Subsonic 6.5

GatorHunter

GatorHunter

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So long story short, a friend of a friend is bragging about hunting at 1500 yards for deer with a 6.5 creedmoor. I don’t know about the truth of it but ballistics say it’s not wise. I don’t want to debate the story, I want to test the theory. After doing all the research in ballistics, his 129gr Hornady whitetail ammo is doing just over 900fps at 1500 yards. This got me thinking of how to test this on ballistics gel. I don’t own a 6.5 in any caliber but I do have a few boxes of 6.5 129 gr Hornady interlocks. I picked them up when my friend was getting started with his 6.5 Grendel build. Has anyone loaded subsonic 6.5 Grendel or any 6.5 for that matter? I have it figured out that I need to do about 950-980fps at the muzzle to shoot a block of ballistic gel at 50 yards. Is it possible to go this low?
 
At 1000 yds with 140gr Sierra Match King the bullet drop is 350+ inches. L That’s like 34moa or 120 elevation clicks on the scope. Not something I would do for hunting.
Subsonic is going to be much worse.
 
AJC1 said:
Will less kill absolutely. Is it ethical, not my thing.
Click to expand...
+1

Ive killed a couple with sticks and more with a 22 than probably all of my center fires combined..... Though since we haven't had the farm (damage control permit) for 20 plus years, it's possible my centerfires have caught up.

Thats a 40gr bullet at about 900fps, and it works great if you can place it into a soft spot on the skull, upper vertebrae, or heart.
My personal limit for making those shots from a braced position, and when i was doing it alot, was about 100yds.

Ive shot my CM and other rifles out past 1500yds, and at least for MY skill level, making a first round HIT on a deer size target is more luck then ability.....much less landing the bullet where i want it to go.


As to how those bullets will perform at lower velocities. I dunno honestly, but I think one of the issues with downloading is that you lose some of the centrifugal force (bullets rpm is based on launch speed and twist, and degrades slower than velocity) that would help the bullet expand.

It would certainly be interesting to try and see, ive never done it.
 
Last edited:
GatorHunter said:
Has anyone loaded subsonic 6.5 Grendel or any 6.5 for that matter? I have it figured out that I need to do about 950-980fps at the muzzle to shoot a block of ballistic gel at 50 yards. Is it possible to go this low?
Click to expand...

Subsonic Grendel will not cycle the AR15, so if somebody handloaded some 6.5 Grendel to subsonic velocity, it would probably be in a bolt gun.

It is easy to figure out what the MV needs to be for 950-980 fps at 50 yards. The question is, what weight & BC of bullet? Then just plug the variables into a ballistic calculator. For example, Hornady SST 123 gr. bullet has a BC of .51 plug those in and pick a starting velocity....I picked 1000 fps and the ballistic calculator says 980 fps at 50 yards, so maybe a little fast, being at the top end of your needs and potentially going over. You could load for 980 and and be at 962, pretty much a sweet spot for your testing. A different bullet with a different BC will likely need a slightly different velocity.
 
Atavar said:
At 1000 yds with 140gr Sierra Match King the bullet drop is 350+ inches. L That’s like 34moa or 120 elevation clicks on the scope. Not something I would do for hunting.
Subsonic is going to be much worse.
Click to expand...

At 1500 yards, the 6.5 creedmoor has 90 feet of drop. I’m not looking to shoot that far or even use it for anything other than testing. I just need to load up a really slow batch of ammo that will fire from a rifle into a gel block. I’m just trying to see what the interlock bullet will do at really low speed. I’ll only be shooting close range with it simulating the speed it would have at 1500 yards. I’m only doing it to prove a point to a friend
 
AJC1 said:
Subsonics are about high mass and high sectional density. Will less kill absolutely. Is it ethical, not my thing.
Click to expand...
I totally agree, that’s why I’m trying to figure out how to test this without having to shoot at 1500 yards into a gel block. I just need to slow the bullet down to the speed it would be at 1500 yards
 
LoonWulf said:
+1

Ive killed a couple with sticks and more with a 22 than probably all of my center fires combined..... Though since we haven't had the farm (damage control permit) for 20 plus years, it's possible my centerfires have caught up.

