UPDATED: Head scratching day at the range

[Eric Musgrove]

2 days prior I did a test with my 6.5 PRC( Browning X-bolt Pro 24" barrel) using H1000, Hornady brass (all that I could get) 143gr E-LDX and Win LR primers, seated to 2.950(mag length) I started at 57 grs and had loaded up to 60gr in .2 gr increments
I hit a fantastic node at 58.6 - 3129 fps, 58.8- 3086 fps, 59.0 3129 fps. 59.2 3137 These three shots were also a bug hole in the target see shots 10,11,12. The barrel was clean prior to the test and I fouled it with 3 rnds of the Hornady factory 143eldx, which also registered over 3000 fps that day, which was about 200fps faster than when the barrel was new that made me go hmm? It also shot a decent group which before it did not seem to like. I shot all of the loads taking along time for the thin fluted barrel to cool between shots.
At 59.4 grs the velocity started to drop off down to 2969 and then around 3000 until the last shot of 60 grs which was 3197, I think this was barrel heat. I had no pressure signs up through the 60 grs. Temp around 80-85 by the time I got to the end. I went home poured over the data, decided to load up 59 grs and go back shoot a group at 100 and 200 yards. I also cleaned the bore again.
2 days latter I returned and fouled the bore with 2 shots of 57.0 and then started my 3 shot group at 100 with 59 gr. The speeds were 2982,2969,2969 temps about the same as before, had pressure signs with ejector marks on all 3 cases and the group was horrible. I put the gun in the truck and came home. I am still not sure what to do, or what is going on. Barrel wasn't fouled enough? What caused the pressure when I had none before with a full grain higher? Crony is garbage? I was so excited about this load and not sure what to do next. Wanted to use it for an up coming ID Bull elk hunt.
Sorry for the long post, tried to eliminate some questions we all usually ask.

 

[lancetkenyon]

First, I would quit cleaning so much. I have found some rifles like up to 15 shots to properly refoul after a complete cleaning. I don't clean rifles until the groups open up or pressures climb (carbon ring). That may be @ 40 rounds, may be @ 400+.
Were your second day loads with virgin brass still? Or FL sized once fired?
Same lot powder and bullets?
What chrono are you using?
2969fps is not bad from a 24" with a 143 and H1000. 3150+ seems WAY hot with H1000. Maybe with RL26 run at its limits in a 26".

 

[RockyMtnUT]

First, I would quit cleaning so much. I have found some rifles like up to 15 shots to properly refoul after a complete cleaning. I don't clean rifles until the groups open up. That may be @ 40 rounds, may be @ 400+.
Were your second day loads with virgin brass still? Or FL sized once fired?
What chrono are you using?
2969fps is not bad from a 24" with a 143 and H1000. 3150+ seems WAY hot with H1000. Maybe with RL26 run at its limits in a 26".

This

Just got done helping a friend with his rifle with similar problem. Tried and tried to narrow down the causes. #1 cause was he was cleaning it too much/frequently and creating more issues than needed. Let that barrel foul up then figure out other variables if present.

 

[shinbone]

"What caused the pressure when I had none before with a full grain higher? "

This is the interesting question, and a clean bore is not causing over pressure. I've had similar occurrences, and was never able to figure out what was the cause. I, too, am interested to learn what's going on to cause an overpressure situation with less powder . . . ?

 

[med358-boise]

I am not a big fan of the ladder system. For the following reasons:

1) Your data point is a single round per load. A sub 20 fps extreme spread is not bad so consider you realy don't know whether shot 1 was at the bottom of its ES and shot 2 was at the top of its ES. So what looks like 5 fps could really be 25 fps.

2) Ladder's are typically done at 200 yards, if you have a 3/4 inch rifle (not bad) and two charge weights that look like they are 1/4" apart, the respective groups could generate groups centered 1.5" apart.

3) 200 yards introduces greater shooter error than 100 yards.

Try using Optimal Charge Weight Method at 100 yards and for that size case, I would go in .6 grain incrmenets. To cover all your bases load Load 1 = 57.6, 58.2, 58.8, 59.4, Load 5 = 60.0. Shoot them in a round robin order on 5 different aiming points; i.e, Shoot Load 1 thru 5, then Load 5 thru 1, then load 1 thru 5 each on its own repsective aiming point. You should find two loads with a very similar groups size and a very similar POI relative to POA. Split the difference between those two loads. See attached sample target below. On the target below, load 7 and 8 (upper right) are the optimal loads so the final load is then 46.2. In this case I used .4 increments becuase the base load is in the 40s.

I have found this method to be much more reliable and consistent than the ladder method.

 

[lancetkenyon]

"What caused the pressure when I had none before with a full grain higher? "

This is the interesting question, and a clean bore is not causing over pressure. I've had similar occurrences, and was never able to figure out what was the cause. I, too, am interested to learn what's going on to cause an overpressure situation with less powder . . . ?

