Advice about pressure signs

[lazyengineer]

Yes. Gold Dot builds pressure faster than most cup and core bullets from what we’ve seen so far.

I wondered about that. I have a hunch that a hot load in a Gold Dot, may not be so hot a load in another. I feel like their jackets are.... sticky(?) in the bore. It seems like they love to foul and leave a lot of copper behind. It makes me wonder if the bullets drag more or something, as they go down the bore. Maybe I'm wrong, has anyone else noticed that copper patches after running Gold-Dot reloads seem to take more effort to get the copper out?

[LRRPF52]

The Gold Dots resist being driven into the lands, so they need to be worked-up separately from any other 120gr cup and core published data.

Basic load development protocols apply. Change a component and do your due diligence with another work-up.

Nosler Partitions are the same way. That Partition wall inside the jacket does not like being swaged into the lands, whereas most cup and core bullets just squeeze into the rifling nicely.

[fdbyrne78]

I finally got home to look at some data.

Hornady factory 123SST loads chrono at 2548 out of this barrel with no pressure signs. The 123 EDLM/AR Comp load that caused me to start this thread chrono'd at 2498 fps with an ES of 10 for a 5 shot load. Using my Hornady comparator these measure 1.670" to the ogive and I hit the lands at 1.694" so definitely not into the lands.

I don't think that changes any thing mentioned previously. I'm still likely over pressure for my gun. The thing that has me confused, well more confused than everythign else anyway, is that I don't think I had pressure signs running my carbine lower with H2 buffer. I don't think I started chewing up brass until I went to the Magpul PRS stock with rifle tube, spring, and buffer. That's easy enough to test by swapping lowers next time I'm on the range.

[Harpoon1]

……….lhas anyone else noticed that copper patches after running Gold-Dot reloads seem to take more effort to get the copper out?

I took Bryan Litz advice a while ago and started using “abrasives” to clean the barrel. It’s much less labor intensive and time consuming. He recommends JB Bore Paste but I have used Iosso alternatively with similar results. I don’t have the stamina or desire to use solvents anymore after using his method. The longer you go between intervals, the dirtier the barrel, the more copper or carbon foulIng, the more beneficial the use of abrasives. YMMV.

This whole video is very worthwhile but, you can skip ahead to 41:45 for his cleaning recommendations.

https://youtu.be/_6TAMM-fz-c

[Klem]

They both vary 9,000 to 20,000psi over and under actual pressure test breech readings. They aren’t consistently-under SAAMI MAP. That’s the problem.

You could take Hodgdon’s and Western Powder’s cumulative data and enter each combination into QL to compare against their measured pressure test breech numbers if you have a lot of time on your hands.

You will see numbers all over the map relative to the real-world numbers.

Which is why it is wise to consult multiple sources, and not just QL. And start 10% low.

[BowChamp]

These seem to be the threads I learn the most from.

Thanks to everyone posting here.

[Rosecrans1]

Also adding that many on this site and many who have moved on from "The Grendel" have stated that the 6.5 Grendel is one of those cartridges that you DO NOT want to base loads on by trying to read pressure signs. By the time that case shows signs of over-pressure, you have very likely exceeded industry safe pressures for the cartridge. Granted, ARC doesn't have an awful lot of published loads but everyone should still adhere to what little is published and is posted "by a trusted authority". This is especially true in an AR platform.

[Fess]

By the time that case shows signs of over-pressure, you have very likely exceeded industry safe pressures for the cartridge.

This is something that everyone who reloads the Grendel and ARC needs to know and I am certain that it frustrates a lot of people. There is really no way to know when you are right at "AR-bolt-safe" pressure. Typical overpressure signs don't start until you are significantly past it.
As an aside, I would love to know the strength of CMMG's "mutant" bolt. It is significantly larger than the standard AR15 bolt, so I wonder if it would tolerate a "Super Grendel" load with brass that was strong enough.

[StoneHendge]

I finally got home to look at some data.

Hornady factory 123SST loads chrono at 2548 out of this barrel with no pressure signs. The 123 EDLM/AR Comp load that caused me to start this thread chrono'd at 2498 fps with an ES of 10 for a 5 shot load. Using my Hornady comparator these measure 1.670" to the ogive and I hit the lands at 1.694" so definitely not into the lands.

I don't think that changes any thing mentioned previously. I'm still likely over pressure for my gun. The thing that has me confused, well more confused than everythign else anyway, is that I don't think I had pressure signs running my carbine lower with H2 buffer. I don't think I started chewing up brass until I went to the Magpul PRS stock with rifle tube, spring, and buffer. That's easy enough to test by swapping lowers next time I'm on the range.

