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308 Subsonic drop calc

B

bowhunter_0311

Sergeant
Full Member
Minuteman
Dec 24, 2010
109
1
38
South Texas
#1
I have messed around with the JBM calc, with no luck found what I am after. I am trying to get drop on my hand loaded subs I just want ballpark figures, just to get on my 12x12 steel that I shoot at. I know 50yds= about 10moa/100yds= about 17.5moa with out setting a target every 25 to 50 yds to figure it out, to save time on next outing need some help.

20in 1/10
5.1gr titegroup
150gr hornady with cannalure
running about 850 to 900fps.

And yes the 150's shoot nice out of the 1/10 twist. I didnt expect it but they do and have yielded good accuracy at 100yds.
 
#3
Re: 308 Subsonic drop calc

Ya I have that and was putting it in there 875fps is about average. Not good with operating that program.

More info on what I am looking for, I have my 100yd zero with my regular loads I want to be able to throw a sub in there dial the drop and shoot it. dont want to have to rezero for it guess that was the problem that I was having with JBM. Still couldnt come up with what seemed to be accurate drops with the data that I already have at 100yds.
 
#4
Re: 308 Subsonic drop calc

Well, I'd do tables for both...get it zeroed on your supersonics, and then shoot the a group with your subs. With a large enough target you should be able to measure the distance. 1" at 100yds is roughly 1 MOA. Dial in the difference and test your subs zero...adjust as needed but it should be pretty close. Then remember that number as your subsonic zero. Your JBMs should now work for both loads from their appropriate zeros. Dirty, but it should work for what you're trying to accomplish.
 
#5
Re: 308 Subsonic drop calc

Bowhunter,

For your sub loads do you use any kind of case filler? Also, do you use large rifle primers or large pistol? I'm have some of the Hornady 150's and I use Titegroup for most of my plinking pistol loads so I'm interested to try and make a .308 subsonic load.
If you don't mind my asking, what kind of accuracy are they yielding at 100yds?

Thanks,

Frank
 
#6
Re: 308 Subsonic drop calc

Frank,
No case filler, titegroup is insinsitive to case position.

Large rifle primers.

Getting about a moa to just a hair over moa at 100, like you I had a good bit of 150horns and some titegroup sittin around. Found the load on hodgdon website for 308 subs, and that is how I have been making them since.

Just make sure they are flying straight before sending them through a can.
 
#7
Re: 308 Subsonic drop calc

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Megahoser</div><div class="ubbcode-body">Well, I'd do tables for both...get it zeroed on your supersonics, and then shoot the a group with your subs. With a large enough target you should be able to measure the distance. 1" at 100yds is roughly 1 MOA. Dial in the difference and test your subs zero...adjust as needed but it should be pretty close. Then remember that number as your subsonic zero. Your JBMs should now work for both loads from their appropriate zeros. Dirty, but it should work for what you're trying to accomplish. </div></div>

Ya I know how to do it on the range was just trying to cut out the leg work. Just couldnt figure out JBM so I will just do it on the range thanks...
 
#8
Re: 308 Subsonic drop calc

Sounds good, around moa sounds good enough for me and it would be nice to have a little quieter round sometimes. I'm going to load some up and give'em a try. Unfortunatly no cans are permitted here in Michigan. Thanks for the info.
 
#9
Re: 308 Subsonic drop calc

Just curious for why you are using 875for FPS? The transonic range is 1050fps unless your altitude is over 5000 feet or you have some out of the ordinary temperatures.
I use trail boss for my .308 sub rounds and it works well.

madd0c
 
#10
Re: 308 Subsonic drop calc

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: madd0c</div><div class="ubbcode-body">Just curious for why you are using 875for FPS? The transonic range is 1050fps unless your altitude is over 5000 feet or you have some out of the ordinary temperatures.
I use trail boss for my .308 sub rounds and it works well.

madd0c </div></div>

Well there are a few reasons number one being I shoot in a few different states I go back to Tx and Va not so much Va any more and I wanted to make sure that were not going to be louder for whatever reason.

Second I know that it is a good bit under the supersonic range. But if I were to get a little more powder in there that I wanted I didnt want to go above speed of sound.

I picked up a box of cor-bon subs a while back, the box had it listed as running 1050 fps. So I went out shooting them. It was a hot day. Shot them then shot mine there was a very BIG difference. It wasent like shooting a super but it was not what I would consider quiet.

