6mm Creedmoor barrel twist?
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Hugnot
Well-Known Member
Go for the 110 A-Tip in the 7 twist, if it's OK for 115's it will work for the pricy & trendy A-Tip.
Bullet length data from JBM. The A-Tip is 1.307 inches long & has a .160 inch long aluminum tip. Since aluminum weighs more (greater density) than plastic, I included it in the bullet OAL.
Now & then I gets to buy partial boxes of bullets real cheap that don't shoot too good from other shooters, like sideways bullet holes or substandard trajectories & poor accuracy at long ranges due to BC degradation (not flying good, like wobbling) indicated by low Sg values.
A simple Sg analysis from Berger:
bergerbullets.com
and
Here the bullet wizards indicate doubts regarding optimum accuracy with bullet having Sg values in excess of 2.0. I think this has some validity & prefer to not get into super fast twist barrels that would optimize bullet use to real long pointy bullets. Why go for an excessive fast twist when not needed. Sort of looks like bullet trends and barrel twist rates are determined by ignoring analysis.
In addition the US Government, like the DOD, having access to huge amounts of funding has determined acceptable Sg value ranges.
"A launch gyroscopic stability factor between 1.5 and 2.0 is usually specified, to insure .sample safety margin under worst case conditions. Thus for the 7.62mm NATO cartridge. the 12 inch twist rate is an excellent choice for the 168 grain Sierra International (M852) bullet, and a 10 inch twist barrel should be selected for the M 118 or 190 grain Sierra Matchking bullets."
Production of zillions of rounds of ammo demands logical & reasonable analysis. It is assumed these data would also apply to 6mm bullets.
The M118 is a 173 plus grain boat tail, .308 diameter bullet and has the best aerodynamic qualities of those .30 bullets tested. An additional qualifier would bullet form factor, obtained by dividing the bullet
Bullet length data from JBM. The A-Tip is 1.307 inches long & has a .160 inch long aluminum tip. Since aluminum weighs more (greater density) than plastic, I included it in the bullet OAL.
Now & then I gets to buy partial boxes of bullets real cheap that don't shoot too good from other shooters, like sideways bullet holes or substandard trajectories & poor accuracy at long ranges due to BC degradation (not flying good, like wobbling) indicated by low Sg values.
A simple Sg analysis from Berger:
Twist Rate Stability Calculator
Our newly updated Twist Rate Stability Calculator not only tells you what your SG is, but it also lets you know if you are reaching your optimized BC.
bergerbullets.com
and
Here the bullet wizards indicate doubts regarding optimum accuracy with bullet having Sg values in excess of 2.0. I think this has some validity & prefer to not get into super fast twist barrels that would optimize bullet use to real long pointy bullets. Why go for an excessive fast twist when not needed. Sort of looks like bullet trends and barrel twist rates are determined by ignoring analysis.
In addition the US Government, like the DOD, having access to huge amounts of funding has determined acceptable Sg value ranges.
"A launch gyroscopic stability factor between 1.5 and 2.0 is usually specified, to insure .sample safety margin under worst case conditions. Thus for the 7.62mm NATO cartridge. the 12 inch twist rate is an excellent choice for the 168 grain Sierra International (M852) bullet, and a 10 inch twist barrel should be selected for the M 118 or 190 grain Sierra Matchking bullets."
Production of zillions of rounds of ammo demands logical & reasonable analysis. It is assumed these data would also apply to 6mm bullets.
The M118 is a 173 plus grain boat tail, .308 diameter bullet and has the best aerodynamic qualities of those .30 bullets tested. An additional qualifier would bullet form factor, obtained by dividing the bullet
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Hugnot
Well-Known Member
In addition the US Government, like the DOD, having access to huge amounts of funding has determined acceptable Sg value ranges.
