Hi. I am a long time reader first time poster. I have been looking at the Rem 700 SPS-T and the new SPS-T AAC-SD. My question is- Does the 20 inch barrel affect the 1:12 using 175 grain SMKs. I have shot 175 out of 1:12 with pretty good results (the rifle more than me), but with a longer barrel. But there have been some comments that make me think there may be a problem. Also the hoopla about the AAC-SD being 1:10 put some doubt in my mind about the slower twist/heavy bullet/shorter barrel combo. Any help would be great.
- Thread starter Beaker
- Start date
Re: 20 inch 308 Twist?
The 175's should shoot fine with the 20" 1 in 12 tiwst. Mine did. However, due to barrel length and Remingtons chambers, velocity will most likely be pretty low. The SPS Tactical is a great little rifle and shoots very well. Before I re-barreled it, mine loved 155 Lapua Scenars and 155 AMAX. I was able to push them fast enough to stay supersonic out past 1K.
The 175's should shoot fine with the 20" 1 in 12 tiwst. Mine did. However, due to barrel length and Remingtons chambers, velocity will most likely be pretty low. The SPS Tactical is a great little rifle and shoots very well. Before I re-barreled it, mine loved 155 Lapua Scenars and 155 AMAX. I was able to push them fast enough to stay supersonic out past 1K.
Re: 20 inch 308 Twist?
You will be fine with either the 1-10 or 1-12 twist. With the 175s you might be looking in the low 2600 range with Handloads from the 20" factory tube. Me personally id get the 10 twist
You will be fine with either the 1-10 or 1-12 twist. With the 175s you might be looking in the low 2600 range with Handloads from the 20" factory tube. Me personally id get the 10 twist
Re: 20 inch 308 Twist?
I have used 1/10, 1/11.25 and 1/12 and they all shoot 175 SMKs good. With a shorter tube Id opt for 1/10 or 1/11.25
I have used 1/10, 1/11.25 and 1/12 and they all shoot 175 SMKs good. With a shorter tube Id opt for 1/10 or 1/11.25
Re: 20 inch 308 Twist?
Thanks for the info. I guess I'll have to get the AAC-SD. Just out of curiosity, what causes the problem with the slower twist/ shorter barrel?
Thanks for the info. I guess I'll have to get the AAC-SD. Just out of curiosity, what causes the problem with the slower twist/ shorter barrel?
Re: 20 inch 308 Twist?
what problem?
what problem?
Re: 20 inch 308 Twist?
I had heard that the 1:12 out of a shorter barrel may not stabalize the heavier rounds. I was curious as to why. There seems to be a leaning toward the 1:10. I know the 1:12 has done yeomans work for years but with the shortere barrels becoming more popular thought I could mis-step easily and be out some money.
I had heard that the 1:12 out of a shorter barrel may not stabalize the heavier rounds. I was curious as to why. There seems to be a leaning toward the 1:10. I know the 1:12 has done yeomans work for years but with the shortere barrels becoming more popular thought I could mis-step easily and be out some money.
Re: 20 inch 308 Twist?
45 gr. of Varget pushes 178 amax's to 2700 out of my factory barreled LTR. I was a little concerned too after reading some posts on the subject here but after a day of 1K shooting with it in 85 to 90 degree weather, staying supersonic was no problem with a couple of 5" groups to boot
.
okie
45 gr. of Varget pushes 178 amax's to 2700 out of my factory barreled LTR. I was a little concerned too after reading some posts on the subject here but after a day of 1K shooting with it in 85 to 90 degree weather, staying supersonic was no problem with a couple of 5" groups to boot
okie
Re: 20 inch 308 Twist?
Thanks Okie, so many thongs in shooting are counter-intuitive. Heavy bullets go farther, short barrels may be more accurate, t keeps you looking for the next- "Aha got ya", moment.
Thanks Okie, so many thongs in shooting are counter-intuitive. Heavy bullets go farther, short barrels may be more accurate, t keeps you looking for the next- "Aha got ya", moment.
Re: 20 inch 308 Twist?
I shot out 145 grain monarchs out to 800 yards hitting 36"x36" steel just fine with my SPS-T. Tried the federal match 168 gr, recalibrated scope, and i couldnt hit as often as i did with the 145s. I thought it was error on my part at first, but im happier with results that the 145gr gave me.
