375 SOCOM

[98Z5V]

 

[dpete]

35 minutes ago, 98Z5V said:

 

Yup.  They's a little big.

[Radioactive]

7 hours ago, dpete said:

Yup.  They's a little big.

My grin is getting bigger by the post.

[dpete]

@Radioactive   The one word to describe this rifle is Impressive.  For an AR15 the recoil is fairly impressive but not ungodly.  About as hard as my 308AR was but much quicker.  The bark this thing has when a round is touched off is also impressive.  The first comment from the guy next to me at the range today was, "wow is that thing loud".

This was by far the easiest load development I have ever had for a rifle of any caliber, impressive!

Ok, cutting to the chase, putting pictures where the claims are.

 

 

Upper right and lower left fliers

 

 

 

 

All targets are 5 shot groups at 50 yards. Sierra 200 grain Flat Points over  AR-Comp.  Considering these bullets have the ballistic coefficient of a smooth rock they sure shoot great and I can see why those with experience with the 375 say its the bullet of choice.

 

 

[98Z5V]

41 minutes ago, dpete said:

@Radioactive   The one word to describe this rifle is Impressive.  For an AR15 the recoil is fairly impressive but not ungodly.  About as hard as my 308AR was but much quicker.  The bark this thing has when a round is touched off is also impressive.  The first comment from the guy next to me at the range today was, "wow is that thing loud".

This was by far the easiest load development I have ever had for a rifle of any caliber, impressive!

 

 

All targets are 5 shot groups at 50 yards. Sierra 200 grain Flat Points over  AR-Comp.  Considering these bullets have the ballistic coefficient of a smooth rock they sure shoot great and I can see why those with experience with the 375 say its the bullet of choice.

 

 

This one right there is the keeper, brother.  Single-digit SD, ES 20...   That's the one.  You're going 0.3 on the charge, narrow that down, either side of this one, and see if anything it better.  Or not - that's pretty damn great, right there.  

You see any pressure signs with that load?

[98Z5V]

Every 0.6 grains, you're hitting a node, and it's getting tighter when you're going up.  That last one was 46.4grains.  You think you can jump that, without hitting pressure signs, another 0.6gr, to 47.0 even?   That'll be another accuracy node, if the pressure is safe.

[dpete]

Just now, 98Z5V said:

This one right there is the keeper, brother.  Single-digit SD, ES 20...   That's the one.  You're going 0.3 on the charge, narrow that down, either side of this one, and see if anything it better.  Or not - that's pretty damn great, right there.  

You see any pressure signs with that load?

Nothing that screamed at me STOP!

[98Z5V]

1 minute ago, dpete said:

Nothing that screamed at me STOP!

I'd risk it, built 3 of them at 46.7, just to check pressure, and run 5 at 47.0 if that 46.7 pans out.  You'll hit another mode at 47. 

But then, I'm a dumbass like that...  

[dpete]

12 minutes ago, 98Z5V said:

Every 0.6 grains, you're hitting a node, and it's getting tighter when you're going up.  That last one was 46.4grains.  You think you can jump that, without hitting pressure signs, another 0.6gr, to 47.0 even?   That'll be another accuracy node, if the pressure is safe.

46.4 gr may be slightly over pressure as it is but there weren't any signs of it.  Watching the powder climb up inside the case neck as the charges went up made me wonder how it is claimed 47 gr is even possible and not have the bullet seriously compressing the powder.

Edited June 7, 2020 by dpete

[dpete]

Just now, 98Z5V said:

I'd risk it, built 3 of them at 46.7, just to check pressure, and run 5 at 47.0 if that 46.7 pans out.  You'll hit another mode at 47. 

But then, I'm a dumbass like that...  

Here is a quickload data sheet run by someone with way more experience with the 375 Socom.200 gr Sierra FP load data - 1.webp

 

[98Z5V]

Damn, brother - you're already 1.2 grains above the max pressure, as they're advertising it.  I had no idea max pressure was 35k psi.  They're calling max pressure at 45.2 on the AR-Comp. 

Be happy with what ya got, then?...   That load is a keeper. 

[dpete]

4 minutes ago, 98Z5V said:

Damn, brother - you're already 1.2 grains above the max pressure, as they're advertising it.  I had no idea max pressure was 35k psi.  They're calling max pressure at 45.2 on the AR-Comp. 

Be happy with what ya got, then?...   That load is a keeper. 

Here is where the 47 gr load idea came from.  https://www.shootersforum.com/wildcat-cartridges/99551-ar-15-375-socom.html

As I said I don't see how 47 gr even fits in the case with a bullet on top of it not compressing the schit out of the powder.  Scroll down to post #10 in that thread. 

He got 100fps less speed with .6 gr more powder and with 2.170" COAL.  My COAL was 2.175".  If his was one of the first barrels made by Tromix then I think its safe to assume his and my barrels are both 18".  The 18" barrels have since been replaced by 16" and 20"

[dpete]

@Radioactive  If you haven't already, read this thread about 375 Socom and what he says about subsonic use.  http://458socomforums.com/index.php?topic=2791.0

Whether or not his statements are factual or not I have no idea.

[98Z5V]

@Big Bore is here, too.  Let's get him into this.  If he's been running this, and testing it - then trust what he states.  