Turn off your gas COMPLETELY and take 5 shots. If there are pressure signs, then the pressure signs are caused by pressure. If not, then what you are reading as pressure signs are caused by timing. You may still be overpressure (I won't get into the discussion about some German dude's software) but your downside is likely limited to a broken bolt lug. I've found that timing issues will ultimately result in a broken extractor and that extractors can break at very inopportune times and are not often easily removed from a barrel extension in the field (along with bolt lugs).

Hornady ammo likely uses CFE 223 and/or LeveRevolution which is slower than AR Comp and will have a later pressure peak

[fdbyrne78]

78.

Yes, that is hot load - beyond SAAMI.

Suggest 25.8 max, or SH's 26, but no more.

I went back to the range tonight and shot 25.6 up to 26.0. 25.6gr still showed ejector marks and chrono'd at 2410 fps. Still single digit ES's all the way up to 26.0 with reasonably small groups even though I was shooting fast to get my shots in before it got dark. I'll load some more up and go lower still until I don't see any more marks.

I know that I could get more velocity with CFE or Lever but I've not had good results with either. I love the accuracy of AR Comp but I have a feeling that by the time I find a load that doesn't damage the brass that I really won't be very happy with the velocity. I'm averaging almost exactly 20 fps difference for each .2gr change in charge weight. If that holds on the way down then going to 24.6 would put me at 2310 fps which to me is disappointing in a 20" barrel. Maybe I was expecting too much.

I had intended to shoot a few with the gas turned off as suggested but I didn't bring enough ammo and at this point I'm pretty sure it isn't a gas issue. I might still try it the next time I get to the range.

[Harpoon1]

I went back to the range tonight and shot 25.6 up to 26.0. 25.6gr still showed ejector marks and chrono'd at 2410 fps. Still single digit ES's all the way up to 26.0 with reasonably small groups even though I was shooting fast to get my shots in before it got dark. I'll load some more up and go lower still until I don't see any more marks.

I know that I could get more velocity with CFE or Lever but I've not had good results with either. I love the accuracy of AR Comp but I have a feeling that by the time I find a load that doesn't damage the brass that I really won't be very happy with the velocity. I'm averaging almost exactly 20 fps difference for each .2gr change in charge weight. If that holds on the way down then going to 24.6 would put me at 2310 fps which to me is disappointing in a 20" barrel. Maybe I was expecting too much.

I had intended to shoot a few with the gas turned off as suggested but I didn't bring enough ammo and at this point I'm pretty sure it isn't a gas issue. I might still try it the next time I get to the range.

Accuracy, by and large, is a function of harmonics/barrel timing.

Find an ignition system, (powder/primer combo), that gives you the best speed with lowest ES/SD and lack of pressure signs. Then adjust your seating depth to find an acceptable accuracy node.

Working within the confines of a max COAL mag length and jamming the bullet down into the cartridge reducing powder capacity complicates things but, accept the challenge!

[JDub]

Mag length( not into the lands) tells us nothing.

Have you measured too be sure you are not into the lands?

I had a satern barrel once. Got rid of it because I had the same issues yours is showing only it did it with factory amax and eld-m ammo. Turns out it was short throated.

Me too. I had a Satern 18" button rifled barrel that shot factory 123gr. Hornady A-Maxes to around 2550fps with flattened primers and ejector swipes. Factory rounds would not fall free after they were chambered and pressed in manually. I really wanted to believe is was gas but I tried everything but the signs remained.

Problem was that that barrel was a shooter. Sub MOA all day with factory and hand loads.

It felt like dating a hottie that you know has STDs...possibly worth it but wise to part ways.

Forgot to mention that the same factory rounds would produce 2450fps in a 20" Wilson Combat barrel with no pressure signs.

[fdbyrne78]

I went back to the range with a variety of charge weights from a variety of different powders. I used AR Comp, Benchmark, Varget, BLC(2), and CFE223. Still ran into ejector swipe earlier than I figured. I still need to go lower to find charges with no swipes.

While processing some brass I realized something that I'd like to get some opinions on. The fired cases are coming out with a 1.223" length to shoulder using the proper comparator. I'd sized the cases to 1.213" previously because my other Grendels produce fired brass that measures 1.217" or 1.218". It seems that the chamber/bolt combination for this rifle allows for significantly longer cases than my other Grendels. I swapped the BCG's between the Grendels and the results were kind of interesting... at least to me. With this rifle, I can bump the shoulder back to 1.218" and they chamber just fine. If I try to chamber that same round in my other Grendel it won't return to battery. My 1.213" cases do allow the BCG to return to battery in that other Grendel. Both bolts have bolt head depth measurements .137" so the variance is somewhere else.

