring to a parallel planer circular touch point on the bullet.
The throat is a complex shape, so the toolmakers are not cutting tools to a set std. Hornady cuts a circle just below groove diameter….maybe related to land diameter. Sinclair cuts a throat snap in their tool to replicate how different ogive shapes touch off at different points.
The same is true for the CBTD measurement. They are not comparable across brands because there is no set std for how to cut the tools. It would be nice if SAAMI created a std for how to measure this and publish it.
Let me simplify OAL selection. Find your land touch point. Does it fit in your mag and eject? Back off about 0.010”-0.015” for a hunting load. Use OCW to find a best powder charge. If accuracy needs improved after that, just start at 0.015” and start shortening until groups shrink and start to open up. That is your spot.
Book OAL is a number required to fit the magazine, fit the SAAMI chamber and document what OAL was used for pressure measurements.
Book OAL is a number required to fit the magazine, fit the SAAMI chamber and document what OAL was used for pressure measurements.
kilotanker22
New member
I use the same method. However, I start jam minus .020" like he does. When the throat begins to erode accuracy will diminish. Then I seat slightly longer in the same .003" increments. That has seemed to work very well for me. Usually, a single extension of .003" is what it takes to get me back into that barrel time node. I continue this until I reach past mag length then re-barrel. I have gone through two barrels with this method and it has worked beautifully.As long as it fits in the magazine or you dont mind single feeding it should be fine.
I have given up measuring off the lands. They erode and move over time, giving you a moving point of measure. Also i have not found a specific distance that correlate to accuracy.
I currently use eric cortinas method. I seat at factory col. Then i seat in 0.003 increments deeper to tune to the barrels harmonics. Usually 5-7 groups total 1 at each seating depth will tell me what i need to know. This has given me the best accuracy.
Heres his video, stop chasing the lands.
https://youtu.be/oRXlCG9YZbQ
The late Dan Hackett (a benchrest competitor) wrote in the 1995 Precision Shooting Reloading Manual that he had a 40X in 220 Swift that would not shoot five shots into better than 3/8" a 100 yards. He was seating 0.020" off the lands. One day, when he changed bullets to one with 0.015" shorter ogive, he accidentally turned the micrometer on his seating die the wrong way. Instead of backing out 0.015", he seated this bullet deeper by 0.015". 0.015" of shorterness plus 0.015" of erroneous direction put the bullet 0.030" deeper into the case than he intended. Add that to the intended 0.020" off the lands, and he was 0.050" off the lands instead of 0.020". He got 20 rounds loaded before he noticed the error. He considered pulling the bullets and reseating to get the "right" 0.020" of bullet jump. But he shrugged and decided to shoot these bad loads in practice rather than go to all that trouble. When he did, to his surprise he got two 0.25" groups and two true bugholes in the ones (between 0.1" and 0.2").
Per Berger's article, one can speculate that 0.020" or 0.015" or 0.025" or 0.030" or whatever number is best (they've all been recommended as best at one time or another), but it is unwise to limit your exploration to only 0.020"-or-shorter or 0.020"-or-longer or any other fixed range of values. Some VLDs have been as much as almost a 0.25" off the lands before they started to shoot their best (longer ogives tend toward longer jumps some portion of the time, but not always). Mid Tompkins won more gold medals shooting at 1000 yards than anybody else ever has, seating his bullets in contact with the lands. Scot Satterly says he's been winning with almost 0.125" jump for awhile now.
0.020" does seem to work often, but you can't prove it is best in your gun with your bullet until you try a range of seating depths. Consider Berger's method. Going from 0.020" to 0.150" in 0.003" increments makes sense for finding the true minimus in group size, but it will take trying 44 different seating depths. So roughing your optimum depth in using bigger increments will save ammo. Once you've bracketed the best spot, then start looking at the small incremental changes.