Thats a 40gr bullet at about 900fps, and it works great if you can place it into a soft spot on the skull, upper vertebrae, or heart.
My personal limit for making those shots from a braced position, and when i was doing it alot, was about 100yds.

Ive shot my CM and other rifles out past 1500yds, and at least for MY skill level, making a first round HIT on a deer size target is more luck then ability.....much less landing the bullet where i want it to go.


As to how those bullets will perform at lower velocities. I dunno honestly, but I think one of the issues with downloading is that you lose some of the centrifugal force (bullets rpm is based on launch speed and twist, and degrades slower than velocity) that would help the bullet expand.

It would certainly be interesting to try and see, ive never done it.
Click to expand...


That’s all the interesting stuff I’m trying to test. I’m just wondering if it’s smart to slow a light bullet down that far. I don’t need the rifle to cycle. I’ll probably turn the gas system off and use it as a single shot.
 
Double Naught Spy said:
Subsonic Grendel will not cycle the AR15, so if somebody handloaded some 6.5 Grendel to subsonic velocity, it would probably be in a bolt gun.

It is easy to figure out what the MV needs to be for 950-980 fps at 50 yards. The question is, what weight & BC of bullet? Then just plug the variables into a ballistic calculator. For example, Hornady SST 123 gr. bullet has a BC of .51 plug those in and pick a starting velocity....I picked 1000 fps and the ballistic calculator says 980 fps at 50 yards, so maybe a little fast, being at the top end of your needs and potentially going over. You could load for 980 and and be at 962, pretty much a sweet spot for your testing. A different bullet with a different BC will likely need a slightly different velocity.
Click to expand...

I need a muzzle velocity of right around 950 for it to drop to 920 which would match what a 6.5 creedmoor would be at 1500 yards. I ran it all through my ballistics app. I have a ton of screen shots of the velocities I’ll need. But im more concerned with case fill, bullet actually exiting an 18” barrel, or any other factors im not thinking of yet
 
So basically the ballistic table says that Hornady whitetail 129gr is doing 918 fps at 1500 yards. I can do the math and figure out a muzzle velocity to be at 918 at 50 yards. I just have no idea what powder to use. So far the only rifle I have to test this with is an 18” 6.5 Grendel.



IMG_8697.png
 
I played with quickloads a bit and to launch at around 950-1000fps your only pushing about 8-10Kpsi. Id probably try with 8208 or other normal grendel powder and back it down till you get your velocity or erratic results.
You could also use a pistol powder with longshot hs-6 range taking about 5gr to get your velocity.

Ive loaded alot of grendel, and ive played with quickloads alot, but ive never tried to load DOWN a grendel.
one thing to be aware of is getting a bullet stuck, I did that with my 300aac trying to get it as quiet as possible without a suppressor. 750-800fps was about as slow as i could go with that set up and heavy lead bullets. light jacketed bullets will likely behave differently.
 
I have loaded gallery or mouse fart loads in a 6.5x55 Swedish military mauser. I was using a light and very off-book charge of Unique so I won't quote it here, but some quick internet research will find similar loads compatible with most medium centerfire cartridges.

In this case, I was using up some random bullets lying around for casual practice, and my loads were +/- the trans-sonic threshold at the muzzle. Observations should be considered qualitative, as scientific testing of subsonic performance beyond "minute of firewood block" accuracy was not my priority. 140 Nosler HPBT match bullets did not stabilize from my barrel. Unknown (likely Sierra) 120 SP Factory second was stable and quite accurate even at extended range. 139 M41 FMJ pulldown was reasonably accurate and stable. 162 Cast GC was stable with poor accuracy, possibly losing stability with oval holes at 70ish yards. 160 Hornady RN was stable with poor accuracy., also possibly losing stability at longer distances I did put some of the 120 Sp through soft targets and found terminal results unimpressive even compared to non-expanding handgun bullets at full velocity. Penetration through hardwood blocks was impressive, superior to full power FMJ 9mm, with all loads other than the match bullets that were clearly tumbling. Hardwood blocks up to 6" diameter were easily penetrated. Some bullets of various types recovered from snowbanks showed deformation and possible tumbling during penetration, but little to nothing of what we would term expansion as expected from a HP rifle bullet.
 
