6.5prc excess pressure, or not?

[Geezedtee]

Hi.
My friend has a Bergara B14 HMR in 6.5prc with a 24" barrel.
Firing new factory loaded Hornady 143gr ELD-X Precision Hunter ammo the V3 chrono reads 2930fps average. The air temp has been between 16 and 10 degrees Centigrade. He is getting ejector imprints on the fired cases but no stiff bolt opening.
I am re-loading the cases for him and finding loose primer pockets in virtually every case after that first firing. Also, when fed into a Redding type S bushing die it's a tight fit requiring more lube than my 6.5x55 or .243 and making a grating noise.
I've measured the fired cases using a Hornady shoulder comparator and the readings are:
1.676" new factory cartridge
1.680" 1xfired empty case before sizing
1.681" 2xfired empty case before sizing
Is this an excessive pressure issue or an overly large chamber?
Have any of you 6.5prc guys found the same?

 

[Coyotefurharvester]

What primer are you using? Your length seems reasonable.

 

[Tucker65]

That's right about the same velocity I got with factory ammo out of the last 3 rifles I put together. All 3 had 24" Proof carbon barrels. No pressure signs or ejector marks on any of the brass fired.

 

[Plumsask]

What primer are you using? Your length seems reasonable.

Factory ammo

 

[Straightshooter1]

Hi.
My friend has a Bergara B14 HMR in 6.5prc with a 24" barrel.
Firing new factory loaded Hornady 143gr ELD-X Precision Hunter ammo the V3 chrono reads 2930fps average. The air temp has been between 16 and 10 degrees Centigrade. He is getting ejector imprints on the fired cases but no stiff bolt opening.
I am re-loading the cases for him and finding loose primer pockets in virtually every case after that first firing. Also, when fed into a Redding type S bushing die it's a tight fit requiring more lube than my 6.5x55 or .243 and making a grating noise.
I've measured the fired cases using a Hornady shoulder comparator and the readings are:
1.676" new factory cartridge
1.680" 1xfired empty case before sizing
1.681" 2xfired empty case before sizing
Is this an excessive pressure issue or an overly large chamber?
Have any of you 6.5prc guys found the same?

I've been firing Lapua 144 FMJ's recently as I fire form some brass and break in a new barrel using Accurate's MagPro. With 61.2 grs my MV average was at 3013 fps out of a 26" barrel with no pressure signs. I ran a ladder last week with that powder from 61.2 grs to 62.5 grs and hand no bolt lift issue with any of the loads. However, like you, I did get ejector imprints on the 62.5 load and the primers (Fed 200's) were quite cratered with somewhat sharp raised edges and flattened. So, though there was no bolt lift issue, the other signs were definitely indicating high pressure. Yet according to my QuickLoad software, that load was just under the SAAMI max of 64,991, though QL also showed the load to me at 101.5% filled. Having made adjustments to QL base on previous MV data, this 62.5 grs of MagPro was giving me just over 3,100 fps.

Now, as for my cases that were fired, the primer pockets were swaged and no loose pockets were found. Using my Sinclair headspace gauge tool in my comparator, it measures my go-gauge at 1.648 and that's what I size my brass to. My fired brass measures 1.650. Therefore, you can see I get a .002 bump on my necks when I size my brass.

Since a Hornady gauge can be quite different from a Sinclair gauge and can different calipers, one can't really compare my numbers to yours to see how that relates to your chamber. But, since we're talking about a "comparator" measurement, it looks like you 2x fired brass is fireformed at 1.681" (only .005 more than factory, per your comparator). If you're chamber is really that much bigger than mine, then that means you've got a lot more volume in the cases, which will produce less pressure than with the same powder load in my chamber. So, I don't see any issue with the size of your cases as you've stated.

Besides my 6.5 PRC, I only reload for my .308 and there it indeed takes more pressure to size the PRC cases than my .308's. That to be expected given the dimensions of the PRC case. What you describe for your sizing doesn't sound unusual to me. You might take measurement of other parts of a fired case, like at the body-shoulder junction and the web area ~ .200 above the base to see what the expansion is like. . . especially since you note loose primer pockets.

 

[Geezedtee]

What primer are you using? Your length seems reasonable.

Thank you. CCI BR2

I've been firing Lapua 144 FMJ's recently as I fire form some brass and break in a new barrel using Accurate's MagPro. With 61.2 grs my MV average was at 3013 fps out of a 26" barrel with no pressure signs. I ran a ladder last week with that powder from 61.2 grs to 62.5 grs and hand no bolt lift issue with any of the loads. However, like you, I did get ejector imprints on the 62.5 load and the primers (Fed 200's) were quite cratered with somewhat sharp raised edges and flattened. So, though there was no bolt lift issue, the other signs were definitely indicating high pressure. Yet according to my QuickLoad software, that load was just under the SAAMI max of 64,991, though QL also showed the load to me at 101.5% filled. Having made adjustments to QL base on previous MV data, this 62.5 grs of MagPro was giving me just over 3,100 fps.