At the time when I did the load work up for the subs I only had 100 yds to shoot on. That has since changed and I want to shoot them further so I will see how the ones that I have left over do at father distances. And if need be up the powder charge a little bit...
 
#11
Re: 308 Subsonic drop calc

Find the most accurate load in the high 900's or as close to 1000 fps as possible. No need to drop down to 875 fps.

With 1050fps you may still get a crack due to the airflow around the bullet (I think its called dynamic flow)going supersonic, although the bullet is subsonic.
 
#12
Re: 308 Subsonic drop calc

Well, I tried the load... I am not getting reliable results between 5.1-5.3gr. I am having some bullets not making it out of the barrel (24" 1in10" twist savage). The couple that did work @ 5.1gr were real quiet but up @ 5.5gr they are quite a bit louder. Also, the 5.5gr loads were not accurate, for me, at 30yds.
 
#15
Re: 308 Subsonic drop calc

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 725franky</div><div class="ubbcode-body">Well, I tried the load... I am not getting reliable results between 5.1-5.3gr. I am having some bullets not making it out of the barrel (24" 1in10" twist savage). The couple that did work @ 5.1gr were real quiet but up @ 5.5gr they are quite a bit louder. Also, the 5.5gr loads were not accurate, for me, at 30yds. </div></div>

Well you got me...for the ones that did make it out of the barrel did you get a speed on them and are you sure that you are getting 5.1-5.5gr.
Not questioning your reloading skills just trying to help you problemsolve I have yet to have one problem with this load and have been shooting it for some time now.
 
#16
Re: 308 Subsonic drop calc

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bowhunter_0311</div><div class="ubbcode-body">I have messed around with the JBM calc, with no luck found what I am after. I am trying to get drop on my hand loaded subs I just want ballpark figures, just to get on my 12x12 steel that I shoot at. I know 50yds= about 10moa/100yds= about 17.5moa with out setting a target every 25 to 50 yds to figure it out, to save time on next outing need some help.

20in 1/10
5.1gr titegroup
150gr hornady with cannalure
running about 850 to 900fps.

And yes the 150's shoot nice out of the 1/10 twist. I didnt expect it but they do and have yielded good accuracy at 100yds.</div></div>

Run you normal load on JBM. On the answer sheet note the MOA elevation (first field in the Output Data)

Go back to the input page. Set up the data for your subsonic load. Enter the MOA number in the elevation box in the group that includes sight height (check it is in MOA!)

At the bottom ensure that the option for "elevation correction for zero range" is UNCHECKED.

This analysis gives you the drops for the subsonic load assuming the rifle is zero'd for your normal load. You can then dial in the correction and should be close!

My analysis for my SS load is 13MOA low on a 200gr Lapua SS bullet at 1050fps, for what that is worth

Andy
 
#17
Re: 308 Subsonic drop calc

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bowhunter_0311</div><div class="ubbcode-body">

Well you got me...for the ones that did make it out of the barrel did you get a speed on them and are you sure that you are getting 5.1-5.5gr.
Not questioning your reloading skills just trying to help you problemsolve I have yet to have one problem with this load and have been shooting it for some time now. </div></div>

Bowhunter,

I wasn't running the loads across a chronograph so I don't know what the speeds were. As for the powder charge weight, I am using an Ohaus 10-10 balance beam scale (which I have cross checked with my Lyman 1000XP) and I weighed each charge. So, as far as I can determine with my equipment, the load weights should be right.
There were a couple things I am wondering though; one: if I should maybe try seating the bullets past the cannelure (maybe add a crimp too with a Lee FCD) and two: if maybe I should be using large rifle magnum primers (to see if it would help to give more reliable ignition). Bowhunter, maybe there is an elevation diffence between us that contributes to the loads working differently for me; also, maybe my longer barrel is another contributing factor.

For the rounds that did fire at 5.1gr, they sounded about the same as .22LR Wolf MT ammo (target velocity 1050fps).
 
#18
Re: 308 Subsonic drop calc

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Chanonry</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bowhunter_0311</div><div class="ubbcode-body">I have messed around with the JBM calc, with no luck found what I am after. I am trying to get drop on my hand loaded subs I just want ballpark figures, just to get on my 12x12 steel that I shoot at. I know 50yds= about 10moa/100yds= about 17.5moa with out setting a target every 25 to 50 yds to figure it out, to save time on next outing need some help.

20in 1/10
5.1gr titegroup
150gr hornady with cannalure
running about 850 to 900fps.

