Velocity Difference Between Win and NATO Brass?

[little_scrapper]

I am about to start a load work up for my AR10, 18" 308/762 1:10. Suppressed. Using 175gr SMK over Hodgdon H4895

All the load data I see is from longer barrels and Winchester brass. I am working with 1F M118LR Brass.

Any info on differences between brass using the same load in each? Please advise.

Thank you,

L_S

 

[918v]

41 grains of H4895 in a NATO case.

 

[little_scrapper]

41 grains of H4895 in a NATO case.

Last ladder I was using 168 gr SMK's. I believe the best group I got was about .85 MOA with 41.1 gr H4895 so you may very well be correct. However, I really didn't know what I was doing and didn't have proper target set, and didn't wait for barrel cool down, and didn't clean every 10 or so rounds. Etc. etc.

I went ahead and loaded up a bunch of 175's, from 39.0 gr to 41.7 gr. in 0.3 gr increments. My intent is to try to find my optimal charge weight (OCW) range. Hodgdon lists 40.8 gr is max charge for H4895. I will definitely be looking for pressure signs as my top load is about 1 gr over that. However, I went up to the max listed for the 168s and had ZERO pressure signs at all.

This will be my third ladder ever and I think I have a much better handle on how I need to proceed. Seated my rounds head to ogive 2.235 to be more inline with the M118LR which my rifle likes. I have a proper target sheet set up. However this will be my first time shooting off a bipod (atlas CAL) so that throws an unknown in.

 

[918v]

Hodgdon lists 42.7 grains as max in a Winchester case.

 

[little_scrapper]

Hodgdon lists 42.7 grains as max in a Winchester case.

Not for a 308 service rifle? AR10. Unless I have been misinformed as to what is considered a service rifle.

 

[stello1001]

Maybe load more rounds way over book max. Book max is usually never actual max and I only say to go way above so you can find where you start getting pressure. At least then, you'll know exactly what max pressure is for YOUR rifle.

 

[little_scrapper]

That will be my next trip. I will load a progression of one or two rounds and look for where I start getting pressure signs.

 

[918v]

Not for a 308 service rifle? AR10. Unless I have been misinformed as to what is considered a service rifle.

Service rifle means M1A

 

[little_scrapper]

I was told Service rifle meant AR semi/full auto type. M1A hasn't been in service for along time. lol

Regardless, I am going to range in an hour. Going to be a nice balmy 35 F this afternoon. I will be bringing a chrono I bought a couple months ago, a bunch of M118LR with head stamps from several different years. 2002, 2003, 2004, 2010, 2016 & 2019 as well as my hand loads to compare velocities.

 

[clcustom1911]

I was told Service rifle meant AR semi/full auto type. M1A hasn't been in service for along time. lol

Regardless, I am going to range in an hour. Going to be a nice balmy 35 F this afternoon. I will be bringing a chrono I bought a couple months ago, a bunch of M118LR with head stamps from several different years. 2002, 2003, 2004, 2010, 2016 & 2019 as well as my hand loads to compare velocities.

You're getting the context of cartridges mixed up

The only "service rifle" to fire a 308 was the M14.

"Service rifle" when talking about 223/5.56, is a 20" barrel M16.

And yes, 41g of H4895 is a solid charge, like you already know. Why dont you pull apart 4 or 5 rounds of your M118LR and weigh the charges to check? That's what I did when I as shooting 308.

 

[Steel head]

Typically Winchester brass is pretty roomy so hit pressure with more powder than a lot of other brass manufacturers.

 

[918v]

I was told Service rifle meant AR semi/full auto type. M1A hasn't been in service for along time. lol

Regardless, I am going to range in an hour. Going to be a nice balmy 35 F this afternoon. I will be bringing a chrono I bought a couple months ago, a bunch of M118LR with head stamps from several different years. 2002, 2003, 2004, 2010, 2016 & 2019 as well as my hand loads to compare velocities.

AR10 rifles are just as strong as bolt guns. They can use regular book loads. Service rifle loads are specifically tailored to the M1A gas system.

 

[little_scrapper]

I appreciate the replies guy. Can I get some post range trip analysis? Was having issues getting the chrono working but when it did register as I recall the lower velocities were low 2400's. The top loads were approaching 2600 fps.

It this was your groups...

 

[clcustom1911]

Between 40.8 and 41.4 you had a point of impact shift which indicates your approximate "node" area. If it were me, I'd do 5 each at 40.8, 41, 41.2, and 41.4 again to check/confirm numbers if your chrono allows it.

 

[little_scrapper]

I don't get it. 41.1 even without the low flier is all over the place. Maybe I just don't fully understand yet. Can you explain the thinking?

My purpose was to try to find an Optimal Charge Weight (OCW) range that will be resilient to my lack of process control. That being said Im looking at 39.6 and 39.9 as they are near identical groups with near identical central POI. Thinking I can work in that area and try to tighten the groups with seating depth and practice. I am not that good so much of that spread is almost certainly my utter lack of skill and experience.

I am all ears and will take any advice I can get.

 

[clcustom1911]

It's not necessarily any one group per se, when you find a accuracy node, the point of impact will shift as you enter the node area, then shift again once you're out of it. Notice on your OCW, all impacts were above the point of aim until you got to 40.8, they shifted down until you exceeded 41.4. I'd be willing to bet that impact shift coincided with a velocity of 2550-2575 FPS or so.

When you combine the point of impact shift with the velocity data, you'll should notice a velocity flat spot and SD's get low for the groups in the impact shift.


Does that kind of make sense?

@Skookum and a few others can probably articulate this better than I. He is quite the man when it comes to this subject

 

[little_scrapper]

I understands what you are saying. Not sure it makes sense about an accuracy node. 41.1 doesn't look like an accuracy node to me. Also, not sure I want to be pushing 175 gr SMK's at 2600 fps as a norm. Im almost never going to shoot past 400-500 yards.

However, I still need to try IMI 4064 and Varget. Hodgdon H4895 is the only powder I have loaded so far.

I may even start using lighter bullets like 150 gr.

 

[918v]

I would play around 40.5, also with coal in .005” increments. If they exceed 2.8”, get Knights mags.

 

[little_scrapper]

Im seating bullets to 2.235 at the ogive and OAL is running 2.84ish

 

[918v]

I got my best at 2.810” with that combo.

 

[little_scrapper]

noted. The M118LRs seems to be running 2.815+-