LoonWulf said:
I played with quickloads a bit and to launch at around 950-1000fps your only pushing about 8-10Kpsi. Id probably try with 8208 or other normal grendel powder and back it down till you get your velocity or erratic results.
You could also use a pistol powder with longshot hs-6 range taking about 5gr to get your velocity.

Ive loaded alot of grendel, and ive played with quickloads alot, but ive never tried to load DOWN a grendel.
one thing to be aware of is getting a bullet stuck, I did that with my 300aac trying to get it as quiet as possible without a suppressor. 750-800fps was about as slow as i could go with that set up and heavy lead bullets. light jacketed bullets will likely behave differently.
Click to expand...
I'd try red dot... famously good for reduced rifle loads at low velosity
 
I’ve always heard 13 grains of red dot will work in rifle cartridges not that I would try it and I suggest you don’t either but it’s what I heard not sure it would do what you want it to and @GatorHunter do you really Believe Your Friend in what He is saying I for one can’t believe it I’m not saying he didn’t but I am saying the difficulties of that kind of shooting are immense………..


Let alone not ethical in imho everyone’s eyes
 
horsemen61 said:
I’ve always heard 13 grains of red dot will work in rifle cartridges not that I would try it and I suggest you don’t either but it’s what I heard not sure it would do what you want it to and @GatorHunter do you really Believe Your Friend in what He is saying I for one can’t believe it I’m not saying he didn’t but I am saying the difficulties of that kind of shooting are immense………..


Let alone not ethical in imho everyone’s eyes
Click to expand...
I don’t believe his friend at all. That’s what got me thinking about testing this. A 6.5 creedmoor, with the ammo he’s using, has almost 90 feet of drop at 1500 yards. The ballistics table for my bdc scope says that on 3 power, the bottom of the scope is 1100 yards. Using the drop calculations, you would still have to aim 40 foot above the deer to make the shot.
 
AJC1 said:
The subsonic is to recreate the ballistics with much more control at shorter range.
Click to expand...
How are you going to recreate supersonic ballistics with a subsonic load? I don’t understand?
Are you talking about just trying to replicate terminal performance instead of ballistics?
 
Last edited:
I'll let you do you, but with some googling, I found a lot of information on the 7mm TCU cartridge downloaded with cast bullets and either Unique or Red Dot. This cartridge is comparable to the 6.5 GR in capacity.
 
AJC1 said:
The subsonic is to recreate the ballistics with much more control at shorter range.
Click to expand...
Correct. I don’t want to have to shoot 1000 yards to recreate the ballistics of what the claimed range would be. After I get a few bullets into ballistic gel around 920fps I’ll never need this load again
 
Atavar said:
How are you going to recreate supersonic ballistics with a subsonic load? I don’t understand?
Are you talking about just trying to replicate terminal performance instead of ballistics?
Click to expand...
Yes, I’m trying to see what a 129gr interlock does at 920fps into a gel block.
 
Random 8 said:
I'll let you do you, but with some googling, I found a lot of information on the 7mm TCU cartridge downloaded with cast bullets and either Unique or Red Dot. This cartridge is comparable to the 6.5 GR in capacity.
Click to expand...
Thank you, I didn’t know they were close
 
In my experinces with shooting cast loads in 260 rem with RCBS 6.5-140 and Lee 266-140 at around 1,600 fps, one of the biggest challenges is overcoming the transonic barrier while staying within the confines of bullet RPM as it pertains to the limitations of cast bullets and rifle twist. If you manage to keep your jacketed bullet on target I think you'll see a wound channel consistent with a yawing projectile.
 
I'll save you the trouble. The softest 6.5 bullet I know of is the Nosler 129 grain ABLR. That one is rated to expand down to 1300 FPS. Everything else I am aware of requires 1600 FPS impact velocity or higher to expand. 900ish is not going to expand. You can kill a deer with that, but I wouldn't much like my chances of hitting the CNS at 1500 yards.
 
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