And yes the 150's shoot nice out of the 1/10 twist. I didnt expect it but they do and have yielded good accuracy at 100yds.</div></div>

Run you normal load on JBM. On the answer sheet note the MOA elevation (first field in the Output Data)

Go back to the input page. Set up the data for your subsonic load. Enter the MOA number in the elevation box in the group that includes sight height (check it is in MOA!)

At the bottom ensure that the option for "elevation correction for zero range" is UNCHECKED.

This analysis gives you the drops for the subsonic load assuming the rifle is zero'd for your normal load. You can then dial in the correction and should be close!

My analysis for my SS load is 13MOA low on a 200gr Lapua SS bullet at 1050fps, for what that is worth

Andy </div></div>


Thanks as soon as I get some time here in a bit I will give this a shot. This was the info that I was after.
 
#19
Re: 308 Subsonic drop calc

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 725franky</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bowhunter_0311</div><div class="ubbcode-body">

Well you got me...for the ones that did make it out of the barrel did you get a speed on them and are you sure that you are getting 5.1-5.5gr.
Not questioning your reloading skills just trying to help you problemsolve I have yet to have one problem with this load and have been shooting it for some time now. </div></div>

Bowhunter,

I wasn't running the loads across a chronograph so I don't know what the speeds were. As for the powder charge weight, I am using an Ohaus 10-10 balance beam scale (which I have cross checked with my Lyman 1000XP) and I weighed each charge. So, as far as I can determine with my equipment, the load weights should be right.
There were a couple things I am wondering though; one: if I should maybe try seating the bullets past the cannelure (maybe add a crimp too with a Lee FCD) and two: if maybe I should be using large rifle magnum primers (to see if it would help to give more reliable ignition). Bowhunter, maybe there is an elevation diffence between us that contributes to the loads working differently for me; also, maybe my longer barrel is another contributing factor.

For the rounds that did fire at 5.1gr, they sounded about the same as .22LR Wolf MT ammo (target velocity 1050fps). </div></div>


Man you have me scratching my head on this been reloading for a few years now but never had a problem like this. I would say make a few more some with crimp and some without and shoot over a chrony. My elevation is 16ft. where I am at... Would adding a crimp slow the bullet from leaving the brass thus giving it more time to increase velocity???

How big was the spread on them at 30yds. when they were working for you?
 
#20
Re: 308 Subsonic drop calc

I just loaded up 3 rounds at 5.1gr of TiteGroup; and I set up the chronograph. I seated the bullets just deep enough to cover the cannelure and I gave them a moderate crimp with a Lee FDC. The first round did not exit the barrel; so, after I cleared the bullet, I made sure to tip the gun back and tap it to make sure the powder would get the full effects of the primer. And that actually worked! The next 2 rounds fired just fine.

Measured velocities:
IMG_20110905_120242.jpg

IMG_20110905_120252.jpg


The target (I was shooting from prone at 50 yards):
IMG_20110905_120405.jpg

The grid on the target is 1"x1".

Interesting the difference in velocity between your rounds and mine.
 
#21
Re: 308 Subsonic drop calc

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bowhunter_0311</div><div class="ubbcode-body">


Man you have me scratching my head on this been reloading for a few years now but never had a problem like this. I would say make a few more some with crimp and some without and shoot over a chrony. My elevation is 16ft. where I am at... Would adding a crimp slow the bullet from leaving the brass thus giving it more time to increase velocity???
<span style="color: #3333FF">It was my hope that the crimp would help raise the pressure before the bullet started moving; thus allowing the powder to ignite better. (Basically what you just said
wink.gif
)

My elevation is right about 800ft. I don't think that is enough difference to make a significant change in load behavior. </span>

How big was the spread on them at 30yds. when they were working for you?

<span style="color: #3366FF"> The spread for the 5.5gr loads was right about 4"</span></div></div>
 
#22
Re: 308 Subsonic drop calc

Just retried the 5.5gr load. I loaded 3 rounds but I didn't use a crimp, I just made sure to tip the gun back before shooting; and all the round fired. The velocities were: 791, 768, 829fps.
The updated target:
IMG_20110905_124936.jpg

The fastest shot was the highest shot and all three went into about 1" from 50 yards.
 
#23
Re: 308 Subsonic drop calc

Mabey the different lots of powder are causing the differece in velocity. I highly doubt that though. Weird that there is that much of a change.
Also never had to make sure that the powder was sitting on the primer. Glad to see that you have it working for you somewhat...
 
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