Need help with pressure/velocity spike

[archp625]

I need some help again. I have 126 rounds through my barrel. I cleaned the barrel 86 rounds ago.

I did a pressure/velocity ladder. Figured out where my node was.

Next I loaded for 3 shot groups in the ladder test. I did notice a 60 FPS increase when I did this. Still not a big issue. No hard bolt lift and no swipe on the case.

I’m shooting a CA Ridgeline in 6.5 PRC, 147 grain ELDM 0.020” off lands. Reloader 26 powder And Fed 210M primers. The powder charge is 54.7 grains at 2950. It climbed to 3000 FPS with swipe on brass.

I loaded 10 rounds of what I found to be the ideal load so I could shoot two 5 shot groups, one to see what size group and to get my final ES and start loading more at that for distance.

Everything was great shots 1-5. Es was 5. Shot 6 was 22 FPS fast than 5. I thought that’s weird. Maybe something I did on the charge. Shot the 7 5 FPS fast than the 7. Shot 8 - 9 and started getting a swipe. And climbed 50 FPS faster than the first 5. I didn’t shot the 10th. Something isn’t right.

What are your guys thoughts?

The only thing I can think of is either one my barrel speed up quiet a bit or I need to clean really good and my pressure/velocity will go back down.

 

[BIGEYES]

Some thoughts: You are firing a long bearing surface bullet through a relatively small bore. You have 40 rounds through the barrel. Thoroughly clean the barrel. Double check your charge weight of powder. Check all fired case lengths to be certain they are under maximum length. How much has the ambient temperature varied from one shooting session to the next? Your load might be exceeding maximum FOR THAT BARREL.

 

[archp625]

Some thoughts: You are firing a long bearing surface bullet through a relatively small bore. You have 40 rounds through the barrel. Thoroughly clean the barrel. Double check your charge weight of powder. Check all fired case lengths to be certain they are under maximum length. How much has the ambient temperature varied from one shooting session to the next? Your load might be exceeding maximum FOR THAT BARREL.

I cleaned the barrel at 40 rounds. I’m at 126 rounds now. All case are below max case length. Charge weight was with a Chargemaster lite. I always throw a 50 gram after to make sure it’s still good. The ambient temp has fluctuated from 43-63.

I did a pressure test at the time 55.5 was the max. I’m at 54.7.

 

[BIGEYES]

arch, Sorry that I wasn't clear about cleaning. Unless I am misunderstanding, your last cleaning was 40 rounds ago. Too many rounds IMO since cleaning. I'm not saying this is causative; but I believe it could contribute to the problem that you are having.

 

[archp625]

arch, Sorry that I wasn't clear about cleaning. Unless I am misunderstanding, your last cleaning was 40 rounds ago. Too many rounds IMO since cleaning. I'm not saying this is causative; but I believe it could contribute to the problem that you are having.

Last cleaning was 86 rounds

 

[archp625]

I’m hoping it’s just a cleaning issue. I usually clean when accuracy starts to drop. Here is a 5 shot group right before the pressure spike

 

[BIGEYES]

Its a head scratcher. Wish I had more to offer. Good luck.

 

[archp625]

I appreciate you helping though. I’m new to reloading and don’t want to get hurt. So I’m trying to get answers from way more knowledgeable people than me.

 

[BuckSnort]

Are you letting it cool between shots?

As the bullet heats up with each shot it can build pressure (speed) especially if the round is chambered for a bit before you pull the trigger..

 

[fraz01]

All good thoughts posted above. Getting a swipe on the case base is way to much pressure. You want to look for faint ejector marks on the previous fired case as you should see signs of pressure before a swipe. I would back the charge down 2 to 2.5 grains and work from there. RL 26 is great powder, but in my experience you want to go slow working up loads to max loads.

 

[archp625]

Are you letting it cool between shots?

As the bullet heats up with each shot it can build pressure (speed) especially if the round is chambered for a bit before you pull the trigger..