I really don't mind keeping my brass separate for different guns. I also don't want to have to if I don't need to. Would an apparent headspace of .010" have any impact on the marks that I'm seeing? Obvoiusly case life may suffer from oversizing the cases and I get that part.

[grayfox]

That first rifle has, in my terms, a long chamber. I had one or 2 in the past that did that also, my fired brass in them came out 1.224-1.227; it was going to be a pain for me to keep brass separate b/c you only need to bump the shoulder back ~0.003 from fired length... and I wasn't looking forward to doing that all the time, so I got rid of those barrels. If you continually resize down to the 1.213 on that brass you'll wind up stretching weakening and hardening it far too soon.
I only want a barrel/chamber that behaves in normal terms as far as brass stretching during the firing cycle.

[fdbyrne78]

So, I'm still chasing this problem and could use some more advice. I did single charges of various powders looking for the highest velocity I can get with each before seeing ejector marks on the brass. I start running into problems at 2275 fps with AR Comp, 2325 for Benchmark, 2300 for Varget, and 2325 for BLC2. That's with a 20" barrel and 123 ELDM's just to recap.

I'd be fine with some of those numbers except those numbers aren't nodes, their upper limits. There is probably an accuracy node I could find, but only by going even slower. I've tried 3 different BCG's, two different lowers (one rifle buffer one H3 carbine buffer).

AR Comp gives me single digit ES and SD's for 5-shot groups with excellent accuracy. I'm not looking for a hot rod load, but don't think I should have to settle for 2200 fps out of a 20" barrel either.

I have two specific requests for input.

First, how fast can you push a 123gr bullet out of your 20" barrel before harming your brass? I'm trying to see if I have unrealistic expectations for my barrel and this input would go a long way to helping me understand that.

Second, if I have to get a new barrel to achieve my goals, what are my options? I really like a 20" barrel with a relatively heavy contour and I'd prefer it to be fluted. That's just my preference. I can't really find anything out there that has those specs. I don't want to say that money is no object, but if I end up buying a new barrel I'd prefer to buy once and cry once vs. throwing hundreds or thousands of dollars into bullets and powder trying to find something that works.

[Zeneffect]

What is your distance to lands?

[fdbyrne78]

What is your distance to lands?

Right around 0.020".

[VASCAR2]

If I was in your situation fdbyrne78 I’d take a close look at the ejector. Is the tip rounded or is it beat up. You might consider clipping a couple coils off the ejector spring. It is not unheard of to get ejector swipe just because you have a long ejector or a stout spring. I’d compare the ejector and springs between your different AR-15 bolts. I think your ejector swipe is not consistent with some of the velocities which I think are well below 52,000 psi.

I have one 6.5 Grendel AR-15 that marks the brass more than my others. If your primer edges are still round and not flat plus good consistent ejection I think I’d do some investigation on the ejector. There are forum members who trim coils off their ejector spring to get less damage to their brass.

[Zeneffect]

with a .020 jump I would have to agree with VASCAR2 here. You arent jamming causing the overpressure.

[fdbyrne78]

If I was in your situation fdbyrne78 I’d take a close look at the ejector. Is the tip rounded or is it beat up. You might consider clipping a couple coils off the ejector spring. It is not unheard of to get ejector swipe just because you have a long ejector or a stout spring. I’d compare the ejector and springs between your different AR-15 bolts. I think your ejector swipe is not consistent with some of the velocities which I think are well below 52,000 psi.

I have one 6.5 Grendel AR-15 that marks the brass more than my others. If your primer edges are still round and not flat plus good consistent ejection I think I’d do some investigation on the ejector. There are forum members who trim coils off their ejector spring to get less damage to their brass.

Good suggestion. I forgot to mention that I pulled the ejector and rounded the edges. I checked it up in a drill press and ran a fine diamond file over the edges. It didn't help which really pissed me off because I was sure that was it. I then pulled out the spring and clipped a couple coils. After that I still had the marks but ejection was really weak. Most of the brass landed on the shooting bench with one stovepipe which had never happened before.

After that I tried a different bolt in the same carrier. When that didn't help I threw in the BCG from my 16" BA upper that has no issues and again, no change.

I have to admit, I did a lot of checking things and rechecking things since my last post because I really feel like I should be able to figure this out and I honestly hate asking for help.

I may try loading them another 0.020" shorter and trying again. I've never measured neck tension so I guess it's possible that I don't have the jump I think I do after the bolt cycles.