"A launch gyroscopic stability factor between 1.5 and 2.0 is usually specified, to insure .sample safety margin under worst case conditions. Thus for the 7.62mm NATO cartridge. the 12 inch twist rate is an excellent choice for the 168 grain Sierra International (M852) bullet, and a 10 inch twist barrel should be selected for the M 118 or 190 grain Sierra Matchking bullets."
Production of zillions of rounds of ammo demands logical & reasonable analysis. It is assumed these data would also apply to 6mm bullets.
The M118 is a 173 plus grain boat tail, .308 diameter bullet and has the best aerodynamic qualities of those .30 bullets tested. Kind of wonder why the DOD with all their wisdom, money & hi tech gear did not go over a 2.0 Sg value. Possibly, anecdotal info was inadequate.
An additional qualifier would bullet G7 form factor, obtained by dividing the bullet sectional density by G7 BC. This is another way for bullet/twist selection.
This indicates the Hornady 6mm 110 A-Tip crushes all other 6mm bullets.
My nice 6mm CM bullet/twist selection is an 8 twist, shooting the cheap but nice 105 Barnes Match Burners ($0.30 each), having a Sg in the 2.6 range depending on conditions.
105 Barnes Match Burners G7 form factors probably are 1.0, not as good as the other bullets, but if needed I could spend about $0.11 more per bullet and shoot 108 H ELDM's; I would do this for over 600 yard use.
108 H ELDM Sg values would have a nice comfortable Sg value of "A launch gyroscopic stability factor between 1.5 and 2.0". But the advantage of an 8 twist is that it allows the use of lighter & shorter, zippy varmint bullets like the 6mm 80 grain ELDMVT and adequate Sg values for Berger 105's. All the number stuff corresponds with actual shooting but buying 115 & 110 A-Tip bullets for my 8 twist would be a waste of money.
"A launch gyroscopic stability factor between 1.5 and 2.0 is usually specified, to insure .sample safety margin under worst case conditions. Thus for the 7.62mm NATO cartridge. the 12 inch twist rate is an excellent choice for the 168 grain Sierra International (M852) bullet, and a 10 inch twist barrel should be selected for the M 118 or 190 grain Sierra Matchking bullets."
Production of zillions of rounds of ammo demands logical & reasonable analysis. It is assumed these data would also apply to 6mm bullets.
The M118 is a 173 plus grain boat tail, .308 diameter bullet and has the best aerodynamic qualities of those .30 bullets tested. Kind of wonder why the DOD with all their wisdom, money & hi tech gear did not go over a 2.0 Sg value. Possibly, anecdotal info was inadequate.
An additional qualifier would bullet G7 form factor, obtained by dividing the bullet sectional density by G7 BC. This is another way for bullet/twist selection.
This indicates the Hornady 6mm 110 A-Tip crushes all other 6mm bullets.
My nice 6mm CM bullet/twist selection is an 8 twist, shooting the cheap but nice 105 Barnes Match Burners ($0.30 each), having a Sg in the 2.6 range depending on conditions.
105 Barnes Match Burners G7 form factors probably are 1.0, not as good as the other bullets, but if needed I could spend about $0.11 more per bullet and shoot 108 H ELDM's; I would do this for over 600 yard use.
108 H ELDM Sg values would have a nice comfortable Sg value of "A launch gyroscopic stability factor between 1.5 and 2.0". But the advantage of an 8 twist is that it allows the use of lighter & shorter, zippy varmint bullets like the 6mm 80 grain ELDMVT and adequate Sg values for Berger 105's. All the number stuff corresponds with actual shooting but buying 115 & 110 A-Tip bullets for my 8 twist would be a waste of money.
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Hugnot
Well-Known Member
My 8 twist 6mm CM is capable of producing fine accuracy with the cheap (inexpensive) Barnes Match Burner, 105 grain hollow point bullet and a variety of 4350 powders. The 105 Barnes Match Burner is one of the least expensive 105 grain hollow point boat tail bullets and is one of the shortest at 1.20 inches.
