6.5 PRC Load Dev - Did annealing change pressure?

[JM151]

Alright all. I thought I had a really good load with 6.5 PRC, Berger 156, ADG, gm210m, and N565 @59.2.

With virgin brass I had avg velocity of 3072 and .8 MOA on a 10 shot group (see first picture and second picture ). After FL resizing and trying out my new Mark 2 db annealer I loaded up some more. Note on FL sizing I didn’t bump shoulder yet because the case was still fitting into chamber.

Round 2 at the range. I noticed couple loads the bolt was a little stiff on closing. On some loads I noticed stiff bolt lift and ejector swipe on case heads. Put my chrono (Garmin) on and was recording avg 3100fps (third picture). Why did I have the sudden increase in pressure and velocity? ***barrel has already sped up and had to back it down from 59.9 to 59.2 to get back to 3070 fps. Was it because of annealing or should have I bumped the shoulder a little? Virgin brass had a measurement of 1.645 BTS, 1x fired 1.650 BTS, and 2x fired 1.653.

Round 3 at range. Decided to back off the charge as I was into pressure for some reason. Loaded up 3 loads 10 shots each: 58.6, 58.8, and 59. The 10 shot groups are pictured in sequence below. Not really sure how to read these groups. It looks like 58.8 has vertical dispersion which I believe we want to stay away from. Which one should I further evaluate or should I go back to 59.2 and bump shoulder down to 1.648?

 

[JM151]

Note on the 59 target the flier was due to really hot barrel. When I saw impact I touched barrel and it was hotter than I intended it to get. This was after already shooting 27 rounds. I immediately picked up the gun and put in truck with AC running to cool it down. After about 15 min cool down the last 3 loads were in cluster.

 

[Cactus kid]

i dont think that is a flier i think that is just in the cone of fire. Just personal experience with the 6.5 and running them very hot.

Did you over anneal the brass? I know that making the brass too soft will cause pressure like warning signs.

also 3100 fps with a 156 seems like you are going to be riding the edge of what the cartrige is capable of doing. Maybe back off more than half a grain, maybe 2 grains and see how that does.

 

[JM151]

@Cactus kid no I don’t believe it’s over annealed. Annealing was done with Annealer Mark 2 DB not the flame method.

I’m confused why I had increase in pressure and velocity after I annealed it and FL sized. The 59.2 load was solid with virgin brass. I wouldn't think resizing would cause an increase in pressure or would it?

 

[Cactus kid]

@Cactus kid no I don’t believe it’s over annealed. Annealing was done with Annealer Mark 2 DB not the flame method.

I’m confused why I had increase in pressure and velocity after I annealed it and FL sized. The 59.2 load was solid with virgin brass. I wouldn't think resizing would cause an increase in pressure or would it?

I wouldnt think it would. best answered by someone who is more knowlegeable than I.

I had a similar issue when used the 156 and virgin ADG brass. I dont anneal, but after a couple firings I was getting stiff bolt lift.

Eventually I switched to hornady brass and 147 eldm. I started getting pressure signs with that after a loading. I dropped the charge 2 grains and it seemed to solve the problem. velocity loss was not enough to worry about.

 

[huntnful]

Sounds like you were pretty close if not in pressure to begin with. 59gr. N565 is a stout charge with a 156 Berger. Then not bumping the shoulder allowed zero expansion of the case to absorb any of the pressure.

I personally think you are just way too hot to begin with. Those are high speeds and a high charge for a 156.

Annealing is the last thing to cause the issues. But you’re so close to pressure, any small thing will be a dramatic change. Temperature, case swell, head space/shoulder bump, new powder. I’d drop down a grain for sure.

Riding the line of pressure isn’t worth the issues IMO. Give up 50FPS and have no worries moving forward

 

[HGL]

Annelaing the brass and changing nothing else (i.e. bushing, mandrel, sizer, etc.) can certainly have an effect on neck tension. Different neck tension can have an effect on pressure, albiet its usually minimal. But if you are close to max already, it could become an issue.

Not saying it is the "culprit" but a possibility.

 

[JM151]

@huntnful I would agree that I’m into pressure and I think you’re right and need to back down a grain see what happens. When I did a ladder test to find pressure I made it to 60.4 before I had hard bolt lift. I know that there are other signs that show pressure but I always take it to hard bolt.

I’ll try resizing back down to 1.648 or is that to much bump? 2x firing I’m at 1.653. I’ll also try reducing the charge like you mentioned. I’m curious now how much resizing affects pressure.