Now, as for my cases that were fired, the primer pockets were swaged and no loose pockets were found. Using my Sinclair headspace gauge tool in my comparator, it measures my go-gauge at 1.648 and that's what I size my brass to. My fired brass measures 1.650. Therefore, you can see I get a .002 bump on my necks when I size my brass.

Since a Hornady gauge can be quite different from a Sinclair gauge and can different calipers, one can't really compare my numbers to yours to see how that relates to your chamber. But, since we're talking about a "comparator" measurement, it looks like you 2x fired brass is fireformed at 1.681" (only .005 more than factory, per your comparator). If you're chamber is really that much bigger than mine, then that means you've got a lot more volume in the cases, which will produce less pressure than with the same powder load in my chamber. So, I don't see any issue with the size of your cases as you've stated.

Besides my 6.5 PRC, I only reload for my .308 and there it indeed takes more pressure to size the PRC cases than my .308's. That to be expected given the dimensions of the PRC case. What you describe for your sizing doesn't sound unusual to me. You might take measurement of other parts of a fired case, like at the body-shoulder junction and the web area ~ .020 above the base to see what the expansion is like. . . especially since you note loose primer pockets.

Many thanks for your reply. I will measure the web area between none fired and fired case. I did wonder if the chamber was so large that it allowed the case to recoil onto the bolt face during expansion, thus imprinting the ejector marks. But that wouldn't explain the loose primer pockets, would it?

 

[Hohn]

Thank you. CCI BR2

Many thanks for your reply. I will measure the web area between none fired and fired case. I did wonder if the chamber was so large that it allowed the case to recoil onto the bolt face during expansion, thus imprinting the ejector marks. But that wouldn't explain the loose primer pockets, would it?

The bergara chamber is likely a bit generous. High radial clearance plus high headspace explains all your observations. Remember, SAAMI allows inexplicably huge tolerances on these things and they still meet saami spec. 0.010” headspace is acceptable to saami but not to me.

 

[Geezedtee]

The bergara chamber is likely a bit generous. High radial clearance plus high headspace explains all your observations. Remember, SAAMI allows inexplicably huge tolerances on these things and they still meet saami spec. 0.010” headspace is acceptable to saami but not to me.

Well that explains a lot thanks. My normal procedure with my 6.5x55SE is to just neck size with a Lee collet die and let the case fire form to my chamber, then I use a body die to bump the shoulder 2 thou, followed by the collet neck die. Matters aren't helped with the 6.5PRC as the only dies I could find in the UK were the Redding type S bushing die (at the moment Lee don't make a Collet neck die for 6.5PRC).
Question; Can I re-set the type S die to not bump the shoulders and just neck size with it?

 

[whatsupdoc]

If you have loose primer pockets after ONE firing using factory ammo I would not reload those cases.

 

[Geezedtee]

If you have loose primer pockets after ONE firing using factory ammo I would not reload those cases.

OK, but why are they so loose? Are any other 6.5PRC Hornady 143gr ELD-X Precision Hunter ammo users experiencing this?

 

[Djfergus]

How many rounds down the barrel? Pressure may come down a little after the barrel gets burnished in. I have a 6mm-PRC that Ive used once fired Hornady 6.5 prc brass with. I got around 4 firings of hot loads before the pockets became to loose to use. I've also shot a 6.5 prc with a bartlein & 147 factory Hornady ammo but haven't reloaded those. They didn't show pressure signs. 2900fps with a 28"

 

[Geezedtee]

How many rounds down the barrel? Pressure may come down a little after the barrel gets burnished in. I have a 6mm-PRC that Ive used once fired Hornady 6.5 prc brass with. I got around 4 firings of hot loads before the pockets became to loose to use. I've also shot a 6.5 prc with a bartlein & 147 factory Hornady ammo but haven't reloaded those. They didn't show pressure signs. 2900fps with a 28"

85 shots (60 factory, 25 reloads). But as I said in my post it's the factory ammo that is showing ejector indents and loose pockets after 1 shot.

 

[Djfergus]

85 shots (60 factory, 25 reloads). But as I said in my post it's the factory ammo that is showing ejector indents and loose pockets after 1 shot.

Yeah, I figure that's it's got enough rounds on it. It may very well be the ammo itself. The eldx has a very thick jacket and pretty long bearing surface but still no reason to be hot if the factory got the load right. How much does your case shoulder grow from unfired? You may have minimum headspace.


Never mind on headspace, I just saw your earlier post. Could just be hot factory ammo.

 

[drop_point]

I'm not too far into my 6.5 PRC barrel, but I've only shot handloads. No pressure sings at 2980 fps 143 gr ELD-X, ADG brass, over published maxed. No ejector swipes, no cratered primers. I'm running a Proof pre-fit on a BigHorn.

 

[Hohn]

If strongly recommend casting your chamber and measuring it with a micrometer.

 

[Coyotefurharvester]

There is a primer pocket gage, you could pull a new factory rd and check the pocket. Load the new brass, shoot and see if the pocket expanded. Also measure at the .200 line before and after, see if the pocket diameter and base diameter change correspond.