I'd be wanting to get a 1:10 soon though.
I shot out 145 grain monarchs out to 800 yards hitting 36"x36" steel just fine with my SPS-T. Tried the federal match 168 gr, recalibrated scope, and i couldnt hit as often as i did with the 145s. I thought it was error on my part at first, but im happier with results that the 145gr gave me.
I'd be wanting to get a 1:10 soon though.
Re: 20 inch 308 Twist?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: okiefired</div><div class="ubbcode-body">45 gr. of Varget pushes 178 amax's to 2700 out of my factory barreled LTR. I was a little concerned too after reading some posts on the subject here but after a day of 1K shooting with it in 85 to 90 degree weather, staying supersonic was no problem with a couple of 5" groups to boot .
okie </div></div>
Dang. Thats quick. 45gr Varget under 175 SMK's is giving me 2695 fps out of a 700P.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: okiefired</div><div class="ubbcode-body">45 gr. of Varget pushes 178 amax's to 2700 out of my factory barreled LTR. I was a little concerned too after reading some posts on the subject here but after a day of 1K shooting with it in 85 to 90 degree weather, staying supersonic was no problem with a couple of 5" groups to boot
okie </div></div>
Dang. Thats quick. 45gr Varget under 175 SMK's is giving me 2695 fps out of a 700P.
Re: 20 inch 308 Twist?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: wareagle700</div><div class="ubbcode-body">Dang. Thats quick. 45gr Varget under 175 SMK's is giving me 2695 fps out of a 700P. </div></div>
Varies from rifle to rifle. My thirty year old Remington 700 ADL sporter 308 with a 22 inch barrel has a 1:10 twist. My perception is that the 1:12 twist is for lighter "varmint" loads rather than the heavier 308 bullets.
All else equal, lighter bullets start out faster with a flatter trajectory, but lose velocity faster than heavier bullets. When the lighter bullet loses its velocity, it starts dropping faster and faster. Heavier bullets retain their velocity better, thereby staying above the speed of sound to longer ranges and hitting harder at longer ranges.
"Supersonic", "more than the speed of sound", is affected by the altitude, temperature, and barometric pressure, essentially, the density of the air. Here it may be counter-intuitive. Sound goes slower in less dense conditions, i.e. higher altitude and higher temperature. Staying above the speed of sound avoids the buffeting and accuracy robbing effects of going from supersonic to transonic to subsonic. 22 long rifle match ammo starts out deliberately subsonic to avoid going transonic and subsonic between the muzzle and 100 yards.
A 1977 Winchester catalog shows the 308 Winchester cartridge was available in 110, 125, 150, 180, and 200 grain loadings. An old Federal catalog added 220 grains. I believe the ability to handle any 308 ammunition is why general purpose 308 barrels were 1:10 and "varmint" barrels were 1:12.
Now, we have more choices with 155, 165, 168, 170, 172, 175, 178, and 190 grain bullets, plus long Very Low Drag (VLD) bullets, etc. And the split between lighter and heavier 308 bullets is blurred by the differences between rifles with different barrels giving different velocities and handloads which may get more than factory loadings.
The M14 used 1:12 for the 147 grain bullet, and was considered OK with the 173/168 match loading. When the military was developing the M24, they decided that 1:11.25 for the 175 Sierra Match King out of a 24 inch barrel was optimum.
Personally, if I planned to shoot 175 or greater weight bullets, I'd go with a 1:11.25 or faster twist, expecially in a tube shorter than 24 inches. I'm considering the SPS tactical AAC with the 1:10 twist for my lightweight, maneuverable, walk about bolt action rifle and the 5R in a heavier stock like an A5 or AICS for my static position rifle.
A twist that is satisfactory in a given barrel with today's 175-190 grain Sierra Match King with a given powder and handload may not be sufficient for tomorrow's 175-180 super very low drag bullet. Of course, if one is using handloads or shoots enough to burn out a barrel in a year, handling future bullets may not matter.
If one is looking at subsonic (less than about 1,100 feet per second), the 1:10 twist is probably the best choice.
IMO and FWIW and YMMV.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: wareagle700</div><div class="ubbcode-body">Dang. Thats quick. 45gr Varget under 175 SMK's is giving me 2695 fps out of a 700P. </div></div>
Varies from rifle to rifle. My thirty year old Remington 700 ADL sporter 308 with a 22 inch barrel has a 1:10 twist. My perception is that the 1:12 twist is for lighter "varmint" loads rather than the heavier 308 bullets.