 

[JM151]

@HGL I used a bushing to size neck back down and used expander mandrel to have .001 neck tension.

 

[JM151]

@huntnful how would you read those 3 groups 58.6, 58.8, and 59. The 58.6 I didn’t have any pressure signs but not happy with the ES.

 

[SloppyJ]

A lot of "new" in there so I assume the gun is new too. I'm going to say the velocity difference is partly due to the barrel speeding up. It could also have to do with the neck tension you're putting on the bullets. Whats the difference in a sized neck diameter and a loaded one? Also, was the seating depth the same? You could have jammed them into the lands. This should be measured from the ogive and not the COAL.

 

[JM151]

@SloppyJ yeah the gun is new (built by the man Dallas), but I got about 300 rounds down it. I believe it already sped up cuz I had to back down my charge already. I was loading 59.9 and had to back down to 59.2 to get same velocity.

My neck tension is at .001”. They are all loaded at .020” off the lands.

 

[sveltri]

I’m going to ask an unpopular question but are you cleaning that gun? I have to clean my PRC and 243 AI, they both develop carbon rings. Carbon rings will definitely spike pressure.

 

[Vern400]

I anneal regularly and have no issues. Annealing softens the brass and it can cause it to grow just a tad more as you fire and resize, but for sure you're checking your overall length of the cases right? If your empty case it's the end of the neck machining you got a big fat problem.

In principle annealing a little bit too much doesn't matter from a pressure standpoint. Only if you created a terrible surface finish on the ID of the neck and bullets were hard to shove in. Most of the time when you anneal the brass is softer and bullets insert with less Force. As a matter of fact, that is why I anneal brass because when I don't I can feel a big difference in the bullet insertion Force. After annealing they're a little bit more slippery and more consistent in the force required to shove the bullet in.

When you're running an overbore caliber and running near Max it can be very sensitive to carbon ring, temperature variations, all kinds of stuff.

 

[JM151]

I’m going to ask an unpopular question but are you cleaning that gun? I have to clean my PRC and 243 AI, they both develop carbon rings. Carbon rings will definitely spike pressure.

Only cleaned it twice so far. I typically don’t clean till after hunting season and sits in the safe for couple months.

 

[JM151]

I anneal regularly and have no issues. Annealing softens the brass and it can cause it to grow just a tad more as you fire and resize, but for sure you're checking your overall length of the cases right? If your empty case it's the end of the neck machining you got a big fat problem.

In principle annealing a little bit too much doesn't matter from a pressure standpoint. Only if you created a terrible surface finish on the ID of the neck and bullets were hard to shove in. Most of the time when you anneal the brass is softer and bullets insert with less Force. As a matter of fact, that is why I anneal brass because when I don't I can feel a big difference in the bullet insertion Force. After annealing they're a little bit more slippery and more consistent in the force required to shove the bullet in.

When you're running an overbore caliber and running near Max it can be very sensitive to carbon ring, temperature variations, all kinds of stuff.

Yeah I trim per Berger’s reloading manual “trim length”. I’m starting to think it’s because of the sizing and not bumping the shoulder any yet. I think I’m going to test two different things: 1. Reduce charge. 2. Try sizing back to .003 BTS of virgin brass.

 

[sveltri]

Only cleaned it twice so far. I typically don’t clean till after hunting season and sits in the safe for couple months.

I’m guessing you have a carbon ring, do you have a bite scope?

 

[JM151]

I’m guessing you have a carbon ring, do you have a bite scope?

No I don’t.

 

[pbroski]

In my experience, virgin brass will take a higher charge than when the case is once fired to achieve the same velocity. In other words, it's totally normal to have to reduce the charge after the first firing. If the charge is not reduced, pressure will be higher and as a result, so will the velocity. I think this is what you are experiencing. Has nothing to do with annealing.

And as other have stated, probably a good idea to go down at least a grain.

 

[coleman]

In my experience, virgin brass will take a higher charge than when the case is once fired to achieve the same velocity. In other words, it's totally normal to have to reduce the charge after the first firing. If the charge is not reduced, pressure will be higher and as a result, so will the velocity. I think this is what you are experiencing. Has nothing to do with annealing.

And as other have stated, probably a good idea to go down at least a grain.

I’ve heard this from a few people as well. Sounds to me like this is what’s happening, especially since those loads would seem to be right in the edge.