Should lighter (less weight) bullet having low form factors and velocities in the 3300 fps range be wanted an 8 twist would be a good selection. The lighter hi velocity plastic tipped bullets would extend point blank ranges on small targets and produce more expansion vs. ice pick effects.
In addition to fine accuracy, easily available small rifle primers may be used. CCI 41's work with extruded powders like the 4350's and the hotter Rem 7 1/2 is a good choice for ball powders like Staball 6.5. Cheap once fired 6.5 Creedmoor Federal brass necked down & turned to .268.
Velocities were about 3000 fps. 5 shot
Practicality is always a good consideration when making a selection. I hope to try the Hornady 108 grain ELDM's at 1000 next month. The 6mm Dasher is a common caliber used at the 1,000 yard BR match at a local range, probably using 105's or close to that. I would select a 7.5 twist for the longer 105 Berger or similar.
Should lighter (less weight) bullet having low form factors and velocities in the 3300 fps range be wanted an 8 twist would be a good selection. The lighter hi velocity plastic tipped bullets would extend point blank ranges on small targets and produce more expansion vs. ice pick effects.
In addition to fine accuracy, easily available small rifle primers may be used. CCI 41's work with extruded powders like the 4350's and the hotter Rem 7 1/2 is a good choice for ball powders like Staball 6.5. Cheap once fired 6.5 Creedmoor Federal brass necked down & turned to .268.
Velocities were about 3000 fps. 5 shot
Practicality is always a good consideration when making a selection. I hope to try the Hornady 108 grain ELDM's at 1000 next month. The 6mm Dasher is a common caliber used at the 1,000 yard BR match at a local range, probably using 105's or close to that. I would select a 7.5 twist for the longer 105 Berger or similar.
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Great information guys. I was going to do a 1-7.5 twist, but he had this one (7 twist) in stock. Diamond fluting and 24 inches long plus a custom muzzle brake. I changed out the bolt shroud and bolt head to PTG. Did away with the barrel nut, changed the trigger group to the savage 8-ounce trigger and sear but I had to have them clearance the side of the action to change it from the bottom bolt release. New bottom metal to take AI mags. The goal was to make it a twin to my Savage 308 I built last year.
I have custom actions on everything else but sometime being different is OK!!
I have custom actions on everything else but sometime being different is OK!!
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I've shot lots of 6mms, 6saum to 6br. I run 7.5 in everything, but 7.75 in the Saum. I do have a seekins havak 6cm that's an 8tw. 7.5 does everything well, however I am in montana with decent elevation and DA. Shot everything from 90-115 in the 7.5 and all has been well. The most important thing to check, is bore diameter. I highly recommend a 237 VS a 236 bore. The 6cm is a bit overbore and some fire cracking will start, and with a 236 bore diameter, jacket pressure is increased. Light jacket bullets under more pressure, with some fire cracking, is a combination for bullet failure, especially if you're pushing the creed to its potential of 3100+, my womans prs rifle is a 7tw, 237 bore and it's running around 2950fps, has 1300 rounds on it, and the throat doesn't look great, but have never had a jacket failure. Just something to keep in mind!
Hugnot
Well-Known Member
The OP made no mention of how he will use the 6mm CM.
The 6mm CM is one of my favorite rounds. I shoot about 3500 rounds per year & primer availability is a consideration, & SRP's are an easy buy at LGS and I use them in the 6mm CM, no problems with extruded powders. I like to shoot rodents, small targets, at various ranges.
I am working on 80 grain H ELDMVT (low FF & thin jackets) loads for the 6mm CM and have had no problems with bullet blow ups yet @ 3400 fps, 8 twist, fair accuracy, real flat trajectories . I got over 3,600 fps with a 6mm AI, 10 twist, no blow ups but poor accuracy, despite Miller Sg estimates of adequate plastic tip stability, this also occurred in other rifles. The Miller Sg estimation works good with many bullets, except the new ELDMVT's that have large empty voids under the plastic tip.