Per Berger's article, one can speculate that 0.020" or 0.015" or 0.025" or 0.030" or whatever number is best (they've all been recommended as best at one time or another), but it is unwise to limit your exploration to only 0.020"-or-shorter or 0.020"-or-longer or any other fixed range of values. Some VLDs have been as much as almost a 0.25" off the lands before they started to shoot their best (longer ogives tend toward longer jumps some portion of the time, but not always). Mid Tompkins won more gold medals shooting at 1000 yards than anybody else ever has, seating his bullets in contact with the lands. Scot Satterly says he's been winning with almost 0.125" jump for awhile now.
0.020" does seem to work often, but you can't prove it is best in your gun with your bullet until you try a range of seating depths. Consider Berger's method. Going from 0.020" to 0.150" in 0.003" increments makes sense for finding the true minimus in group size, but it will take trying 44 different seating depths. So roughing your optimum depth in using bigger increments will save ammo. Once you've bracketed the best spot, then start looking at the small incremental changes.
I have had a different experience. For example, 223 with Hornady 75g OTM. I seated at 2.243 to get all points at or below the recommended 2.250. I shot 5 shot groups at each seating depth for a total of 35rnds. I still have some testing to do. my shooting was poor that day, I only had a 7x scope at 100yds, and My target, given my magnification, was less than idea. However I managed to go from about a 2in group down to a 1in group with that testing. considering my AR has a budget $90 brownells barrel on it, not too bad, but I am going for sub moa.
2.243
2.240
2.237
2.234
2.231
2.228
2.225
My method came from Eric Cortina, and it has worked exceptionally well for me. The theory is there are several nodes, like a sine wave. and you just need to tune for small adjustments to tweak the timing when the bullet leaves the barrel.
https://www.youtube.com/watch?v=oRXlCG9YZbQ
2.243
2.240
2.237
2.234
2.231
2.228
2.225
My method came from Eric Cortina, and it has worked exceptionally well for me. The theory is there are several nodes, like a sine wave. and you just need to tune for small adjustments to tweak the timing when the bullet leaves the barrel.
https://www.youtube.com/watch?v=oRXlCG9YZbQ
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Berger and Satterly would not contradict your results, obviously, but might suggest that protocol simply doesn't cover a wide enough range of possible optimum seating depths to be sure you found the best one. Your tightest group may well be waiting for you somewhere outside those endpoints, just as Hacket's bugholes were.
There's some fairly extensive data on the Precision Rifle Blog showing the additional velocity flat spots you find as you seat deeper get wider, so not the pattern of a simple sinusoid.
There's some fairly extensive data on the Precision Rifle Blog showing the additional velocity flat spots you find as you seat deeper get wider, so not the pattern of a simple sinusoid.
Thanks for all the responses. My concerns on exceeding 2.800" by .020" to end up with 2.820" have been answered. As long as I am not 'on the lands' pressure buildup will not be a concern. I hadn't thought about whether fitting in the magazine would be an issue since I use a single feed magazine sled.
I struggle somewhat with the guy in the video (hard to watch him) but understand where he is coming from on finding the seating 'guardrail' by jamming the bullet. This seems similar to finding where 'in the lands' your bullet seats with the Hornady OAL gauge. I will try his jam vs in the lands method and see if there is really any difference in my groups.
I struggle somewhat with the guy in the video (hard to watch him) but understand where he is coming from on finding the seating 'guardrail' by jamming the bullet. This seems similar to finding where 'in the lands' your bullet seats with the Hornady OAL gauge. I will try his jam vs in the lands method and see if there is really any difference in my groups.
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reynolds357
New member
I seat where they group best but still fit in mag. (Assuming it's not a straight Bench rest rifle.I'm working on enhancing accuracy of my Ruger RPR 6.5 CM using 140 gr Hornady ELD Match bullets. Published cartridge OAL from both Hornady and Lyman is 2.800". Using Hornady's OAL gauge, I have determined the maximum overall cartridge length for my RPR to be 2.850. Backing off 0.030" for bullet jump gives me 2.820", which exceeds the published OAL by 0.020". Anyone see any issues with this?
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