I let it cool between the two 5 shot groups. has far as the 5 shot groups go its wasnt rapid firing but I would shot. then shot a minute later.

 

[ID_Matt]

Have seen pressure spikes with RL26 above 80 or so degrees but that does not appear to be the case here. My only guess is maybe a carbon ring forming in the barrel? Was brass head space set the same? 54.7 gr's shouldn't be too warm....

 

[Mule3006Elk]

Pressure sign. Back down. There's good information which clearly states brass/primers don't show pressure signs until pressure is very high. Meaning, a pressure sign doesn't imply you just went over pressure. Conversely some primers with thin cups can flatten well before one is at pressure.

What is the min/max grains for this powder/bullet combination?
The barrel length of your rifle vs. tested barrel length in your reloading manual?
Primer & brass are you using vs. tested primer/brass in your reloading manual?

 

[Mule3006Elk]

Borescope can help you sort out if you do/do not have a buildup within the bore itself.

 

[VAHunter01]

I don’t think it has to do with a dirty barrel. If that’s the case, you’re way too high in the first place.

Why not just back off a bit more and see what happens?

I don’t have much experience with R26, so I’m not sure how it behaves at max pressure.

If I had to guess, I’d say you were very close to being over max, and something (such as heat, variance in charge weight, etc) pushes you over the edge to show signs on your brass.

What brass are you using? I’ve saw quite a few weird things with Hornady brass, and don’t use it anymore.

 

[archp625]

I don’t think it has to do with a dirty barrel. If that’s the case, you’re way too high in the first place.

Why not just back off a bit more and see what happens?

I don’t have much experience with R26, so I’m not sure how it behaves at max pressure.

If I had to guess, I’d say you were very close to being over max, and something (such as heat, variance in charge weight, etc) pushes you over the edge to show signs on your brass.

What brass are you using? I’ve saw quite a few weird things with Hornady brass, and don’t use it anymore.

I am using Hornady Brass. I think i am going to clean the gun really well and start my ladder test again. I probably wont go through as many but at least i know where to start.

 

[fraz01]

Another way to estimate pressure increase that you don't hear much about anymore is measuring the case web OD .200 above the case base for non-belted cases. It is best to use a micrometer but a good caliper will give an idea of what is happening. Rule of thumb I use on once fired cases is at .0005 expansion I am starting to get to max.

 

[wind gypsy]

You're right at the round count that barrels typically speed up. Speed = pressure. This is why people say you shouldn't do load dev until your barrel is "broken in". I either relearned this same lesson a couple weeks ago on a barrel with 140ish rounds or just ran into an issue of powder lot variance, TBD.

There might be additional factors like a carbon ring, once fired brass shows pressure different than virgin, powder temp sensitivity, etc. I'd reduce your charge and assume the pressure you're seeing is going to be there going forward with the same brass condition, powder, temperature, etc now that the barrel is broken in.

 

[wyosam]

I'm a second guess for rounds warming up while chambered. Did it cool all the way out between those 5 shot strings, or did the second string have a warm start (even if only a little)? That is the simplest explanation for what you describe. Barrel with 80 rounds since cleaning shows big increase in pressure over a 5 shot string all of a sudden? Seems highly unlikely. Whatever the cause, if you're that close to over pressure, I'd go find the next node down.

 

[archp625]

I'm a second guess for rounds warming up while chambered. Did it cool all the way out between those 5 shot strings, or did the second string have a warm start (even if only a little)? That is the simplest explanation for what you describe. Barrel with 80 rounds since cleaning shows big increase in pressure over a 5 shot string all of a sudden? Seems highly unlikely. Whatever the cause, if you're that close to over pressure, I'd go find the next node down.

I shot 5 factory loads first to make sure my chronograph was set up exactly how i wanted it. Plus i like to shot a few times before the "real" group test. I let it cool down for 5 minutes. Then I shot my first 5 round group. Everything was great. ES of 7 and 0.5'' 5 shot group at 100y. Let it cool 5 minutes then shot the next 5 shot group. That is when all hell broke out.