The Miller analysis has doubts about fine accuracy when Sg values are over 2.0. I would not want to buy 1,000 or so bullets that proved to be inadequate for my use so I pay attention to Miller. I like to buy bullets in 500 lots but only after shooting 100 & doing some simple stat work. Fast twist rates & high velocity magnify any bullet imbalance/defect & result in a sad buyer's remorse (waste) should money be spent on 1,000 bullets. I look at an Sg value that will assure best performance with an intended bullet at all conditions. Occasionally, I get to buy bullets that were rejected for various reasons including accuracy problems, like improper twist rate for bullet. My favorite & cheap 6mm bullet is the 105 Barnes Match burner @ 3,000 fps, Sg in the 1.6 range, 8 twist.
The smaller 6mm Dasher using 105 Berger VLD's with 7.5 twist is a frequent winner at local 1000 YD BR matches, Sg 1.64 @ most temps, elevation 3500, about 2850 fps. High accuracy demand but fixed distance, don't know about 108 ELDM performance if any.
The 6mm CM is one of my favorite rounds. I shoot about 3500 rounds per year & primer availability is a consideration, & SRP's are an easy buy at LGS and I use them in the 6mm CM, no problems with extruded powders. I like to shoot rodents, small targets, at various ranges.
I am working on 80 grain H ELDMVT (low FF & thin jackets) loads for the 6mm CM and have had no problems with bullet blow ups yet @ 3400 fps, 8 twist, fair accuracy, real flat trajectories . I got over 3,600 fps with a 6mm AI, 10 twist, no blow ups but poor accuracy, despite Miller Sg estimates of adequate plastic tip stability, this also occurred in other rifles. The Miller Sg estimation works good with many bullets, except the new ELDMVT's that have large empty voids under the plastic tip.
The Miller analysis has doubts about fine accuracy when Sg values are over 2.0. I would not want to buy 1,000 or so bullets that proved to be inadequate for my use so I pay attention to Miller. I like to buy bullets in 500 lots but only after shooting 100 & doing some simple stat work. Fast twist rates & high velocity magnify any bullet imbalance/defect & result in a sad buyer's remorse (waste) should money be spent on 1,000 bullets. I look at an Sg value that will assure best performance with an intended bullet at all conditions. Occasionally, I get to buy bullets that were rejected for various reasons including accuracy problems, like improper twist rate for bullet. My favorite & cheap 6mm bullet is the 105 Barnes Match burner @ 3,000 fps, Sg in the 1.6 range, 8 twist.
The smaller 6mm Dasher using 105 Berger VLD's with 7.5 twist is a frequent winner at local 1000 YD BR matches, Sg 1.64 @ most temps, elevation 3500, about 2850 fps. High accuracy demand but fixed distance, don't know about 108 ELDM performance if any.
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I have 4 rifles in it. All have 7.5 twist barrels. The 2 that is dedicated to long range targets both take the 110 A Tips out to 1600 yards +. No problems with stabilization. So far that's from 500' to 5800' elevation.
As far as use, it will just be a long-range target rifle. Maybe a local match at some point but mostly just for some long-range fun with low recoil. I had all the parts laying around except the barrel. The 110 A-Tip or something that works at distance will be fun to play with.
Yup the 7 twist he has on hand will work fine. I wouldn't go slower than 7.5 honestly.
I have had 6 different 6 cm rifles and they are all 8 twist with 26 -28 inch barrels. One 7.5 that wasnt as accuate as the others. I'm at 4600 feet and mostly shoot 115 Bergers for 1000 yard Benchrest and hunting and have not seen any issues with stability. I run them over 3050 to 3100 with RL 26 or superformance in hunting rifles and they shoot well. Have shot them on gongs at a mile. Also plink with the 112 Match Burners with good accuracy.
How have the 110s performed on game, any experience?
