I need to put together bullet drop data for a shoot this weekend, and i dont have a chrono. I am shooting a rem 700 sps tactical 20"barrel, usng fed GMM 168 smk. does anybody have muzzle velocity data out of a 20" barrel? Im @ 1250'. thanks in advance, I know it won t be exact to my gun, but i need to get in the ballpark .-J
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Range Report help! need chrono data 168 gmm
- Thread starter Urquell23
- Start date
Re: help! need chrono data 168 gmm
I shoot a Rem SPS AAC-SD with a 20" barrel, I ran 10 rounds over the chrony and averaged 2470fps. What distance are you shooting? I use the shooter application and have data out to any distance for mils or moa.
I shoot a Rem SPS AAC-SD with a 20" barrel, I ran 10 rounds over the chrony and averaged 2470fps. What distance are you shooting? I use the shooter application and have data out to any distance for mils or moa.
Re: help! need chrono data 168 gmm
I am also interested in this, I am running same rifle with same round. I want to get a ballpark number, and then double check it with my hard dope.
I am also interested in this, I am running same rifle with same round. I want to get a ballpark number, and then double check it with my hard dope.
Re: help! need chrono data 168 gmm
MIl/ MIl 650 yards. 168SMK FGGM @ 2470fps.
100 yard zero 2282fps. Density altitude 675ft above sea level
Yards - Velocity- Mils (up)
150- 2191.4 - 0.3
200- 2102.5 - 0.7
250- 2015.7 - 1.2
300- 1931.3 - 1.7
350- 1849.5 - 2.3
400- 1769.6 - 2.9
450- 1692.1 - 3.5
500- 1617.6 - 4.2
550- 1545.8 - 4.9
600- 1477.5 - 5.7
650- 1412.3 - 6.5
If you know your height above/below sea level that you will be shooting I can get more accurate drop ranges. As well as temperature.
MIl/ MIl 650 yards. 168SMK FGGM @ 2470fps.
100 yard zero 2282fps. Density altitude 675ft above sea level
Yards - Velocity- Mils (up)
150- 2191.4 - 0.3
200- 2102.5 - 0.7
250- 2015.7 - 1.2
300- 1931.3 - 1.7
350- 1849.5 - 2.3
400- 1769.6 - 2.9
450- 1692.1 - 3.5
500- 1617.6 - 4.2
550- 1545.8 - 4.9
600- 1477.5 - 5.7
650- 1412.3 - 6.5
If you know your height above/below sea level that you will be shooting I can get more accurate drop ranges. As well as temperature.
Re: help! need chrono data 168 gmm
Not in any way questioning your data, but 2470 fps seems awful slow for a 20" pipe. I get 2591 out of an 18" 10-twist barrel bolt gun and 2713 out of a 22" bolt gun (400 ft elevation, ~30% humidity, 65 degrees F). Although every barrel is different (even on the same weapon model), I would estimate you should expect somewhere in the neighborhood of 2650 fps using FGMM 168s from a 20" barrel, unless that particular barrel type is relatively slow for some reason. Based on your altitude and an MV of 2650 fps, here are drops estimated by the JBM Ballistics Calculator:
Range Drop Drop
(yd) (MOA) (mil)
0 *** ***
100 -0.0 -0.0
200 -1.8 -0.5
300 -4.6 -1.3
400 -7.9 -2.3
500 -11.6 -3.4
600 -15.9 -4.6
700 -20.8 -6.1
800 -26.5 -7.7
900 -33.1 -9.6
1000 -40.7 -11.8
Just remember, every rifle is different, so YMMV. Getting solid MV data with your specific rifle is going to be the only way to know for sure.
Not in any way questioning your data, but 2470 fps seems awful slow for a 20" pipe. I get 2591 out of an 18" 10-twist barrel bolt gun and 2713 out of a 22" bolt gun (400 ft elevation, ~30% humidity, 65 degrees F). Although every barrel is different (even on the same weapon model), I would estimate you should expect somewhere in the neighborhood of 2650 fps using FGMM 168s from a 20" barrel, unless that particular barrel type is relatively slow for some reason. Based on your altitude and an MV of 2650 fps, here are drops estimated by the JBM Ballistics Calculator:
Range Drop Drop
(yd) (MOA) (mil)
0 *** ***
100 -0.0 -0.0
200 -1.8 -0.5
300 -4.6 -1.3
400 -7.9 -2.3
500 -11.6 -3.4
600 -15.9 -4.6
700 -20.8 -6.1
800 -26.5 -7.7
900 -33.1 -9.6
1000 -40.7 -11.8
Just remember, every rifle is different, so YMMV. Getting solid MV data with your specific rifle is going to be the only way to know for sure.