All else equal, lighter bullets start out faster with a flatter trajectory, but lose velocity faster than heavier bullets. When the lighter bullet loses its velocity, it starts dropping faster and faster. Heavier bullets retain their velocity better, thereby staying above the speed of sound to longer ranges and hitting harder at longer ranges.
"Supersonic", "more than the speed of sound", is affected by the altitude, temperature, and barometric pressure, essentially, the density of the air. Here it may be counter-intuitive. Sound goes slower in less dense conditions, i.e. higher altitude and higher temperature. Staying above the speed of sound avoids the buffeting and accuracy robbing effects of going from supersonic to transonic to subsonic. 22 long rifle match ammo starts out deliberately subsonic to avoid going transonic and subsonic between the muzzle and 100 yards.
A 1977 Winchester catalog shows the 308 Winchester cartridge was available in 110, 125, 150, 180, and 200 grain loadings. An old Federal catalog added 220 grains. I believe the ability to handle any 308 ammunition is why general purpose 308 barrels were 1:10 and "varmint" barrels were 1:12.
Now, we have more choices with 155, 165, 168, 170, 172, 175, 178, and 190 grain bullets, plus long Very Low Drag (VLD) bullets, etc. And the split between lighter and heavier 308 bullets is blurred by the differences between rifles with different barrels giving different velocities and handloads which may get more than factory loadings.
The M14 used 1:12 for the 147 grain bullet, and was considered OK with the 173/168 match loading. When the military was developing the M24, they decided that 1:11.25 for the 175 Sierra Match King out of a 24 inch barrel was optimum.
Personally, if I planned to shoot 175 or greater weight bullets, I'd go with a 1:11.25 or faster twist, expecially in a tube shorter than 24 inches. I'm considering the SPS tactical AAC with the 1:10 twist for my lightweight, maneuverable, walk about bolt action rifle and the 5R in a heavier stock like an A5 or AICS for my static position rifle.
A twist that is satisfactory in a given barrel with today's 175-190 grain Sierra Match King with a given powder and handload may not be sufficient for tomorrow's 175-180 super very low drag bullet. Of course, if one is using handloads or shoots enough to burn out a barrel in a year, handling future bullets may not matter.
If one is looking at subsonic (less than about 1,100 feet per second), the 1:10 twist is probably the best choice.
IMO and FWIW and YMMV.
Re: 20 inch 308 Twist?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Beaker</div><div class="ubbcode-body">Thanks for the info. I guess I'll have to get the AAC-SD. Just out of curiosity, what causes the problem with the slower twist/ shorter barrel? </div></div>
The revolutions per minute (RPM) of a bullet is what makes it go straight, just like a thrown football. The RPM gives it gyroscopic stability. The RPM is a result of muzzle velocity times barrel twist times some constant. A barrel that is shorter with less velocity and/or less twist will launch a given bullet with less RPM.
The RPM which is needed will change with velocity and distance, so a bullet with an RPM which is fine out to some distance may slow down enough in its rotation to become unstable and start tumbling or going sideways at a greater distance.
The RPM needed for adequate stability is a function of the distance to which stability is desired and the physical characteristics of the bullet. A bullet which is short for its weight will have more mass away from the center of its mass than a longer bullet of the same weight. So the rotational speed (RPM) of the shorter, fatter bullet will tend to decay slower than a similar weight longer bullet. The shorter fatter bullet will keep its rotational speed, and therefore its gyroscopic stability, longer. So a VLD bullet may need more twist than a similar weight shorter bullet launched at the same muzzle velocity.
FWIW and YMMV.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Beaker</div><div class="ubbcode-body">Thanks for the info. I guess I'll have to get the AAC-SD. Just out of curiosity, what causes the problem with the slower twist/ shorter barrel? </div></div>
The revolutions per minute (RPM) of a bullet is what makes it go straight, just like a thrown football. The RPM gives it gyroscopic stability. The RPM is a result of muzzle velocity times barrel twist times some constant. A barrel that is shorter with less velocity and/or less twist will launch a given bullet with less RPM.
