Seeking advice - 6.5 prc reloading

[J.B.]

It’s been a few years since I’ve done any load development, and was under-informed at best when I last did it. Looking for advice on how to proceed following a ladder test as per Form’s pain free reloading system.

Specs as follows:
6.5 PRC - 22” IBI barrel ~140 rounds fired
Once fired Hornady brass
Fed 215 magnum primer
H1000
130 TMK
2.935”

I Loaded up 8 rounds at 56, 57, 58, 59, 60, 60.5, 61, 61.5 grains.

First pic of case heads with brass primers are factory 147 eldm loads. Easy chamber, easy extraction, primers are pretty flat.

Second pic is reloads labelled according to charge weight. They all chambered a little snug, I seem to have this no matter what I reload. Is this a function of brass being fire formed to the chamber?
56, 57, easy extraction but some shine and extractor marking on case heads.
58 - maybe a little lift to the bolt. Extractor mark
59 - snug bolt lift. Extractor mark.
60 - heavy bolt lift. Extractor mark.

Weather was sun/cloud 55 degrees. Barrel was never warm to touch. Unfortunately I don’t have a garmin, though a buddy has one I could shoot some rounds past and get a velocity reading. I’m not too hung up on speed, but 3000+ would be nice.

Target pic - shots in cardboard are all sight in from previous range session after scope remount with factory 147s.
Four shots in sticker just right of center are 56-59, 60 is just left of center. I think this combo shows promise, would like to shoot a 10 round group with a single charge.

My question is, how should I proceed? I’ve never seen pressure this much below book max, but I haven’t developed for a ton of rifles either. When hitting pressure, the velocity should be decent regardless of a lower charge weight, correct?
I was thinking of loading 15 or so at 57.5 and shooting a group (with a chrono). Verify at distance if they group good.
Thoughts???

 

[bigunit]

Before continuing, I would find why closing the bolt is tight. It could be you're not resizing the brass enough or that the bullet is jammed into the lands which would cause excessive pressure. Looking at the brass, i would say you're already at pretty high pressure at 57 gr. Without a chrono, its pretty hard to determine what's going on and ladder test is a bit of a waste of time and components.

 

[Caseknife]

Agree with @bigunit, suspect you are up against the lands. Try seating them to 2.92", or figure out where they hit the lands and back off a bit. Are there any marks on the bullets after chambering a tight round and then removing without firing?

 

[Nine Banger]

57gr is the end of the road for H1000. Read the signs.

 

[J.B.]

Before continuing, I would find why closing the bolt is tight. It could be you're not resizing the brass enough or that the bullet is jammed into the lands which would cause excessive pressure. Looking at the brass, i would say you're already at pretty high pressure at 57 gr. Without a chrono, its pretty hard to determine what's going on and ladder test is a bit of a waste of time and components.

I believe I have found the issue with tight chambering. I loaded a dummy round long, and chambered it. Came out at 3.011 with light rifling marks. Sharpied one set to 2.935 and it came out with a stripe on it, but no marks from rifling.
Then I measured my spent brass and it was all coming out between 2.033 and 2.038. The shorter the casing, the easier it chambered. SAAMI spec is 2.020 - 2.030.
So I need to trim my brass, did not expect that from 1x fired, but should have checked. Rookie mistake. That should clear the chambering issue.
Once that is done I will load a ladder, maybe 56-60 with brass I know chambers good, and shoot them with a chrono. @Caseknife good chance 57 is the ceiling, but could I be hitting pressure from long necks?

 

[bigunit]

Ah yes. Makes sense. I use a borescope to find my approximate trim length. Take your longest piece of brass and put it in the chamber with bolt closed and you can see where the end of the case mouth sits in the chamber.
This is my 6.5 prc with a piece of brass trimmed to i believe 2.020"

 

[J.B.]

Ah yes. Makes sense. I use a borescope to find my approximate trim length. Take your longest piece of brass and put it in the chamber with bolt closed and you can see where the end of the case mouth sits in the chamber. View attachment 1048401
This is my 6.5 prc with a piece of brass trimmed to i believe 2.020"

Oh that’s slick. I don’t have a bore scope either, just getting into this all.

If the neck is getting jammed, that could essentially create a very tight crimp on the bullet, causing pressure?

 

[Samson7x]

Do you have an OAL gauge? How much jump to the lands? I'd also borrow that Garmin to see where you're at. You may have to consider changing powders as well.

 

[bigunit]

Oh that’s slick. I don’t have a bore scope either, just getting into this all.

If the neck is getting jammed, that could essentially create a very tight crimp on the bullet, causing pressure?

Yes. Absolutely. I trim with the lee case length gauge. Not every firing but I measure all cases before loading to make sure they're all within spec. The bore scope is just to see what the max length actually is. Some guys dont like to trim because they are afraid of getting a carbon ring build-up in the chamber but that hasn't happened to me yet. Im surprised your brass is stretched that much after one firing. Doing a .002 shoulder bump with full length sizing dies should minimize case stretch in the future. You will need comparators to measure shoulder bump but can also just chamber sized rounds until your bolt closes without resistance, then lock your dies at this spot and that will work for your chamber.

 

[J.B.]

Do you have an OAL gauge? How much jump to the lands? I'd also borrow that Garmin to see where you're at. You may have to consider changing powders as well.

I don’t no…based on what I checked this morning, I’m pretty sure I’m not jamming them, and that it’s a case length issue. I’ll trim a few tonight and recheck.
I’ll get my hands on the garmin before I do more shooting.

 

[J.B.]

Yes. Absolutely. I trim with the lee case length gauge. Not every firing but I measure all cases before loading to make sure they're all within spec. The bore scope is just to see what the max length actually is. Some guys dont like to trim because they are afraid of getting a carbon ring build-up in the chamber but that hasn't happened to me yet. Im surprised your brass is stretched that much after one firing. Doing a .002 shoulder bump with full length sizing dies should minimize case stretch in the future. You will need comparators to measure shoulder bump but can also just chamber sized rounds until your bolt closes without resistance, then lock your dies at this spot and that will work for your chamber.

The 1x factory load brass I measured was 2.022-2.026. So getting around 10 thou of stretch. Seems like a lot to me? The ladder loads I fired are back below 2.030, but still chamber tight, likely due to pressure? When I resize they jump back to 2.035 ish.

 

[bigunit]

Was this rifle assembled by ibi or another smith? Im assuming you're canadian by the ibi barrel? Im wondering if you should check headspace. 10 thou does seem like a lot of case stretch. Are there marks near the case mouth that look like the case was too long?