I saw weird shiit like you're talking about, with my Grendel loads.  Built everything off the original 18" Mk-12-ish (SPR) gun, and came up with a stellar load at 28.5 grains.  Second Grendel was the 12.5".  I thought the primers looked cratered - same load.  I went into it again, and hit another node at 27.5 grains.  Kept that for awhile.  Then comes another 18" "lighter Grendel", the 16" M4 Grendel, and finally the 16" Mk12 Mod H Grendel...  All of them went on the chrono, on the same day, same 27.5gr load. The 16" Mod H has a higher muzzle velocity than the 18" SPR gun.  WTF?!  The 16" was perfect for that barrel length and charge - the charge fully burned up before the projo left the 18" SPR...  and dragged and the end of the barrel.

So, since ALL the 27.5gr loads looked the same at the 28.5gr loads, as far as primers looking cratered.  Dump all that old 27.5 ammo, and load up all new ammo back to the original 28.5gr load.  All the velocities came back up, the accuracy was there, and the 18" guns outperformed the 16" guns, as far as muzzle velocity goes.

I'll dig out my numbers on that - they're all in my permanent notebook.

Ballistics are WEIRD, brother...  

[98Z5V]

Grendel loads, muzzle velocities, 27.5gr Accurate 2520:

12.5" = 2239 fps

16" = 2385 fps

18" = 2309 fps

That 16" SMOKED the 18".  Accuracy on those loads were there, but that never should have happened...

28.5gr Accurate 2520:

12.5" = 2369 fps

16" = 2495 fps

18" = 2534 fps

NOW we're talking.  Accuracy was there again - like it was originally - on the next higher node.  These things just slightly crater primers, and when I built that 12.5", I got paranoid about it and backed the load down.  Never should have done that, in hindsight. 

[dpete]

Looking at the speed increases per .3 gr increase in powder charge:

44.9gr  =  2355 fps

                                     -9 fps  WTF? 

45.2gr  =  2346 fps

                                    +43 fps

45.5gr  =  2389 fps

                                    +15 fps

45.8gr  =  2404 fps

                                    +14 fps

46.1gr  =  2418 fps

                                    +17 fps

46.4gr  =  2435 fps

Given the seemily consistant mid teen fps speed increases toward the top of the ladder.  Is it worth pushing the pressure envelope with an additional .6gr of powder to get what might be 30 more fps out of a 47.0gr load?

[98Z5V]

13 minutes ago, dpete said:

Given the seemily consistant mid teen fps speed increases toward the top of the ladder.  Is it worth pushing the pressure envelope with an additional .6gr of powder to get what might be 30 more fps out of a 47.0gr load?

Nope, not with the grouping you've got at 46.4, and that 35k psi threshold that you posted from quikloads.  You're already above that 35k psi threshold, according to their load info, and that was 35k at 45.2.  I'd keep what you have - which is a great group, great SD and ES...   and run that thing...  You have a winner, right there. 

Edited June 7, 2020 by 98Z5V

[Boot_Scraper]

Good stuff @dpete! Helluva round. If you had to, you could throw the cartridges at the perp and still inflict some damage. 

[Radioactive]

7 hours ago, dpete said:

@Radioactive  If you haven't already, read this thread about 375 Socom and what he says about subsonic use.  http://458socomforums.com/index.php?topic=2791.0

Whether or not his statements are factual or not I have no idea.

10-4

I have read many of big bore’s posts. The guy is a wealth of knowledge.
 

The 325 gr maker bullets seem like they are gtg for subsonic use. I’ll not be running a ton of rounds down range with this as it’s going to be a dedicated house gun that should be close to 357 mag energy. Did I need this? No but I wanted it so... we will see how it works out.

[Radioactive]

I’m sure you have seen it too but I have read (it may have been big bore), that the socom round can go to hi pressure with very little change like a light switch. no early or slow signs of over pressure. Also that you may be over the 35k mark with no signs. I think the 35 k is just for bolt concerns and some of the gas components not a cartridge or barrel concern. Be careful is all I’m saying. Several of those loads look like they are plenty accurate at 50 yards pick one and move out to 100 + and see if they still meet your needs for hunting accuracy.

[dpete]

1 hour ago, Boot_Scraper said:

Good stuff @dpete! Helluva round. If you had to, you could throw the cartridges at the perp and still inflict some damage. 

It would probably leave a mark.  Bare projectile straight out of the box in a slingshot could do some major damage!

[dpete]

33 minutes ago, Radioactive said:

 Several of those loads look like they are plenty accurate at 50 yards pick one and move out to 100 + and see if they still meet your needs for hunting accuracy.

@Radioactive  Thanks.  Hunting accuracy is already met.  Up here in the northern WI woods we don't have fields to shoot over.  The longest shot I can pull off out of one of my stands is about 60 yards.  The longest I've ever taken on a deer is maybe 150, but that was mid state over a grown out clearcut.  I've used my suppressed Blackout and 200 grain Makers on deer close to town in my bow stands.

[dpete]

Here is some perspective on that 5 shot group that was 46.4 grains of AR-Comp.

 

That copper dot at the top of the target square is the flat bottom of one of the 200 grain bullets used.  The bullet itself is sitting on its nose in the middle of the holes made by 4 of the 5 shots.  The 5th hole is to its right.  Nextdoor is the target without the bullet.

[Radioactive]

I’d say “good to go”!

[98Z5V]

Yep, that was the Keeper.  Very well done, brother.