Once fired brass vs virgin.
The dreaded, and well known "6.5PRC chamber/die issue" where the SAAMI chamber is cut smaller than the SAMMI dies can size down to.
Carbon ring.
Environmental conditions like temperature (although unlikely with H1000).
Seating depth changes
Neck tension changes
Actual charge weight variations depending on how you are measuring them.

This next comment is not to throw any blame on the OP, but, not knowing what actual pressure signs might be there? Once you get to overpressure, speeds can do weird things.

 

[lancetkenyon]

I am not a big fan of the ladder system. For the following reasons:

1) Your data point is a single round per load. A sub 20 fps extreme spread is not bad so consider you realy don't know whether shot 1 was at the bottom of its ES and shot 2 was at the top of its ES.

2) Ladder's are typically done at 200 yards, if you have a 3/4 inch rifle (not bad) and two charge weights that look like they are 1/4" apart, the respective groups could be centered 1.5" apart.

3) 200 yards introduces greater shooter error than 100 yards.

Try using Optimal Charge Weight Method at 100 yards and for that size case, I would go in .6 grain incrmenets. To cover all your bases load Load 1 = 57.6, 58.2, 58.8, 59.4, Load 5 = 60.0. Shoot them in a round robin order on 5 different aiming points; i.e, Shoot Load 1 thru 5, then Load 5 thru 1, then load 1 thru 5 each on its own repsective aiming point. You should find two loads with a very similar groups size and a very similar POI relative to POA. Split the difference between those two loads. See attached sample target below. On the target below, load 7 and 8 (upper right) are the optimal loads so the final load is then 46.2. In this case I used .4 increments becuase the base load is in the 40s.

I have found this method to be much more reliable and consistent than the ladder method.

A "Ladder test" is best done at 400+ yards. Even 600+ is very telling for barrel harmonics and vertical dispersion. Which is what a ladder test is for.

Find 3 or 4 in a row with very little vertical dispersion, and that is a good node. If your velocities are even 80fps, that shows how forgiving that node will be to velocity swings.

A ladder is not for best ES/SD.

 

[Eric Musgrove]

First, I would quit cleaning so much. I have found some rifles like up to 15 shots to properly refoul after a complete cleaning. I don't clean rifles until the groups open up or pressures climb (carbon ring). That may be @ 40 rounds, may be @ 400+.
Were your second day loads with virgin brass still? Or FL sized once fired?
Same lot powder and bullets?
What chrono are you using?
2969fps is not bad from a 24" with a 143 and H1000. 3150+ seems WAY hot with H1000. Maybe with RL26 run at its limits in a 26".

Both test days were with FL sized once fired brass, same 8# jug of powder and same box of bullets. Pro-Crony used for years always seemed reliable prior.

 

[lancetkenyon]

Both test days were with FL sized once fired brass, same 8# jug of powder and same box of bullets. Pro-Crony used for years always seemed reliable prior.

Good, good, good, try another chrony from a buddy?
Any close up clear photos of the case heads from your top end loads?

 

[Eric Musgrove]

Once fired brass vs virgin.
The dreaded, and well known "6.5PRC chamber/die issue" where the SAAMI chamber is cut smaller than the SAMMI dies can size down to.
Carbon ring.
Environmental conditions like temperature (although unlikely with H1000).
Seating depth changes
Neck tension changes
Actual charge weight variations depending on how you are measuring them.

This next comment is not to throw any blame on the OP, but, not knowing what actual pressure signs might be there? Once you get to overpressure, speeds can do weird things.

There was no virgin brass used, in the first day there was no heavy bolt lift, or case marks, flat primers, other than speed is there something I would be missing?

 

[RockyMtnUT]

.

 

[david g ranes]

Same primers?
Same bullet seating depth?
Powder scale reading deadnuts? What is the scale?

Might swab your chamber with a bore mop and done alcohol to make sure you have no residual oil left in the chamber I have had that show pressure signs for me in the past. David

 

[Eric Musgrove]

Good, good, good, try another chrony from a buddy?
Any close up clear photos of the case heads from your top end loads?

No that brass has already been processed and RTL. This is a pic of the 59.0 load, maybe some how the shoulder bump was more on the first set of brass? Less bump more pressure? It was sized on a different day but I am sure I measured them.

 

[med358-boise]

A "Ladder test" is best done at 400+ yards. Even 600+ is very telling for barrel harmonics and vertical dispersion. Which is what a ladder test is for.

Find 3 or 4 in a row with very little vertical dispersion, and that is a good node. If your velocities are even 80fps, that shows how forgiving that node will be to velocity swings.

A ladder is not for best ES/SD.

I think the OP is trying to find a good load. Conducting any load testing with 1 round per charge at 200, 400, or 600 is just not dispositive. At 400 and 600, other variables impact the results too much in my opinion.

My experience has been it is much more effecient to start with a load that is a "known good load at 100 yards" and then confirm its performance at 200, 400, and 600. As opposed to starting with data that is based on a) a sample size of 1 for each element of the analysis and b) where factors such as shooter error are magnified.