Re: help! need chrono data 168 gmm
That could easily be the case, but I have a second bolt gun (completely different manufacturer/barrel) with a 22" barrel that gives an avg. MV for FGMM 168s of 2724 fps. It's also possible my chronograph is reading on the high side, although drops at various distances predicted by JBM using those MVs are very, very close, if not dead on to what I actually observe.
In general, I've found with several rifles/barrels in lengths of 16" (1), 18" (1), 22" (2), and 24" (1), that they differ in MV on average by about 25 fps per inch of barrel length. Using that criteria with the factory 24" barrel test MV value for FGMM 168s of 2650 fps, I'd still expect something like 2550 fps from a 20" barrel. Again, not doubting your numbers in the least, I just wanted illustrate the point that MVs can vary widely from different barrels of the same length, even from two guns of the same model/same manufacturer.
The only way to know for sure is to determine MV with your specific rifle/ammo, and then verify that the drops you actually observe at various distances match (or come very close) to those predicted by a ballistic calculator using the specifc MVs obtained with that rifle/ammo. If the OPs MV differs from either of the ones we posted by 50 fps or more, he's looking at a difference in POA and POI of 6-8 inches (or more) at 600 yd. I just wanted to make sure the OP was aware of the inherent liability of using someone else's MV data before arriving at his upcoming match, so he will have some idea of what corrections might need to be made in the event that his POI is way high (or low) based on drops calculated from someone else's MV data. As long as he's aware of it, hopefully it won't be an ugly surprise at the upcoming match.
That could easily be the case, but I have a second bolt gun (completely different manufacturer/barrel) with a 22" barrel that gives an avg. MV for FGMM 168s of 2724 fps. It's also possible my chronograph is reading on the high side, although drops at various distances predicted by JBM using those MVs are very, very close, if not dead on to what I actually observe.
In general, I've found with several rifles/barrels in lengths of 16" (1), 18" (1), 22" (2), and 24" (1), that they differ in MV on average by about 25 fps per inch of barrel length. Using that criteria with the factory 24" barrel test MV value for FGMM 168s of 2650 fps, I'd still expect something like 2550 fps from a 20" barrel. Again, not doubting your numbers in the least, I just wanted illustrate the point that MVs can vary widely from different barrels of the same length, even from two guns of the same model/same manufacturer.
The only way to know for sure is to determine MV with your specific rifle/ammo, and then verify that the drops you actually observe at various distances match (or come very close) to those predicted by a ballistic calculator using the specifc MVs obtained with that rifle/ammo. If the OPs MV differs from either of the ones we posted by 50 fps or more, he's looking at a difference in POA and POI of 6-8 inches (or more) at 600 yd. I just wanted to make sure the OP was aware of the inherent liability of using someone else's MV data before arriving at his upcoming match, so he will have some idea of what corrections might need to be made in the event that his POI is way high (or low) based on drops calculated from someone else's MV data. As long as he's aware of it, hopefully it won't be an ugly surprise at the upcoming match.
Re: help! need chrono data 168 gmm
My biggest concern was that in a worst case scenario you might be completely off the target to start the match. As long as the MV/drop you decide to go with gets you on target to start at whatever distance you're shooting, you should be able to adjust your elevation up or down as needed. Completely missing the target with sighters is a nightmare. Been there, done that. Your spotter/scorer can be a good resource in that case as they may be able to tell you from your bullet trace whether you're high or low. Hopefully, you'll be on and GTG at the start. In any event, good luck with the match and hope you have fun. Let us know how everything goes.
My biggest concern was that in a worst case scenario you might be completely off the target to start the match. As long as the MV/drop you decide to go with gets you on target to start at whatever distance you're shooting, you should be able to adjust your elevation up or down as needed. Completely missing the target with sighters is a nightmare. Been there, done that. Your spotter/scorer can be a good resource in that case as they may be able to tell you from your bullet trace whether you're high or low. Hopefully, you'll be on and GTG at the start. In any event, good luck with the match and hope you have fun. Let us know how everything goes.
Re: help! need chrono data 168 gmm
That is some good data. Thank you for the info. I am curious what the differences are between the 20 and the 18" with the same ammo. Anybody have that data?
That is some good data. Thank you for the info. I am curious what the differences are between the 20 and the 18" with the same ammo. Anybody have that data?
Re: help! need chrono data 168 gmm
For .308 in that barrel length range, a general rule of thumb is that you might expect to lose ~25 fps per inch of barrel length, so ~ 50 fps going from 20" to 18". This has been very close to dead on for MVs determined with my different barrel lengths using various ammo. However, it's only a guideline and could potentially vary from 15-30 fps per inch barrel length in different rifles.
For .308 in that barrel length range, a general rule of thumb is that you might expect to lose ~25 fps per inch of barrel length, so ~ 50 fps going from 20" to 18". This has been very close to dead on for MVs determined with my different barrel lengths using various ammo. However, it's only a guideline and could potentially vary from 15-30 fps per inch barrel length in different rifles.