The RPM which is needed will change with velocity and distance, so a bullet with an RPM which is fine out to some distance may slow down enough in its rotation to become unstable and start tumbling or going sideways at a greater distance.
The RPM needed for adequate stability is a function of the distance to which stability is desired and the physical characteristics of the bullet. A bullet which is short for its weight will have more mass away from the center of its mass than a longer bullet of the same weight. So the rotational speed (RPM) of the shorter, fatter bullet will tend to decay slower than a similar weight longer bullet. The shorter fatter bullet will keep its rotational speed, and therefore its gyroscopic stability, longer. So a VLD bullet may need more twist than a similar weight shorter bullet launched at the same muzzle velocity.
FWIW and YMMV.
Re: 20 inch 308 Twist?
"Dang. Thats quick. 45gr Varget under 175 SMK's is giving me 2695 fps out of a 700P."
Yeah wareagle, I thought it was very quick too. I'm very happy with the barrel, especially concidering its factory.
Right SouthTH, good info. Just a reminder to the OP and anyone interested, like
STH referred to, you're trying to match barrel twist to bullet length, not so much weight. Thus, the reason all these comparitively speaking "newer" 155's do so well shot from faster twist barrels normally associated with heavier bullets.
okie
"Dang. Thats quick. 45gr Varget under 175 SMK's is giving me 2695 fps out of a 700P."
Yeah wareagle, I thought it was very quick too. I'm very happy with the barrel, especially concidering its factory.
Right SouthTH, good info. Just a reminder to the OP and anyone interested, like
STH referred to, you're trying to match barrel twist to bullet length, not so much weight. Thus, the reason all these comparitively speaking "newer" 155's do so well shot from faster twist barrels normally associated with heavier bullets.
okie
Re: 20 inch 308 Twist?
I shoot 175 SMKs and 178 AMAXs from my 20" factory 1:12 SPS-T out to 1K with good results. Not sure if the 1:10 would do better, but I have no complaints.
And yes, 45.0 of Varget in Lapua brass gets me right at 2600 fps.
I shoot 175 SMKs and 178 AMAXs from my 20" factory 1:12 SPS-T out to 1K with good results. Not sure if the 1:10 would do better, but I have no complaints.
And yes, 45.0 of Varget in Lapua brass gets me right at 2600 fps.
Re: 20 inch 308 Twist?
Great info and food for thought. Thanks to everybody. I'm not in a great hurry so I think I can pick up the newer AAC-SD when one appears. I hadn't thought about the VLD's nor was I thinking ahead.
Great info and food for thought. Thanks to everybody. I'm not in a great hurry so I think I can pick up the newer AAC-SD when one appears. I hadn't thought about the VLD's nor was I thinking ahead.
Re: 20 inch 308 Twist?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: okiefired</div><div class="ubbcode-body">45 gr. of Varget pushes 178 amax's to 2700 out of my factory barreled LTR. I was a little concerned too after reading some posts on the subject here but after a day of 1K shooting with it in 85 to 90 degree weather, staying supersonic was no problem with a couple of 5" groups to boot .
okie </div></div>
I know this is an old thread but while looking back in my records for something else I realized I gave some false info here. On my last chrony sesion my average for this load in this LTR was 2606, NOT 2706, which is how I remembered it. Thanks wareagle for sticking a question mark in my brain or I might not have caught it. All else in the post is true. Sorry for the misinfo.
okie
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: okiefired</div><div class="ubbcode-body">45 gr. of Varget pushes 178 amax's to 2700 out of my factory barreled LTR. I was a little concerned too after reading some posts on the subject here but after a day of 1K shooting with it in 85 to 90 degree weather, staying supersonic was no problem with a couple of 5" groups to boot
okie </div></div>
I know this is an old thread but while looking back in my records for something else I realized I gave some false info here. On my last chrony sesion my average for this load in this LTR was 2606, NOT 2706, which is how I remembered it. Thanks wareagle for sticking a question mark in my brain or I might not have caught it. All else in the post is true. Sorry for the misinfo.
okie
Re: 20 inch 308 Twist?
Good info from everyone, thanks. I guess I just ended the debate- I stumbled into an AAC-SD 700. So 10 twist it will be.
Now I have to go shopping...
Good info from everyone, thanks. I guess I just ended the debate- I stumbled into an AAC-SD 700. So 10 twist it will be.
Now I have to go shopping...
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