6.5 Creedmoor Pressure Issues

[SonoranPrecision]

Sorry in advance for the wall of text. Earlier this year I put together a new rifle, TL3, 26” Proof prefit. Shot the load from my other 6.5cm (42.2gr H4350, 140 hybrid) for the first 150-200 rounds to let the barrel speed up. Initial velocity was around 2830, and after ~200 rounds was up to 2860 which seems fast, but I had no pressure signs so I wasn’t worried. Did load development with 140 rdf’s, and found velocity flat spots at 41.8 (2840 FPS) and 42.2 (2875), still H4350. Tested up to 42.8 with no pressure to speak of. Loaded up a few at 42.2 and shot a match. All was well. A month later and the same load, same batch, is shooting 2900 FPS, with minor pressure signs. So I decided to drop down a node and run some seating depth tests and I started getting some erratic stringing (could partly be barrel heat, it’s still summer in AZ and barrels just get hot.). So I tried to shoot a group with my old load (42.2gr h4350 over a 140) and I got heavy bolt lift, ejector marks, and a shit group. I’m thinking maybe carbon ring? When I got home I cleaned the barrel real good and soaked the throat with solvent. Is there anything else I might be missing?

 

[918v]

I have found that in most cases Hodgdon’s data is about 1 grain under where you’ll get pressure signs in 70 deg weather. That’s the cushion. You’re pushing it.

 

[SonoranPrecision]

I have found that in most cases Hodgdon’s data is about 1 grain under where you’ll get pressure signs in 70 deg weather. That’s the cushion. You’re pushing it.

That aside, it doesn’t explain the sudden pressure spike. Or the velocity for that matter. Most people are seeing 2800-2840 at that charge weight and barrel length.

 

[918v]

A lot of people see sudden pressure when going over book max. Then they wonder why when the answer is obvious. You’re over max. Just because it wasn’t doing it before doesn’t mean anything. It’s doing it now and it’s cuz you’re over max.

 

[TheOfficeT-Rex]

Check for carbon ring buildup. It explains the sudden speed up. Use a foam earplug to stop up the chamber, let some carbon cleaner sit for 10 mins or so, and have a bronze or nylon brush chucked in a drill to clean the chamber real quick.

 

[Bullspotter]

While i do not know about what a carbon ring will do, I will ask about your powder scale, May be off a grain? throwing a bit heavy by chance? Just a thought.

 

[NoDopes]

Is it possible that powder lost some moisture content and by weight has more power? I used to leave some of my ACP45 powder in the Dillon.. but I was always running those loads way low. Probably not a good idea in retro.
(Yes, I know this is old thread, just curious)

 

[Srgt. Hulka]

I shoot 42.4 grains of H4350, and 140 gr ELDM, in my JHR, with a velocity of 2858, and I show no signs of over pressure.

 

[SonoranPrecision]

Is it possible that powder lost some moisture content and by weight has more power? I used to leave some of my ACP45 powder in the Dillon.. but I was always running those loads way low. Probably not a good idea in retro.
(Yes, I know this is old thread, just curious)

Turns out 918v was right. I was right on the edge when I developed the load, and the summer heat pushed it over the edge. I backed off and did a load development at a lower charge range. Sitting at 41.5 grains now and still getting 2860fps with a 140 hybrid, so I’m happy.

 

[918v]

I don’t like pushing the limit. For example, when switching between lots of bullets, I have found that many times the new lot has different length bullets than the old lot. My new lot of SMK is .015” longer than my old lot. So now I have to increase my COAL. If I were in the lands with a max load then the simple change in bullet lots would induce a pressure problem.

That’s why I stay away from the lands and below max with powder charges.

 

[TxWelder35]

Use one of these to check for carbon ring

https://www.amazon.com/Teslong-Borescope-Side-View-Semi-Rigid-Smartphone/dp/B07TTQF24F

 

[clcustom1911]

Turns out 918v was right. I was right on the edge when I developed the load, and the summer heat pushed it over the edge. I backed off and did a load development at a lower charge range. Sitting at 41.5 grains now and still getting 2860fps with a 140 hybrid, so I’m happy.

Yeah man, 41.5 of H4350 is usually answer with 140's pretty much regardless of brass. I've used 41.3-41.5 in Hornady, Lapua, Prime, Federal, and Nosler with success. 42.8 with 130's in the same brands of brass as well. It works in 38 degrees and 100 degrees.

 

[NoDopes]

I haven't seen much mention of Alpha brass here (at all actually). It was pretty consistent on the batch I ordered.

Was trying to work up a consistent load and started trying to get exact crimp pressure. Only to quickly find out eldx bullets are very inconsistent in diameter. If I wasn't going for light crimp I would never have known. I guess weight sorting bullets would solve that, but I haven't started that yet. I'm probably doing this backwards. Lol.

 

[bobke]

I’ll agree that 41.5 H4350 works well in all of my 6.5CM’s with 140 class bullets, and is my
‘go to’ load, but would also offer a cautionary note regarding some Federal brass that I picked up at range-weighed 172-174gr, where my various lots of Hornady weigh in at 147-153gr. Would either avoid the heavy brass, or redevelop your load around same, to be safe.

 

[TxWelder35]

I haven't seen much mention of Alpha brass here (at all actually). It was pretty consistent on the batch I ordered.

Was trying to work up a consistent load and started trying to get exact crimp pressure. Only to quickly find out eldx bullets are very inconsistent in diameter. If I wasn't going for light crimp I would never have known. I guess weight sorting bullets would solve that, but I haven't started that yet. I'm probably doing this backwards. Lol.

Why are you crimping 6.5cm ammo?

 

[NoDopes]

Actually, I meant .003 neck tension.

 

[GIXXER2000]

I ran this combo in my 6.5cm 26in 1-8 Twist Bartlein barrel with 140 Hybrids at 42.6 H-4350 210M with a C.O.A.L of 2.87 AVG FPS 2818 SD of 6.4.
Now I run a 26in 1-7 Twist Bartlein barrel with 144 Hybrids at H-4350 at 42.6 210M with a C.O.A.L of 2.91( full 20 off the lands) AVG FPS 2832 SD 3.8. I use Hornady brass with no issues. I do take the time to prep it and anneal every other firing and get 8 firings before i scrap it. Yes there are other brass to choose from but I have never needed to.

 

[Darkside-Six]

Carbon ring. Check to make sure you don’t have build up.